To help define its mitigation obligation, BPA contracted with state agencies and tribes to develop wildlife loss assessments to document the actual impacts of each dam. The assessments looked at the footprint of each dam, along with the resulting reservoirs and their inundation impacts.
The federal, state, and tribal resource managers used the Habitat Evaluation Procedure (HEP) to assess the wildlife habitat losses. In some cases, wildlife habitat gains were also identified because the construction of the dams created new habitats. For example, Lake Roosevelt, behind Grand Coulee Dam, provided new habitat for waterfowl and other species.
The Council adopted HEP and its “currency,” the habitat unit or “HU,” as the primary metric for its wildlife mitigation guidance. Across the region, however, there was a lot of variation in how the resource managers implemented HEP and interpreted the HEP results. There was no consensus on how much mitigation was appropriate or how much was left to do.
As a result, BPA used the loss assessments not for precise statements of mitigation responsibility but as a starting point to help size its mitigation response.