From July 6-8, I worked at the USGS Debris Flow Flume in Blue River, Oregon with my supervisor Joe and two other CVO employees, Matt (another hydrologist) and Kelly (the electronics/equipment guy). The flume is basically a big cement slide built into a hill, with a steel holding tank at the top and a runout pad at the bottom, so that debris flows of sand, rocks, and dirt can be generated and studied. There are lots of places for sensors and video cameras, so that just about everything can be measured and recorded. It's an amazing place! I was really excited about this trip, because it was the only opportunity for field work related to the projects I'm actually working on at CVO, and the only chance to get into the field with Joe (otherwise all the trips have been helping out other groups). The goal of the project is to better understand how (and how fast) water flows after it breaks through a natural dam. Dams can be built when debris flows, avalanches, or glaciers block a drainage and water begins to accumulate behind it. This can become a major threat, because if the blockage fails, lots of water and debris can be released really fast. Joe and Matt are investigating the way water behaves when a dam is broken, or breached.
The actual experimental procedure is going to take place in mid-August, which was really disappointing because I thought I was going to miss it all. But it turned out that Matt wanted to do a trial run so they would know the best way to set up the equipment for the real deal. So I got to help after all! And this was probably a little more fun, because we didn't have to constantly worry about all of the equipment- we only had a little bit set up, so we could focus more on what was actually happening, rather than worrying about all of the electronics and sensors.
How do you come to understand what happens when a dam is breached, you ask? Why, you build a dam and then breach it, of course! Our goal was to build a dam made of compacted sand, dump a whole bunch of water behind it, then break the top of the dam and film the water pouring over and eroding away the sand. I'll explain the whole process through pictures:
This is the flume. It's 90 meters long, and there are 264 stairs along the left side to the top. Trust me... I did them. Twice.
This is my boss, Joe. He is preparing some water level sensors, which we used to measure how fast the water was flowing out of our "lake" through the dam.
We wanted to use the flattest part of the flume, so we had to extend the walls onto the runout pad. This was the trickiest part of the whole setup- it's hard to get cement blocks in just the right place with a backhoe! It took us a day and a half to set up all 18 wall extensions, with their support blocks behind them. Here I'm trying to direct the block into the right place as Kelly carries it with the bucket of the backhoe.
Finally, all 18 wall extensions are in place! We tested the dam-building frame, then removed it and lined the whole flume with rubber so it wouldn't leak.
Then we built the frame for the dam. The black pipes on the ground are a drain, so that too much water wouldn't accumulate inside the dam and cause it to fail from the inside-out.
To build the dam, we added tongue and groove boards to the frame, one at a time, filling it with sand and compacting it after each addition. The orange box there is the "Hulk Electro," and awesome compactor that works like a push lawn mower... it definitely helped the construction go much faster. (Kelly is in the foreground in the white t-shirt, Joe is in the back in green)
It still took several hours to build the dam!
Finally finished! It looks pretty good, doesn't it? Too bad we're going to destroy it...
Time to fill it with water! The white tubes have water level sensors inside them, and the cords coming out of the left side of the dam are attached to pressure sensors, so we can (ideally) tell how much water is seeping inside the dam. Our pressure sensors didn't work, but the water level sensors worked great!
Overhead shot of the setup. Joe and I are sitting under the green and white umbrella, setting up the computer program I wrote to log the data from all of the sensors. I was so nervous we would get everything set up and then my program would fail, but it worked just fine. Whew!
We wanted to be the ones to break the dam, but the water appeared to have its own ideas... we knew it was time to get rolling when water appeared at the base of the dry side of the dam.
A little scoop with the shovel, and poof! The dam was gone! It took a total of about four minutes for the whole thing to be swept away. I got to throw confetti into the water, so the cameras could track the motion of the flow. We got some good video footage, and I think they're already working hard to plan the setup for the official run next month.
(Many thanks to Matt, who shared the USGS photos from the trip with me so I could show my friends and family what's going on)
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