Contrasting extreme runoff events in areas of continuous permafrost, Arctic Alaska

Abstract

Spring snowmelt floods in the Arctic are common and can be expected every year, mainly because of the extensive snow cover that ablates relatively quickly. However, documentation of extreme flows (both low and high) ¡n the Arctic is lacking in part because extreme flows are relatively rare and gauging sites are very sparse, with most of short duration, in the nested Kuparuk River research watersheds on the North Slope of Alaska, two large summer floods have been observed {July 1999 and August 2002) in the headwaters; these high flows are contrasted to the low flows (drought conditions) observed in the summers of 2005 and 2007. It is clear that the continuous permafrost and the limited near-surface storage in the shallow active layer are responsible for both the high and low flow responses. Or, stated another way, the active layer is a poor buffer to both floods and droughts. When contrasting summer floods with snowmelt floods, it is clear from flood frequency analyses that the smaller, high-gradient headwater basins will be dominated by summer floods while those watersheds draining the low gradient coastal plain will be dominated by snowmelt floods. The two summer floods in the headwaters had flows that were three to four times greater than the largest measured snowmelt flood, while on the coastal plain the 2002 summer storm for the whole of the Kuparuk River only produced the maximum summer runoff of record that was about 1/4 of the maximum snowmelt flood, so, on the coastal plain and even for the Greater Kuparuk River that drains across the coastal plain, snowmelt floods dominate. Drought conditions prevail in summers when the limited surface water storage in the active layer and surface water bodies is depleted because evapotranspiration exceeds precipitation.

Basin Hydrology

“…Kane et al (2008) found that the highest flow on record for Imnavait and Upper Kuparuk rivers (basin areas 2.2 and 146 km 2 , respectively) were the result of summer rain ( Fig. 10.11).…”

“…Kriet et al (1992) noted that runoff generated by localized summer storms in the Upper Kuparuk basin appears only as a slight increase in discharge at the basin outlet, and the time difference between their respective hydrograph rises varied from 3 days during a late July 1979 storm, to 8 days during low flow periods. For the large Kuparuk basin (area 8,140 km 2 ), Kane et al (2008) observed that unlike snowmelt in which the entire basin can contribute runoff, summer rain seldom significantly covers the whole basin so that rainfall floods do not exceed peak flows from snowmelt ( Fig. 10.11).…”

“…Locally, rain can fall on entire small basins and produce peak discharges that match or exceed their snowmelt peaks. Kane et al (2008) found that while most annual floods of the small Upper Kuparuk River occur in the snowmelt season, it is the large rain events that produce the floods of record. However, as basin size increases, individual high flows generated by rainfall in parts of the basin are diluted by non-event discharge from those areas away from the rain centroid.…”

Using Snow Fences to Augument Fresh Water Supplies in Shallow Arctic Lakes

“…For example, an extremely dry summer and fall occurred in 2007. During that year, the Kuparuk River at Deadhorse had its lowest end-of-summer flow since 1971, when the U.S. Geological Survey initiated streamflow gauging at this site (Kane et al, 2008). The impact of the 2007 drought on the surface storage deficit was evident during the 2008 snowmelt runoff and annual water yield (Arp et al, 2012).…”

Using Synthetic Aperture Radar to Define Spring Breakup on the Kuparuk River, Northern Alaska

“…McNamara et al (1998) found that snowmelt provides up to 80% of the annual runoff from the Kuparuk River. Summer precipitation is also important in causing increased runoff from the Kuparuk River because the underlying permafrost limits the potential subsurface storage of water (Kane et al, 2003(Kane et al, , 2008.…”