Thesis Director: Barnali Dixon, Ph.D.,
University of South Florida at St. Petersburg
This study analyzes the environmental impact of wildfires on soil erosion in the surrounding watershed of the burn area. Depending on the severity and frequency, wildfrres can have detrimental effects on the soils and hydrology of an ecosystem. Since severe wildfires alter the vegetation cover and the properties of the soil, researchers are often concerned with changes in sedimentation after a wildfire and its implications for watershed hydrology. Adverse changes to sedimentation can result in increases in surface runoff, soil erosion, sediment delivery to nearby streams, and peak flows. Assessing post-fire soil erosion risk is crucial in prioritizing watershed protection and mitigation efforts. A GIS-based model was used to estimate soil loss rates before and after California's 2010 Pozo frre. Rainfall erosivity, soil erodibility, conservation practice, topographic and land cover management factors before and after the fire were compiled in a GIS, where the Revised Universal Soil Loss Equation (RUSLE) was computed to estimate soil loss rates. Soil erosion values were classified into five erosion risk potential classes (low to high risk). Water quality data (TDS and TSS) for the Salinas watershed area was obtained from the EPA STORET Central Warehouse and used to determine the actual hydrological impact of the Pozo fire on the Salinas watershed and to verify RUSLE results. Percentage area of erosion 'hot spots' (moderately high to high risk) increased from 5.5% to 5.9% in the 30m and increased from 5.7% to 6.2% in the 90m model. These results indicate that the Pozo wildfire led to greater risk of erosion in the burn area. In the wet season before the fire (Dec 2009-Jan2010), 442 mg/1 of TDS and TSS were found in the Salinas watershed, and 1,376 mg/1 were found in the wet season directly after the fire (Dec 2010-Jan 2011). These results demonstrate that there was an increase in TDS and TSS downstream after the fire compared to before, and suggest that the Pozo fire is one plausible explanation for this increase. In addition, this study determined the impact of digital elevation model (DEM) resolution on RUSLE results, as slope affects soil erosion and is represented in DEMs. The RUSLE model was run using 30m and 90m DEM resolutions for the topographic factor. The 30m model yielded maximum soil loss values of 341 tonnes ha-1 yr-1 for both pre-and post-fire models, while the 90m model yielded maximum soil loss values of 185 tonnes ha-1 yr-1 for the pre-fire run and 197 tonnes ha-1 yr-1 for the post-fire run, suggesting that soil erosion models using coarser resolution DEM data can underestimate maximum soil loss values.
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Fernandez, Amada, "The Impact of Wildfire on Soil Erosion using a GIS-integrated RUSLE Model and the Influence of DEM Resolution on Model Results" (2018). USFSP Honors Program Theses (Undergraduate). 226.