Annual discharge from Cottonwood Creek basin is estimated to have averaged 73,000 acre-ft during a 19-year base period, water years 1938-56, equivalent to an average annual runoff depth of 3.6 inches over the 380 square-mile drainage area. About 30,000 acre-ft per year comes from Deer Creek basin, a tributary drainage of 155 square miles.
Yearly streamflow is highly variable. The discharge of Bluff Creek above Lake Hefner, near Oklahoma City, a small sub-basin of 1.62 square miles in Deer Creek basin, has varied from 484 acre-ft in 1951 to 55 acre-ft in 1956, a ratio of 9 to 1 during the period of record 1950-58.
Highest runoff within a year tends to occur in the spring months of April through June, a 3-month period that, on the average, accounts for about 60 percent of the annual discharge of Cottonwood Creek. Lowest streamflow usually occurs in August and September. Occurrence of no flow in some years has been observed in the lower part of the basin and in the upper parts of Bluff Creek and Chisholm Creek basins. Variation in daily streamflow is such that the estimated average discharge of 97 cfs (cubic feet per second) for Cottonwood Creek just upstream from Guthrie is exceeded only 12 percent of the time and the daily discharge is more than 16 cfs only half of the time. There is no flow at the site about 7 percent of the time, assuming conditions of basin development prevailing in the last decade.
Base flow in parts of the basin is augmented to some extent by seepage from reservoirs. In Bluff Creek basin, the seepage from Lake Hefner toward Spring Creek is 0.2 to 0.3 acre-ft per day; that toward Bluff Creek ranges from 1.7 to 3 acre-ft per day, depending on variation of reservoir level in the top 6 feet of capacity; and that toward Dry Creek is 0.3 to 0.4 acre-ft per day. Low flow in Chisholm Creek is sustained by sewage effluent from The Village, averaging 3 acre-ft per day.
The surface waters of Cottonwood Creek basin are hard but in general are usable for domestic and irrigation supplies. Evidence indicates brines are present in upper Chisholm Creek. The chemical character of the waters varies from a sulfate, chloride type of water in the major part of the basin to a calcium, magnesium bicarbonate type of water in tributaries in the lower part of the basin.
This report gives an estimate of the average discharge at several sites in Cottonwood Creek basin for a 19-year base period, October 1937 to September 1956. Duration curves of daily discharge for Bluff Creek above Lake Hefner are shown for the period of record and for the base period. The low-flow part of an estimated duration curve for Cottonwood Creek near Guthrie is given. Monthly and annual discharge records for Bluff Creek above Lake Hefner are presented. The results of 99 discharge measurements on Cottonwood Creek near Guthrie (through December 1961) and of 312 discharge measurements at 29 other sites in the basin are tabulated.
(available as photostat copy only)