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How are potholes formed? Senior Geotechnical & Pavement Engineer Prasanna Punchihewa shares his answer below:
A: Potholes typically occur in thin asphalt surfaced, spray sealed and unsealed pavements.
Potholes form in thin asphalt and spray sealed pavements when moisture makes it way beneath the wearing course (asphalt or spray seal layer) through excessive voids and a segregated/cracked surface. Once the pavement base course (first gravel layer) is saturated, the fine particles within the base course are brought to the surface through the voids and cracks upon by moving traffic.
Eventually, the wearing course loses the support and potholes are formed.
Moisture beneath sealed pavements could also occur due to low bitumen content, aging, oxidisation, hardening, and an incorrect mix design of the wearing course material.
In unsealed pavements, the development of potholes is triggered by stripping of the surface material, and the infiltration of water with fine particles carried away by wheel action on the surface.
Inadequate permeability, inadequate surface drainage and excessive rutting are the typical causes.
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Why does structural behaviour change in different types of soil? We passed this question on to Engineering Geologist John Westerson - take a look at his answer below!
A: All soils are made up of an arrangement of solid particles and voids.
At a basic level, the structural makeup of a soil is largely determined by a combination of shape and size distribution of the solids. You can relate this to a well-graded angular soil packing tightly with good interlock between larger particles and with the smaller particles packing most of the space in-between, compared to a uniformly graded soil with rounded clasts effectively stacking around and on top of each other with relatively large void spaces between them (sand on the beach for example).
The void spaces are filled with varying quantities of air or water which has a direct effect on the strength of the soil. Using beach sand as an example, we know that in its dry state the sand is loose and does not have a great deal of strength and will flow through your fingers. However, add some water and partially saturate the same material, the surface tension of the water particles creates a suction that acts to bind the solid particles, enabling you to mould the sand and construct your sandcastle - add too much water and the soil liquefies.
The beach sand concept is true of all soils in that the relationship between solids, void spaces, air, and water controls the potential for behavioural change in the soil structure. But that’s only part of the story. Mineralogy and consolidation history are also important considerations, especially when we are looking at a soil from an engineering perspective. In short, better-consolidated soils are denser, have smaller void spaces, and therefore present a lesser risk of settlement when loaded. Settlement occurs when the soil is loaded and the void spaces are crushed. If water is present in the voids then it has to find a way out before the void spaces can be compressed. In soils (e.g. sand) with good connectivity between void spaces (and favourable boundary conditions), this can happen relatively quickly following initial loading. If a soil has poor connectivity between void spaces (e.g. clay) then for the same load the water will take longer to expel.
Conversely, when some soils (e.g. clay) and tertiary soft rocks (e.g. claystone and mudstone) are unloaded (think deep excavations) an immediate reduction in pore water pressure occurs; they can also experience a component of elastic rebound. If below the water table, groundwater flows back into the newly expanded voids equalising the pore water pressures giving rise to what we know as 'base heave'.
A related example worth noting concerns excavations in built areas where soils on neighbouring sites are already loaded. In these cases the sidewalls of the excavation can provide an unconfined free space for water from the neighbouring site to flow into, this can effectively dewater the soils beneath neighbouring building foundations and present a very real potential for settlement and damage to those buildings.
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Is it true that animals can predict earthquakes? We passed this question on to Geotechnical Engineer Dr Luke Storie - take a look at his answer below!
Earthquake prediction is something us mere humans strive to be able to do someday. The best we can do at the moment is estimate the likelihood or probability that an earthquake of a certain magnitude will occur at a given location, often providing a return period such as 1-in-1000 year or 1-in-500 year, which can be quite confusing - no one can say exactly when a big earthquake is going to happen. We have done some amazing things with sensors placed on the ground surface that record small to large shaking events, including recent advances in GPS equipment that have allowed “silent” earthquakes or slow slip events to be detected. Some have wondered, though, whether our animal friends hold the key to predicting earthquakes, or at least giving us an early warning.
There are a lot of anecdotal reports of animals becoming agitated and fleeing from earthquakes before they happen. As early as 373 BCE, rats, weasels, snakes, and centipedes were reported to have left their homes and headed for safety several days before a destructive earthquake. There have been reports of wild animals leaving nesting areas before earthquakes and pets and farm animals becoming restless hours before a large shake. However, these observations have typically been made after the earthquake has occurred and it has often been difficult to directly correlate the animal behaviour specifically to earthquake prediction.
An earthquake forecast was made in China decades ago, based on small earthquakes and animal activity. People stayed out of their homes and when a large earthquake did occur, they avoided the widespread destruction that occurred. In some Italian towns, it is common practice to sleep in your car if you feel smaller tremors in case a large earthquake follows, which has been passed on from generation to generation. However, many large earthquakes are not preceded by any precursory events. In the example from China, the next large earthquake event was not able to be predicted in the same way and thousands of people died.
It is thought that some animals can detect signals that humans cannot, such as tilting of the ground, variations in electrical or magnetic fields, and changes in groundwater. One study suggested animals’ instinctual fight or flight response may have evolved over millennia to be able to detect these things and act as a sort of early warning system. Some animals are also thought to have a heightened sensitivity to an earthquake’s primary seismic waves (P-waves) that arrive before the secondary (S-waves), shaking waves. This could explain why animals have been observed reacting and running away right before the ground starts to shake.
Last year, Germany’s Max Planck Institute of Animal Behaviour and the University of Konstanz investigated whether cows, sheep, and dogs can actually detect early signs of earthquakes. They attached sensors to animals in Northern Italy, where a lot of earthquakes occur every year, and recorded their movements over several months. The data showed that the animals were unusually restless hours (up to 20 hours!) before earthquakes occurred and the closer the animals were to the epicentre of the earthquake, the earlier they started behaving strangely. It is early days for this research, but next they want to use the global animal observation system Icarus on the International Space Station to observe a larger number of animals over a longer period of time.
It may not be that animals can strictly predict earthquakes, but this latest research may find that their heightened senses could help us develop an earthquake early warning system.
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Can a computer generate a truly random number? We passed this question on to Data Engineer Nathan McDougall - take a look at his answer below!
Computers are essentially rule-following machines. They’re designed to do exactly what they’re told, and do it exactly the same way every time. But we—the human programmers—need to decide what those rules are. If we want a computer to generate random numbers, we need to create a set of rules to do it.
So, can we create a set of rules which can be used to generate truly random numbers? Well, it depends on what you mean by “random”. This is a bit of a philosophical question, but generally when we say something is truly random, we mean that it doesn’t follow any pattern at all; it’s completely unpredictable. If that’s what we mean by random, then unfortunately computers cannot generate truly random numbers, because any mathematical rule which someone comes up with to generate random numbers also happens to perfectly describe the mathematical pattern that those numbers follow. Anyone can follow the same rules as the computer, and get the same sequence of numbers: so those numbers are predictable and not truly random.
But that’s not the end of the story. Even if the numbers generated by a computer are not completely unpredictable (because they follow a rule), it might be that the rule that they follow is complicated and does a very good job at coming up with numbers that look random. For these special number-generating rules, if you didn’t know in advance what that rule was, it would be extremely hard to work it out from looking at some numbers which have been generated. Even if there is a pattern to the numbers (so the numbers are technically predictable), the pattern itself is basically unpredictable (and nearly undetectable). This kind of randomness is called pseudorandomness, and when someone talks about computers generating random numbers, this is almost always what they are referring to.
Over the past century, computer scientists and mathematicians have come up with better and better pseudorandom number generators, and the consensus is that these sets of rules create sequences of numbers that are basically as unpredictable as truly random numbers. As engineers and scientists using random numbers for simulations and analysis, pseudorandom numbers actually have a number of benefits over truly random numbers as well, because the sets of pseudorandom numbers are reproducible. Reproducible results are always important in engineering analysis, and pseudorandomness gives a convenient way to achieve this while still getting the kinds of unpredictable sequences of numbers we need.
In case you’re sceptical about how well pseudorandom numbers really do the job: you probably rely on them every day! The whole internet is kept secure, including passwords and banking transactions using (really, really big) pseudorandom numbers. Generally, though, a little bit of outside randomness is used as a starting point, for example using the time on the clock. You can try this yourself: if you have a digital stopwatch, you can press the start button, wait a bit of time, and then press the stop button and look at the millisecond digit: it’s changing so fast that the exact number that it lands on when you press the stop button is basically random. Every so often, computers can do the same thing with their own internal clocks to add a bit of external randomness into the mix. This is usually enough for everyday applications, but in exceptional cases, truly random sources can be used, like lava lamps, or radioactive decay.
In short, it depends on what it means for something to be “truly random”, but for all intents and purposes, computers can produce numbers that appear indistinguishable from truly random ones, and that’s good enough, even if they aren’t random in a philosophical sense. The use of these pseudorandom numbers requires careful consideration, but they provide a powerful tool for engineers and can be relied upon for incredibly important applications.
How do I choose a sustainable Christmas tree? Principal Environmental Consultant Jo Ferry has some ideas – take a look below!
A: With Christmas fast approaching, I’m sure you have all been wondering what to do about a Christmas tree this year - here are some options to help you pick a Christmas tree this festive season, ranked from most sustainable to least sustainable:
1. Decorate a living tree or another plant on your property
- This option really has the lowest environmental footprint because it won’t cost you anything and there will be no waste.
- The tree will also continue to give back by absorbing carbon dioxide and helping you and your family breathe.
2. Opt for a living tree from a local nursery that is planted after use
- A nice tree might cost you a little, but it will give back for years to come. You can plant it in a pot and reuse it each year! There’s also no waste and you will be supporting a local nursery in the process.
3. Go for an artificial tree made from upcycled or recyclable materials
- Driftwood, pallets or cardboard make great cheap, and low-carbon alternatives to traditional fake Christmas trees. There are plenty of products on the market or get creative and make your own!
- If you decide to buy your alternative artificial tree, think about buying local and ask the company to minimise the packaging that comes with it.
- If you decide to make your own, make sure you close the loop by recycling the materials after use.
4. A cut Christmas tree from a local supplier
- Christmas tree farms may be taking up valuable land that could be used for food production, and once the trees are cut down, the carbon they have absorbed will eventually be released into the atmosphere again. The transportation and disposal of the trees also increased their environmental footprint.
- If you decide to buy a cut Christmas tree, choose one that is grown locally and check that the tree will not end up in the landfill when you are finished with it. Buy from a charity group if possible!
5. Purchase a high-quality artificial tree which you keep for 10 years+
- Artificial trees are generally made of plastic and not designed to last a lifetime so they are definitely not at the top of the list. However, looking after your tree is one way to make this option greener.
- Again, buy local and look for reduced packaging (although remember to hold onto the packaging so you can store the tree securely throughout the year).
6. Cheap artificial tree that is discarded after 1-2 uses
- This is the least sustainable option - Santa will put coal in your stocking if you go for something that is not going to last past Christmas Day!
Why do soldiers break stride on a bridge? We passed this question on to Physicist and Senior Acoustic Specialist Darran Humpheson - here's what he has to say:
A: The answer to this question has nothing to do with the varying stride length of marching soldiers or the steepness of the bridge. It dates back to 1831 when a brigade of British Army soldiers were marching across Broughton Suspension Bridge in England. History notes that the bridge broke apart - throwing dozens of men into the water. Thereafter, new orders were sent out by the British Army that soldiers crossing a bridge must break stride to stop the unfortunate event occurring again.
The footfall from each soldier imposed a simultaneous downward force on the bridge at a rate which likely coincided with the natural resonant frequency of the bridge. As the soldiers marched, the initial small movement of the bridge in an up and down motion was amplified, and the ‘vibration’ or rate of displacement grew to such a point that the bridge broke apart.
The same observation occurred in London in 2000. The newly opened Millennium Bridge was soon closed and redesigned after pedestrians caused the bridge to resonate.
Interestingly, as people walked across the bridge, they started to walk in unison to match the lateral side-to-side movement of the bridge. This ‘marching’ caused even more movement of the bridge. Dampers had to be fitted to remove the lateral movement.
Why are diamonds the hardest material on Earth? We passed this question on to Engineering Geologist George Brink - take a look at his answer below:
It is a common misconception that a diamond is the hardest thing you will find on planet Earth; this honour actually goes to former Springbok rugby player Bakkies Botha. We can, however, ignore this oversight, as there is every indication that Bakkies is not even from this planet…
Diamond is the hardest naturally occurring material on Earth and an allotrope of carbon (allotrope - one of two or more forms in which an element may exist, another form of elemental carbon being graphite). To explain however why diamonds are so hard while graphite is soft (think the lead in your pencil), it is necessary to delve deeper (pun intended) into how diamonds are formed and their resultant crystalline structure. The differing properties of graphite and diamond arise from their distinct crystal structures. Diamonds are formed under conditions of extreme heat and pressure, the likes of which are mostly only achieved deep (150 – 250km) within the Earth’s crust.
Here, temperatures average 900 - 1300 degrees Celsius and pressures are many times that of atmospheric pressure at the Earth’s surface. Under these conditions, carbon atoms are arranged tetrahedrally in a very strong, rigid three-dimensional crystalline structure to form the extremely hard, high-density material we know as diamonds. In graphite, however, carbon atoms are arranged to form a layered structure (i.e. exist as sheets of carbon atoms) and weak bonds between layers allow these to move relative to each other, which means the material is more deformable (i.e. softer).
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.
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….
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.
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.
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.
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!
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.
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.
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”
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:
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.
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!
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.
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.
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.
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.
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.
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).
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!
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:
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:
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:
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:
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.
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.
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.
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.
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!
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).
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
Height of can in cm
Diameter of can in cm
Diameter of spaghetti / mm
Volume of can in cm3
Quantity of spaghetti per can
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.
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.
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
What’s not to love about the great 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.
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.