Ben Houston, GroundPoint Engineering

Understanding Ecosystem Impacts

We need to understand what, if any, specific environmental risks exist, how big or small that risk is, and if that risk can be eliminated or reduced in some way as part of the project.

Many of the impacts on the plants and animals that are near a micro hydropower site can be traced back to changes in the stream that are caused by the micro hydro system. For example, we may observe changes in plant and animal communities in a stream, but those changes can largely be traced back to changes in sedimentation, water quality, or the amount of water in the stream. These types of impacts, that can be traced back to earlier impacts of the micro hydropower system, are called “third order” impacts.

First-order impacts describe general changes in the amount of water available downstream of a site, such as bypass removal.

Second-order impacts describe changes in physical characteristics resulting from first order impacts. These effects include increased sedimentation and changes in water quality caused by slower stream flows or lower water levels.

Third-order impacts describe the ecological response to first and second order changes. These include the impact that changes in water quality and streamflow have on plants and animals. Some fish species may have trouble swimming upstream in lower water levels, or plants may have trouble growing if the nutrient levels along stream banks change.

All hydropower projects will have to address issues related to species of concern and connectivity of the aquatic ecosystem. Fish passage is likely going to be a key issue, as well as maintaining minimum instream flow requirements to support key species of concern. The instream flow requirements will also impact the availability of water for power production. Read more about water flow and energy production here.

Keep in mind that many dams across NY have been in place for over 100 years, and the resulting ecosystem, while obviously impacted by the dam, has become mature and well established. Modification of the dam risks modification of the existing ecosystem and the services it provides, and the value of that ecosystem and services must be weighed against what might be predicted to occur if the dam gets removed. As an example, sediments trapped on the upstream side of a dam may contain decades worth of chemical contamination from agricultural and industrial runoff, and the movement of those sediments may pose a critical ecological risk to the biological communities adjacent and downstream of your project.

Regardless of the ultimate risks posed, conducting a thorough review of existing biological communities is going to be a critical part of your environmental analysis. Certain information can be obtained online and through various maps, but ultimately you may need to conduct your own surveys, particularly if your initial investigations indicate there may be some key species in your project area. See our additional guidance on Map Data here.

Biological Surveys

The ecology of many organisms associated with stream habitats is finely attuned to both high and low water flow conditions as well as to water quality, suggesting that even small changes in small streams, including partial or complete dam removal or hydropower turbine installation, might have important effects (either negative or positive) on the stream biota. Enhancing and maintaining aquatic connectivity along the watercourse will strengthen the ecological integrity of the stream. Biological surveys are an important part of assessing both the ecological integrity and the risks associated with a particular stream.  

The Saw Kill Project included several studies of plants and animals and was designed to be conducted both before and after turbine installation or dam modification to discover which species of conservation concern are present, address impacts to those species, and identify species that indicate stream condition and changes. These studies are directed at the biota that are generally assessed in connection with stream management planning and permit applications for stream disturbance.

Habitat Impacts

Bypass Removal- If a certain amount of water is diverted from the stream channel in order to pass through a turbine and then returned farther downstream, stream banks and organisms could be affected in the length of the stream where flow was reduced. Reduced flow in this “bypass reach” will impact organisms that rely on steady flow conditions, and lower water levels may expose portions of the stream bed that might otherwise remain saturated or underwater. Temperatures in the water may increase as shallower water heats up more easily in the sun, and dissolved oxygen may decrease as an unintended consequence. Any diversion of flow from a stream for hydropower should be minimized to reduce the potential impact of removing water from the stream.

Land cover affects stream quality- Any man-made changes to the land along the streambanks (riparian zone) may affect shading that trees provide, sediment transportation, hydrology, and water chemistry. These changes can then alter the shape of the stream bed, water quality in the stream. These changes in riparian zone land use have been found to then alter the types and number of macroinvertebrates, which are a critical part of the stream’s food chain. These changes travel up the food chain and can lead to degraded fish populations, including species of concern such as eels.

Nutrients- The location of wastewater treatment plant outfalls in relation to hydropower bypass flow can be critical. Any bypass implemented to support hydropower that could reduce flow in the stream has the potentially to magnify any potential negative impacts of nutrients entering the stream at the wastewater outfall. Lower flows in the stream mean higher average concentrations of nutrients and/or other constituents after the outfall location, placing additional stress on the stream ecosystem in the immediate downstream reach until the flow is returned.

Barriers- The dam functioning as a barrier for aquatic species is an existing issue. Certain hydropower design options show promise in enhancing fish passage at some level. Because the effectiveness of such designs on enhancing passage is unknown for eels in particular, rigorous monitoring of eel presence downstream and upstream should be conducted in conjunction with more traditional passage enhancements such as ladders and buckets. See more on our discussions related to fish passage on the Saw Kill.

Feature Image courtesy of Bard College.


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