ABSTRACT:
Gullies with large reliefs, 15 to 20 feet, were accurately mapped with timelapse aerial photographs. Contour maps (0.5-foot) of the gully area provided a general study of changes in the valley floor, headcut, and gully erosion by overlaying successive topographic maps. Plotting individual cross-section points achieved the desired accuracy of ± 0.05-feet for surveys on bare ground. Sheet and rill erosion also were determined to the same accuracy with low-altitude, time-lapse aerial photographs. Soil movement was determined for each stereomodel and algebraically summed. Net, 9-year soil erosion was 130 tons/acre, resulting in average annual erosion of 14 tons/acre. Average annual sediment delivery ratio of 53% was determined using the 7.7-ton-per-acre average annual sediment yield for the 75-acre watershed. Universal soil loss equation calculations predicted an annual soil loss of 37 tons/acre, resulting in a sediment delivery ratio of 21%. The sediment delivery of 53% for the photogrammetric study compared to the 21% computed with the USLE emphasizes the need for continued study of sediment delivery.
Footnotes
Ralph G. Spomer is an agricultural engineer with the Watershed Research Unit, Agricultural Research Service, U.S. Department of Agriculture, Federal Office Building, Council Bluffs, Iowa 51502; Robert L. Mahurin is a hydrologic technician with the Watershed Research Unit, ARS, USDA, 207 Business Loop 70 East, Columbia, Missouri 65201. Trade and company names are included for the benefit of the reader and do not imply an endorsement or preferential treatment of the product listed by the U.S. Department of Agriculture or cooperating agencies.
- Copyright 1984 by the Soil and Water Conservation Society
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