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Water-Balance Simulations of Runoff and Reservoir Storage for the Upper Helmand Watershed and Kajakai Reservoir, Central Afghanistan

Scientific Investigations Report 2007-5148

Prepared in cooperation with the U.S. Agency for International Development
By:
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Abstract

A study was performed to provide information on monthly historical and hypothetical future runoff for the Upper Helmand watershed and reservoir storage in Kajakai Reservoir that could be used by Afghanistan authorities to make economic and demographic decisions concerning reservoir design and operation, reservoir sedimentation, and development along the Helmand River. Estimated reservoir volume at the current spillway elevation of 1,033.5 meters decreased by about 365 million cubic meters from 1968 to 2006 because of sedimentation. Water-balance simulations indicated a good fit between modeled and recorded monthly runoff at the two gaging stations in the watershed for water years 1956-79 and indicated an excellent fit between modeled and recorded monthly changes in Kajakai Reservoir storage for water years 1956-79. Future simulations, which included low starting reservoir water levels and a spillway raised to an elevation of 1,045 meters, indicated that the reservoir is likely to fill within 2 years. Although Kajakai Reservoir is likely to fill quickly, multiyear deficits may still occur. If future downstream irrigation demand doubles but future precipitation, temperature, and reservoir sedimentation remain similar to historical conditions, the reservoir would have more than a 50-percent chance of being full during April or May of a typical year. Future simulations with a 10-percent reduction in precipitation indicated that supply deficits would occur more than 1 in 4 years, on average, during August, September, or October. The reservoir would be full during April or May fewer than 1 in 2 years, on average, and multiyear supply deficits could occur. Increased sedimentation had little effect on reservoir levels during April through July, but the frequency of deficits increased substantially during September and October.

Study Area

Additional Publication Details

Publication type:
Report
Publication Subtype:
USGS Numbered Series
Title:
Water-Balance Simulations of Runoff and Reservoir Storage for the Upper Helmand Watershed and Kajakai Reservoir, Central Afghanistan
Series title:
Scientific Investigations Report
Series number:
2007-5148
Edition:
-
Year Published:
2007
Language:
ENGLISH
Publisher:
Geological Survey (U.S.)
Contributing office(s):
North Dakota Water Science Center
Description:
iv, 17 p.