HR: 1340h
AN: H33C-0487    [Abstracts]
TI: Temporal and spatial controls on variability in water repellency for prediction of runoff from burned watersheds
AU: * Luce, C
EM: cluce@fs.fed.us
AF: USDA Forest Service, Rocky Mountain Research Station, Boise Aquatic Sciences Lab 316 E Myrtle, Boise, ID 83702 United States
AB: Prediction of runoff in catchments affected by wildfire is an extreme example of the ungauged basin problem. After wildfire, there is an increase in the risk of severe erosion, floods, and debris flows, often resulting from water repellency. The transient nature of wildfire effects on soils makes the gauging information from affected systems anecdotal in nature; so modeling is required to assimilate the scattered observations and provide for prediction of runoff from newly burnt watersheds. While most water repellency research has focused on the strength of water repellency and its duration for time scales of seconds to seasons measured at the point scale, there is a lack of information on spatial variability of water repellency and the temporal variation of the spatial properties at multi-annual time scales. The lack of spatial information on water repellency both results from and perpetuates a lack of modeling using information on water repellency to predict runoff from burned watersheds. The recently developed FERGI model uses information on the fractional water repellent area to predict runoff from burned hillslopes and catchments. Modeling a catchment requires information to describe the spatial and temporal variations in the fractional water repellent area. Spatial controls on initial water repellency include vegetation density, fire severity, and soil texture, which can be mapped with remote sensing. At finer scales, there is high connectivity of water repellent areas on soils with greater than 70% water repellency; so fractional repellency is adequate information for prediction of runoff for the great majority of storms. In addition, observations on the temporal decay of water repellency show a spatial organization to the water repellency caused by erosion where repellent areas contribute water to non-repellent areas, further supporting use of a fractional repellent area. Measurements of burned areas on different parent materials show that the fractional area of water repellency declines to levels less than 70% within 3-years of the fire. The decrease in fractional area is linear in time, falsifying the hypothesis that decay in water repellency is caused solely by random innovations, which would predict an exponential decay.
UR: http://www.fs.fed.us/rm/boise/
DE: 1815 Erosion and sedimentation
DE: 1821 Floods
DE: 1824 Geomorphology (1625)
DE: 1860 Runoff and streamflow
DE: 0400 Biogeosciences
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting