Forested watersheds in the Southeastern U.S. provide high quality water vital to ecosystem integrity and downstream aquatic resources. Excessive sediment from human activities in forested watersheds is of concern to responsible land managers. Prescribed fire is a common treatment applied to Southeastern Piedmont forests and is becoming increasingly important under the threat of higher fuel loads, and higher intensity storm events from changing land uses and climate. Several studies have been conducted to evaluate the impacts of fire on sedimentation processes with conflicting conclusions. Measuring the amount of runoff and erosion from fire-induced forested watersheds is difficult due to the high variability inherent in these systems. Erosion simulation models assist in relieving the time and resources consumed measuring these effects. The process-based Water Erosion Prediction Project (GeoWEPP) is widely used in the Western U.S. to predict erosion resulting from forest fires, but has yet to be tested in Southeastern Piedmont settings. The objective of this study was to evaluate the effectiveness of the GeoWEPP model in predicting sediment amounts from low-, moderate- and high-intensity forest fires on pine stands of the Sumter National Forest in the piedmont region of South Carolina. GeoWEPP simulation results were compared to observed sediment production from two ongoing prescribed burn studies in the Enoree and Long Cane Ranger Districts. Erosion measurements were conducted using 48 silt fences placed on hillslopes within 22 x 22 m plots. The measurements were collected biennially following low- and high-intensity prescribed burnings of the forested plots. The annual observed erosion amounts averaged 0.014 and 0.022-kg/m (width) for the Enoree and Long Cane sites respectively. Modeling results from the simulations of the same sites averaged 1.94-kg/m width of fence and 0.55-kg/m (width) annually. The model largely over predicted the amounts of erosion at these low levels. However, the average observed erosion amounts and average GeoWEPP predictions of 0.01 t/ac/yr were well below the tolerable soil loss value (T-value) of 0.41 t/ac/yr during the unburned, low-, and high-intensity forest fire conditions of the treatments. Predicted erosion exceeded this value only for high-intensity fires followed by high-intensity storm events (>20-yr return periods). These results suggest that low-intensity fires may not elevate sediment loading above tolerable rates; however, higher-severity fires can cause soil erosion and sediment loading at levels of concern in water quality degradation. Land topography, fire intensity and soil surface texture type are key variables to predicting soil erosion and runoff. We conclude that this model may be a useful tool to land managers for evaluating and predicting the effects of fire on erosion following forest fires. This study is the first to evaluate the effectiveness of the GeoWEPP model in predicting runoff and sedimentation in Southeastern piedmont watersheds. From this initial testing, recommendations were made to improve the model for applications in the Southeast.
| Identifer | oai:union.ndltd.org:NCSU/oai:NCSU:etd-06252007-113339 |
| Date | 08 August 2007 |
| Creators | Crumbley, Tyler Autry |
| Contributors | Ge Sun, John King, Steve McNulty |
| Publisher | NCSU |
| Source Sets | North Carolina State University |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://www.lib.ncsu.edu/theses/available/etd-06252007-113339/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dis sertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to NC State University or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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