Habitat - Fish Passage Technical Assistance
Date Published: April 2001
Number of Pages: 63
Author(s): Eric Gower, Ethan Espie, Brian Benson and Paul Sekulich
Over the past 62 years, the Washington Department of Fish and Wildlife (WDFW) has purchased approximately 840,000 acres of Wildlife Area land, scattered throughout almost every county in the state. Due to the increasing interest in fish passage issues, the Habitat and Lands Services Program initiated an inventory of fish passage barriers and water diversions on all agency owned and/or managed lands. The Salmonid Screening, Habitat Enhancement and Restoration Section (SSHEAR) was assigned this task. The purpose of the inventory is to document and prioritize for correction all fish passage problems including culverts, dams, lake screens and unscreened or inadequately screened water diversions to ensure compliance with Washington State laws. According to RCW 77.55.060, “All dams or obstructions across or in a stream shall be fitted with a durable and efficient fishway” and RCW 77.55.040 requires that water diversions be fitted with a screen to prevent fish from entering the diversion.
Salmonids of the Pacific Northwest have long been impacted by structures installed in streams incorrectly or with no regard to the salmonid life cycle. Thousands of juvenile salmonids are killed every year when they enter inadequately screened or unscreened water diversions, by mutilation from a pump turbine or being stranded in irrigation canals as the irrigation season comes to a conclusion. Culverts, dams, and abandoned lake outlet screens also have a very detrimental impact on salmonid populations. When these facilities result in a barrier to fish migration, spawning and rearing habitats become inaccessible.
Each year, more of these structures become barriers to fish migration and because watersheds are continually being altered (e.g., development, logging, roads etc.), the hydrological dynamics of the watershed are substantially altered as well. Culverts, fishways, lake outlet screens, and water diversions that were once designed for a defined annual flow, are now incapable of managing the increased flow. Culverts become velocity barriers and eventually scour huge plunge pools that in most circumstances result in large outfall drops. Even hydraulic drops less than one foot are a potential barrier to adult chum salmon, juvenile salmonids and other fish species. Recent studies have shown that these small hydraulic drops can limit juvenile production by rendering valuable rearing habitat inaccessible. Screened water diversions that are not properly maintained can also begin impinging salmonids, either killing them or carrying them into the diversion system.
In cooperation with the Lands Division, SSHEAR staff designed a Wildlife Area Scheduling Index to organize the inventory. To establish the scheduling index of wildlife areas, a questionnaire was designed to collect information on the number of known fish passage problems, stock status, stock mobility, and high profile fish passage issues of public interest. This enabled SSHEAR staff to gain the knowledge and expertise of Wildlife Area Managers. In December of 1997, the questionnaire was mailed to all Regional Lands Coordinators and Wildlife Area Managers. After the index was calculated for each area, they were stratified according to the time of year in which the inventory could be accomplished. Eastern areas will be scheduled in the spring and summer months and the western areas will be inventoried in the fall and winter months. The Methow Wildlife Area ranked highest in priority for eastern Washington.