Abstract–Low-flow Characteristics of Streams in the Puget Sound Region


Low-flow Characteristics of Streams in the Puget Sound Region, Washington

Periods of low streamflow are usually the most critical factor in relation to most water uses. The purpose of this report is to present data on low-flow characteristics of streams in the Puget Sound region, Washington. and to briefly explain some of the factors that influence low flow in the various basins.

Presented are the data on low-flow frequencies of streams in the Puget Sound region. as gathered at 150 gauging stations. Four indexes were compiled from the low-flow-frequency curves and were used a basis to compare the low-flow characteristics of the streams. The indexes are (1) low-flow-yiled index, expressed in unit runoff per square mile; (2) base-flow index, or the ratio of the median 7‑day low flow to the average discharge; (3) slope index, or slope of annual 7‑day low-flow-frequency curve; and (4) spacing index, or spread between the 7‑day and 183-day low-flow-frequency curves. The indexes showed a wide variation between streams due to the complex interrelation between climate, topography, and geology.