Grays River Watershed and Biological Assessment, 2006 Final Report.

Abstract

SummaryThe Grays River Watershed and Biological Assessment was funded to address degradation and loss of spawning habitat for chum salmon (Onchorhynchus keta) and fall Chinook salmon (Onchoryhnchus tshawytscha). In 1999, the National Marine Fisheries Service listed lower Columbia River chum salmon as a threatened Evolutionarily Significant Unit (ESU) under the Endangered Species Act of 1973 (ESA). The Grays River watershed is one of two remaining significant chum salmon spawning locations in this ESU. Runs of Grays River chum and Chinook salmon have declined significantly during the past century, largely because of damage to spawning habitat associated with timber harvest and agriculture in the watershed. In addition, approximately 20-25% of the then-remaining chum salmon spawning habitat was lost during a 1999 channel avulsion that destroyed an important artificial spawning channel operated by the Washington Department of Fish and Wildlife (WDFW). Although the lack of stable, high-quality spawning habitat is considered the primary physical limitation on Grays River chum salmon production today, few data are available to guide watershed management and channel restoration activities. The objectives of the Grays River Watershed and Biological Assessment project were to 1) perform a comprehensive watershed and biological analysis, including hydrologic, geomorphic, and ecological assessments; 2) develop a prioritized list of actions that protect and restore critical chum and Chinook salmon spawning habitat in the Grays River based on comprehensive geomorphic, hydrologic, and stream channel assessments; and 3) gain a better understanding of chum and Chinook salmon habitat requirements and survival within the lower Columbia River and the Grays River.The watershed-based approach to river ecosystem restoration relies on a conceptual framework that describes general relationships between natural landscape characteristics, watershed-scale habitat-forming processes, aquatic habitat conditions, and biological integrity. In addition, human land-use impacts are factored into the conceptual model because they can alter habitat quality and can disrupt natural habitatforming processes. In this model (Figure S.1), aquatic habitat-both instream and riparian-is viewed as the link between watershed conditions and biologic responses. Based on this conceptual model, assessment of habitat loss and the resultant declines in salmonid populations can be conducted by relating current and historical (e.g., natural) habitat conditions to salmonid utilization, diversity, and abundance. In addition, assessing disrupted ecosystem functions and processes within the watershed can aid in identifying the causes of habitat change and the associated decline in biological integrity. In this same way, restoration, enhancement, and conservation projects can be identified and prioritized.A watershed assessment is primarily a landscape-scale evaluation of current watershed conditions and the associated hydrogeomorphic riverine processes. The watershed ass...

Effects of Wetland Restoration on Floodplain Hydrodynamics under Extreme Flooding Conditions

“…They attributed the avulsion event to increased sediment load, channel constriction by levees, and mobilization of stored sediment by above-average precipitation (May and Geist 2006). Although not documented by May and Geist (2006), these processes may be altering the morphological characteristics in the Grays River downstream of the Highway 4 Bridge as well.…”

“…The Grays River subbasin has been identified as critical in the recovery of salmon and steelhead in the lower Columbia River (LCRFRB 2004), and the recovery plan cites severe channelization (with the loss of backwater habitat and riparian habitat degradation) as major factors affecting native fish populations. Road building and timber harvesting in the Grays River have increased the sediment production in the watershed by an order of magnitude above background conditions (May and Geist 2006). In 1999, a channel avulsion occurred just upstream of the Highway 4 Bridge (Figure 1), in which two meander bends were cut off (May and Geist 2006).…”

“…Road building and timber harvesting in the Grays River have increased the sediment production in the watershed by an order of magnitude above background conditions (May and Geist 2006). In 1999, a channel avulsion occurred just upstream of the Highway 4 Bridge (Figure 1), in which two meander bends were cut off (May and Geist 2006). They attributed the avulsion event to increased sediment load, channel constriction by levees, and mobilization of stored sediment by above-average precipitation (May and Geist 2006).…”