Academic journal article The Geographical Review

Snowshed Contributions to the Nooksack River Watershed, North Cascades Range, Washington

Academic journal article The Geographical Review

Snowshed Contributions to the Nooksack River Watershed, North Cascades Range, Washington

Article excerpt

In Whatcom County, Washington, as elsewhere in the western United States, demands on water resources are increasing. Most water-policy research concentrates on allocation and distribution, attending much less to the possible dynamics of the source regions: high-elevation snowsheds. Persons and organizations interested in agricultural, fishery, hydropower, municipal, and recreational water uses show keen interest in every drop that flows down the rivers and streams of the western United States (Rodda 1995). Indeed, in many cases, such as the Nooksack River Basin, in the northwestern corner of the North Cascades Range, Washington (Figure 1), rivers are already legally overallocated, and demand exceeds supply (Gillilan and Brown 1997 Benjamin and others 1999). More important, research suggests that snowfalls and water supplies are declining in the western United States and that they will be significantly influenced by climate changes through this century (Parson 2000).

My research determines the contribution of high-elevation snowshed meltwater to the Nooksack River watershed, a contribution previously estimated to be very large during the dry summer (Fountain and Tangborn 1985; Pelto 1993). Knowing the proportional contribution of glacier water is important, particularly because the glaciers are shrinking rapidly in the region (Harper 1993; Pelto 1993, 1996; Pelto and Riedel 2001). Several studies in the western United States speak to diminishing glacier size, the result of several years of negative mass balance (Marston and others 1989; McCabe and Fountain 1995; Chambers 1997). Any moisture shortage noted over glacier surfaces must also occur over nonglacierized portions of high-elevation snowsheds; links among glacier mass balance, seasonal snowpacks, water supply, and climate changes are therefore critical. If glacial recession continues at the present rate, the glaciers and their contributions to summer meltwater may be permanently lost. In that case, summer streamflow s will decrease, and water-management policies within the watershed will be drastically affected (Hulme and others 1999).

The Nooksack Basin displays significant variability, including a glacierized alpine region, heavily forested mountainous uplands, and a highly developed lowland. The important role of the river system is increasingly evident as population growth, well-established agriculture and industry, a salmon population listed as a threatened species, and expanding water-based recreation and tourism stress a fully allocated surface-water supply. Determining the limits of the basin's sustainable water supply requires an understanding of the complex watershed hydroclimate.

Runoff displays significant spatial and temporal variation in the Nooksack Basin. Temporal heterogeneity arises from the intra-annual, interannual, and secular changes in temperature, precipitation, and other climatic factors (Lins 1999). Given the relatively small area of the watershed, the temporal variations generally occur in phase across the basin. Spatial heterogeneity results from the climatic, topographic, biotic, land-use, and pedologic variability within the basin. Dividing the watershed into subunits maximizes the landscape homogeneity within each area and provides a framework for analyzing runoff variations related to hydroclimatic differences between glacierized and unglacierized subbasins (Meier and Tangborn 1961). My study estimates the contribution of high-elevation snowshed meltwater to the Nooksack watershed, in the belief that knowledge of hydroclimatic variability will contribute to designing land- and water-resource-management programs that address increasing competition among users.

THE NOOKSACK BASIN

The Nooksack Basin offers an opportunity to test the hypothesis that glaciers and adjacent snowsheds in the North Cascades contribute up to 25 percent of the summer streamflow (Pelto 1993). …

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