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This river can be switched on and off

This river can be switched on and off

The trouble with a lot ofreal world experiments is that you can't have a control group. If you're researching, say,how riverbanks are affected by erosion, then either you have toobserve the erosion happening in the wild, with lots of messy variableslike weather and climate and wildlife, or you have to rely on tiny scale modelsor computer simulations. You can't take an actual river,let it erode its banks for a while, then stop the water, rebuild everything, and just run it againwith one thing changed.

Unless you build your own river,which is exactly what the University of Sherbrooke in Canadahas done. Will you start the pumps, please! – So I’ve done a lot of studiesin nature, on real rivers. You do get excellent information, but you can't pick outspecific variables and play with them. We built this with the ideathat we can study sediment transport on a scale that representsclose to a small river or creek. The water starts in the reservoir.

The pumps pump from the reservoir,and then it discharges into the approach channel,which is made to be very large, so that we diminish any turbulence that might be brought in thereby the pumps. After that, we have a weir, and then itarrives in the river and goes down. And that's where we do our experiments. And the river fallsover an overflow into a sediment trap. From the sediment trap,it goes back into the reservoir. It’s a recirculating system.

Probably takes 2 or 3 minutesfor the water to recirculate. It is all repeatable. We can adjust the pumpsfor a certain level, have that one day, come back a week later and have the same flowcoming through the system. We have two 70kW pumps. At the moment, we have 800 liters persecond, and we have room for another pump. – Okay, compared to the Mississippi,this doesn't look that big. But here's how powerful it is.

We anchored down a GoPro camerato get those shots near the weir,and the water just blasted it away. One of the team herehad to wade into save it before it got washed into the basin,never to be recovered. “Thank you, Basim!” So it does a very good job ofrepresenting small rivers. And the processes that happenhere are much more related to, say, a river than small laboratories. Obviously, in larger riversyou have more scales of turbulence.

But those scales,they should be similar in our size. – I've seen a small scale model years ago,when I visited the Bay Model in California. It's a 1:1000 scalecopy of the San Francisco Bay, which means it's the sizeof a football field. But the 1960s engineers who builtit had to stick a load of copper strips into the base to make the water behavelike it would at full scale. By all accounts, they did really well,particularly for before computers, but it's no comparison to having a modelthat is closer to real-world size. – This summer we were looking at erosioninduced by a bank,.

An artificial bar we put in. Throughout the worldthere's a problem in understanding how much erosion is going to happenfor a given flood. So as an engineer,you want to be able to run a model that will tell you how much bank erosionyou'll have in the future. We would also, next year,like to start looking at ice cover and the effect of ice on thingslike bank erosion and floods. Because ice related floodingis a huge problem. Having a river where you can modelice would be quite unique.

– A lot of this work can be donewith computer simulations now, but the code for those simulationsstill has to be validated and checked somewhere like this. And sometimes the researchers here are working on things that there isno computer model for, which surprised me. I assumed that simulating waterwas pretty much a solved problem, but no. There are still new technologiesthat need to be tested, and one of them is up theregetting the aerial shots for this video. – To model this riverwith a particle interaction model.

Would take many days,months, years to run. We have projects involving large scaleparticle image velicometry. This is a new technique with a drone,you'll take the water surface and then you can have a velocity,which you can then relate to a discharge: how much water is moving through a sectionof river per second. And having a method of measuring dischargewithout actually going into the river is very useful, because it's very difficultto go into these rivers at high flows. It’s very dangerous, in fact. The water surface can be affectedjust by the general wind,.

But then that can influenceor bias the results of the flow we actually want to measure. – And sure, by the grand scales ofwaterparks and white water rafting centres, this isn't the biggestartificial river in the world, but it is one that's built for research. Even if that does mean thatthe team here wouldn't let me bring my own inflatable tubeto ride down it. Nobody has ever been downon an inflatable tube. It's an interesting idea,but I don't think I would advise it.

I don't think I would advise it!

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