Reservoir Operational Performance Subject to Climate and Management Changes in the Willamette River Basin, Oregon

Abstract

Reevaluation of the reliability of reservoirs in meeting operating objectives is needed as the landscape and operational priorities change. This study examined the individual and collective changes in reservoir performance at the 13 flood regulation projects within the Willamette River Basin (WRB) in Oregon. By applying a scenario-based analysis, derived as part of a broader collaborative modeling project, operational performance was evaluated in response to climate and operational change scenarios. Results indicated that, for the climate scenarios analyzed, primary operating objectives of flood risk reduction and meeting summer biological opinion (BiOp) flow targets were unlikely to be affected. Modest reductions in the ability to fully refill the reservoirs and to meet spring BiOp flow targets were found, particularly under the more severe warming scenario. However, refilling the reservoirs 2 weeks earlier was effective in reducing the storage deficit introduced by climate change without compromising the ability to meet other operational objectives. Drawdown scenarios for maintenance of aging infrastructure had minimal effect at the system scale. While the model was limited by the number of climate scenarios represented and in its ability to represent the full range of variability of this large basin, the results cumulatively suggested that the hydrologic changes associated with the range of climate change examined were not likely to substantially reduce the reliability of the Willamette Project in meeting operational objectives. Where potential deficiencies emerged, they could largely be mitigated through simple operational changes. Instead, it is likely that changes in the sociopolitical landscape (e.g., water rights allocations) and management of water quality (e.g., temperature, harmful algal blooms) will be as or more important than hydrologic changes in reducing reservoir performance in meeting operational objectives.