Puyallup Streamflow Trends Completed

9722-9EG - Trends in Streamflow in the Lower Puyallup River Basin, and Comparisons to Instream Flows and Water Use - Completed FY2004

Introduction and Background - The Puyallup Indian Reservation covers about 28 square miles and is located along the lower reaches of the Puyallup River in Pierce County, Washington. Because the reservation is located in the lowest part of the Puyallup River basin, virtually all water-related activities in the basin affect the Tribe's water resources. Furthermore, the Puyallup River itself runs through the reservation, so it is an important direct water resource, especially as it is related to fish. The Puyallup Tribe of Indians is interested in better understanding the water resources of the river. To improve that understanding, the Tribe would like to have additional information on their water resources and those of the basin. In consultation with the USGS, the Tribe decided that further study of trends in flows of the Puyallup River and other streams in the lower Puyallup basin would be most useful to meet their needs. They would also like to compare flow on the Puyallup River to regulatory minimum instream flows for the river, as established in the Washington Administrative Code (WAC) 173-510.

Objectives - The objectives of this study are to:

1. Determine if flows of the Puyallup River and other selected streams in the lower Puyallup basin have changed significantly over the past 20 years.
2. Determine the fraction of time that flows on the Puyallup River have not met minimum instream flows, again over the past 20 years.
3. Determine how trends and variability in flows in the Puyallup River and other selected streams are related to any trends and variability in climate, as indicated by long-term records of precipitation and ground-water levels in or near the basin.
4. Estimate the potential impact of changes in water use in the basin over the past 20 years on stream flow.

Relevance and Benefits - This study will address the second major mission goal of the USGS 2000-2005 Strategic Plan of better understanding the Nation's environment and natural resources. The study will help to better understand how water use impacts streamflow, especially in a regulatory framework. The study also addresses two of the five water issues identified in the USGS Washington Water Science Center Science Plan-water availability and Endangered Species Act issues. Locally, the data are very important to the Puyallup Tribe of Indians, Washington State Department of Ecology, and other parties who desire to resolve questions about managing stream flows in the Puyallup River basin.

Approach

1. Streamflow records for the Puyallup River at Puyallup (12101500) and Puyallup River at Orting (12093500) gages will be evaluated from 1981 through 2000 to determine if any statistically significant changes and/or trends are present. Annual mean discharge will be evaluated to determine any overall changes in water discharged from the basin. To determine changes in seasonal low flows, monthly mean discharge for the months of July, August, September, and October, and annual minimum seven-day mean flows will be evaluated.
2. Streamflow records for the Puyallup River at Puyallup also will be evaluated over the period 1988 - 2000 to determine the fraction of time minimum instream flows were not met.
3. Trends in annual precipitation will be evaluated and compared to trends in observed streamflow. Trends in ground-water levels of a few (3-5) selected shallow wells will be evaluated.
4. The impacts of water use will be evaluated using data from USGS 5-year compilations and water rights certificates and permits.