Flow Regime and Ecosystem Interactions in Spring-Dominated Streams: Implications for Selecting Instream Flow Methods

¹ R2 Resource Consultants, 15250 N.E. 95th St., Redmond, Washington, 98052-2518.
² Seattle Public Utilities, Cedar River Watershed. 19901 Cedar Falls Road SE, North Bend, Washington 98095

Abstract

Spring-dominated streams (SDS) are known to differ from runoff-dominated streams (RDS) in a number of ways. Stability of flow and temperature are two characteristics most often associated with spring-dominated streams, but other ecosystem attributes may also differ. The effects of altered flow regimes may also differ between these two system types. Relationships between flow and fish habitat have been widely studied in RDS, and a variety of instream flow methodologies/models have been developed to quantify these relationships. The applicability of these methods and models to SDS has not been tested. In this paper, we summarize information on spring-dominated streams, addressing the questions of (1) how key habitat components of salmonid fish differ between spring- and runoff-dominated streams and (2) how changes in flow regime may affect spring- and runoff-dominated streams differently. Implications for selecting/ developing methods applicable for evaluating flow needs of spring-dominated streams and impacts associated with water abstraction are discussed.