RUNOFF FROM SIMULATED RAINFALL IN 2 MONTANE RIPARIAN COMMUNITIES

Riparian ecosystems are the final terrestrial zone before runoff water enters a stream. They provide the last opportunity to decrease non-po int source pollution delivery to streams by removing sediments from ov erland water flow from uplands and roads. To quantify processes of sed iment transport, filtration and deposition, it is necessary to determi ne runoff characteristics for the area. A rotating boom rainfall. simu lator was used to evaluate the effects of 3 vegetation height treatmen ts (control, 10-cm stubble height, and clipped to the soil surface) in 2 montane riparian plant communities (grass and sedge) on runoff char acteristics. Each rainfall simulation event consisted of 2 phases, a d ry run of about 60 min followed by a wet run approximately 30 min late r. There were no differences in time to runoff initiation for either d ry or wet runs that could be attributed to vegetation height treatment s for either plant community. It usually required more time for runoff to be initiated in the sedge community compared to the grass communit y. Generally, there were lower equilibrium runoff percentages from dry runs in the sedge community compared with the grass community. These differences were less during wet runs. Several runoff parameters had c haracteristics of runoff from water repellent soils. The organic layer on the soil surface exhibited signs of water repellency that reduced the water infiltration rate during the initial stages of a rainfall si mulation. These results indicate that runoff and infiltration processe s in the surface organic horizon of riparian zones may not respond in the classical manner. This characteristic has important implications i f criteria developed in areas with less organic matter on the soil sur face are used to manage overland flow in the zone. Additional studies are needed to fully describe infiltration and runoff processes in ripa rian plant communities.