Grays River Watershed and Biological Assessment Final Report 2006.

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...

Evaluating Cumulative Ecosystem Response to Restoration Projects in the Columbia River Estuary, Annual Report 2007

“…A study in a similar forest type on a smaller river in the Pacific Northwest, which measured individual sloughs and not catchment-scale metrics and therefore cannot be directly compared with our results, found variation among sloughs even within the same region (Hood 2002). Further, virtually the entire Grays River watershed has been logged leading to an unstable sediment supply that influences current conditions (May and Geist 2007). In the absence of knowledge regarding historical equilibrium conditions, the hydraulic geometry of reference swamps existing in and responsive to the current environmental matrix may provide the most suitable model for restoration design.…”

“…Sediment accretion rates will be important to the prediction of restoration trajectories in the region. Although there is evidence of highly increased sediment mobilization in upper portions of the Grays River catchment as a result of logging and human activities, and dramatic channel movements in the lower river where our study sites occur (May and Geist 2007), over-dike flows with the potential for sediment deposition on the study site occurred only on a limited basis associated with large winter floods of the Grays River during the 20th century. In the two years following hydrologic reconnection, the mean sediment accretion measured in six locations was 2.4 cm/yr, substantially greater than the historical levels measured by radiocarbon dating.…”