Optimizing Selective Withdrawal from Reservoirs to Manage Downstream Temperatures with Climate Warming

Abstract

Selective withdrawal systems can take advantage of thermal stratification in reservoirs to manage downstream temperatures. Selective withdrawal might also help adapt operations to environmental changes, such as increased stream temperatures expected with climate change. This exploratory study develops a linear programming model to release water from different thermal pools in reservoirs to minimize deviations from target downstream temperatures. The model is applied with representative thermal dynamics to Lake Spaulding, a multipurpose reservoir on the South Fork Yuba River in California with climate warming represented by uniform increases in air temperature. Optimization results for thermal pool management with selective withdrawal are compared to a single, low-level outlet release model. Optimal selective withdrawal hedges the winter release of cold water to decrease summer stream temperatures. With climate warming, selective withdrawal can help lessen stream warming in the summer but at a cost of warmer stream temperatures in winter. As numerous assumptions are made, particularly regarding representation of thermodynamics, modeling improvements are needed to further develop selective withdrawal optimization models; several improvements are discussed.