Tag Archives: dams

Beavers, some of the best dam builders

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I ran for water commissioner in 2016 (Oakland county, Michigan; I’ll be running again in 2020), and one of my big issues was improving our rivers. Many are dirty and “flashy”. Shortly after a rain they rise too high and move dangerously fast. At other times, they become, low, smelly, and almost disappear. There are flash floods in these rivers, few fish or frogs, and a major problem with erosion. A big part of a solution, I thought, would be to add few small dams, and to refurbish a few others by adding over-flow or underflow weirs. We had a small dam in the middle of campus at Michigan State University where I’d taught, and I’d seen that it did wonders for river control, fishing, and erosion. The fellow I was running against had been removing small dams in the belief that this made the rivers “more natural”. The Sierra Club thought he was right doing this; the fishing community and some homeowners and MSU alumni thought I was. My problem was that I was a Republican running in a Democratic district. Besides, the county executive, L. Brooks Patterson (also a Republican) was a tightwad. Among my the first stops on my campaign trail was to his office, and while he liked many of my ideas, and promised to support me, he didn’t like the idea of spending money on dams. I suggested, somewhat facetiously, using beavers, and idea that’s grown on me since. I’m still not totally convinced it’s a good idea, but bear with me as I walk you through it.

Red Cedar River dam as seen from behind the Michigan State University Administration Building.

Small dam on the Red Cedar River at Michigan State University behind the Administration Building. The dam provided good fishing and canoeing, and cleaned the water somewhat.

The picture at right shows the dam on the Red Cedar River right behind the Administration building at Michigan State University, looking south. During normal times the dam slows the river flow and raises the water level high enough to proved a good canoe trail, 2 1/2 miles to Okemos. Kids would fish behind the dam, and found it a very good fishing spot. The slow flow meant less erosion, and some pollution control. The speed of flow and the height of the river are related; see calculation here. After a big rain, a standing wave (a “jump”) would set up at the dam, raising its effective height by three or four feet. Students would surf the standing wave. More importantly, the three or four feet of river rise provided retention so that the Red Cedar did little damage. Some picnic area got flooded, but that was a lot better than having a destructive torrent. Here’s some more on the benefits of dams.

Between July 31 and Aug 1 the Clinton River rose nine feet in 3 hours, sending 130,000,000 cubic feet of water and sewage to lake St Clair.

Between July 31 and Aug 1 the Clinton River rose nine feet in 3 hours, sending 130,000,000 cubic feet of water to lake St Clair.

The Sierra club supported (supports) my opponent, in part because he supports natural rivers, without dams. I think they are wrong about this, and about their political support in general. Last night, following a 1 1/2 inch rain, the Clinton River flash flooded, going from 5.2 feet depth to 14 feet depth in just two hours. My sense is that the natural state of our rivers had included beavers and beaver dams until at least the mid 1700s. I figured that a few well-designed dams, similar to those at Michigan State would do wonders to stop this. Among the key locations were Birmingham, on the Rouge, Rochester, near Oakland University, Auburn Hills, and the Clinton River gorge, and near Lawrence Technical University. If we could not afford to build man-made dams, I figured we could seed some beaver into nearby nature areas, and let the beavers dam the rivers for free. It would bring back the natural look of these areas, as in the picture below. And engineers at Lawrence Tech and Oakland University might benefit from seeing the original dam engineers at work.

Beaver dam on a branch of the Huron River. Beavers are some of the best dam builders.

Beaver dam on a branch of the Huron River. A rather professional and attractive job at a bargain price.

Beavers are remarkably diligent. Once they set about a task, they build the basics of a dam in a few days, then slowly improve it like any good craftsman. As with modern dams, beaver dams begin with vertical piles set into the river bottom. Beavers then fill in the dam with cross-pieces, moving as much as 1000 lbs of wood in a night to add to the structure and slow the flow. They then add mud. They use their hearing to detect leaks, and slowly plug the leaks till the dam is suitably tight. Most of the streams I identified are narrow and pass through wooded areas. I think a beaver might dam them in a few days. Based on the amount of wood beavers move, and the fact that beavers are shaped like big woodchucks, I was able to answer the age-old question: how much wood would a woodchuck chuck if a woodchuck could chuck wood — see my calculation here.

Me, visiting the DNR to talk beavers

Me, visiting the DNR to talk beavers

There are a few things to check out before I start hiring beavers to take care of Oakland county flooding, and I have not checked them all out yet. Beavers don’t necessarily build where you want or as solidly, and sometimes they don’t build at all. If there are no predators, beavers can get lazy and just build a low-water lodge and a high water lodge, moving from one to the other as the river rises and falls. Hiring a beaver is like hiring an artistic contractor, it seems: you don’t necessarily get what you ask for, and sometimes you get more. Given the flash flooding we have, it’s hard to picture they’d make things worse, but what do I know? In some cases, e.g. the Red Run near the 12 towns drain, the need is for more than a beaver can deliver. Still, without beavers, the need would be for a billion gallons of retention on the Clinton alone, a 10 billion dollar project if carried out as my opponent likes to build. So, with no budget to work with, my next stop was at the Department of Natural Resources Customer Service Center (Lansing). I had some nice chats with beaver experts, and I’m happy to say they liked the idea, or at least they were not opposed. I’ve yet to talk to the Michigan director of dams, and will have to see what he has to say, but so far it seems like, if I get elected in 2020, I’ll be looking for some hard-working beavers, willing to relocate. I’d like to leave it to Beaver.

Robert E. Buxbaum, August 2, 2018. I still don’t get the Sierra Club’s idea of what a natural river would look like, or their commitment to Democrats. In my opinion, a river should include beavers, fish, and fishermen, and drainage should be done by whoever can do it best. Sierra club folks are welcomed to comment below.

Weir dams to slow the flow and save our lakes

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As part of explaining why I want to add weir dams to the Red Run drain, and some other of our Oakland county drains, I posed the following math/ engineering problem: if a weir dam is used to double the depth of water in a drain, show that this increases the residence time by a factor of 2.8 and reduces the flow speed by 1/2.8. Here is my solution.

A series of weir dams on Blackman Stream, Maine. Mine would be about as tall, but somewhat further apart.

A series of weir dams on Blackman Stream, Maine. Mine would be about as tall, but wider and further apart. The dams provide oxygenation and hold back sludge.

Let’s assume the shape of the bottom of the drain is a parabola, e.g. y = x2 , and that the dams are spaced far enough apart that their volume is small compared to the volume of water. We now use integral calculus to calculate how the volume of water per mile, V is affected by water height:  V =2XY- ∫ y dx = 2XY- 2/3 X3 =  4/3 Y√Y. Here, capital Y is the height of water in the drain, and capital X is the horizontal distance of the water edge from the drain centerline. For a parabolic-bottomed drain, if you double the height Y, you increase the volume of water per mile by 2√2. That’s 2.83, or about 2.8 once you assume some volume to the dams.

To find how this affects residence time and velocity, note that the dam does not affect the volumetric flow rate, Q (gallons per hour). If we measure V in gallons per mile of drain, we find that the residence time per mile of drain (hours) is V/Q and that the speed (miles per hour) is Q/V. Increasing V by 2.8 increases the residence time by 2.8 and decreases the speed to 1/2.8 of its former value.

Why is this important? Decreasing the flow speed by even a little decreases the soil erosion by a lot. The hydrodynamic lift pressure on rocks or soil is proportional to flow speed-squared. Also, the more residence time and the more oxygen in the water, the more bio-remediation takes place in the drain. The dams slow the flow and promote oxygenation by the splashing over the weirs. Cells, bugs and fish do the rest; e.g. -HCOH- + O2 –> CO2 + H2O. Without oxygen, the fish die of suffocation, and this is a problem we’re already seeing in Lake St. Clair. Adding a dam saves the fish and turns the run into a living waterway instead of a smelly sewer. Of course, more is needed to take care of really major flood-rains. If all we provide is a weir, the water will rise far over the top, and the run will erode no better (or worse) than it did before. To reduce the speed during those major flood events, I would like to add a low bicycle path and some flood-zone picnic areas: just what you’d see on Michigan State’s campus, by the river.

Dr. Robert E. Buxbaum, May 12, 2016. I’d also like to daylight some rivers, and separate our storm and toilet sewage, but those are longer-term projects. Elect me water commissioner.