Yakima River Temperature Model Completed

Development of Water-Temperature Models for Main-Stem Reaches of the Yakima and Naches Rivers, Washington

Problem - Studies have shown that water temperature is often a limiting factor in the survival of salmon during spawning and rearing on the main stems of the Yakima and Naches Rivers. In order to assess how various water-management scenarios might affect water temperature and other habitat characteristics, and ultimately the success of restoring salmonid populations, the Bureau of Reclamation (Reclamation) is using the Ecosystem Diagnosis and Treatment (EDT) model as the decision tool to determine the potential for salmon restoration. The model requires daily maximum temperatures at many locations on the main stems for different reservoir-management scenarios, and these temperatures are currently not available. The main stems are well gaged, and existing watershed and reservoir-management models provide reasonable estimates of main-stem flows for different reservoir-management scenarios. However, little long-term water-temperature data is available on any of the many irrigation drains that can contribute significant amounts of water to the Yakima River.

Objective - The objective of the project is to provide simulated daily maximum water temperatures along the main stems of the Yakima and Naches Rivers during one irrigation season (April through October) for various scenarios of reservoir management. The irrigation season will be during a water year that represents a particular condition (wet, dry, or average year) to be determined by Reclamation. Because of time constraints and limited available data, a detailed simulation of water temperatures will focus on the main-stem reach of the Yakima River from Roza Dam to Prosser Dam (Roza-Prosser Reach). This reach has the most potential for positively manipulating the water temperature through water-management scenarios.

Relevance and Benefits - This investigation is consistent with the long-term program goal of the USGS to "provide and improve long-term environmental and natural resources information, systematic analyses and investigations, and predictive tools for scenario building and decision making about natural systems" (USGS Strategic Plan, 2000). It also supports the Yakima River Basin Water Storage Feasibility Study, which is conducted by Reclamation and represents the research priorities of a broad-based group of local, State, Federal, and tribal water-resources managers in the Yakima River Basin. The USGS is assisting Reclamation as a sister agency of the Department of the Interior. The results of the investigation will contribute to the scientific basis for ongoing management of the river ecosystem.

Approach - The study objective is met by conducting five tasks: (1) collect discharge, water-temperature, and related data along the Roza-Prosser Reach of the Yakima River; (2) select or develop methods for estimating water temperatures at outflows of selected reservoirs and throughout parts of main-stem reaches of the upper Yakima and lower Naches Rivers; (3) construct a process-based water-temperature model for the Roza-Prosser Reach; (4) analyze the potential temperature effects of different reservoir operations on the Roza-Prosser Reach and parts of main-stem reaches of the upper Yakima and lower Naches Rivers; and (5) document the study in a USGS Scientific Investigation Report.