Effects of agricultural conservation practices on the hydrology of Corey Creek basin, Pennsylvania, 1954-60

Abstract

Analyses of data collected from two small basins in northern Pennsylvania during the period May 1954 to September 1960 indicated that changes in land use and land treatment have affected suspended- sediment discharge from the basins. Extensive land use and land-treatment changes have taken place in the 12.2-square-mile Corey Creek study basin, whereas such changes in the 10.2-square-mile Elk Run basin, which is adjacent to the northeast, have been relatively slight. Elk Run basin, which is topographically and hydrologically similar to Corey Creek basin, was used as an external control for the Corey Creek basin study. Multiple-regression analysis showed that of all the variables, runoff correlated most highly with the sediment yield of each basin. Surveys at selected cross-sections of the two streams indicated that most channel changes were in the banks rather than in the bed. At points where the stream channel slope was greater than 70 feet per mile, the average annual change in cross-sectional area at the measured ranges was less than +--2.5 square feet. Filling of the stream channel occurred where the slope was 70 feet per mile or less, and such filling was greater in Corey Creek than in Elk Run. Trend analyses of data from both basins indicated no persistent changers in quantity of runoff, precipitation, or runoff intensity (peakedness), although similar analyses indicated significant changes in the rate of suspended-sediment discharge from both basins. During the period September 1957 to September 1960, sediment discharge from Corey Creek basin decreased by 11 percent relative to the sediment discharge from Elk Run. All, or most, of this decrease was the result of a decrease in sediment discharge during the May to October growing seasons. No significant trends were detected in data collected d-ring the November to April dormant season. A factor, termed the relative erosion potential, was formulated for evaluating the effects of changes in the hydrologic cover conditions. This factor was adjusted for- the effects of diversion terrace construction in the Corey Creek basin. A rank correlation test of the adjusted relative erosion potential versus the growing season Corey Creek-Elk Run suspended-sediment discharge ratio resulted in a correlation coefficient, r=0.71, significant at the 3 percent level. The least-squares regression equation derived from the .same data. was Y=0.276 X - 6.89. where Y was the Corey Creek-Elk Run sediment-discharge ratio and X was the adjusted relative erosion potential. The correlation coefficient was 0.65. significant at the 12 percent level. Standard error of estimate was 0.44. or about ?20 percent of the observed variation in the sediment-discharge ratio.