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Home  > Question of the Week

Question of the Week



Permalink What is the environmental impact of a micro-hydro system?

Answer: The environmental impact of micro-hydro systems is usually small but by no means absent altogether. When water is diverted or dammed, or when structures installed in the stream channel interfere with the natural flow of the water, there is an environmental impact. However, compared to large hydropower dams, micro-hydro systems have a smaller footprint and generally lower environmental impacts. Even so, there are several local, state, and federal agencies that may want environmental impacts to be assessed for a micro-hydro project.

There are a number of environmental considerations for micro-hydro systems, including the following:

• Water-quality issues such as turbidity and sediment from the system’s construction and operation
• Diversion of streamflow creating lower flow conditions in the main stream channel
• Wildlife and migratory-fish impacts
• Historical significance and aesthetics
• Changes in and impacts on stream ecology (e.g., algal communities, changes in food chains, stranding of benthic invertebrates living on the bottom and banks of the stream, and loss of aquatic habitat)
• Changes in nutrient transport and cycling
• Changes in water temperature due to lower flow
• Changes in dissolved-oxygen levels

Micro-hydro systems that are nonconsumptive and "run of river"—meaning that the natural water flow and elevation drop is used to generate power and the water is directed back into the stream—generally have a small environmental impact. This is an important point to remember and communicate when local regulators ask about environmental impacts. However, diverting water out of the steam, even temporarily, affects the stream’s ecosystem. For example, diverting too much of the water for even a short distance can prevent the natural migration of aquatic organisms and raise the water temperature enough to kill aquatic life.

These effects can be compounded if other ecosystem changes also occur, such as the removal of streamside brush or timber that was providing stream shading and other ecological benefits. Not only will the immediate stream ecology be affected, but the downstream ecology is likely to change as well. This, of course, depends on your particular case—are you using a run-of-the-river system or stored pondage? Maybe your system is on a high-head stream and will have limited or no impact on fi sh or other aquatic organisms. Always carefully plan your system to prevent salamanders, snakes, crawdads, and other aquatic creatures from entering the pipeline and turbine or being otherwise harmed.

Projects should be designed to divert the minimum amount of water required. In many areas, streamflow fluctuates with drier and wetter periods of the season. Many sites will not always have a sufficient streamflow to both provide water to the turbine and maintain a low environmental impact. Therefore, the volume of water diverted to the turbine must be managed. In many areas of the U.S., including the Ozark Mountains and Appalachian Mountains, this may require that diversions and penstocks be shut off during dry periods of the year. Of course, this would affect your hydropower system's "design flow."

There are simple design considerations that can help mitigate a hydropower system’s environmental impacts. For example, an intake placed in the water channel should be located where it takes on characteristics of its environment.

To learn more about how your project will affect the environment, visit the biology department at your local university or talk to an aquatic biologist at your local fish-and-game department office. By doing such research in advance, you will be prepared to answer questions as you prepare to permit the project.

The relatively small environmental impact of a well-designed micro-hydro system means it can be a sustainable solution to energy needs. However, if your project is near public areas or a neighbor’s property, what it looks like can significantly affect the public’s opinion of that impact. In fact, thoughtfully integrating micro-hydro equipment into the natural landscape may help reduce its environmental impact. Remember, micro-hydro projects that produce renewable power and avoid visually disturbing the natural environment with the intake, pipe, cables, and other equipment demonstrate how to produce energy in a more sustainable manner.

You can learn much more about micro-hydro technology in these ATTRA publications:

Micro-Hydro Power: A Beginners Guide to Design and Installation

Micro-Hydro Power: Is It Right for My Farm?

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