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Low-Head Hydropower Project Phases and Activities

Impacts from a low-head hydropower project can result from activities that occur during each phase of the project: site evaluation, construction, operation, and decommissioning and reclamation.

What Activities Occur During the Site Evaluation Phase?

The purpose of site evaluation is to determine whether a given site is suitable for a low-head hydropower plant. The technical and financial viability are specific to each site. Activities would include map studies, surface hydrology and floodplain mapping, delineation of drainage basins, and estimates of flow. The power capacity of a site depends upon the amount of water available and the head (i.e., the drop in elevation from the water source to the power generator). An estimate of the power in kW is given by the following equation:

P = 7QH

In this equation, Q is the flow rate in cubic meters per second and H is the head in meters.

A topographic survey would be performed during the site evaluation phase in order to establish the basic project design and layout to locate the intake and powerhouse; dam or weir; access roads, pipes, or canals; and other project components.

Geological investigations would include drilling when necessary. Borrow areas for sand and gravel would be delineated and tested. If the site was not accessible, access roads would need to be constructed to support such activities. Ecological studies would concentrate on the terrestrial and aquatic biota of the project area. Surveys might be conducted during this phase to determine whether cultural resources are present in the project area.

What Activities Occur During the Construction Phase?

A large portion of the low-head hydropower project area could be impacted by site preparation activities such as clearing and grading; construction of the intake system, which could include a dam or weir; construction of access roads, canals, tunnels, and pipelines; construction of the powerhouse and installation of the turbine and generator; construction of an electrical substation and transmission line; and preparation and use of material and equipment laydown areas. Concrete ingredients (e.g., sand, aggregate) may need to be extracted and hauled to the site if an appropriate borrow area cannot be found on the site. A refueling station (with diesel and gas storage tanks) would likely be used during construction.

What Activities Occur During the Operation and Maintenance Phase?

No additional land-disturbing activities and associated impacts are anticipated during the operation phase. Routine operation of a low-head hydropower facility to produce electricity would most likely be automated, and not require on-site personnel. Weekly monitoring and maintenance activities would ensure safe and consistent operation. Maintenance activities could include periodic replacement of various facility components.

What Activities Occur During the Decommissioning and Reclamation Phase?

Decommissioning of a low-head hydropower plant could range from mothballing to full removal of turbines, generators, and other equipment for reuse or for scrap. Buildings, concrete pads, foundations, and intake and tailrace facilities would be removed. Any dam or weir could either be removed or left to maintain the head pond for adapted aquatic biota and recreational activities. A decommissioning plan would need to be prepared and approved prior to the actual decommissioning of the project.

Underground components would be removed to a depth of at least three feet to ensure an unobstructed root zone for revegetation. More deeply buried components might be abandoned in place.

Following removal of site components, site reclamation and revegetation would mitigate some impacts, such as soil erosion, habitat fragmentation, and visual impacts.