Flood-prone area maps of three sites along the Trans-Alaska Pipeline, Alaska

Abstract

The Bureau of Land Management requested on May 3, 1979 that the U.S. Geological Survey determine the base (100-year) flood-plain limits at three sites (fig. 1) along the Trans-Alaska Pipeline System Highway (Haul Road) between the Yukon River and Prudhoe Bay in order to issue land-use permits. The Alaska Department of Transportation and Public Facilities (ADOT) has constructed maintenance camps at Coldfoot and adjacent to the Jim River near Pump Station 5. The site along the Sagavanirktok River near Pump Station 3 is under consideration as a site for potential development. An analysis of the flood data available at nearby gaging stations, at prior flood-survey sites, and from regional flood analyses was made. The discharge of the 100-year flood was calculated for the three sites using methods described by U.S. Water Resources Council (WRC, 1977) and given in Lamke (1979). Next field examination was made of the sites. Flood-deposited debris upon the overbank flood-ways was used to determine elevations of the maximum evident flood at the three flood-prone sites mapped. The maximum evident floodmarks for these floods were at elevations and locations which indicated that they were independent of ice scars. Ice scars higher than the highest flood debris were found at the Jim River site. Flood evidence of recent peaks was also used as an aid in determining the base flood boundaries. These limits have been delineated on aerial photographs of the sites. Surveying was limited to that necessary to adequately define the base flood boundaries; step-backwater computations were not made. Although some additional pertinent information is shown on the photographs, no attempt was made to delineate areas of inadequate local drainage or seasonal problems of high ground-water tables. Aerial photographs of the three sites were obtained from North Pacific Aerial Survey, Inc., with the permission of Alaskan Natural Gas Transportation Co. One photograph was obtained from Air Photo Tech, Inc., with the permission of Aleyska Pipeline Service Co.