Ask An Engineer

Ask An Engineer

It’s NZ Recycling Week this week and to bring you some top recycling tips, we thought we’d recycle this Ask an Engineer piece that Principal Environmental Consultant Jo Ferry answered for us earlier this year:

We know that plastic is bad for the environment so we should be putting it in our recycling bin to be repurposed. But in NZ we only recycle category 1 and 2 plastics. What happens to the other ones that we put in our recycling bin?

The number in the triangle on plastic packaging indicates what the container is made from. Plastics 1 and 2 are the most commonly used plastics and are the easiest to recycle. A large proportion of these plastics are recycled in New Zealand and turned into new products.

Plastics 3 to 7 are made from a range of different materials that are typically not recycled in New Zealand. The first reason for this is because they are not used as much as plastics 1 and 2. As a result, there is less of them to collect, which makes it more expensive to collect and transport them to a central location for recycling. The second reason is the materials they are made up of are harder to recycle. They may be made of tougher materials, which are harder to break down into pellets, or material that is too soft, such as soft plastic packaging which gets tangled in the sorting equipment. In addition, because we do not have a large manufacturing sector in New Zealand, there are limited markets for the sale of these materials. All in all, it is currently not economically viable to collect, transport, process and recycle most of these types of plastics in New Zealand.

When plastics 3-7 are put into your recycle bin, they are taken to a materials recovery facility (MRF) and sorted. Most of these materials are then sent offshore for processing and recycling. Plastics 3-7 are commonly left mixed together and baled as mixed plastic. These bales are exported, mainly to countries in Asia, where they are separated into their different types and turned into plastic pellets. The plastics are then used as feedstocks for the manufacturing industries in those countries.     

While it is great that these materials are recovered and recycled, the process is not foolproof. Contamination within the loads, either through poorly cleaned containers or non-recyclable materials being included, is a big issue which results in a significant amount of plastic being rejected.

We can all do our part to reduce the impacts of plastic recycling on the environment and our communities in the choices we make every day. Choose products that are not packaged in plastic, take your own container to your local sushi shop, or let manufacturers know when their use of plastic is excessive. When you do purchase products in these low value plastics, before putting them in the recycling bin check that they are the type of plastic that is accepted by your local recycling service (this is different across New Zealand), and that all containers are well cleaned.

If you are in doubt about a container being recyclable or not, play it safe and landfill it.

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Carrying on from last week's theme of emergency alerts, we thought we'd ask Senior Acoustics Specialist Darran Humpheson, why are some sirens and emergency alarms high pitched and others low pitched? Take a look at his answer below:

Sirens and emergency warning alarms need to be clearly audible and attract a listener’s attention. However, the choice of warning sound depends upon the context of the local environment.

For example, an emergency vehicle siren is used to warn people in the immediate vicinity of the vehicle. The siren must be loud enough to be heard within a vehicle with windows closed and music playing. Tsunami sirens are like emergency vehicle alarms except that there are multiple alarms separated by distances of approximately 1km, which provides the necessary coverage to alert people inside and outside buildings.

The character of the sound is important, as a varying sound level will attract attention more so than a sound which is of a constant volume. The pitch or frequency of the sound is important too. Unlike low-frequency sound, high-frequency sound in the most sensitive part of the human hearing range (2,000 to 4,000 Hz) is used to attract the listener’s attention and to locate the source of the sound. High-frequency sound has a short wavelength, whereas low-frequency sound has a long wavelength. Hence sounds that have a short wavelength can be very directional and easy to locate. Think about the speakers in your car - the high-frequency tweeters are usually positioned higher in the car closer to the ears whereas the larger bass speakers are either in the boot (subwoofer) or bottom of the doors.

One warning alarm which is unusual is the sound produced by foghorns. These devices need to emit sound that will travel large distances (kms) and through fog and around coastlines (rocks, cliffs, etc). Since low frequency has a long wavelength, the sound will diffract (bend) around obstacles and there will be little attenuation due to atmospheric/molecular absorption (especially since there are greater levels of water molecules in the air).

So, sound with a low frequency will travel larger distances but listeners will not necessarily be able to locate the source of the sound. Foghorns are therefore a warning device informing the ship not to move any closer.

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If you have a smartphone, you’ve most likely received an emergency mobile alert – a loud, attention-grabbing notification informing you of any potential disasters or emergency measures that need to be undertaken.

When it comes to disaster prevention, communication is critical and how you communicate effectively to lessen the impact of disaster is vital.

On 13 October, T+T will host a webinar covering the importance of communication to help prevent disaster, and we’re delighted to have former NZ PM Helen Clark, Head of Advisory for BBC Media Action Lisa Robinson, and Chief of UN Asia-Pacific Office for Disaster Risk Reduction Loretta Hieber Girardet join us to share their perspective.

Feel free to sign up for it here - https://event.webinarjam.com/channel/StayorGoNow

T+T’s Technical Director for DRR, Bapon Fakhruddin, will be on the panel, and for this week’s Ask an Engineer we’re asking him some questions on how emergency mobile alerts work.

What is an EMA?

An EMA or emergency mobile alert is a cell broadcasting technology that enables the rapid alert dissemination of emergency messages within a target area, making it useful in time of the emergency.

The alerts are designed to keep people safe and are broadcast to all capable phones from targeted cell towers.

Where do they come from?

Only authorised emergency agencies such as the National Emergency Management Agency (NEMA), Civil Defence Emergency Management Group (CDEM) are allowed to send an EMA to the public. EMAs are messages about emergencies from these agencies sent directly capable mobile phones.

How does that system work?

In any emergency, NEMA/CDEM would be able to select keywords from a pre-defined list that best describe the situation. The system then uses these words to automatically compose an alert message in a smart-coded format. The message would have information about the time and place of the potential threat, the current risks and recommended response actions. EMAs use a different channel than that of SMS text messaging which can get congested due to the volume of messages and calls made during an emergency.

It uses Common Alerting Protocol (CAP) - an international, non-proprietary digital message format for exchanging all-hazard emergency alerts to ensure common data exchange.

To safeguard the use of the EMA system in New Zealand, set criteria must be met before issuing a message, including that:

  • There is a perceived immediate threat to life

  • Other communications methods have been explored and found to not be suitable/effective

  • A two-person approval has been met (think the old two key turn from the movies). 

The reason this is so important is to ensure the EMA system is not used excessively or inappropriately, which could increase individuals complacency, or even disenfranchise them from the EMA system.

Research has shown that many communication methods are designed to achieve 70% of individuals within a community, relying on other messaging sources (‘word of mouth’) to reach the rest of the community. The biggest benefit of the EMA system is its targeted and effective rapid reach within the community, likely nearer the 90% mark (although its actual reach is something that needs to be researched further). 

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How do you soundproof a room? We passed this question on to Darran Humpheson - Senior Acoustics Specialist. Take a look at his answer below!

I’m one of those individuals that likes peace and quiet, but sometimes I want the ability to play my very varied music collection (think Iron Maiden to Vaughan Williams) either really loud or without having my 18-year-old daughter complaining about Dad’s rather poor taste in music. The answer – a soundproof room.

How do you start?

I’m lucky that one of the internal walls in my audiophile listening room (big floor standing speakers and leather couch) is constructed of brick with a separate plasterboard wall on the opposite side where my son plays his drums and his Xbox.

The brick adds mass and density, vital to controlling low-frequency sound and the separate plasterboard wall isolates both sides so increases the level of sound reduction. Some nice dense acoustic insulation in the cavity of the wall absorbs any sound that gets through. Carpet and heavy curtains within the room help absorb and dampen the room so the music is crisp and not muddled due to multiple reflections off hard surfaces. I’m in the process of fitting seals to the perimeter of the door since sound is like water; it will find any gap and leak out (or in).

So make sure your room is semi-airtight to control any unwanted noise intrusion. Having recess mounted lights and electrical fitting will result in weak points. If you are insulating a ground floor room, then recessed lights are a no-go as sound will pass through the holes in the ceiling.

The keywords are 'block', 'absorb', 'dampen' and 'decouple'. If you are very keen (and have rather deep pockets) you could design a room within a room which is completely decoupled to the rest of the building – recording studios and anechoic champers will do this, or you simply absorb, dampen and add mass in a similar way that movie theatres and home theatres are constructed.

If you live in an apartment and have noisy neighbours, there is unfortunately not much you can do to soundproof your room. Rather, it is more effective to ‘soundproof’ the neighbour’s apartment - with their permission of course. Simple things could include replacing hard floor coverings with rugs or carpet to stop impact sound transfer (noise of people walking on the floor) or moving speakers and TVs away from walls. 

If you’re like me and you don’t want to hear your neighbours, then best do some homework to find out how good the sound insulation is before moving in or check out whether your neighbours love Iron Maiden….

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Why is the eye of a cyclone so calm? We passed this question on to Bapon Fakhruddin, Technical Director - Disaster Risk Reduction and Climate Resilience. Take a look at his answer below!

Tropical cyclones are one of the most dangerous weather events on Earth, but at their core is an area called the “eye” - a roughly circular area of comparatively light winds, clear skies and fair weather found at the centre.

The eye’s diameter is typically around 30-65 kilometres.

Source: NOAA

The eye is surrounded by an eyewall, which is composed of towering clouds, intense severe weather, and the storm’s strongest winds. However, the strong surface winds of the eyewall converging towards the centre never actually reach the exact centre of the storm.  

The positioning of the eye above the cyclone allows air from the atmosphere to sink down inside of it. The eye has the cyclone’s lowest surface pressure, warmest temperature and together with the light wind is what makes the eye calm and free of clouds.

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How come water can evaporate from places where sunlight never shines - like when you put half-dry crockery from the dishwasher in a dark cupboard? We passed this question on to Water Resources Engineer Kate Draper - take a look at her answer below!

A: Sunlight as such has nothing to do with this. The heat which usually comes with sunlight does, as the rate of evaporation changes depending on the temperature. In fact, a plate in the sunshine and a plate in a dark place at the exact same temperature, exact same humidity and the exact same amount of airflow would dry at the exact same rate.

Here is why…

Evaporation is the process of a physical change, where the H2O molecule changes from a liquid to a gas. This happens at a rate proportional to the temperature.

This is an equilibrium equation, where at the same time, some water molecules from the air are undergoing a physical change and condensing back from a gas to a liquid. The rate at which this condensation or “reverse drying” happens is proportional to the humidity in the air.

When the air is at 100% humidity, the exchange is at equilibrium, and the crockery simply wouldn’t dry. The rate at which the drying/evaporation (liquid to gas) and the reverse drying/condensation (gas to liquid) happens would be equal.

In very dry air conditions, the rate of condensation would be significantly lower than the rate of evaporation, so your crockery would dry really quickly.

With this same reasoning, even in Antarctica at negative temperatures, you can dry your washing. If the rate of condensation is slower than the rate of evaporation (or in this case sublimation, the process of a solid changing directly into gas, skipping the liquid phase) then you are in luck with having dry socks to wear the next day. Look up dry valleys if you want to learn more about this.

One of the main influencers of the drying rate is air movement. Theoretically, with no air movement, the air surrounding the crockery, or the washing, becomes humid and perhaps saturated (100% humidity) so heaps of “reverse drying” is going on. When there is a good breeze, this carries away the humid air which contains the evaporated water molecules and refreshes the air immediately adjacent to the crockery/washing with less humid air, hence helping the balance to tip towards the evaporation end, and help the drying process.

So while you will have your crockery dry much faster if you leave it out in the open, it will dry in the cupboard too, just slower.

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Why shouldn't you flush wet wipes down the loo? We passed this question on to Civil Consultant, Costas Chryssafis - take a look at his answer below!

A: 

Disposing wet wipes down the toilet has created a different kind of "pan"demic because these products do not disintegrate in the way toilet paper does. To prove this, look at the picture below.

In the top photo is a wet wipe in the green bucket and toilet paper in the yellow bucket, both left overnight. In the morning, I vigorously stirred both contents. The bottom photo shows that the toilet paper completely disintegrated while the wet wipe remained completely intact such that I could hang it up as in the photo on the right.

Wet wipes are made of synthetic material with strong tensile properties which prevent them from disintegrating readily. They lead to fatbergs in the sewer system which are costly and hazardous to remove. 

Some of the wet wipe products are sold as biodegradable but they do not break down quickly enough to prevent sewer blockages. On top of this, the biodegradation of the synthetic material contributes to the other very serious problem caused by microplastics in the environment.

In short, confine the stuff you put in the loo to the three Ps: Pee, Poop, and Paper.

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What's the difference between a cyclone, a hurricane and a typhoon? We passed this question on to Bapon Fakhruddin, Technical Director - Disaster Risk Reduction and Climate Resilience.

A: 

Hurricanes, cyclones and typhoons are different terms for the same weather phenomenon - they just have different names depending on different geographical places.

  • In the western North Atlantic, central and eastern North Pacific, Caribbean Sea and Gulf of Mexico, this weather phenomenon is called a "hurricane"
  • In the western North Pacific, it's called a "typhoon"
  • In the Bay of Bengal and Arabian Sea, it's called a "cyclone"
  • In western South Pacific and southeast India Ocean, it's called a “severe tropical cyclones”
  • In the southwest India Ocean, it's called a “tropical cyclone”

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Geotechnical engineering often relies on understanding what is beneath our feet. What is the deepest borehole that has ever been drilled? We passed this question on to Senior Engineering Geologist Kevin Hind - take a look at his answer below:

A: 

In our geotechnical work we rarely need to drill boreholes to depths in excess of 50 m. Specialist applications sometimes require much deeper investigations to be carried out. For example, back in the days when I was designing foundations for offshore oil and gas platforms, we would sometimes drill up to 250 m below the seabed because the founding materials were so soft. With water depths commonly in excess of 100 m, the drill string could be between 350 and 400 m in length. It could take a full 24 hours just to recover the drill string once the borehole was completed or weather forced an abandonment.

Oil/gas and geothermal wells can be much greater in both length and depth than anything we see in geotechnical engineering. I differentiate between length and depth as such wells commonly have a significant sub-horizontal component, as illustrated in the drawing below. This allows multiple wells to be drilled from a single offshore platform; a single well to incept multiple oil or gas pockets; or a well head to be located on coastal site rather than an expensive offshore platform (e.g. Pohokura in Taranaki).

Example of a primarily horizontal borehole (source: Rigzone.com)

The longest borehole ever drilled is reported to be the O-14 production well completed in 2017 in Russia’s Sakhalin Island. It is some 15,000 m in length. This is almost twice the height of Mt Everest and 18 times the height of the Burj Khalifa. The truly deep boreholes however are drilled not for oil or gas but purely for scientific reasons. The most famous example is the Kola Superdeep Borehole which was drilled on the Kola Peninsula, a part of Russia that borders Finland. Begun in 1970, the borehole reached a depth of 12,262 metres in 1989. The borehole was stopped because of 180 °C temperatures, crushing pressures and the plastic nature of the “rock”.

The challenging conditions of such deep boreholes have driven development of drilling technology such as down-hole motors, material science and the ability to change drill bits downhole. As a consequence, subsequent boreholes were able to be drilled in far higher temperatures (>260 °C) and at much greater speeds. For example, a 12,000 m long oil well was completed in Qatar in just 36 days, compared to the 20 years required for the Kola Superdeep Borehole.

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The very first NCCRA has just been released and it identifies drinking (potable) water as the most significant risk, nationally. How is drinking water affected by climate change? 

We passed this question on to Climate and Risk Consultant Alex Cartwright and Infrastructure Resilient Specialist James Hughes.  

A: All New Zealand communities rely on a safe and secure water supply, from rural dwellings to our towns and cities. Many water supplies in New Zealand are currently at risk from drought, changes in mean annual rainfall, extreme weather events (including heavy rainfall) and sea-level rise. Climate change is likely to increase the risk associated with each of these hazards.

New Zealand’s first National Climate Change Risk Assessment (NCCRA) aimed to identify key risks for New Zealand, and inform the upcoming National Adaptation Plan. The risks to drinking (potable) water from climate change is significant, and is of top priority for consideration in the National Adaptation Plan.

Let’s have a look at some of the key climate-related hazards that may impact drinking water. We have focused on increased drought conditions, associated with increased temperatures and reductions in rainfall, and touched on the impacts of sea level rise and extreme weather below:

Drought

Drought severity will increase in most regions of New Zealand due to climate change. As well as reducing water availability, increased temperatures and drought conditions can result in higher demand levels, exacerbating supply issues. With population growth expected to increase, this will add further pressure to water supplies.

Periods of drought and high temperature create water shortages through reduced rainfall and increased evapotranspiration. At the same time, people often respond to these warmer conditions by using more water for outdoor purposes, increasing both average and peak water demand further exacerbating the water shortage.

Water demand, both average and peak, can be affected by increasing temperatures, during periods of drought and high temperature as people use more water for outdoor use. This exacerbates water shortages, due to already reduced water availability, as a result of reduced rainfall and increased evapotranspiration. With the majority of properties across our towns and cities not having water meters, managing water demand is difficult. The same can be said for water taken from rivers and other storage facilities for farming and irrigation, where it is often not possible to quantify the water use.

NIWA’s climate change projections show that drought severity will increase in most regions of New Zealand. Droughts are likely to increase in frequency and intensity in already drought-prone areas. While some areas of New Zealand will experience an overall reduction in water availability annually, other areas may experience a lack of water during specific times of need or seasonally. Since 2014, 44% to 66% of councils have implemented water restrictions each year (i.e. hosepipe bans). This range is already significant, and without intervention, is likely to increase with climate change.

Recent drought events have had significant recorded impacts on water supplies around New Zealand. In 2010, for example, Northland experienced the worst drought in 60 years, when its record-low rainfall levels resulted in significant water supply shortages for rural and urban populations. Wellington likewise experienced drought in 2013, coming close to running out of drinking water. During the 2019/20 summer, Northland experienced its driest summer on record, resulting in significant water shortages throughout the region. Waikato and Auckland have also experienced serious shortages at this time.

Increased temperatures and drought can also result in algal blooms, which can contaminate drinking water sources.

Heavy rainfall

Heavy rainfall can lead to contamination of water supplies that rely on freshwater rivers and lakes. In March 2017, Auckland experienced three extreme-intensity, short-duration events (the ‘Tasman Tempest’), which resulted in significant sedimentation of water reservoirs and contamination of a number of the dams supporting Auckland’s water supply.

Sea level rise

New Zealand has nearly 150 mapped aquifers, which provide roughly one-third of its daily supply. Many of these are located along the coast. As sea level rises, coastal aquifers will become increasingly vulnerable to saltwater contamination. Salinisation of coastal aquifers is already occurring in Northland, Auckland, Waikato, Bay of Plenty, Taranaki, Wellington, Tasman, Marlborough, Canterbury and Dunedin. Salinity stress and wider groundwater changes will increase the pressure on water security, impacting both the availability and quality of water.

For more information about this and other risks, take a look at the full NCCRA report here.  

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Why are wavy walls designed that way?

In some places in England, you might come across these “wavy” brick fences, often called “crinkle-crankle” walls. But why is that? We've asked Engineering Geologist Rob Hunter and Geotechnical Engineer Tony Fairclough, take a look at their answer below!

A: 

In some places in England, you might come across these “wavy” brick fences, often called “crinkle-crankle” walls. A straight fence that is only one brick thick is not very sturdy, and can be toppled quite easily with a hard push. However, a crinkle-crankle wall will stand up to a determined assault. 

“The waviness adds significant strength,” says Rob. The arch shape is very strong – we can see it used a lot in architecture. The Gothic period, in particular, made good use of it (refer to almost any old church or cathedral!). Arches, like triangles, are self-supporting and distribute vertical forces down through the arch into the foundation below.

The additional strength gained from arches is why some roofs on houses use corrugated iron, and why some thicker types of cardboard have a layer of corrugated card wedged between two flat sheets.

Tony adds that the arch shape provides a greater strength/load resistance:

"This would help it to stay upright in heavy winds and gives it more resilience if hit by, for example, a horse trying to jump over it. It’s a clever solution, he says, to increase resilience against the most vulnerable load direction while reducing the number of bricks required to build the wall. The total length of a wavy wall would be about 50% more than a straight wall, but the wall is only one brick deep as opposed to the two or more required by a straight wall. Overall, there’s probably a 25% saving in the number of bricks required to build the wavy wall". 

The downside of these walls is that you lose a significant amount of useable land – perhaps that’s why we don’t see them in town or near more modern buildings.

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How does a roading authority choose the speed around tighter corners? How do they know a corner should be taken at 35km/h?

How does a roading authority choose the speed around tighter corners? How do they know a corner should be taken at 35km/h? We passed this question on to Monique van Wyk and Janine Sziklasi. Take a look at their answer below!

A: Have you ever driven around a tight corner/curve in the road and felt as if you were being pushed away from the centre of the curve?

This feeling is caused by an apparent outward force, known as the centrifugal force. The centrifugal force is a fictitious reactive force that is felt due to the car’s acceleration towards the centre of the curve around which you are travelling. This acceleration is known as the centripetal acceleration (ac).

Centripetal acceleration requires a centripetal force (Fc) to enable the movement of the vehicle around the curve. The magnitude of the force required is determined by the vehicle velocity (v), the horizontal curve radius (r), and the vehicle mass (m), as shown in Equation 1 and the figure below.

Equation 1                            

The centripetal force increases as the velocity (speed) of the vehicle increases and the radius of the curve decreases. This means that a vehicle travelling along a curve with a radius of 50 m will require a greater force to stay on the road than the same vehicle moving at the same speed along a curve with a radius of 100 m. This explains the need for lower speeds to be adopted around tight corners.

When travelling on a flat road around a curve, this force is produced by sideways friction between the vehicle tyres and the road surface. The frictional force (f) therefore needs to equal the centripetal force to keep the car from sliding off the road.

The reliance of the centripetal force on friction alone can cause problems during wet weather. Road friction is reduced when the surface is wet, which can subsequently cause a vehicle to slide off the road. It is for this reason that curved roads are often banked, as indicated in the below figure. This is called super-elevation.

 

With super-elevation, friction is not the only force contributing to the required centripetal force. The road is also exerting a force on the car towards the centre of the curve. This allows the same curve to be taken at a higher speed without sliding off the road. Solving for the forces presented in the figure above, we get Equation 2.

Equation 2 

With this equation, we can solve for the maximum velocity that a vehicle can travel around a curve. This concept provides the basis for designing horizontal curves in different speed environments. In reality, however, there are a number of other factors that also influence the speed at which a vehicle can safely travel around a curve, such as visibility, vertical geometry, and proximity to other horizontal curves. Roading authorities consider all of these factors when designing curves.

Design guidance specifies minimum curve radii for roads based on their operating speeds. In some road environments, the specified minimum curve radii cannot be achieved due to terrain restrictions. This results in tight curves that cannot be driven safely at the operating speed, so safe advisory speeds are chosen. This is often the case for curves with an advisory speed of for example 35 km/h. The advisory speed defines the maximum speed at which the curve may be comfortably negotiated under good road and weather conditions.

So apart from solving complex equations – how else can a road authority choose this curve advisory speed.  Usually it is through the use of a “ball-bank indicator” or “side thrust gauge.” This instrument mounted inside a vehicle has a steel ball sealed in a curved glass tube that is free to roll transversely under the influence of those forces acting upon it.  When the vehicle traverses a curve, the centrifugal force on the vehicle will cause the ball to roll out to a fixed position in the gauge. The relationship used between advisory speed (VA) and ball-bank indicator value (bA) is bA = 20.4 – 0.125VA.

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Could you (not that you should ever) surf in a tsunami?

In a purely theoretical situation (you should absolutely never attempt this), is it physically possible to surf the wave of a tsunami? We asked Coastal Engineer Tom Shand.

A: While it may theoretically be possible, it’s highly inadvisable because they’re not waves as you know them.

Unlike swells generated by wind, tsunami are generated by a displacement of water. This occurs most often when an earthquake lifts the seabed, resulting in a bulge at the surface (because water is incompressible), but can also occur by landslides (both underwater and into the water), volcanos and meteor impacts. Trying to generate tsunami using explosives was a hot topic during World War Two, and Prof T D Leech at the University of Auckland undertook testing using explosives off Whangaparaoa. Thankfully, all they generated were ripples, but it was concluded that detonating two million kilograms 8 km from shore would produce a wave 10-12m in height.

After these waves are generated, they propagate away from the area of generation. Unlike wind-generated waves which only move the surface water, tsunami tend to move water right down to the seabed, so they carry a lot more energy and move much more quickly (typically 500-700km/hr compared to 15-30km/hr for wind waves). When they reach the shoreline, that energy is ‘squeezed’, and they become much larger than they were offshore (i.e. a tsunami that is only 1m in deep water may reach 5 or 10m in shallow water). And rather than only being around 50-100 m in length like wind waves, they extend kilometres offshore. This means instead of breaking and quickly dissipating energy, they continue to be pushed onshore – more like a tide than a wave (hence tidal wave).

The question of whether anyone could surf a tsunami probably depends on your definition of 'surf'. Most tsunami will arrive as a surge of water which would be too low (not steep enough) to be caught. In very shallow environments the front face of a tsunami may steepen enough to ‘break’ and approach the shore as whitewater (a bore) so if you were in the right place, theoretically you could catch it. However, you’d be surfing straight towards shore, then when you reached land you’d probably be pushed through trees and buildings, and then pull back out to sea with all the debris the tsunami has picked up (including you), and then maybe returned to shore by the next wave for more of the same. And so the answer to the question is… maybe, in just the right circumstance you could have a very brief moment of ‘surfing’, but it would be highly inadvisable and very dangerous.

However, two similar types of non-wind waves have been surfed. The first are tidal bores which are also very long waves (tides) which are compressed as they enter a river mouth, steepening enough to break. Because these are ‘predictable’ (unlike tsunami), people know where and when they will be breaking and do occasionally surf these waves. The second are waves generated when glaciers carve off and collapse into water. These waves will have shorter periods more like wind-waves and so if they strike the right bit of shoreline (or ice) they may ‘break’. There’s some footage 10:30 here of surfers in ridiculously thick wetsuits ‘surfing’ these waves between lumps of ice. Wouldn’t be my first pick for a surf destination.

Biodegradable, compostable - what's the difference?

We passed this question on to Contaminated Land Consultant Gen Palmer - take a look at her answer below!

A: This can be tricky to get your head around and the words are often used interchangeably. However, there are some key differences between compostable and biodegradable products which are important to understand so we can dispose of things correctly.

Biodegradable simply means that something will break down through the action of living organisms, usually microbes, over some period of time. This may be in an aerobic (with oxygen) environment or anaerobic (without oxygen) environment. Some products will leave behind residual components when they have broken down completely. 

Compostable is a subset of biodegradable and means that a material will break down into its natural components, under aerobic conditions, in a similar time frame as organic matter. The benefit of composting is that the end product is nutrient-rich and useful for gardening. Composting can consist of a green waste heap at the end of your garden or a commercial composting facility where oxygen levels, temperature and moisture are strictly controlled to create optimum conditions for microbes to break down the material. Many compostable products are designed for disposal at a commercial composting facility and will not break down fully, if at all, under non-ideal conditions (eg. home compost or landfill).

Biodegradable and compostable products lose their value if disposed of in a landfill. Without aerobic conditions, some products will produce methane and hydrogen sulphide when they decompose. Other products will not degrade at all. Unfortunately, there are not many standards (yet) around compostable and biodegradable products and local councils are not all commercially composting. The best thing you can do when buying products is to think of how you will dispose of them at the end of their life and if you have access to the disposal method they were designed for.

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What caused the huge wave at Banks Peninsula?

An 11.82m wave was recently recorded off Banks Peninsula. What causes a huge wave like that? We passed this question on to Coastal Engineer, Peter Quilter - take a look at his answer below!

A: Review of the wave Environment Canterbury buoy data indicates maximum wave heights from the storm occurring on Wednesday evening. These were caused by strong southerly winds blowing over fetch distances exceeding a thousand kilometres of ocean.

While the buoy did show a recorded maximum wave height of 11.8 m, a more representative wave height of 5.5 m was also recorded at this time, referred to as the significant wave height which considers the average of the top-third largest waves. A maximum wave height of up to twice the significant height is not uncommon in large sea states. The wide variability in measured wave heights can be conceptually understood at a basic level by considering any point on the sea surface as representing the combined effects of many different wave components superimposed over each other. These different wave components commonly move at different speeds and directions with a different crest spacing, resulting in a variable, hummocky and ever-changing sea surface oceanographers describe as a wave spectrum.  NIWA states their wave buoy is located approximately 17 km off the coast in 80 m of water depth. This location measures wave heights before they enter shallower coastal waters where they begin to lose their energy and reduce in size.

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What happens to plastics we put in our recycling bin?

We know that plastic is bad for the environment so we should be putting it in our recycling bin to be repurposed. But in NZ we only recycle category 1 and 2 plastics. What happens to the other ones that we put in our recycling bin?

The number in the triangle on plastic packaging indicates what the container is made from. Plastics 1 and 2 are the most commonly used plastics and are the easiest to recycle. A large proportion of these plastics are recycled in New Zealand and turned into new products.

Plastics 3 to 7 are made from a range of different materials that are typically not recycled in New Zealand. The first reason for this is because they are not used as much as plastics 1 and 2. As a result, there is less of them to collect, which makes it more expensive to collect and transport them to a central location for recycling. The second reason is the materials they are made up of are harder to recycle. They may be made of tougher materials, which are harder to break down into pellets, or material that is too soft, such as soft plastic packaging which gets tangled in the sorting equipment. In addition, because we do not have a large manufacturing sector in New Zealand, there are limited markets for the sale of these materials. All in all, it is currently not economically viable to collect, transport, process and recycle most of these types of plastics in New Zealand.

When plastics 3-7 are put into your recycle bin, they are taken to a materials recovery facility (MRF) and sorted. Most of these materials are then sent offshore for processing and recycling. Plastics 3-7 are commonly left mixed together and baled as mixed plastic. These bales are exported, mainly to countries in Asia, where they are separated into their different types and turned into plastic pellets. The plastics are then used as feedstocks for the manufacturing industries in those countries.     

While it is great that these materials are recovered and recycled, the process is not foolproof. Contamination within the loads, either through poorly cleaned containers or non-recyclable materials being included, is a big issue which results in a significant amount of plastic being rejected.

We can all do our part to reduce the impacts of plastic recycling on the environment and our communities in the choices we make every day. Choose products that are not packaged in plastic, take your own container to your local sushi shop, or let manufacturers know when their use of plastic is excessive. When you do purchase products in these low value plastics, before putting them in the recycling bin check that they are the type of plastic that is accepted by your local recycling service (this is different across New Zealand), and that all containers are well cleaned.

If you are in doubt about a container being recyclable or not, play it safe and landfill it.

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The Māori and original name for Hamilton is Kirikiriroa, which refers to the fertile soil along the length of the Waikato River. What is this soil and what is so special about it? 

We asked senior soil scientist, Nick Rogers and volcanic risk specialist Alec Wild to explain:

A: "Commonly, rocks are placed in geological groups based on their location. For example, greywacke (a grey sandstone) is part of the Waipapa Group because it was originally identified in the Central North Island, although it is found throughout NZ. 

However, unlike rock groups, soil names are normally described based on what they physically appear like (for example, loam or topsoil). 

Most soils are formed from eroded rock, so they are effectively very small bits of weathered rock. 

However, others are made from materials that are deposited on top of the ground. 

The soils of the Waikato are made up from a cover of ash from the multiple volcanic eruptions over millions of years combined with fine, fertile material (alluvial) that's been spread across the land by the Waikato River. 

The alluvial material has subsequently been transported downstream by the river and been deposited on the surrounding land, along the way.

Hamilton/Kirikiriroa’s alluvial deposits comprise pumice and other volcanic material washed down the Waikato River from Taupō and the Mamaku Plateau. These flood plain deposits are particularly fertile and are also easy to dig, making it excellent soil for farming and agriculture, so it's easy to understand why Māori valued this soil so much that they named the area after it.

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What's better for the environment - taking the stairs or taking the lift?

We all know for our general health we're better taking the stairs but are there environmental benefits, in terms of carbon emissions, as well? We passed this question on to Environmental Engineer Hunter Douglas - take a look at his answer below:

A: As with any assessment of environmental effects, comparing carbon emissions of two activities is going to involve a few assumptions. The efficiency of lifts varies widely depending on their age, technology, speed, number of floors served, use patterns, how full they are, whether or not they’re counter-weighted, and even their software (for working out the most efficient way to service a building with multiple lifts). What we can do is take an illustrative case study as a starting point. That can tell us whether there’s a really clear answer, or whether we should do a deeper study with more data. Let’s take our T+T Auckland office (6 floors including basements, 1224 kg capacity, 9 seconds to travel 3 floors, geared traction lift with a motor generator drive (if I had to guess)) as that representative example.

I used this calculator from one manufacturer and I got that around 185-270 Watt-hours of energy is used per lift “movement”, depending on how many movements they assume per year (it’s not clear). I’m not sure what each “movement” is, so let’s take a rough average and assume one trip of 3 floors. This report from a company that gamifies taking the stairs reckons that a 7-storey building with 3 lifts and 460 employees uses 98.9 GW of energy for its lifts each year. If we scale that to our 6-storey, 2-lift building and assume the same number of movements, that comes to 275-400 Watt-hours per movement. Taking the middle result between the sources sounds reasonable to me, so let’s assume 270 Watt-hours, or 972 kJ. (To understand the range, we could repeat the analysis using the upper and lower estimates.)

We then have to convert this energy into greenhouse gas emissions, which are typically reported in terms of carbon dioxide equivalent. Using this calculator from the Energy Efficiency & Conservation Authority, I got that our 972 kJ lift trip accounts for around 35 grams of carbon dioxide emitted when using the relatively clean energy from the NZ grid. (Or around 87 g if that had come from burning coal.) As a check, using emissions factors from the Ministry for the Environment, I get around 26 g of CO2 for grid electricity, so let’s split the difference to a nice, round 30 grams. That’s about the same amount of CO2 emitted by a car travelling 150 m. Other factors, such as your mode of transport and dietary choices, seriously dominate your carbon footprint over your choice of lift vs. stairs.

Speaking of diet, though, what about the extra calories you expend when climbing the stairs? That’ll vary a bit based on your size and fitness, but 5 calories is a reasonable guess for 60 steps (3 flights in our building). Using some rough, UK-based numbers from Mike Berners-Lee at The Guardian, if you get those 5 calories from bananas, that accounts for just 1-2 g of carbon dioxide emissions. But if you get them from a cheeseburger, that accounts for around 20 g – which is getting close to a lift ride using electricity from the grid here in New Zealand!

Long story short, if reducing emissions is your goal, focus first on transport and purchasing habits. Taking the lift has an impact, but that’s lessened if you’re sharing the ride or you’re in a shiny new lift. But if you want to do your health and the planet a favour, take the stairs! And go easy on the cheeseburgers.

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Can Sound Waves Destroy Buildings? 

If you've ever been to a loud concert or a pumping house party, you've likely felt and experienced the vibration of sound. But can sound waves destroy a building?

We passed this question on to Acoustic Consultant Aaron Healy - take a look below: 

A: The short answer is probably, but not at levels that most people would ever experience, and likely at a frequency below what humans can hear.

Let’s start by understanding what a sound wave is. The human ear is able to detect the pressure variations transmitted through the air from a vibrating source such as a loudspeaker. The rapid compression and rarefaction (expansion) of the air molecules near to the source create these pressure variations. A similar effect occurs on adjacent molecules and sound energy travels out from the source in all directions as shown in the diagram below – like a domino effect from the tuning fork. Sound waves are therefore multiple pressure variations.

Single pressure waves travelling through air, such as shock waves from explosions, can obviously destroy buildings.  Unlike sound waves, shock waves have a single compression which can be unlimited in intensity. For example, a comet in 1908 caused a pressure/shock wave (air blast) estimated at 300 dB which flattened 2,000 km2 of trees in Russia.

Because sound waves are pressure variations, sound (in air) has a finite maximum intensity. The maximum sound pressure difference that can exist between two wave peaks would be twice atmospheric pressure (202 KN/m2), which is equal to a sound level of 194 dB.  In comparison, at 25 metres from a jet engine the sound level would be around 130 dB. At this sound level, the pressure is 63 N/m2, not nearly enough to damage a building by itself. Even at 194 dB it is improbable that sound waves will destroy a building.

Where sound waves could be damaging is when the continuous vibration of the building structure caused by the sound waves coincides with the resonant frequency of the building - vibration in the structure would continuously amplify potentially resulting in some form of damage.

The resonant frequency for most buildings is between 2-4 Hz. It is possible that sounds in this frequency range could cause some form of cosmetic or structural damage to a building. As an example, rock concerts held at heritage buildings in the UK, have resulted in minor damage to weak plaster and lead windows as a result of resonance from the low-frequency bass noise.  However, as the human audible range is between ~20 Hz and 20,000 Hz, any sounds which could excite the natural frequencies of a building will not be audible.

To summarise it is possible that sound waves could destroy buildings if they are at least:

  • Too loud to technically be called sound waves (single pressure wave) and/or
  • Too low a frequency to be called a sound (i.e. inaudible).

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Why is a tunnel a relatively safe place to be in an earthquake?

It may seem strange, but tunnels are a relatively safe place to be when an earthquake occurs. But why is that? We asked Engineering Geologist Rob Hunter, “Why is a tunnel a relatively safe place to be in an earthquake?”. Take a look at his answer below!

A: Thanks for the tunnel question – I love tunnels!  Case histories from all over the world including our very own case studies from road and rail tunnels near Kaikoura, have shown that tunnels perform really well in earthquakes – better than most above-ground structures.

Being located beneath the ground, tunnels are very good at moving with the ground rather than swaying from side to side like buildings.  The swaying motion in buildings can cause structural damage, break windows, cause chimneys to collapse, and can cause injuries from moving and falling furniture like bookcases.  Tunnels however, are supported from above, below and on both sides, and usually have tunnel linings which have been engineered to prevent collapse and dropout of blocks from the tunnel roof and walls.

Don’t sleep easy just yet though. One of the biggest hazards in a tunnel is fire, and most fires are generated from car crashes….which are more likely to occur during an earthquake.  So especially when driving in a tunnel, stay alert and drive safe.

Tunnels aren’t completely immune from earthquake damage though! Tunnel entrances are generally located close to steep slopes where there can be risks from rockfalls or landslides induced by earthquakes.  These can block the entrances, so make sure you take a packed lunch before driving through, just in case.  There are also risks where tunnels cross fault lines…..but it’s very rare for faults to sever tunnels, and if they do, turn around, return to the entrance, eat your lunch and wait for someone to unblock the tunnel portal. 

So in short, tunnels are not unsafe places to be in earthquakes.  It wouldn’t be much fun, and it would probably feel pretty claustrophobic to be in there, but rest assured, you’re not going to be knocked down by a bookcase, the floors above won’t fall on you, and you’ll most likely live to tell the story!

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If motorways had loop-de-loops in them, how fast would an average car have to go to get around without falling off?

We posed this question to Transporation Engineer Janine Sziklasi and Physicist + Acoustic Engineer Darran Humpheson. Take a look at their answer below. 

A: To answer this question, we’ll need to consider the size of the loop-de-loop, and we’ll need to understand the forces acting on a car as it travels around the loop.

If the car were travelling just under the minimum speed required to make it around the loop without falling off, the most likely place it’s going to fall would be at the very top of the loop.

At this topmost location, there are two forces acting on the car in the vertical direction: the gravitational force (Fg) and the normal force (FN) (we’ll neglect any forces from friction and air resistance for simplicity).

The gravitational force is simply gravity pulling the car towards Earth.

The normal force is a support force that a surface exerts on an object in contact with that surface. In this case, as the car travels through the loop, there is a normal force of the loop pushing the car towards the centre of the circle. This means that, at the top of the loop, the normal force would be acting downwards on the car.

As these are the only two forces acting on the car, we get the following equation for the net forces:

Equation 1:                                                               

Finally, we need to consider centrifugal force and centripetal force (Fc).

Picture being on a merry-go-round as a kid, for example. As the merry-go-round spins faster, the harder it becomes to stay on. Your body wants to fly off, but you continue to hold on. The feeling of wanting to fly off the merry-go-round is called the centrifugal force. It isn’t a real force, but an apparent one. It describes the tendency of an object to leave a circular path and fly off in a straight line.

The force you’re using with your hands to hold onto the merry-go-round and keep you from falling off is called the centripetal force. Centripetal force is the force on an object towards the centre of a circle that keeps it moving along that circular path.

In our car scenario, the speed of the car is responsible for the apparent centrifugal force. At the top of the loop, the force of gravity and the force of the loop on the car (the normal force) are keeping the car from breaking through the loop, acting as the centripetal force. If the loop all of a sudden ended, the car wouldn’t continue in a circular motion: It would continue in a trajectory from where the track ended.

The centripetal force is equal to the net forces acting on an object moving in a circular path, which gives us:

Equation 2:

We can equate our two equations, Equations 1 and 2, to get the following:

The equation for the gravitational force is: 

Where m is the mass of the object (the car), and g is the acceleration due to gravity, which is 9.8m/s2 on Earth.

The equation for centripetal force is:

Where m is the mass of the object (the car), v is the velocity (speed), and r is the radius of the circular path (in this case, the radius of the loop).

If the car is travelling just under the minimum speed required to make it around the loop, the normal force at the top of the loop would be equal to zero. This is because the car would be just out of contact with the loop, meaning that it couldn’t push back on the car to exert a force. If the normal force were slightly greater than zero at this point zero, that would mean the car would be in constant contact with the track and make it the whole way around.

Considering this, and carrying out a little algebra, we get the following:

Equation 3:

In Equation 3, we can see that the mass (m) is cancelled out. This means that the velocity is dependent only on the acceleration due to gravity and the radius of the loop. We can now use this equation to work out the minimum speed the car would need to be travelling to not fall off the loop. Let’s assume the loop has a radius of 10m:

Any car would need to be travelling at approximately 36km/h to make it around a loop with a 10m radius, regardless of its weight. For example, a motorbike or a bicycle would also need to travel at least 36km/h to stay on the loop-de-loop track.

Using the same equation, we can calculate how fast a car would need to be travelling to make it around loops of various sized radii:

Radius (m)

Speed (km/h)

10

36

20

51

30

62

40

72

50

80

 

If you were to do this in real life, you would need to be travelling faster than these minimum speeds to stay on the loop due to the influence of forces such as friction and air resistance. The current Guinness World Record for the largest loop-de-loop in a car used a 19.49m high track. However, we’ll leave that to stunt drivers and certain YouTube channels.

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Netflix's 'Tiger King' captivated audiences during lockdown. A question that sprung to our minds was, "Why can't you release captive tigers into the wild"?

Take a look at Ecologist Kat Longstaff's answer below:

There’s a number of reasons you unfortunately cannot release captive-bred tigers back into the wild:

  • Many captive breeding facilities (like that demonstrated in Tiger King) are not accredited wildlife/conservation organisations and subspecies have been interbred, which creates hybrids. This messes with the genetic diversity of subspecies of tigers and loses traits that have evolved to adapt to their unique habitats, e.g. a tiger from Indonesia wouldn’t do so well in frozen valleys of Russia and vice versa. Inbreeding is another issue that impacts the health of tigers.
  • Captive-bred tigers have not had to hunt for their own food so are lacking skills that are gained from the mother as cubs, locating, stalking, capturing and dispatching prey. Without this exposure, they are not competent predators in the wild.
  • Captive tigers associate humans with food. This is a twofold problem - the tigers lack the innate fear of humans that wild tigers have making them susceptible to poaching, while their boldness can bring them closer to human populations that can cause conflict resulting in the culling of tigers.
  • Wild tigers have vast home ranges and are territorial – captive tigers have been confined to hideously small enclosures and have not carved out their own territories from reaching maturity.

The conservation of tigers depends on protecting their threatened habitats in the wild, and reducing human conflict. Make ethical choices in products you buy, support registered wildlife charities, and if you really want to see a tiger only visit accredited registered zoos that are part of genuine conservation programs.

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Auckland is undergoing a severe drought at present with water storage levels dropping below halfway for the first time in 25 years. With that in mind, we asked Senior Project Manager Matt Tolcher, "How do we save water?"

Take a look at his answer in the video below:

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How do foils work on America's Cup yachts? How do foils make such a large yacht with many people on board sit and fly above the water? 

Take a look at Civil Engineer Keith Dickson's answer below:

A: 

Almost exactly the same way that the metal wings on a 747 can lift 440 tonnes off the ground at a speed that’s the same as the self-imposed speed limit of many top-end German cars (i.e. at around 240 km/hr).

In simple terms, the difference between the boats and a plane is that water is far more dense than air – so you can develop a lot of lift at low speed with smaller wings. America's Cup boats take off at around 8 km/hr.

America's Cup boat wings are made largely with carbon fibre and fibreglass resin (they need massive strength to take the loads applied on such small wings).  It is highly likely that they have kevlar in the leading edges as it’s a certainty that they will strike weed, bits of driftwood etc and at relatively high speeds. Carbon fibre has excellent stiffness and strength, however, it also shatters pretty well if you hit it hard. Kevlar has lower strength but massive toughness and therefore excellent impact resistance through absorption and dispersion of the energy of the impact (which is why it’s the key component of bulletproof vests and woven into bulletproof suits (yes these do exist!).  

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How do you make sure ground isn't contaminated - and what happens if it is?

Take a look at Contaminated Land Consultant Natalie O'Rourke's answer below:

A: The first step is to engage a contaminated land specialist, preferably someone who loves acronyms (like SQEP). Contaminated land specialists often come from a range of formal training, and can comprise environmental scientists, environmental engineers, geologists, hydrogeologists, chemical engineers, and many more. They’re a friendly bunch.

In short form, they will:

-          Identify previous uses or activities that may be sources of contamination

-          Design a sampling plan for a site investigation

-          Collect samples of potentially contaminated media (this could be of soil, groundwater, surface water, soil gas, ambient air or building materials, depending on the issues)

-          Send samples to a laboratory for testing

-          Interpret the laboratory data and assess the risk with respect to potential receptors (human health and the environment) and the regulatory setting

If contamination (generally taken to be chemical concentrations above background levels) is found, do not panic. Contamination can exist without posing an unacceptable risk to human health or the environment. So what happens next depends on the risk assessment as well as overarching regulatory requirements. Depending on the specifics of the site, it’s possible that no further action would be required. Or, further stages of site investigation may need to be undertaken to delineate contamination and to help understand whether remediation is required. If remediation is required, there are lots of fun options to consider depending on what is being remediated, but that’s a story for another time.

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With Lockdown measures still in place, the roads are little emptier to what we're used to. But what happens to the traffic light signals now that the roads are empty? Do they remain the same or change?

We passed that question on to Transportation Engineer Matan Aharon.

A: 

The majority of traffic signals in New Zealand are connected to a system called SCATS, which automates the amount of time a light is green. One of the ways it does this is by using detector loops in the road (the rectangular-shaped boxes in the seal you often see in lanes at traffic lights) which detect metal objects passing through them. Using this information SCATS works out how busy each road at an intersection is, as well as how busy the network is as a whole, and adjusts timings to suit the overall network.

In the situation that we currently have which has very little traffic on the road, SCATS will have reverted to its minimum programme times. The lights for empty roads will appear to change very quickly if you’re watching them tick over, and they will usually react a lot more quickly to waiting vehicles than usual. Sometimes SCATS will even skip an unused road if there are no car detectors or pedestrians buttons which trigger the system.

The system gives priority to main roads, so some signals may not change at all unless a vehicle or pedestrian triggers the system from a direction other than the main route.

There are also some signals in the country which are on simple timers, not yet connected to SCATS, and so these will remain about the same.

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Although Easter has just passed, we thought we'd ask our Structural Engineers Geoff Radley and Alex Vink to put their egg-ceptional heads together to give this question a crack:

Q: Why are eggs stronger when standing vertically than when they are lying down horizontally? 

A: Eggs are ovoids where the sharper the curve, the more rigid or stronger it is. Hence why the tips of eggs are harder to crush than their sides. Their curved shape when squeezed distributes pressure all around the shell evenly. In engineering terms, this pressure experienced by the shell are in plane shear or tangential forces and stress in the normal direction is negligible.  It has been recognised in structural engineering that curved membranes or shells are more efficient than flat or straight members in resisting external pressure or gravitational loading. Hence arch bridges and domed roofs were in abundance historically. 

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With working from home arrangements well underway, it's not uncommon for parents to be interrupted by the shouting, hollering and the general hullabaloo of kids with pent up energy. But how loud are kids? We passed that question on to Acoustics/Noise Specialist Lindsay Leitch. Here's her response:

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In this new era of working from home with kids in tow, it may already be painfully obvious that children can be pretty noisy. But how loud are they?

Firstly, we need to consider what constitutes a sound. A sound is created by something that vibrates, such as an engine, or a musical instrument, these vibrations travel through the air as a pressure wave - like ripples in a pond. When your ears detect these pressure variations, they are converted into electrical impulses that are transmitted to your brain and interpreted as sounds. An amazing amount of information can be transmitted through variations in frequency (how high or low a sound is), loudness, duration and a lot of more subtle factors such as for speech and whether it is pleasurable or annoying.

So how do you measure sounds? A microphone works roughly in the same way as your ears. The diaphragm of the microphone picks up the pressure variations and converts them to electrical signals. If the microphone is connected to a sound level meter, these sounds can be measured in units of pressure (Pascals - Pa) then converted to decibels (dB, a logarithmic scale).

The acoustics team in Christchurch and Auckland took a few sound level measurements in and around their homes offices of typical sounds using a phone app.

Activity

Sound pressure level, dB

Family eating lunch and conversation (small table so at 1m)

57 dB, 2 min

Mother telling off child at 3m

61 dB, 6 seconds

Standing while watching the kettle boil

66 dB

Son playing Xbox with headphones on

51 dB

Outside feeding the chicken

56 dB

On the patio

45 dB

In my office

 

34 dB with window closed

41 dB with window open

45 dB with music on

In the lounge with the window open where I’m working and my partner is doing crochet

39 dB

Partner talking at 2m

41 dB

Boiling the jug (highly reverberant room)

65 dB

At desk working

42 dB

Outside house, port in distance, no traffic

45 dB

Kids playing swingball

66 dB

Children yelling at each other (1m)

80 dB

And finally, to answer the original question – how loud are my children? I gave my two boys the challenge of seeing how high they could get the sound level to measure on my phone app. The result? 95 dB. Ouch. If you had that level of sound all day you would quickly go deaf!

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Desert Road, Near Mt Ruapehu 

Have you ever driven past these peculiar cliff formations? Wonder what they are and how they got there?

Engineering geologist Kevin Hind has an explanation for these strange-looking cliffs below:

A: 

Those are just the different layers of ash and pumice that have been deposited from various volcanic eruptions. Some layers are really loose and so get eroded by wind and rain whereas others are a little more resistant for a variety of reasons – usually, the sandy materials erode more readily than the finer ash material which can be a bit more clay-rich and sticky.

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Ever wondered how you know where to drill a well? We asked hydrogeologist Tara Forstner, "How do you find well water"? 

Take a look at her response below!

A: 

Well water, also called groundwater, is found everywhere.

Groundwater is simply subsurface water that fully saturates pores/cracks in soils, unconsolidated and bedrock formations.

Therefore, a very simple answer to 'how do you find well water' could be countered with, ‘how deep are you willing to go?!’ It is not a matter of what location has groundwater, but rather a question of how DEEP do you have to go to find bore water.

A number of factors affect the depth to groundwater, such as climate, topography, geology, and seasonality. Groundwater/surface water can be thought of as a singular system in many cases.

Streams, lakes, and the sea level, are surface representations of the water table intersecting the topography. Therefore, within close proximity to these features and at lower relative topographies (such as floodplains), we often have a higher confidence in determining depth to groundwater.

However, there are too many exceptions to go into, such as perched areas (where groundwater may seasonally exists above the water table), or where streams are disconnected from the water table. Surface water – groundwater hydraulic relationships are often not straightforward and a good conceptual model is required.

In addition, just because we know where the water is doesn’t mean we can always effectively use it. Well water abstracted for the purpose of household use or irrigation also has to consider the aquifer yield - this is how much water you can actually get out of the aquifer. This is where geology becomes very important, as even though you may be in saturated ground, a well screened in clay is not going to be nearly as productive as a well screened in sand.

a)       Simple description of “typical” groundwater system. http://geologylearn.blogspot.com/p/blog-page_90.html

b)       Example of a more complex system, such as karstic (limestone geology).

https://web.northeastern.edu/protect/2017-check-in-protect-develops-deeper-understanding-of-contaminant-transport-in-karst-aquifers/

Q. Although there is no definitive answer to the question ‘How long is a piece of string’, there has to be one with ‘How long is a can of spaghetti’?

You could lay the spaghetti out end-to-end and measure it out that way. But is there a way you could calculate the length while keeping the pasta within the tin?

We asked physicist and acoustic engineer, Darran Humpheson to answer this perplexing pasta problem.

A. I was given an 820g tin of spaghetti. The data on the can says it is 52% spaghetti (48% sauce). I measured the height and diameter of the can and estimated the diameter of the spaghetti at 6mm.

I then calculated the volume of the spaghetti in the can. Dividing this by the cross-sectional area gave me the total length of spaghetti.

The working figures:

Can of Spaghetti

11.5

Height of can in cm

10

Diameter of can in cm

6

Diameter of spaghetti / mm

903.2

Volume of can in cm3

52%

Quantity of spaghetti per can

469.7

Volume of spaghetti per can in cm3

Once I had worked out these numbers, I put them into the following formula to figure out the length of spaghetti:

The final calculation was that there should be 16.61 metres of spaghetti in the can.

We verified the answer by literally laying out the spaghetti end to end. See the video below of how we did it!

The total length was 16.24 metres. That makes the expected and actual answers only 37cm apart – pretty good calculations! Although the final answer means you get slightly less spaghetti than you would expect for what you pay.

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Located in Wyoming, USA, Devils Tower is a peculiar lone formation that rises tall above the surrounding grassland and pine forests.

But how was it formed?

Senior Engineering Geologist Kevin Hind has an idea.

A: Devils Tower was formed from magma that has risen up through weaker sedimentary rocks. It may or may not have been part of an established volcano or it was a new volcano erupting through the surface – no one really knows. Once the magma stopped rising, it cooled and solidified. As it cooled it shrank in size, with cracks opening up in the characteristic columns - like what happens in mud when it dries. Over time, the weaker sedimentary rocks were eroded away around the tower leaving the stronger volcanic rock behind.

Cooling columns or columnar jointing of this type can be seen in the lava at Auckland Grammar School although they are not as high quality or as strong and therefore not as large or prominent. This is likely because they formed within lava on the surface rather than a slowly cooling subsurface mass.

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Bumper-to-bumper. Feet tapping between accelerator and brake pedal in a metronome-like fashion. Movement on the roads slows down to what feels like a glacial drip.

Welcome to March Madness.

Traffic congestion picks up, and, for Aucklanders in particular, frustration picks up too. March is officially underway and we thought we'd ask Transportation Engineer Matan Aharon:

What is March Madness? Why does it happen and how do we cope with the busyness it brings?

A: March Madness is generally considered the biggest headache of the year for Auckland’s transport system. It’s the time of the year when both roads and public transport demand is at its heaviest. 

This is due to a combination of factors; all primary and secondary students are back at school, about 100,000 university students are back to classes, there are the fewest number of people taking holidays, there are generally fewer sick days taken in summer and as the roads get busier, more people try out public transport as a way of avoiding congestion. 

The summer roadworks construction season also puts pressure on the road network at the same time, with closures and diversions in place. During March Madness, Auckland Transport tries to find ‘spare’ buses in the fleets of operators and deploy them where daily data shows the squeezes are worst, but this can only help so much. 

There are lots of things we can do to cope with the busyness. We can try alternatives to driving such as bussing, cycling or e-scooters, we can carpool either with co-workers, friends or through apps like SmartTravel, consider changing when you travel to avoid the peak congestion or even work from home to avoid the congestion altogether.

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The buzz around EVs (electric vehicles), is, well, electric.

EV ownership in New Zealand and Australia has seen exponential growth over the past decade with savings on petrol and a reduced carbon footprint among the leading purchasing reasons for consumers.

But for those particularly concerned about reducing their carbon emissions, it isn’t just the vehicle itself that needs to be factored into the equation – the source of energy must be accounted for as well.

In New Zealand, 80% of our energy comes from renewable sources. In Australia, 80% of their energy comes from coal.

The question on our minds is:

Is it still considered “green” to use an EV in a country reliant on non-renewable energy sources?

We asked T+T Environmental Engineer Rob van de Munckhof and below is his detailed answer:

A:

The question is not quite as simple as it seems at first, but assuming you mean “green” to be carbon emissions two aspects need to be considered. Firstly, the carbon footprint associated with the manufacture of the vehicles and secondly the carbon footprint associated with running the vehicle.

The estimated carbon emissions during the manufacture of an electric vehicle have been calculated at 8.8 tonnes CO2e which can be compared to a standard petrol vehicle at 5.6 tonnes CO2e and a hybrid vehicle at 6.5 tonnes of CO2e. This shows that the manufacture of electric vehicles emits nearly 60% more carbon than the manufacture of normal petrol vehicles. This is commonly reported as stating that electric vehicles are worse for the environment than petrol vehicles but ignores the carbon contribution in use.

During use, many electric vehicle sellers highlight the CO2 emissions as 0, where in reality the emissions depend on the source of electricity used. As the question highlights this varies significantly, with NZ sourcing approximately 80 % of our electricity from renewable sources which have zero carbon emissions where certain states in Australia rely heavily on coal and on average only has 15% renewable sources.Saying this, as indicated in the opening statement, “green” can mean many things, and the above calculations assume you are charging your vehicles entirely off the grid. A number of surveys have been undertaken in Europe and North America looking at the link between electric vehicle ownership and home solar. The surveys have indicated that electric vehicle owners are more likely to have home solar than non-electric vehicle owners (although the proportion is still less than 30%). Using home solar to solely charge your vehicle would reduce the lifetime running emissions to 0.

Like petrol vehicles, the fuel (or in the case for electric vehicles energy efficiency) varies depending on the size of the car. The efficiency is commonly reported as kWh/ 100 km with efficiencies ranging from 15.7 kWh/ 100 km for the Hyundai Ioniq to 24 kWh/ 100 km for bigger vehicles such as the Tesla Model X.

In New Zealand this works out to be approximately 2 to 3 kg of CO2e per 100 km, while in Australia this works out to be approximately 14 to 22 kg of CO2e per 100 km on average. It is worth noting that the carbon emission factors vary throughout Australia with the emission factors for Tasmania similar to NZ while the emission factor for Victoria is significantly higher (0.15 kgCO2e per kWh for Tasmania compared to 0.9 overall and 1.02 for Victoria).  This can be compared to the emissions from normal petrol vehicles such as a Toyota Corolla of 14 kg of CO2e per 100km, or 9 kg of CO2e per 100km, for a hybrid Prius or up to 23 kg of CO2e per 100km for a large SUV such as Toyota Highlander.

Based on a travel distance of 100,000 km, the total carbon emissions can be calculated as follows:

 

 

Manufacturing emissions (tonnes CO2e)

Running emissions  (tonnes CO2e)

Total  (tonnes CO2e)

New Zealand

Standard petrol vehicle

5.6

14

19.6

Large petrol vehicle

5.6

23

28.6

Small electric vehicle

8.8

3

11.8

Large electric vehicle

8.8

4.5

13.3

Australia

Standard petrol vehicle

5.6

14

19.6

Large petrol vehicle

5.6

23

28.6

Small electric vehicles

8.8

14

22.8

Large electric vehicle

8.8

22

30.8

Electric vehicles in Victoria

8.8

18 to 28

27 to 37

 

Therefore, in New Zealand, owning an electric vehicle can significantly reduce your carbon emissions. In Australia, if you rely on the grid, owning an electric vehicle will increase your carbon emissions comparing similar sized vehicles and is worse if you live in Victoria.

The other factor associated with electric vehicles is the impact on urban air pollution. Studies have determined that over 1700 people die prematurely in Australia and nearly 400 people in New Zealand due to exposure to emissions from vehicles in particular emissions of nitrogen oxides and fine particulate. Electric vehicle emissions have zero tail pipe emissions and therefore reduce the potential emissions to the communities where the vehicles are used. Further, emissions of nitrogen oxides and fine particulate from power stations are tightly controlled to ensure these are not causing any significant effects to surrounding communities.

In summary driving an electric vehicle in New Zealand reduces both your carbon emissions and the health impacts from tailpipe emissions. In Australia, generally unless you use your own solar panels to charge your EV, driving an electric vehicle will increase your carbon emissions but will reduce the potential health impacts from tailpipe emissions.

In both scenarios, if you really want to reduce your carbon emissions, ditching the car and walking or cycling will make the most difference with both walking and cycling generating no carbon emissions and being better for your overall health.  With one third of vehicle trips in New Zealand less than two kilometres, and two thirds less than 6km leaving your car at home is easy.

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When it comes to water on Earth, you could say that we’re only scratching the surface.

Hydrogeology (not to be confused with Hydrology), is the study of groundwater and is part of the service offerings we provide here at T+T. But what does a Hydrogeologist do? What sort of work do they deal with?

We passed that question on to Hydrogeologist Kevin Ledwith:

Q: What does a Hydrogeologist do?

A: Earth is known as the blue planet because of its abundance of water, however only a small percentage (about 0.3%) is usable by humans. It’s estimated that 98% of all this useable freshwater exists as groundwater, however the vast majority of it is hidden away from view. Occasionally groundwater moves fast and makes a spectacular display in a geyser, an underground cave, or a large spring, but for the most part, it moves very slowly and exists in small pore spaces underground.

Depending on where you are in the world, groundwater can be either the solution or the problem. Areas of the planet with low rainfall or polluted surface waters depend on groundwater as a source of drinking water, for irrigation, and to maintain healthy ecosystems. Whereas, construction projects that require earthworks below the water table (e.g. basements or tunnels) need to temporarily pump groundwater away from areas in order to build foundations in suitably dry conditions.

Regardless of where you are in the world, groundwater requires careful monitoring and management to ensure that it remains available in sufficient quantities, is safe to consume, and will not create land stability or engineering related problems. Enter the role of the Hydrogeologist!

A Hydrogeologist is a person who studies the flow of water underground, compared with Hydrologists who are primarily concerned with surface water. They tend to be either office-based or field-based, or they may work in a combination of these environments. Hydrogeologists are responsible for identifying and assessing the location, quantity and quality of valuable groundwater resources so that future development works do not negatively affect humans or natural and built environments.

The science of Hydrogeology deals with how water gets into the ground (recharge), how it flows in the subsurface (through aquifers) and how groundwater interacts with the environment and surrounding soil, rock and surface waters (rivers, lakes, and the ocean). To access groundwater, it is necessary to drill into aquifers and to install wells, these wells are then either used for water supply or to monitor how groundwater levels change with time.

Hydrogeologists are trained in mathematics and sciences including physics, chemistry, biology, geology, geography, and environmental science. They draw on knowledge and skills in these areas to collect and interpret data, apply scientific and engineering principles, and to present their work in reports. Some of their day-to-day tasks include:

  • Visit sites to supervise drilling or to collect groundwater level or quality data from wells
  • Compilation of groundwater information from previous reports and datasets
  • Data analysis. Depending on the project, this may involve relatively simple calculations or may require more sophisticated statistical analyses
  • Use of specialist software to predict how and where groundwater will occur in the future
  • Preparing drawings, maps, graphs, and tables to support technical reports
  • Preparation of interpretative reports to provide advice for non-technical audiences

Governments and councils depend on professional Hydrogeologists to ensure that human health and environmental regulations are appropriate and are adhered to. To achieve this, sometimes it is required for a Hydrogeologist to attend local Hearings and Environment Courts as an expert-witness relating to enforced laws, policies or legislation.

Groundwater plays an important role in a large diversity of projects at Tonkin +Taylor. Our Hydrogeologists are awarded the opportunity to solve a wide array of complex problems involving multiple specialist areas. Their efforts positively contribute to society, directly impact urban and rural communities, and help protect natural and built environments. In return, they are given the surety of a challenging but rewarding career. A selection of projects that Tonkin +Taylor’s Hydrogeologists have worked on recently include:

  • Protecting and securing drinking water from contamination
  • Planning for future water supply challenges associated with population growth
  • Building resilience against climate change and natural hazards
  • Assessing potential engineering impacts of construction dewatering projects, including assessments of tunnels, basements, and other excavations
  • Assessing potential effects on the environment, ensuring that proposed projects do not: impact existing groundwater users, induce the depletion of rivers or intrusion of saltwater into aquifers, cause land stability or engineering problems, create water contamination issues 

For more, check out the hydrogeology page and stay tuned for some upcoming infographics!

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It's been a fantastic three months for our interns, and, with it being their final week here at T+T, we decided to switch up our Ask An Engineer slot and hand it over to our interns! 

We've fired through a novelty question:

Why do socks disappear and what can we do to mitigate this? 

A: It’s 7am and you’re getting ready for work. You shower, get dressed and reach for your socks… and realise you can’t find two that match. Amid the scramble, you wonder to yourself, just where do these socks go?

This question has haunted humanity for years. While it’s not one we can answer, we felt sure that we might be able to contribute to the debate “why it is that socks disappear?” and “what we could do to prevent or mitigate their loss?” Rather than ask just one engineer, we called upon the brightest minds of tomorrow – the 2019 T+T interns (engineers, scientists, and business services professionals) – to answer this most pressing question, before waving them off to another year of study.

The interns quickly identified five major variables that influence sock loss:

  • Care
  • Storage method
  • Washing and drying technique
  • Sock characteristics
  • Household residents

Variable one: care

‘Care’ includes factors such as relative income compared to the price of socks, and personality traits. If you’re as laid back as Bob Marley was, you probably don’t worry much about the odd misplaced sock or whether you have a matching pair. Similarly, if you have a high enough income that the price of socks doesn’t concern you, you may be more prone to sock loss. It’s debatable whether the Queen of England has ever even realised that sock loss was a thing. Meghan and Harry, however, might be a bit more conscious of the phenomenon in future.

Variable two: storage method

This is actually a multi-factor issue. Factor one: do you pair your socks together when you put them away? Our merry band of interns hypothesised that those who lack motivation for the proper pairing of socks when storing would be more prone to loss of individual socks. Factor two: the bigger the space you launder and store them in, the more room you have to lose your socks. Combine these two factors together, and you’ve got a veritable equation for losing socks.

Variable three: washing and drying technique

Just how often do you do the washing? Do you dry your clothes using a machine, or on the line? Our interns thought that those that wash more frequently, lose socks more frequently. The interns could have digressed at this point onto whether ‘tis nobler to lose a sock occasionally or have smelly socks, but fortunately for us they moved on to address drying technique. The group thought those drying socks on lines in windy areas may be more prone to losing. Here’s hoping that one of them goes back to university and suggests scientific study comparing average rate of sock loss between Wellington and everywhere else in New Zealand. It wouldn’t be the oddest study out there, after all.  

Variable four: sock characteristics

Factors include what size your socks are and what colour they are. Firstly, the group thought that those with smaller feet would be more likely to lose socks, as smaller items are generally easier to lose (keys, anyone?). Unfortunately, they were unable to quickly check this hypothesis amongst themselves as it turns out that they all have awfully average-sized feet. Secondly, if your socks are similarly-coloured to the background in which you remove them, you may be more likely to lose them. Particularly if, for example, you take off your photo-realistic grass socks while walking on a field.

Variable five: household residents

If you have small children, teenagers or dogs, let’s face it: you’re just going to be more likely to lose socks. If it’s small children or teenagers, just write those socks off now. If you have a canine friend in residence, there’s many, many articles online of what to do if your dog swallows a sock (aka very expensive sock retrieval), along with plenty of advice on how to prevent socks from going missing via this route.  The latter, our interns hypothesised, may have been helpful to the owners of the Great Dane who swallowed 43.5 socks.

Sock loss prevention and mitigation

Key variables identified, we asked our interns to discuss solutions that could prevent or mitigate sock loss. At this point, they definitely demonstrated just how creative they could be, with suggestions including:

  • Chameleon socks that change design so they match whatever other sock you are wearing.
  • Adding GPS trackers to socks.
  • Attaching socks together with a magnet – the implications for your washing machine are unknown.
  • Let humans evolve into one-footed beings, so that you never need a pair of socks. We may just have to wait a couple of tens of millions of years for evolution on that one, though – and even then, evolution might not prioritise sock loss as necessitating one foot.

One of their more cunning solutions, perhaps demonstrating some understanding of psychological engineering, was to not in fact attempt to control sock loss in anyway – rather to change the narrative, so that odd socks are perceived as “lucky”. After all, if it worked for bird poop, surely it can work for socks?

Their last solution – which we’re a massive fan of during these hot summer days – is for everyone to migrate to the beach, thus eliminating the need for socks altogether.

Many thanks to our 2019 T+T Summer Interns for their input into this article. We wish them all the best back for their studies this year.

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Another storm has damaged roads and trapped tourists in Fiordland so for this week's AAE, we ask Engineering Geologist Shamus Wallace:

Why is Fiordland so wet and why is Milford Sound one of the wettest places in the world?

A: Orographic Rainfall causing the Foehn effect.

This occurs because New Zealand is located in a part of the world that has a predominantly westerly weather pattern (air flows from west to east), is surrounded by water and has a relatively high and continuous mountain range - the Southern Alps - that creates a ‘barrier’.

Warm air from Australia and the tropics travels across the Tasman Sea, sucking up moisture as it goes. When that air flows into the Southern Alps, it is lifted up and over the Alps. As the Alps are relatively continuous, the air can’t go around as easily as it might if the South Island was smaller landmass. The rising air cools and the moisture condenses and falls as rain. Fiordland is usually the meteorological first port of call, so more moisture falls there, before the weather moves east (often the rainfall moves northeasterly up the west side of the Southern Alps). Once the moisture has fallen, the air now on the eastern side of the Alps, descends again - faster than it when it rose - which causes warm, dry (and windy) conditions in the eastern part of the South Island, while the west is being drenched.

Outside of tropical regions, Milford Sound is one of the wettest places in the world because of its unique conditions. In particular, this is because of the size of the Southern Alps, and the barrier they create to allowing prevailing weather systems to move on, as they might in other locations.  Many other land masses have a similar (but less dramatic) pattern, e.g. the north and east of the Hawaiian Islands are wetter than the south and west, as the Hawaiian chain sits in an easterly weather pattern – the Trade Winds). Northwestern states in the US have a similar climate, with predominantly westerly weather flow/patterns bringing moisture-laden air off the Pacific. This then being stopped by the Cascade Mountains, with high rainfall occurring in coastal Washington and Oregon, and even down to northern California, and eastern areas being significantly drier.

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February 29th - a “phantom date” that shows up every four years.

Adding this extra day at the end of February in years that are multiples of four helps sync up our Gregorian calendar of 365 days with the solar year of 365.2422 days. Leap day and leap year do seem a bit odd, but without it, our calendar would slip relative to the seasons.

With leap day a month from today we thought we’d switch up this week’s “Ask A…” segment, relying on the technical expertise of Siobhan Starck, a Tonkin + Taylor payroll specialist to answer this leap day themed question:

Q: If you're on salary do you get paid for the extra day in February this year, Leap Year?

A: Monthly Salaries are paid using a calculation of your Annual Salary divided by 12 months. This gives you your monthly gross salary.

Yes, there is an extra day in February this year. However, based on the divisor of 12 your monthly gross paid to you remains the same.

If you are paid by the hour and work Saturday the 29th of February, of course, you will be paid for that – likewise, if you are entitled to overtime.

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Q: Why is there a black market for sand? Is there one in NZ and will it become a problem?

T+T's Chief Coastal Engineer Richard Reinen-Hamill has an answer:

A: The black market for sand is driven by construction and land reclamation. However, with sand, not all sand is suitable.

For example, you would think sand for concrete in construction projects in the Middle East would be easy and cheap – you would just use sand from the Sahara Desert, right? Unfortunately Sahara sand
is too smooth and fine-grained and so it has to be imported from further afield.

It’s “suitable sand” that’s increasingly in demand and has become a valuable commodity.

There is a global black market for construction materials to build at a lower cost or to increase construction profits. The international sand and gravel market in the US and UK alone is in the order of $10 billion (USD) and markets such as the Middle East, India and China are all increasing demand for construction aggregate (gravel, sand and rock material used for construction).

In New Zealand, the aggregate market is more regulated and controlled and distance to market from international sources to New Zealand reduces the likelihood of importing bulk materials such as sand.

When Tonkin + Taylor conducted sand source investigations for the beach replenishment of Wellington’s Oriental Bay (in the early 2000s) we were offered beautiful white sand from Western Australia at a low cost, but due to mana whenua concerns and biosecurity risks, we sourced rock and crushed it into sand from a cliff near Nelson.

Q: If you were to fly to Fiji for the Christmas holidays, how many trees would you have to plant to offset your carbon emissions?

Sustainability Engineer Kate Boylan, with help from Environmental Consultants Roger MacGibbon and Kate Draper, has an answer:

Firstly, it feels like my duty to say, that offsetting your emissions is great, but reducing your emissions is the best! So, flying to Fiji (or anywhere) less regularly would be the best thing to do. However, your bags are packed and, being the good human you are, you would like to offset the negative impacts of your holiday flight. Carbon offset calculating websites are becoming popular, but we’ll use good old distances and emissions factors here.

To calculate the emissions, we use an ‘emissions factor’ which allows us to estimate emissions from a unit of activity data (e.g. litres of fuel used). In New Zealand, the Ministry for the Environment (MfE) provides emissions factors for most activities. Many human activities produce multiple Greenhouse Gases (GHGs) at once, however, to allow for meaningful comparisons, we commonly express GHG emissions as carbon dioxide equivalent (CO2-e).

Given you are just one person on the plane taking up just one seat, you are only responsible for a small portion of the flight’s overall emissions. If you are in an economy seat, you are responsible for fewer emissions than those in business or first class, purely because you take up less space.

The flight to Fiji, according to Google, is 2160 km. Assuming you can drag yourself away from the beautiful white sand beaches at the end of your stay, a return trip is therefore 4320 km. Because these flights are less than 3700 km (each way), it is considered short-haul. The emissions factor provided by MfE for an average passenger on a short-haul flight is 0.162 kg CO2-e/passenger.km, including Radiative Forcing Factors (where Radiative forcing factors help account for the wider climate effects of aviation, including water vapour and indirect GHGs (MfE, 2019)).

Therefore the emissions are the total flight distance multiplied by our emissions factor; 4320 km x 0.162 kg CO2-e/passenger.km = 701 kg CO2-e.

MfE also sets out standard ‘sequestration’ rate (carbon sucking up ability) emission factors for some of our common forestry carbon sinks. Planted forests can remove 33,807 kg CO2-e per hectare, whereas naturally regenerating forest can remove 5,097 kg CO2-e per hectare.

So, to offset your Fiji holiday flight emissions of 701 kg CO2e, we would need to plant 207 m2 of planted forest, or regenerate 1376 m2 of natural forest. Let's assume you’re looking to plant some fast-growing trees (e.g. radiata pine), where standard forestry spacing is initially around 1000 stems per hectare.

You would, therefore, need to plant 21 trees to offset your return holiday flights to Fiji.

If you are interested in some further reading, check out the MfE measuring emissions resources online, or for more information on specific sequestration rates see the Carbon Look-up Tables for Forestry in the ETS.

Thanks!
Kate (with help from Roger MacGibbon & Kate Draper)

What’s not to love about the great Kiwi outdoors? Cool, pristine bush, magical vistas and crystal clear waters await those of us who love to roam. But just how safe is it to drink straight from our streams and rivers? We asked one of T+T’s hydrogeologists, Dr Jeremy Bennett.

A: Water, water, everywhere – but which drops can we drink? It depends – water has a ‘memory’ of where it has been, or more specifically, what it has travelled through. Generally, the closer you are to where the water came from (i.e. the sky), the cleaner the water is likely to be. If you’re up the top of one of our many mountain ranges, then the water in the streams has not travelled that far and won’t have too many ‘bad memories’.  As you move down to lower areas, particularly where there are more people or animals, then it is highly likely that the water will be unsafe to drink due to the presence of microbiological contaminants like E. coli and Giardia. When you get sick from these nasties, the vistas are not magical.

The risks of waterborne disease are lower in conservation areas, and many trampers and hikers do drink directly from streams without too much trouble. However, you need to think carefully about where the water is coming from (its catchment). Are there farms or wild animals upstream of your location, or is the area often used by people? Even in the most pristine bush environment, there could be something just around the corner which will make the stream water unsafe to drink without treatment (dead possums are a common one). The Department of Conservation recommends that you boil water if you have any doubts about its quality and Wilderness Magazine has some good tips on collecting water during a tramp.

Q: How were the pink and white formations at Ōrākei Kōrako formed?

Senior Engineering Geologist Kevin Hind has an answer:

A: The light pink/white formation you see in the centre-right of the image is a ‘sinter terrace’. You may have heard of the famous pink and white terraces, which were formed in a similar fashion. These terraces form when warm spring water rises up through the earth’s crust. This water becomes enriched with minerals such as silica and chloride as it flows through the surrounding rock. As the water reaches the earth’s surface it cools. This cooling results in the minerals solidifying creating the terrace-like structure. The bright orange and brown are the result of bacteria and microbes thriving in the warm spring waters.

 

With summer almost upon us and tens of thousands of people already heading for the beach, we asked T+T Coastal Geomorphologist Eddie Beetham:

Q: How do you spot a rip current and what causes them?

A: An area of low wave height and limited breaking located next to an area of larger breaking waves will likely be a rip. A danger of rips is that low energy sections of beach are often more inviting for bathers than a section with breaking waves. Always watch the beach for a few minutes to identify rips before entering the water and swim between the flags.

Rip currents form when waves break on irregular sandbars spaced along the beach. This forces an offshore current to develop between sandbars, as wave energy piling up at the coast is released. The process of wave breaking creates a local area of elevated water level called ‘wave setup’ landward of the breakpoint.

If smaller waves are breaking at a neighbouring section of the beach, a setup differential is established and this drives an alongshore current from areas of high setup (where waves break) to areas of low setup (small wave locations). Setup driven currents converge in lower energy locations between sections of wave breaking and form a seaward directed rip current. The velocity of a rip current typically increases with larger waves and high-speed rips can erode a channel between sandbars that enhances the development of a rip cell.

Q: What happened to all of the debris (rocks/dirt etc) from the Kaikōura Earthquake landslides? Where did you put it after it was taken away? Is it used for other work somewhere? Where does all of the stuff that’s taken out of tunnels go too – like the Waterview Tunnel while Alice was boring the holes?

A: This is a key part of what engineers do – we work with the materials we are given, to use them in the most sustainable, practical ways. Where possible engineers will always try and reuse, recycle or repurpose local material from landslides and major excavations.

These two projects, in particular, dealt with almost unprecedented amounts of soil and rock.

Our Engineering Geologist Nick Peters and Geotechnical Engineer Peter Millar provide their answers below.

Waterview Tunnel

The bulk of the material from Waterview was used to backfill the Wiri Quarry in preparation for an industrial subdivision on the site.

The material that was excavated by Alice (the tunnel boring machine) resulted in a wet slurry, which required substantial drying and conditioning before it could be compacted as engineered fill. The basalt rock that was excavated from the northern end of the tunnel was used for a range of applications including coastal and road engineering following crushing and processing

- Peter Millar

Kaikōura Earthquake Landslide

The landslides that occurred as a result of the Kaikōura Earthquake in November 2016 inundated SH1 and the Main North Line both north and south of Kaikōura. The volume of landslide material generated by these landslides was many hundreds of thousands of m3.  Following the earthquake, the North Canterbury Transport Infrastructure Project (NCTIR) Alliance cleared the landslide material from the road and rail and implemented solutions to allow the transport corridor to be reopened.

Although much of the material was stockpiled, the landslide material was also used in a number of ways, including:

- As fill along sections of SH1 where the road was to be realigned

- Forming small bunds and stopbanks

- To create laydown areas for plant and machinery and other areas like helicopter landing pads

- Some of the trees that came down in the landslides were extracted and made available to local people, for example for carving

Other landslide debris material was stockpiled because it contained organics (i.e. bushes and trees etc) or was too wet to use – this was in part, due to helicopter sluicing that was undertaken to remove unstable material from the slope faces.

- Nick Peters

This week we're switching things up and instead of Asking an Engineer, we're Asking an Ecologist!

Q: Why do lizards in NZ have live young?

Our Ecologist Kat Longstaff has the answer:

A: NZ has over 110 species of native lizard both geckos and skinks (Tuatara are a reptile, but are not lizards).

New Zealand lizards are unusual in that only one, the egg-laying skink which lives near rock pools at the coast, lay eggs. The others are viviparous – they give birth to live young. Vivipary is thought to be an adaptation to New Zealand’s cooling climate during the ice ages. As lizards are ectotherms (do not generate their own heat but need to absorb it from their surroundings), staying within a warm mother ensures the survival of young.

Due to their viviparous nature, native lizards have fewer young than their egg-laying overseas cousins, generally two for geckos and between two and seven for skinks. This is in contrast to the introduced plague skink from much warmer Australia that can lay up to 80 eggs!

Many of our lizard species survive in cold climatic conditions, including alpine environments.

What are the weird holes that you see in the side or top of hills, for example in the Port Hills in Christchurch?

Great question! The answer is that the terrain up in the Port Hills is made up of Loess (rhymes with purse). Loess is composed of wind-blown dust or silt that has been loosely compacted. Most areas of loess were likely formed during glacial periods where there was very little vegetation. Because the build-up of dust/silt is not very well compacted, the loess is extremely prone to being eroded or removed from the hillside, particularly in heavy rain.

This can result in tunnels or gullies forming underneath the soil/grass surface - this is called piping. Some of these are large enough to fit a small person - but you should never get in one!

Loess is found widely across the South Island around the Canterbury Plains and on Banks Peninsula. Areas in China and the United States Midwest have loess deposits tens of meters thick!

Rebekah Robertson (Geologist)

 

Q: Can you please tell me if you can hurry up the pedestrian crossing by pressing the button lots of times to tell the machine there are lots of people waiting?  I have this terrible feeling that you can’t and that’s an urban myth.

Signed

Trent,

Auckland

A: Hi Trent,

Unfortunately not. Pushing the button more than once doesn’t make any difference to the lights at a pedestrian crossing. This is because the lights are programmed in a specific sequence made up of a number of phases. When you push the button the pedestrian phase is called, meaning the pedestrian light will turn green next time it appears in a phase in the sequence. However, once a phase is called pushing the button again doesn’t do anything because the call has already been made.

Thanks,

Matan

Q: Obviously it's more expensive to Uber than to Bus but if your only concern was sustainability, would it be better to Uber to travel to work in an electric car or ride in a fossil fuel-powered bus?

Thanks,

Marie, Wellington.

 

A: Hi Marie,

That’s a great question, thank you for sending it through. Our Sustainability Engineer, Kate Boylan has an answer:

We believe that despite the emissions that our diesel bus fleets emit, they are the more sustainable option. The more people we have on each bus, the less emissions there are per person when that is split evenly. Also, given a standard bus can take around 50 passengers, that’s around 50 cars that are not travelling on the same roads. Even if they are electric or hybrid cars; fewer cars means less congestion, which would make it easier for our buses and public transport vehicles to get around. Less congestion also means that the buses have to stop and start again less often, which saves on fuel, and therefore emissions. Less congestion also means that everyone travelling would save time, and we all know that time is precious, and time is money.

Fewer individual cars on the road saves space. If everyone used a bus, train, or active modes of transport to commute, we would need less road space overall. Just Google image ‘road space cars vs bus’ for some visual examples of this. We would also need less space to be used for car parking at workplaces, this would save you or your company money, as that space could be utilised for something far more useful.

However, vehicles on roads pollute more than just fuel emissions. Vehicles often pollute rubber and brake pad particles to the surrounding environment of roads. Stormwater run-off from our roads flows directly out to sea with these contaminant particles in tow. Buses also contribute these pollutants, however, as we’ve seen visually above, fewer buses are required to transport the same amount of people. Fewer individual cars on the road could also reduce the wear and tear on the road. Currently, high-traffic roads need resealing every seven years. If there was far less traffic on these roads, they could be replaced less often. This would require fewer materials and construction works, therefore a dramatic saving in construction emissions and embodied resource emissions.

As a fare-paying passenger of your local public transport system, you are supporting your local council or transport body. This revenue can help increase the investment in more efficient and better public transport vehicles and overall systems. After all, every dollar you spend is a vote for what you want to see in the world. Our councils are already starting to look into Electric and Hydrogen fuel buses, so they could be cleaner than your Uber in the near future.

Lastly, from a high-level sustainability perspective, buses and public transport represent changing people’s habits to a more sharing and circular economy. Instead of owning cars, electric or otherwise, could we hire them as we need them?

We hope that answers your question - see you on the bus!

Thanks,

Kate

Q: How come the Japan vs Scotland game at the Rugby World Cup was able to go ahead at Nissan Stadium in Yokohama, despite the massive floods caused by Super Typhoon Hagibis? 

Steve, Ruakaka

A: Hi Steve! It comes down to some pretty nifty engineering. The stadium is built on massive pillars that lift it above the flood level of the river. You might remember seeing that the adjacent Shin-Yokohama Park was totally awash, even while the pool game was on. The Park acts as a large flood retarding, or storage basin for the Tsurumi River, and, during a flood, overflows into the Park as it did during Hagibis. After the flood a drainage gate feeds water from the Park back into the river. Result? One flood-beating stadium - so the players at Yokohama stadium get to keep their feet dry! 

 

 

Q: After reading about how raw sewerage leaked into Wellington Harbour last week when the stormwater drains became blocked by a fat berg, I started wondering about whether peeing in the shower could contaminate our harbours and sea life.

I occasionally pee in the shower – I suspect lots of people do but I’m quite happy to put up my hand and admit to it. But now I’m wondering whether my peed-in shower water goes down the stormwater drains and out to sea untreated?

I’d really like to know, from one of your engineers, whether I should continue to pee in the shower or not? 

Sincerely 

John (not my real name)

Timaru

A: Hi John,

Fantastic question! Assuming your house has been plumbed correctly, your shower water (and shower pee) will make its way into the same sewer system as the flush from your toilet. Once your pee has journeyed down the sewer line, it will be treated and made safe to return to the environment.

As I mentioned above, this is all assuming your house is plumbed correctly. In some cases, wastewater is finding its way into the stormwater network, which ends up in the rivers and beaches that we swim in and our fish life live in.

Tonkin + Taylor is working with local councils around the country to track down and resolve these types of issues.  I encourage you to ask your local council about the water quality at your swimming beaches or check out websites like Auckland’s www.safeswim.org.nz.  Safeswim helps keep people informed about public health risks at bathing beaches using a live and forecasted safety rating.

Now, back to the pee. The shower could well be the best location for your pee! By peeing in the shower you are actually conserving the water that would have been used on a toilet flush. As to whether you should pee in the shower or not, if you are confident your plumbing and sewer is in good shape, then I don’t see any reason to change!

 - Ben Perry, Water Engineer

 

Q: Dear Engineers

I have been following Gareth and Jo Morgan’s motorcycle tour through Eastern Europe on Facebook – it’s quite interesting.  I now have a question for your geologists, the Morgans are in Russia and travelling in an area 30 metres below sea level, where does the water from streams and rivers run to when you’re that far below sea level? It can’t run uphill to the sea, can it?

Peter, Invercargill

A: We asked hydrogeologist (groundwater scientist), Dr Jeremy Bennett to respond.

“Great question, Peter! Water cannot run uphill… or can it?

The answer to your question is hinted at in the salty soil of Jo Morgan's Facebook post. The Caspian Sea does not have any natural outlet so the only way is up – evaporation! As the water evaporates, the concentration of minerals gets higher – this is one reason that the Caspian Sea and surrounding area is so salty. A similar process is used in our own backyard to produce table salt at Lake Grassmere near Blenheim. Other places where water evaporates instead of flowing to the ocean (endorheic basins for those who like big words) include Lake Eyre in Australia and the Bonneville Salt Flats in Utah, where fellow Southlander, Burt Munro set the under-1000cc speed record in 1967”

Q: Hi, I have just moved into a place with a swimming pool and am getting quite upset because I keep finding drowned honey bees, bumble bees, worms and skinks in it. Also the occasional German wasp - but who cares about them, right? Is there a way I can prevent this? Would a cover work? And what attracts them to it? Any advice would be much appreciated, it’s so upsetting to see dead bees.

Yours sincerely - Jennifer (Takapuna)

A: Hi Jennifer,

It’s a question that often pops up during summer and we've asked our ecologists to help you with it. Herpetologist (lizard expert) Dr Matt Baber and entomologist (insect expert) Dr Briar Taylor-Smith explain the issues below.

In most of urban Auckland (including Takapuna) there are two species of skink: native copper skinks (Oligosoma aeneum) and the introduced Australian plague skinks (Lampropholis delicata). Copper skinks are nocturnal and don’t move far from the bush and rocks in which they hide away. On the other hand, plague skinks – which are named so because they are found in very high numbers – are active during the day running about on driveways and other open spaces, and are therefore more likely to become trapped in pools. 

Bees need water for drinking, diluting their food and for hive ‘air-conditioning’. They like reliable water sources, so once a colony has decided that it likes your pool, the workers will keep coming back for more. In natural settings, such as streams and lakes, there are places for small animals to stand and drink. The problem with swimming pools is that water doesn’t come all the way to the top, so they have nowhere to stand and if they do fall in, they have no way to escape.

You can help out flying insects by floating things in your pool, such as corks, sticks or kick boards, which will provide a platform for drinking and a gentle slope that will allow them to climb to safety if they do fall in. However, to save lizards and worms (which tend to sink to the bottom), it’s best to invest in a pool cover.

You can create an alternative water source for bees and lizards by placing pebbles in a shallow container. Fill it with water leaving only the tops of the pebbles exposed to provide a safe landing spot for bees. Keep the container in a shady spot in your garden and top it up regularly, especially in hot weather.

Hopefully the bees will find and begin to prefer that as a water source quite quickly and you won’t find as many of our precious critters submerged in the pool.

 

Q: I’m a big fan of Mid-century Modern/Palm Springs architecture... and especially love the stone walls that feature on the more expensive homes built in that style in the 1960s and 70s.

There is a particularly spectacular one on St Johns Rd in Auckland - it is unusually colourful. Would one of your geologists know why it is so different to the other ones around Auckland? - Rachel, Mission Bay.

A: Great observation Rachel! Engineering geologist Kevin Hind and geology graduate Rebekah Robertson have an interesting explanation!

Those rocks have travelled a long way to feature in this stone wall.
They are particularly colourful because the vast majority of them appear to be schist, and schist is predominantly found in the South Island – people may know it as “Queenstown Stone”. 
Schist is typically formed across an entire region through a process called ‘metamorphism’. In many places throughout New Zealand we have a rather boring rock called ‘greywacke’ that is quarried for things like the rock you see under railway tracks (or aggregate). Greywacke around, and under, the Southern Alps is exposed to high pressure and heat, as it is squeezed along the Alpine Fault, turning it to schist. The colours of the schist typically reflect what’s called the different ‘grades’ of metamorphism, meaning the amount of pressure or heat the greywacke has been exposed to. For example, a blue coloured schist would typically have been exposed to higher pressures than a green coloured schist.                       

As the pressure and temperature changes, so does the rock's mineral make up, texture and colour. The colours and the shiny nature of the schists come primarily from the presence of a mineral called ‘mica’ – which, fun fact, is also typically what make things like eyeshadows and other make-up shiny.
The mustard/orange coloured rock in this wall is volcanic and called ‘ignimbrite’ - it has been stained by the presence of iron in its makeup that has multiple segments of other rocks imbedded in it. This type of rock is typically formed from huge super-violent eruptions that send clouds of hot ash, pumice and other rock fragments across the landscape at hundreds of kmph. Perhaps the ignimbrite in this stone wall flew from Taupō all the way to Auckland?
If you have a question for one of our engineers, please contact us via ask@tonkintaylor.co.nz

 

Q: Can wind seriously blow a building over?

- Anna, Lower Hutt

A: That’s a really good question, thanks Anna. Alex Vink, Structural Engineer has an answer!

In a word, yes wind can absolutely blow buildings over. What’s really interesting is all the ways wind can cause structures to fail. 

Wind is mainly caused by the rotation of the earth, which causes the air in the earth’s atmosphere to move. When the wind blows, structures like buildings and bridges obstruct the air flow. This causes the air to flow around the obstruction and generates a pressure or drag on the obstruction. Engineers need to design their buildings and bridges to make sure that they can withstand this pressure.

In a storm, the air particles can move very quickly. This can generate large pressures and drag on buildings. If these buildings and their foundations have not been designed to be strong enough to withstand these large forces that are generated, they can topple or collapse. This happens quite commonly in the Pacific Islands during cyclones.

 

It’s not just large wind pressures that can make buildings or bridges collapse. During the life of a bridge, it will experience a lot of changing wind with different pressures. It may only experience a couple of really big storms, but lots of small gusts of wind can cause the bridge to fail due to a phenomenon called fatigue. Some materials, like steel, get weaker when they are exposed to many cycles of loading (like changing gentle breezes) and when they experience enough cycles, they can break. This is a bit like bending a paper clip back and forward until it breaks.

Perhaps the most famous example of a bridge collapsing due to wind is the First Tacoma Narrows Bridge collapse. The wind caused the suspension bridge to vibrate excessively without the wind speed increasing because the bridge was not able to absorb all the energy from the vibrations. Eventually these vibrations became too big and the bridge became unstable and collapsed. This phenomenon is called aerodynamic flutter. Engineers need to consider these effects when designing bridges.

If you have a question for one of our engineers, please contact us via ask@tonkintaylor.co.nz

Q: If The Wall from the Game of Thrones was built in real life, how deep would the foundations need to be? Would it actually be possible to build it out of ice? NB: The Wall is meant to be 300 miles long, over 700 feet (213m) high, and made of solid ice.

- Grant, Tikitere

A: This is a goodie, thanks Grant. Mark Thomas, Senior Geotechnical Engineer has got the answer!

Mark: "How come I get the question about fictitious magic stuff?!

I know more about soil and rock than I do about ice. I know glaciers get way thicker than that, (~1500m thick) and the Greenland and Antarctic ice sheets are in the order of 2000 to 5000m thick! But they don’t have vertical cliff faces nearly that high.

In order to be strong enough to form a 213m high vertical face, the ice would need to have a theoretical mass strength of at least 2MPa UCS, which doesn’t even take into account defects within the ice. On top of that, Martin Truffer has pointed out that ice doesn’t hold its shape, and I guess that’s where you need a bit of Old Gods magic to keep the whole structure from falling apart.

Building a structural “foundation” for the wall wouldn’t really cut the mustard. You’d really want to dig down and build the wall on solid bedrock. Depending on the strength and fabric of the rock, you might have to dig tens of metres deep to support the steep sides of the wall. Given the size and weight of the wall, you’d probably also induce quite a few localised earthquakes during construction. That could be a problem for nearby masonry castles and forts due to their brittle construction; but less likely to be an issue for a typical wildling hut.

It’s a bit strange that the wall was built out of magic ice. If I was in charge of the wall’s construction, I would have opted for magic rock or magic concrete, which would be much more robust in both a structural sense, and in its resistance to dragons and long summers. Donald Trump, if you’re reading this, give me a call".

- Mark Thomas, Senior Geotechnical Engineer

 

Q: Why is Ramp 4 out of Waterview SO BIG?!

- Andrea, Meadowbank

A: Thanks Andrea, our roading expert Matt Arcus has the answer on this one for you!

At the Northern end of the Waterview Tunnel, the interchange is made up of a complex set of ramps. Each individual ramp crosses over multiple carriageways but ramp 4 crosses the most carriageways.

In order to cross these carriageways AND meet the required road standards and design criteria, ramp 4 needs to be much taller than the other ramps. And with height comes the need for a bigger supporting structure and extra road length to address the change in height (so that driving down ramp 4 isn’t like being on one of the Big 5 at Rainbow’s End).

The roading standards and design criteria are mostly linked to the design speed of the road. Some of the biggies are:

  • Minimum curve radius: how tight you can make the curves - so that the forces keeping you on the road oppose the centrifugal forces trying to throw you off!
  • Superelevation: the amount of pavement banking around the horizontal curves to counteract the effect of centrifugal forces acting on the vehicle
  • Stopping sight distance: the amount of road you need visible in front of you to identify a hazard, react and then come to a complete stop
  • Maximum vertical grade and vertical curve requirements: how steep we can make the road and how much vertical curvature is needed so that we can see over a crest in the road
  • Vertical clearance requirements: how much head room we need between crossing carriageways to allow larger vehicles to pass beneath

Another significant part of designing any road is safety. This can add additional constraints to the design, such as making the shoulders wide enough to see around the bends, or safely accommodate a broken down car.

 

Q: How long will the eruption of the volcano on Kilauea in Hawaii last?

- Paul, Onehunga

A: Good question! One of our resident Volcanologists Alec Wild has got an answer for you!

The short answer is we don’t know! It’s difficult to determine how much magma beneath the volcano is going to be ejected, and over what timeframe, as we cannot directly observe it.

Kīlauea Volcano on Hawaii’s Big Island has been erupting on and off since 1983. However, this most recent phase has formed long cracks in the ground called fissures, along the East Rift Zone to the east of the main vent. The rift zone is a thin strip of land that is being separated, allowing magma to travel up and down. Once the magma reaches the surface and forms fissures, it produces fire fountains and lava flows. Of particular note are the fissures that have formed in a residential subdivision, Leilani Estates, resulting in the evacuation of residents and damage to properties and infrastructure.

The lava level from Kīlauea main summit has dropped, which indicates that the lava could be moving along the rift zone. Volcanologists are monitoring the lava level, seismic data and ground deformation to try and predict where the magma is moving and where it might come up to the surface.

This eruption is considered, based on activity and affected area, similar to the 1955 event which occurred in the same rift area, and lasted 3 months. During the 1955 event with lava flowing both north east and south west of what is now Leilani Estates. Although this is similar, we cannot definitively say that this eruption will be of the same duration.

- Alec Wild, Natural Hazards Specialist, MSc Quantitative Volcanic Hazard and Risk Modelling

 

 

 

Q: I have been transfixed by that dramatic, jagged, golden cliff face that features in the British TV programme, Broadchurch. Would one of your engineers kindly explain (in layman's terms) how it was created.

- Shirley, Remuera.

A: Great question, Shirley. Our legendary engineering geologist Kevin Hind was dead keen to answer!

"The steep cliffs of West Bay in Dorset on England’s Southern coast are made of extremely weak and highly erodible sandstone. They originally formed from layers of sand, mud and shell fragments that settled onto the ocean floor sometime between 183 and 174 million years ago.

It took a whopping 860,000 years for the full 43 metre thickness of cliff to develop! The build-up of sedimentary sand layers happened extremely slowly, forming at an average rate of one metre per 20,000 years. All those horizontal layers of sediment are clearly visible in the cliff face - just like they are in the cliffs of Auckland, which formed in a very similar way.

Years of wave erosion has formed the cliff face itself, most of which occurred since about 6,000 years ago, at the end of the last ice age, when sea levels stabilised at their current levels.

The corrugated look of the cliffs is caused by two things. Firstly, the geology contains two sets of strong sub-vertical joints, along which cliff collapse generally occurs. This results in tall, flat-faced columns, which stand out from the overall cliff face with recesses between them.

This close up image clearly shows the sub vertical joints in the rock formation, this effect is called ‘buttress and groove’.

Secondly, extensive landslips that occur at the top of the cliff within the soil and weathered rock. These landslips occur on a regular basis along the length of the cliff, giving it that serrated and ‘bread knife’ appearance. This, combined with the rock buttresses, give the cliffs their remarkable corrugated appearance".

Unique geology and erosion combined to create the ‘bread knife’ appearance of the cliffs along the Jurassic Coast.

So what about that golden yellow colour?  

"That’s actually the result of an oxidation process enhanced by beautiful cinematography. The rock is naturally a grey-blue colour, but when exposed to oxygen, the mineral ‘pyrite’ (also known as ‘fool’s gold’) changes to yellow limonite – snap – there’s your yellow stone".

- Kevin Hind, Senior Engineering Geologist

 

 

 

Q: Why doesn’t my bike trigger some traffic lights?

Sometimes I have to wait ages for the lights to change when there’s no traffic - Linda, Tauranga.

There are a number of reasons why this could happen, however, the most common is that your bike might not contain enough metal to be detected by the electro-magnetic sensor loops used by the traffic lights system.

You can usually see these sensor loops at the lights, in the pavement as dark rectangular lines near the stop line of each traffic lane.

Other reasons why your bike may not trigger the traffic lights include that you haven’t ridden over or near enough to the sensor loop, or the sensor loop’s sensitivity setting is not high enough. 

To reduce this issue in New Zealand, bicycle-specific sensor loops are sometimes installed where bikes at traffic lights are more common. Some cities also have cycle stop boxes (see photo below) at intersections, with painted symbols to show where the cyclist should stop for detection - Transport Engineer, Jeremy O’Neill.

 

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