The value of getting your hands (and feet) wet

Originally posted on LinkedIn by Dr Kristen Splinter, Lecturer at WRL

Model car simulation

It was a rainy day last Friday when Drs. Felder, Zamani and myself took to introducing close to 550 2nd year water engineering students to the water labs at the Water Research Laboratory. Mark Kulmar and staff at the Manly Hydraulics Lab (MHL) also hosted the students for a tour of their facilities. This annual field trip, which is part of the 2nd year water engineering course (CVEN 2501), is a vital part in the education and learning experience of these students at UNSW as they get to see theory turned into practice. They also get to learn about a career in water engineering and how they can become involved.

When they arrived, students learned a bit about the history of our labs. WRL is one of the largest physical water laboratories in the southern hemisphere and is known as the birth place of Coastal Engineering in Australia. The lab is also known for its pioneering fundamental and applied research in the areas of Applied HydraulicsGroundwater, and Environmental Engineering. The lab is home to a number of large wave and flow through flumes where we conduct our research.

With so much water running through the lab, we need a large water source: the Manly Dam of course! The dam provides an abundant source of water to both the WRL and MHL labs, which after use, is then returned to the creek to maintain environmental flows vital for the health of the Manly Creek and Lagoon system below us. With the rain coming down and water flowing in our labs, the students were bound to get their feet wet and we encouraged them to get their hands wet too!

Intricate web of pipes and culverts

During the tour at WRL, students were introduced to a variety of models currently in use. Our first stop was a model car simulation where we looked at the velocity forces and water depths needed to cause instability in a car in moving water. Students learned about how we can scale down real objects (such a cars) to be able to do these tests in a controlled setting.

As Engineers, we are trying to design in order to minimise risk (to humans) and failure (of a structure). In controlled physical modelling tests, we can test the limits of design and provide guidance back to groups, such as the SES on people safety in floods. As Engineers, we are trying to design in order to minimise risk (to humans) and failure (of a structure).

"As Engineers, we are trying to design in order to minimise risk (to humans) and failure (of a structure)."

This model was done at a 1:18 scale. We discussed the types of scaling we'd use (Froude vs Reynolds) and how we would measured these forces. The students were really impressed that we could do these sorts of tests in the lab.

We then moved on to look at how water below us flows around in an intricate web of pipes and culverts that keeps our Sydney running. The culverts project has been at WRL for 2 years now as part of the Honours thesis with Dr. Felder. Dr. Felder and his students are looking at how changes in inflow (including the direction and magnitude) can impact both the upstream and downstream flows in a culvert system. Our research culvert is designed out of plexiglass so that we can easily see what is happening on the inside.

1.2 m wave flume

The students could see just how complex the water movement is in the system and we could discuss the theory we'd learned in class about continuity and momentum while watching it right before our eyes. It was also an opportunity to show them how we do these measurements using manometers, piezometers and pitot tubes.

We had also discussed these in class but the 'aha' moment always comes when they can see and touch these instruments in real time. The below image is an example of a very large piezometer and pitot tube for the students to see. These instruments allow us to measure the velocity of the water in the culvert as well as the depth.

"Theory is essential in learning, but the 'aha' moment always comes when they can see and touch what you're talking about in real time"

Our next stop was to the 1.2 m wave flume to look at a coastal engineering project and how we might retrofit existing breakwaters to account for climate change (Sea level rise) and increasing storm wave heights. The students again learned about how we scale these projects down in the lab. Can you imagine carrying 6 Ton rocks around?!?!

Doing detailed and specific tests in the lab lets us run design criteria (for example the 1:100 year storm wave and sea level rise) now so we can see if a structure is likely to withstand this event in 50 years time or not. We always want to be well prepared and physical modelling lets us do that.

"In controlled physical modelling tests, we can test the limits of design"

We next popped up to our fishway model where students got to see how we take into consideration environmental flows and fish passage when designing and constructing new dams. While dams may be vital pieces of infrastructure that provide flood mitigation, recreation and hydropower, they come with an environmental effect. Fish need to return to their birth place to spawn, and if we block that off, we run the risk of damaging fisheries.

Fishway model

To mimic a natural river system, dams are now constructed with fish ladders and passageways where we can design with nature to simulate boulders that allow fish lots of spots to rest as they travel up stream and around a dam. This was one experiment we encouraged students to stick their hands in and see how much the flow can change around structures. We also used dye to show them flow pathways and flow velocity differences across the structure.

Our last, but not least stop brought us back to the flooding car. This time, in a real (1:1 scale) model. We got students to see if they could push the car a little while it sat in a pool of water. They were surprised when they could move it with little effort! In this experiment we reflected back on what we learned about buoyancy (why do things float?).

Flooded car - real scale model

We then talked about the forces on the car as the water depth rose (Say in a flooding river) and how this would reduce the net downward force of the weight of the car. In still water, this car could easily be pushed around. Imagine now if the river was flowing as the students saw in our first model?

The take home message of this experiment was to get students to understand that water in flood situations is dangerous. As the water level rises, less and less flow (velocity) is needed to sweep a car (and its passengers) away.

"When water levels reach the bottom of the car body, it's unsafe. Get out."

 

Share this