Surface-water supply for the city of Williams, Coconino County, Arizona.

Abstract

The city of Williams, Arizona, obtains its water supply from reservoirs that impound surface-water runoff. Seven reservoirs provide a storage capacity of 2, 722 acre-feet, about nine times the city1s annual need. However, water shortages occur periodically, mainly because of excessive seepage from the two largest reservoirs- Dogtown and Kaibab Reservoirs. The average annual precipitation at Williams is 21.25 inches; the average winter precipitation is 13.30 inches. Winter precipitation is responsible for most of the surface-water runoff. Between January 1964 and June 1966, the surface-water runoff was 5,810 acre-feet to Dogtown Reservoir and 5,570 acre-feet to Kaibab Reservoir. The average efficiency of the watersheds (percent of precipitation that leaves the watershed as runoff) was 30 percent above Dogtown Reservoir and 16 percent between Dogtown and Kaibab Reservoirs. Seepage losses from the reservoirs were 68 percent of the input to Dogtown Reservoir and 50 percent of the input to Kaibab Reservoir, The highest average monthly seepage rate was 0. 14 foot per day at Dogtown Reservoir and 0. 21 foot per day at Kaibab Reservoir. The average annual evaporation from all the reservoirs is about 46 inches. During the period of record, evaporation was about 6 percent of the input to both Dogtown and Kaibab Reservoirs. If seepage was eliminated from these two reservoirs, evaporation would amount to about 25 percent of the input. A yearly draft rate of 150 acre-feet of water from Dogtown Reservoir and 100 acre-feet from Kaibab Reservoir could have been sustained during the 30-year period 1937-66 if seepage from the reservoirs had been zero. This 250 acre-feet of water combined with about 80 acre-feet from the other reservoirs would more than supply the city’s annual need.