Storm Flow and Sediment Losses From Site‐Prepared Forestland in East Texas

Abstract

Nine small (2.57 to 2.79 ha) forested watersheds in East Texas were instrumented in December 1979 to determine the effect of harvesting and site preparation on storm flow and sediment loss. Three replications of three treatments were used: (1) clearcutting, followed by shearing, windrowing, and burning, (2) clearcutting, followed by roller chopping and burning, and (3) undisturbed control. Prior to treatment, mineral soil was exposed on 3% of the watersheds. Following treatment in June 1981, 57% of the mineral soil was exposed on the sheared and windrowed watersheds compared to 16% on the chopped watersheds. At the end of the second, third, and fourth years' growing season, mineral soil was exposed on 20, 9, and 10% of the sheared and 4, 4, and 3% of the chopped watersheds, respectively. The first year following treatment, mean storm flow was greater from the sheared watersheds (14.6 cm) than from the chopped (8.3 cm) watersheds, with the storm flow from the latter greater than from the undisturbed (2.6 cm) watersheds. Mean storm flow was less from all watersheds the second year after treatment; however, storm flow from the sheared watersheds (5.0 cm) was similar to that from the chopped (3.6 cm) water‐sheds, and both were greater than that from the undisturbed (1.2 cm) watersheds. During the third posttreatment year there was no significant difference in mean storm flow from the sheared and chopped watersheds or from chopped and undisturbed watersheds. Storm flow during the fourth posttreatment year was greater from the sheared watersheds (6.1 cm) than from the chopped (3.5 cm) watersheds, which had greater stormflow than the undisturbed (1.4 cm) watersheds. First‐year sediment losses were greater from the sheared (2937 kg/ha) than from the chopped (25 kg/ha) or undisturbed (33 kg/ha) watersheds. Although second‐year sediment losses were greatly reduced from the sheared watersheds (79.9 kg/ha), they remained greater than losses from chopped (5.5 kg/ha) or undisturbed (5.1 kg/ha) watersheds. Sediment losses from the sheared watersheds (34.6 kg/ha) decreased during the third posttreatment year and were similar to losses from the chopped (5.4 kg/ha) watersheds. During the fourth posttreatment year, sediment loss was greater from the sheared watersheds (165 kg/ha) than from the chopped (16 kg^sol;ha) or the undisturbed (29 kg/ha) watersheds. Although sediment losses were significantly different between treatment,, they were small and below Soil Conservation Service tolerable levels. Mean sediment concentrations and losses from the chopped and undisturbed watersheds were similar during the four posttreatment years. Sediment concentrations from the sheared watersheds, were greater than from chopped or pndisturbed watersheds during the four posttreatment years; however, concentrations the first year after treatment (2119 mg/L) were greatly reduced the second (167 mg/L), third (54 mg/L), and fourth year (331 mg/L).