ASK THE EXPERTS: Microhydro to Control Flooding & Erosion

A diversion takes some water and its energy out of the stream bed.

I am interested in a microhydro power system for a local golf course that has issues with erosion and flooding from an on-site stream. Would microhydro power be an effective way to remove energy from the stream, thereby reducing erosion and potential flooding?

Christian Heymsfield • via

Microhydro systems with penstocks (pipelines) can reduce the risk of erosion and flooding in a stream because they route some of the water through a pipe instead of having it run down the streambed, and because they reduce the speed of the water. The whole job of a hydro system is to take the energy (pressure times flow) out of the water, to be used at the other end of the system where the water is dropped. But there are caveats:

•           Any reduction in erosion or flooding will only be for the length of the pipeline, since the water will be put back into the stream after it goes through the turbine. The water’s head (vertical drop) will be “starting over,” so it will need to flow downhill again before it builds up its original erosive potential.

•           Streams with significant variations in flow can be a challenge for hydro design. Capturing most or all of the energy of high flows requires a large intake, penstock, and turbine (as well as large balance-of-system components, etc.). This means the system will be overdesigned for moderate flows, and may reduce the system’s efficiency. In typical hydro systems, a compromise is frequently made in which higher flows are not completely captured.

•           All of the electrical energy generated needs to be used, “diverted” to a dump load, or sent to the utility grid. The complete system—including the electrical side—needs to be able to handle the peak output of the turbine. Most home systems are designed around an average flow, and don’t bother with capturing the peaks, so the system can be smaller.

•           Capturing a wider range of flows requires equipment that can adjust the system’s capacity to the flow. This can be as simple as using valves to change the number of turbine nozzles in use, or changing nozzle sizes. In larger systems, it could mean automated turbine control.

Begin with detailed measurement of the stream—both head (vertical drop) and flow (measured seasonally). Also, examine the on-site energy load (in kWh). Consider how much energy the stream could make, and what you’ll do with it. It may be that you’ll find a solution to the erosion and flooding problem that will also provide significant energy to the facility. The answer is in the results of a comprehensive resource and load analysis.

Ian Woofenden • Home Power senior editor

Comments (2)

Frank Heller's picture

Interesting use of microhydro. A few thoughts:
o sedimentation will be a problem and the design doesn't appear to address it;
o tailraces can be designed to spread out the water flow and further diminish the energy in the water. I just viewed a boulder field that does that and also handles sediment.
o Sediment really should be taken out or you will need to select a device which is independent of it; Archimedes screw, cross flow turbine, and even our old friend the water wheel---which can be a visual enhancement to a golf course.

Ian Woofenden's picture
Hi Frank, Hydro systems need to deal with proper screening of the intake in any case. This is both to keep the penstock clear, and to reduce erosion of the runner. Modern screens do an excellent job of minimizing the impact, and proper penstock design (continuously downhill) help too. The boulder field you mention sounds like a great idea. One way or another, you want your tailrace to blend back into the watercourse gracefully. Best, Ian
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