This report presents the results of an evaluation of hydrologic data for the Beaver-North Canadian River basin upstream from Canton Lake in western Oklahoma. It examines the climatic and hydrologic data for evidence of trends. The hydrologic data examined includes total annual flow, base flow, and annual peak discharges.
This study was conducted to determine if there is evidence of trends present in hydrologic and climatic data. All available streamflow-gaging station data, with at least 10 or more years of record, were examined for trends. In addition, the data were divided into an 'early' period (ending in 1971), representing conditions before ground-water levels had declined appreciably, and a 'recent' period (1978-1994), reflecting the condition of declining ground-water levels, including the effects of storage reservoirs.
Tests for trend, moving averages, and comparisons of median and average flows for an early period (ending in 1971) with those for the recent period (1978-1994) show that the total annual volume of flow and the magnitudes of instantaneous annual peak discharges measured at most gaging stations in the Beaver- North Canadian River basin have decreased in recent years. Precipitation records for the panhandle, however, show no corresponding changes.
The changes in flow are most pronounced in the headwaters upstream from Woodward, but also are evident at Woodward and near Seiling, which represents the inflow to Canton Lake. The average annual discharge decreased between the early period and the recent period by the following amounts: near Guymon, 18,000 acre-feet; at Beaver, 68,000 acre-feet; at Woodward, 72,000 acre-feet; and near Seiling, 63,000 acre-feet. These decreases, expressed as a percentage of the average flows for the early period, were 91 percent near Guymon, 82 percent at Beaver, 49 percent at Woodward, and 37 percent near Seiling. The medians of the annual peak discharges decreased from the early period to the recent period by the following amounts: near Guymon, 98 percent; at Beaver, 86 percent; at Woodward, 80 percent; and near Seiling, 53 percent. The Guymon gage is not affected by reservoirs; the other three mainstem gaging stations are influenced by reservoirs, but the decreases in annual peak discharges are greater than can be explained by storage in those reservoirs.
Base flows have undergone substantial change, but unlike the annual volumes the base flows show some increases and some decreases. Flow duration analyses show a shift in the distribution of annual flows. Less contribution is coming from large floods that formerly added substantially to the yearly average flows. Near Seiling, for example, the magnitudes of the large flows that occur less than about 20 percent of the time were greatly reduced in the recent period.
A primary mechanism producing these decreased streamflows appears to be the depletion of ground water in the High Plains aquifer that underlies more than 90 percent of the basin. Changes in farming and conservation practices and in water use also may be having an effect.