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U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2008-5070

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Introduction

The Bureau of Reclamation tries to maintain river conditions conducive to salmon recovery while also regulating flows in the Yakima River to meet urban and agricultural water allocation demands in the Yakima River basin. The Bureau of Reclamation is considering water management plans that could potentially change the amount and timing of flows in the Yakima River. For example, the Yakima Basin Storage Project (known as the Black Rock Project) involves the construction of a new reservoir about 48 km east of Yakima, Washington. Under this project, the reservoir would have a maximum capacity of 1,973 hm³ and be filled by water pumped from the Columbia River. Between 616 to 986 hm³ of water from the reservoir would be delivered directly to irrigation canals supplying the Yakima River basin, thereby, freeing up an equivalent volume of water from the Yakima River for enhancing fish and wildlife habitat. The Bureau of Reclamation plans to use the Ecosystem Diagnosis and Treatment (EDT) method described at http://www.mobrand.com/MBI/edt.html to estimate results of the enhancements to habitat quality and quantity from water management alternatives such as the Black Rock Project. The EDT analytical model is a major component of the EDT method and is used to analyze environmental information.

Daily maximum water temperature is a necessary input for the EDT analytical model. In this cooperative study with the Bureau of Reclamation, the U.S. Geological Survey (USGS) used a water-temperature model to generate simulated daily maximum water temperature data for the Yakima River mainstem between the Roza Diversion Dam and the Prosser Dam (Roza–Prosser Reach) (fig. 1) for input into the EDT analytical model.

Purpose and Scope

The purpose of this report is to document a water-temperature model for simulating daily maximum water temperatures along the Roza–Prosser Reach for any given year from April 1 through October 31. This is the approximate time range when water is diverted from the river to irrigate agricultural areas. The model is intended to assess general trends in daily maximum water temperature that may occur when different proposed water management alternatives are used. The model is not intended to simulate daily maximum water temperature with an accuracy of 1.0°C or less on any given day.

The objectives of the project were to (1) collect discharge, water-temperature, and related data along the Roza–Prosser Reach of the Yakima River; (2) develop methods for estimating water temperatures at the Roza Diversion Dam on the Yakima River and at a point on the lower Naches River; (3) apply an existing process-based water-temperature model to the Roza–Prosser Reach to simulate daily maximum water temperature; and (4) document the model.

The USGS was supported in this work through a scientific and financial partnership with the Bureau of Reclamation.

Description of Study Area

The Yakima River is located in south-central Washington and is a tributary of the Columbia River (fig. 1). The Yakima River originates in the central Cascade Range near Snoqualmie Pass (at an elevation of about 914 m) and flows 354 km southeast out of the Cascade Range and onto the Columbia Plateau. The Yakima River then flows into the Columbia River near Richland (at an elevation of 104 m), draining a total drainage basin area of 15,941 km².

Precipitation in the Yakima River basin varies substantially with elevation and season. The high elevations at the crest of the Cascade Range in the western part of the basin normally receive more than 305 cm of annual precipitation (mostly as snow); whereas, low elevations in the rain shadow of the mountains only receive 18 cm of annual precipitation. Most of the precipitation occurs during the late autumn, winter, and early spring seasons; the summers typically are dry. Peak river discharge under natural conditions generally occurs during late spring and early summer because of snowmelt. The Bureau of Reclamation manages six lakes and reservoirs (with a total active storage capacity of about 1,233 hm³) to retain the spring and summer snowmelt from the mountains and to deliver water to agriculture in the lowlands between April and October (Kent, 2004).

The Yakima River basin contains a diverse range of land cover types. About 30 percent of the basin is forested, mostly in the western mountains; 50 percent is rangeland, where sagebrush and bunch grass are the dominant vegetation; and 20 percent is agricultural, mostly irrigated land along the main valley of the Yakima River (Kent, 2004).

The study area for this project is the Yakima River mainstem extending from the Roza Diversion Dam located at river kilometer (RKM) 214 to the Prosser Dam located at RKM 74. From the Roza Diversion Dam, the Yakima River flows in a general southeasterly course past Selah, Washington, to the city of Yakima where the river is joined by the Naches River, then flows past a series of towns including Moxee City, Union Gap, Wapato, Zillah, Toppenish, Granger, Sunnyside, Satus, Mabton, Grandview, and finally Prosser. (For populations of these towns, see table 1.) The river forms the eastern boundary of the 5,260 km² Yakama Reservation (population 31,799), which occupies 23 percent of the southwestern section of the Yakima River basin. The main roads running alongside the river are State Route 82 to the north and State Routes 97 and 22 to the south.

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