March 4, 2010
The 70 km long Elwha River in Olympic National Park was once of the most productive salmon rivers in the Pacific Northwest, this fall it is getting to for the first time flow from the glaciers to the sea, image of watershed from the restoration project. At the headwaters of this stream are two named glaciers Carrie and Fairchild, and four unnamed glaciers, which play an important part in the hydrology of the watershed. The glaciers have retreated considerably since the building of the dams, rapidly since 1980. The result is a significant reduction in late summer glacier runoff than when the stream last flowed naturally. The construction of Elwha Dam (1913) and Glines Canyon Dam (1927) devastated the Elwha River’s salmon runs. Dismantling the Elwha and Glines Canyon dams over the next two years will allow the river to flow freely for the first time in nearly 100 years. The river will run from its headwater glaciers to the sea. Dams alter streamflow by withholding water and then releasing the water to generate power during peak demand periods. This leads to unnatural flows, which interrupt natural variations that are critical to the fish and wildlife species. Besides the ongoing dam removal recent climate change is altering the seasonal flow of the Elwha River. The loss of glacier area has and will lead to ongoing significant changes in summer streamflow in the Elwha River. In the Elwha River from 1950-2006 summer streamflow declined by 25%, spring streamflow by 17%, and winter streamflow increased by 6%. Part of this change is due to the loss of glacier extent in the watershed.
Glaciers act as natural reservoirs storing water in a frozen state instead of behind a dam. Glaciers modify streamflow releasing the most runoff during the warmest, driest periods, summer, when all other sources of water are at a minimum. Annual glacier runoff is highest in warm, dry summers and lowest during wet, cool summers. The amount of glacier runoff is the product of surface area and ablation rate. The North Cascade Glacier Climate Project began annual monitoring program of North Cascade glaciers in 1984. This program has also examined the change in glacier volume and extent in the Bailey Range and Anderson Glacier in the Olympic Mountains.
In the Elwha watershed glacier extent has declined from 2.8 km2 in 1980, to 2.6 km2 in 1990, to 2.1 km2 in 2008.
Fairchild Glacier retreated 300 meters from 1950-1994, topographic map versus aerial photograph, green versus red line. From 1994-2009 another 240 m of retreat occurred as indicated by the orange line. In addition the Fairchild Glacier has separated into three sections by 2009. The greatest concern is the emergence of bedrock outcrops in the midst of the glacier since 1994, burgundy arrows in the 2009 image. This is a key symptom of a glacier that will not survive (Pelto, 2010). This is leading to the breakup of the glacier into smaller easily melted segments. This is a process that we have observed lead to the demise of glaciers like the Hinman Glacier. The emergence also indicates the thin nature of the glacier. The view of the glacier from 2005 illustrates the small area of the glacier that is retaining snowpack, this is not a good sign for survival of this glacier.At the end of the summer melt season a glacier needs to be at least 50% snowcovered, to survive it must have a consistent significant area of snowpack. In 2005 in this August picture only 20% of the glacier is snowcovered and by summers end it was 5%.
The consequent glacier runoff has declined by 750,000-850,000 ft3/day in the summer since 1980. The resultant annual hydrograph for the Elwha River is not the same as it was before dam construction. In particular late summer and fall salmon runs will experience less runoff due in part to declining glacier runoff. Streamflow in the Elwha River has declined 25% during July-Sept. for the 1950-2006 period. The mean summer flow from 1950-1991 was 1034 cfs. From 1992-2009 only two summers had mean streamflow above 1034 cfs. The decline in glacier size is not the principal cause of the summer streamflow decline, but it further reduces the summer low flows. Updated 12/14/2011