Risk assessment of runoff on a range watershed in Brazos County, Texas

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Title: Risk assessment of runoff on a range watershed in Brazos County, Texas
Author: Gwaltney, Tracy Marie
Abstract: A drip type rainfall simulator and an existing watershed study were used to assess relationships between runoff , infiltration , erosion and associated risk thresholds on a range watershed in Brazos County , Texas . The focus of the research was determining erosion risk associated with seasonal variations in precipitation and vegetation . The objectives were to (1 ) develop a climatic profile for Brazos County , Texas , (2 ) evaluate relationships between vegetative cover , infiltration , runoff , and climatic events , (3 ) quantify erosion / runoff risk associated with measured vegetation , soil moisture , and climatic events , and (4 ) identify potential managerial thresholds for erosion risk management on similar range watersheds . The current year climatic profile showed the wettest season was summer with thirty -two percent of the precipitation coming from one rainfall event . Also , October through December was higher than the long -term rainfall average . Pair wise correlations identified season , initial time to runoff , percent litter , annual as the dominant species , soil moisture , amount to runoff and amount to storage as significant (p <0 .05 ) variables affecting runoff and infiltration . Percent saturation and annuals as the dominant species were significant variables affecting sediment yield . During the current study , seasonal variations in precipitation patterns influenced runoff , infiltration , and sediment yield . Spring and summer had the highest infiltration rates while the largest runoff events were in fall and winter . The highest percent of soil saturation coincided with the largest runoff and sediment losses . Minimums of two centimeters (winter and fall ) and three centimeters (spring and summer ) initiated runoff . This rainfall threshold would be exceeded 20 percent of the time based on the climatic profile developed for Brazos County . Peak biomass production for the watershed site was 170 .61 g /m2 . This was above the recommended biomass threshold of 134 .5 to 168 .1 grams /m2 to minimize sediment loss for tallgrass rangeland . Annual sediment loss was 10 .8 grams /m2 , which is negligible . Additional research across a wider array of site variation is needed to identify appropriate thresholds for the Post Oak Savanna ecosystem .
URI: http : / /hdl .handle .net /1969 .1 /491
Date: 2004-09-30


Risk assessment of runoff on a range watershed in Brazos County, Texas. Available electronically from http : / /hdl .handle .net /1969 .1 /491 .

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