The hydrology of ten streams in western Washington as related to several Pacific salmon species

Abstract

Enhancement or possibly even preservation of the Pacific salmon hinges on the careful planning and proper management of the streamflow upon which they depend for spawning. Most spawning activity occurs on reaches of streams where specific hydraulic conditions exist and where stream-channel characteristics and water-quality criteria are met. The present report is the first of a series and is used to present the method of determining preferred spawning conditions and results of the investiagtion of 129 measurements on 14 study reaches of the Dewatto, Cedar, Kalama, and North 'Fork Nooksack Rivers. Subsequent reports, using the same method will present analyses and preferred spawning and rearing discharges for other streams used by salmon. The method consists of measuring water depth and velocities to designate, from area (spawnable) discharge curves, peak, preferred spawning discharges for fall chinook, spring chinook, sockeye, and coho salmon at each reach on each river. Also, streambed gravels, water temperature, suspended sediment, dissolved oxygen, and specific conductance are used to help evaluate river conditions during spawning. In examining the repeatability of the method, tested by analyzing independently each of selected pairs of adjacent reaches on the Cedar River, it was found that the preferred peak discharges from the comparisons varied 4.6 percent for the average of four species and two pairs of reaches. Peak spawning discharges ranged, for the four salmon species on each of the three study reaches of each river, from 50 to 140 cfs (cubic feet per second) on Dewatto River, from 230 to 510 cfs on Cedar River, from 245 to 800 cfs on Kalama River, and from 195 to 710 cfs on North Fork Nooksack River. The results indicate that the methods used and the probable discharge values determined are reasonable and, if economically justified, may be used to select discharges, for salmon spawning and rearing. 2 HYDROLOGY AS RELATED TO PACIFIC SALMON INTRODUCTION The Pacific salmon is an anadromous fish, living in the sea and ascending rivers and streams for spawning, incubation, and early rearing. Five salmon species of Pacific salmon frequenting the Washington streams are sockeye (Oncorhynchus nerka), chinook (O. tsawytscha), coho (O. Kisutch), pink (O. gorbuscha), and chum O. keta). Sockeye, coho, and the spring and fall chinook were investigated in this study; for simplicity, in the rest of this report these three salmon species (with two races of one species) will be referred to as four species. The Pacific salmon utilizes most of the streams in western Washington for spawning and rearing. The most productive spawning activity occurs on reaches of streams where specific hydraulic conditions exist and where certain stream-channel characteristics and water-quality criteria are met. Each salmon species has specific hydraulic prerequisities ranges of water depths and bottom velocities for spawning. The critical channel characteristics include streambed composition and compactness infiltration of water through the gravels, cover and concealment, and the amount of habitation along the streambanks (Royce, 1959). Some factors of water quality which influence spawning are water temperature, suspended sediment, dissolved oxygen, and dissolved-solids concentration. Anadromous fish usually spawn in pool-riffle streams, where the water slope alternates between comparatively level reaches (pools) and comparatively steep segments (riffles). Sand is the predominant bed material in the pools, whereas the bed material of the riffles, where the salmon form their redds (nests), is generally much coarser. Smolt production is highest in stream channels composed of 50-percent riffles and 50-percent pools (Ruggles, 1966). The pools, with proper food production and volume of water, serve as rearing areas for the fry and fingerlings of some salmon species. Riffles also serve as food-production and rearing areas. At present, the streams of western Washington have an abundant supply of water; however, the increasing population and industrial growth is accompanied by an ever-growing demand for water for hydroelectric power generation and other beneficial uses, such as irrigation and municipal supply. Therefore, if the Pacific salmon is to be enhanced or even preserved, the allocation of streamflow, careful planning, and proper management will be necessary.