HR: 0830h
AN: B41C-0908    [PDF]
TI: Post-Fire Overland Flow Frequency, Volume and Quality
AU: * Valeron, B H
EM: valertron@yahoo.com
AF: University of California, Riverside, Department of Soil and Water Science - 084 2217 Geology Building, Riverside, CA 92521-0424 United States
AU: Meixner, T
EM: tmeixner@mail.ucr.edu
AF: University of California, Riverside, Department of Soil and Water Science - 084 2217 Geology Building, Riverside, CA 92521-0424 United States
AB: We present results that assess the importance of post-fire hydrophobicity on runoff generation and the evolution of water quality following a stand-replacing chaparral fire. In September of 2002 85% of Southern California's San Dimas Experimental Forest (SDEF) was burned during the Williams' fire. Following this event, 58 overland flow collectors were installed at discrete locations within a chaparral catchment at SDEF in order to quantify the spatial and temporal frequency as well as the water quality of overland flow during and immediately following precipitation events. Results show that precipitation events that occurred one right after the other, with little drying time in between, led to more frequent and higher volumes of overland flow than those events with dry spells preceding them. This suggests that soil antecedent conditions had an impact on soil infiltration capacity and thus on overland flow generation. These results indicate that soil hydrophobicity was not the most important post-fire hydrologic process as we would have expected more runoff in the first storm of the year and in those following drying periods if it were an important mechanism. The reestablishment of vegetation also influenced runoff processes. As the rainy season proceeded and vegetation recovered, collected overland flow volumes decreased. Interception of precipitation by these plants may have shielded the ground from immediate impact, and lowered the overall intensity of the storm in relation to the soil surface, thus increasing the amount of water that could infiltrate into the ground. Increased evapotranspiration may also be significant, although it was not specifically studied. Spatially, the frequency and quantity of runoff accumulated at each site was a function of the specific contributing slope and the characteristics of that slope. These characteristics include the composition of the soil within the samplers' contributing area, i.e. areas of bedrock yielded more water than areas of sand. The water captured in these collectors has also been analyzed for several chemical constituents. Testing yielded high concentrations of nitrate, ammonium and phosphate immediately following the fire, with declining concentrations as the rainy season continued and vegetation was reestablished. The same was found of mineral nutrients, suggesting that the system was being flushed of post-fire by-products as the season progressed.
DE: 1800 HYDROLOGY
DE: 1806 Chemistry of fresh water
DE: 1860 Runoff and streamflow
DE: 1871 Surface water quality
SC: Biogeosciences [B]
MN: 2003 Fall Meeting