THE HYDROLOGIC IMPACT OF STRAW MULCH ON A BURNED AREA FOR DIFFERENT SOIL MOISTURES, FOURMILE CANYON WILDFIRE NEAR BOULDER, COLORADO

Mountainous watersheds often exhibit an increase in runoff and flash floods after a wildfire. On September 6^th, 2010, the Fourmile Canyon wildfire started to burn in the foothills of the Rocky Mountains near Boulder, Colorado. In an effort to minimize the risk of flash floods in the canyon, Boulder County, aerially applied straw mulch on high-risk areas selected primarily based on slope and burn severity. The purpose of this research is to investigate the hydrologic response, specifically runoff, of a burned area when straw mulch is used. We measured the runoff, at different soil moistures, from approximately 1-m diameter plots. Paired plots were installed in June 2011 in a basin burned by the Fourmile Canyon Fire. Two sets of bounded, paired plot (two control and two experimental plots) were calibrated for 35 days without straw on either plot by measuring volumetric soil water content 2-3 times per week and measuring total runoff for each storm. Straw (5 cm thick) was added to the two experimental plots on 19 July 2011 and also to the funnels of two visual rain gages in order to measure the amount of rainfall absorbed by the straw. Initial results during the calibration period showed nearly linear relations between the volumetric soil water content of the control and experimental plots. It is anticipated that total runoff will be greater on plots with no straw compared to those with straw, under conditions of varied antecedent soil moisture. More results will be forthcoming in the presentation.