Evaluating Reservoir Operations and Other Remediation Strategies to Meet Temperature TMDLs in the Willamette Basin, Oregon

Water managers in the Willamette River Basin face a number of difficult and closely interrelated challenges associated with the Endangered Species Act (ESA), the Clean Water Act (CWA), and other associated concerns. For example, under the CWA, the Oregon Department of Environmental Quality (ODEQ) has recently released a total Maximum Daily Load (TMDL) for temperature in the Willamette Basin. Some of the major factors impacting temperature in the Willamette include operation of the multiple reservoirs, permitted industrial and municipal discharges, land-use types, and irrigation practices. Possible mitigation strategies include changes in land-use to increase shading along streams, installations to cool or store point-source discharges, changes in how and when water is released from the reservoirs, installation of multi-port withdrawal structures on the reservoirs, and remediation of riparian and hyporheic zones. Each of these strategies comes with ecological, economic, and/or social costs and/or benefits that must be weighed and understood before meaningful dialogue about how to best manage the basin can occur. To address this problem a collaborative team from Sandia National Laboratories, the Institute for Water Resources, David Evans and Associates, and the Portland District of the Corps of Engineers have been working with stakeholders in the basin to design and collaboratively develop an integrated systems model of the basin to examine the linkages between the various strategies and their tradeoffs. The model domain includes the main stem of the Willamette, 7 major tributaries, and 12 USACE operated reservoirs. It is built as a series of system dynamics lumped parameter models, and provides real-time feedback and scenario testing capabilities. Outputs from the model include changes in temperature at key monitoring points and costs per kcal of energy saved due to different remediation strategies, relative changes in nutrient loading and CO₂ emissions due to riparian shade planting, impacts on recreational opportunities and the economic impacts of those changes, and salmonid habitat suitability as it relates to temperature. This presentation will describe the technical collaborative processes in which the model was developed and how it will be used to inform reservoir operation and other policy decisions in the basin.