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IIHR project locations.

IIHR project locations.

The Columbia and Snake River basins, the most productive sources of hydropower in the United States, are of great environmental interest because they host the largest salmon population in the contiguous 48 States. Hydropower utilities, federal and state agencies and tribes are actively involved in the protection of endangered species.

Elevated TDG supersaturation may cause gas bubble disease (GBD) in fish. The effect of high TDG concentration is complex and depends on TDG levels, exposure time, and the swimming depth of the fish. The excess of uncompensated gas may form bubbles inside the internal tissues of the affected fish. Exposure to high levels of TDG during long periods of time can also be lethal due to the blockage of blood flow by the bubbles.

State and Federal regulations establish water quality standards relative to TDG to protect aquatic organisms. Total Maximum Daily Load (TMDL) serves as an example of these regulations. TMDL for TDG is the maximum amount of dissolved gas that a waterbody can receive to meet water quality standards. Descriptions of Oregon and Washington TMDL for TDG on the Columbia and Snake Rivers may be found at:
http://www.ecy.wa.gov/programs/wq/tmdl/ColumbiaRvr/ColumbiaTDG.html
http://www.deq.state.or.us/wq/TMDLs/columbia.htm#tdg

As part of the relicensing process, the Federal Energy Regulatory Commission (FERC) requires that hydroelectric projects obtain a water quality certificate. If the project cannot meet the water quality standards they should perform the necessary studies to minimize damage to the environment.

The Federal Energy Regulatory Commission (FERC) requires that hydroelectric projects obtain a water quality certificate.

The Federal Energy Regulatory Commission (FERC) requires that hydroelectric projects obtain a water quality certificate.

Several methods are used to reduce TDG supersaturation downstream of dams and thus minimize fish injury and mortality. The cheapest one is to identify plant operations that minimize the TDG production allowing the project to be in compliance with water quality standards. Other more expensive options are structural modifications such as addition of spillway flow deflectors, diversion tunnels around the project, addition of generating units, training walls separating powerhouse and spillway flows, among others.

Until recently, design projects have required multiple year schedules including: initial field data collection, laboratory modeling, field prototype testing, and then possible refinement in the laboratory. The primary shortcoming of this approach is that laboratory models cannot quantitatively predict the change in TDG from various design alternatives due to model scaling issues. The approach relies on qualitative performance relationships that relate flow conditions with past field experiences.

Numerical simulations have recently become an indispensable tool to understand the physics leading to poor water quality in tailraces. Abatement options can be evaluated allowing utility managers and policy makers minimize negative environmental impacts and financial risks.

Last modified on September 26th, 2012
Posted on March 14th, 2012