Linking Burn Severity to Soil Infiltartion and Runoff in a Montane Watershed: Boulder, Colorado
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Forest fires have an enormous impact on biotic and abiotic variables that control runoff and soil properties in watersheds. Because wildfires do not have a uniform effect on the burned area, significant variability occurs between areas of different burn severity and likely elicits different hydrologic responses within watersheds. Much of the control on this hydrologic response stems from the variability of soil between burned and unburned watersheds. Establishing a linkage between soil infiltration and burn severity may therefore, offer insight into the likelihood of elevated levels of runoff and the likelihood of floods. Although previous studies have sought to establish a quantitative relationship between runoff and burn severity, this relation has not been evaluated with respect to soil moisture and infiltration and varying degrees of burn severity. The Loretta-Linda Basin presents a unique opportunity to compare areas with different burn severities (with the right fork of the drainage experiencing a much higher burn severity than the left), while eliminating most other variables that may occur with greater spatial variability such as elevation, temperature, precipitation, underlying geology, and soil type. Rainfall, soil moisture, runoff, and infiltration data collected over a two-month period were used to evaluate the relationship between burn severity, runoff, and infiltration for the Loretta-Linda basin as a whole as well as for the individual forks of the basin. The impact of varying burn severity on the two sub drainages was further investigated by creating a dynamic simulation model in TopoFlow®. Comparative analysis between the two forks did not show a dramatic difference in the runoff and infiltration relationship between the two burn severities. Variability of field conditions, the presence of parameters affecting runoff not accounted for, and the limitations of point measurements, are reflected by the data analysis and lack of a strong correlation between burn severity, infiltration, and runoff. The use of spatial hydrologic modeling allowed for the investigation of the relative importance of the infiltration parameters as well as the impact of Manning’s n on the response of the basin to rainfall. The modeling results indicate a strong correlation between high burn severity, low infiltration capacity, and elevated discharge volumes.
Ahlstrom, Anna 1988- (2012). Linking Burn Severity to Soil Infiltartion and Runoff in a Montane Watershed: Boulder, Colorado. Master's thesis, Texas A&M University. Available electronically from