Intensive Site Preparation and Sediment Losses on Steep Watersheds in the Gulf Coastal Plain

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Abstract
The hydrologic effects of three methods of intensive site preparation—brush chopping, shearing and windrowing, and bedding on contour—were measured during the 1976 and 1977 water‐years on three small watersheds on steep terrain in northern Mississippi. After site preparation, the treated watersheds were fertilized, limed, sown with clover (Trifolium subterranean L.), and planted with loblolly pine seedlings (Pinus taeda L.). An undisturbed watershed served as a control. Site preparation exposed soil on 37% of the chopped watershed, on 53% of the sheared and windrowed watershed, and on 69% of the bedded watershed. First‐year sediment losses for the chopped, sheared, bedded, and control watersheds were 12.5, 12.8, 14.2, and 0.6 metric tons/ha, respectively. Sediment concentrations for the four watersheds were 2,471, 2,837, 2,808, and 2,127 mg/liter of stormflow. Most of the first‐year sediment losses occurred during months of highest stormflows, November, January, February, and March. Stream channel scouring was a major source of sediment on the site prepared watersheds.Second‐year sediment yields from the chopped, sheared, and bedded watersheds decreased to 2.3, 2.2, and 5.5 metric tons/ha, while sediment from the control watershed decreased to 0.1 tons/ha. Sediment concentrations were 670, 794, 2,346, and 393 mg/liter for the four watersheds. In relation to annual precipitation, total stormflow decreased on all treated watersheds the second year.

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