The effects of log erosion barriers on post-fire hydrological response and sediment yield in small forested watersheds, southern California
Wohlgemuth, P.M.; Hubbert, K.R.; Robichaud, P.R. 2001.
The effects of log erosion barriers on post-fire hydrological response and sediment yield in small forested watersheds, southern California.
Hydrological Processes 15(15): 3053-3066.
Keywords: sediment yield; hydrologic response; fire; erosion control; log erosion barriers; upland watersheds; soil depth; water repellency; erosion barrier
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Wildfire usually promotes flooding and accelerated erosion in upland watersheds. In the summer of 1999, a high-severity
wildfire burned a series of mixed pine/oak headwater catchments in the San Jacinto Mountains of southern California.
Log erosion barriers (LEBs) were constructed across much of the burned area as an erosion control measure. We
built debris basins in two watersheds, each about 1 ha in area, one with LEBs, the other without, to measure post-fire
hydrologic response and sediment yield and to evaluate the effectiveness of the LEBs. The watersheds are underlain
by granitic bedrock, producing a loamy sand soil above large extents of weathered bedrock and exposed core stones
(tors) on the surface. Measured soil water-repellency was similar over the two catchments. Rain gauges measured
348 mm of precipitation in the first post-fire year. The ephemeral stream channels experienced surface flow after
major rainstorms, and the source of the water was throughflow exfiltration at the slope/channel interface. Post-fire
overland flow produced some rilling, but hillslope erosion measured in silt fences away from any LEBs was minor,
as was sediment accumulation behind the LEBs. Stream channels in the catchments exhibited minor net scour. Water
yield was much greater in the LEB-treated watershed. This resulted in 14 times more sediment yield by weight than
the untreated watershed. Average soil depths determined by augering were nearly double in the catchment without the
LEBs compared with the treated watershed. This suggests that differences in water and sediment yield between the two
catchments are due to the twofold difference in the estimated soil water-holding capacity in the untreated watershed. It
appears that the deeper soils in the untreated watershed were able to retain most of the precipitation, releasing less water
to the channels and thereby reducing erosion and sediment yield. Thus, the test of LEB effectiveness was inconclusive
in this study, because soil depth and soil water-holding capacity may have masked their performance.
Moscow FSL publication no. 2001t