|Theurer, F - NRCS|
|Havis, R - CONSULTANT|
Submitted to: Federal Interagency Hydrologic Modeling Conference
Publication Type: Proceedings
Publication Acceptance Date: April 19, 1998
Publication Date: N/A
Interpretive Summary: Problem: Commercial and sport benefits resulting from salmonid fisheries averaged $434 million annually in the Pacific Northwest in the 1970's. Reduced spawning success because of stream sediment loading is one of the major contributors to reduced populations of salmonid species. Major reasons for increases in fine sediment loading to spawning areas are agricultural development and forest harvesting and associated road building. There is a need for simulation tools applicable to widespread geographic locations capable of facilitating informed decisions on alternate land management practices upstream of salmonid spawning habitat. What was accomplished: This paper presents practical modeling tools that were developed to evaluate the effects of upstream sediment loads, on salmonid spawning habitat. These tools are field tested, deterministic simulation models that have general geographic applicability for evaluating the effects of fine sediment loads from agricultural areas or the effects of coarse sediment loads from highland forested areas. The effects of sedimentation, water temperature, and oxygen concentration on the success of salmonid egg incubation and fry emergence are considered. Contribution: The proposed methodology will contribute to better evaluations of agricultural downstream impacts on aquatic habitat. The U.S. Fish & Wildlife Service concluded in 1981 that better assessments of the impact of alternate upstream practices can contribute to alleviate the severe losses experienced by the fishing industry in the Pacific Northwest due to nonpoint pollution sources.
Technical Abstract: Studies have shown that fine sediment intrusion can significantly impact the quality of spawning habitat. Fine sediment intrusion into streambed gravels can reduce permeability and intragravel water velocities, thereby restricting the supply of oxygenated water to developing salmonid embryos and the removal of their metabolic wastes. Excessive fine sediment deposition can effectively smother incubating eggs and entomb alevins and fry. This paper (1) presents a synopsis of models developed as management tools to evaluate the impact of stream sediment load on salmonid survival, and (2) discusses results obtained from field validation studies conducted in the Tucannon River in southeastern Washington and in the Salmon River in central Idaho.