Experimental study of soil erosion control systems

A laboratory experimental rainfall/runoff/infiltration system has been constructed to evaluate the performance of different erosion control systems on steep slopes under reproducible, controlled conditions. The system can investigate the performance of erosion control systems during very early stages of a rainstorm. Thus the fundamental mechanism of how various erosion control systems work can be investigated. The system is comprised of a rainfall-producing module, a soil/erosion-control-system test flume, and a measurement/data collection system. The rainfall module can produce rainfall intensities approaching 254 mm/hr. (10 in/hr.) with an average spatial coefficient of variation of only 4% over a wide range of rainfall intensities. The experimental results obtained using the system represent measurements of surface runoff and sediment yield resulting from nominal rainfall intensities of 50, 125 and 200 mm/hr. (2, 5 and 8 in/hr.) on the upper reaches of a 1 on 2.5 and of a 1 on 4 slopes. Data include the characteristic rising limb of the S-hydrograph, the equilibrium discharge, and the typical recession curve after cessation of rainfall. Results are obtained for unprotected soil slopes and for slopes protected by 12 different natural and geosynthetic erosion control systems. The analysis is focused on the behavior of each erosion control system and how it acts to control raindrop impact and soil detachment, how it reduces flow velocities, and ultimately how it controls sediment detachment and loss from the test plot (short-term performance). The analysis is limited to erosion control systems on the upper reaches of unvegetated relatively steep slopes. The hydraulic characteristics of the erosion control systems were determined based on parametric models obtained for the rising and receding limbs of the overland flow hydrograph. Also, dimensionless retardance and friction coefficients for the erosion control systems investigated were derived from a modified version of Izzard's model for retardance coefficient.