Date of Award:

1-1-1998

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Watershed Sciences

Advisor/Chair:

James P. Dobrowolski

Abstract

A significant source of sediment in many watersheds is that associated with the layout, construction, and maintenance of roadways. Much work has been done in more mesic forested environments with little or none in semiarid systems. Acc urate estimation of runoff and sediment yield from native surfaced roads located in semiarid mountainous ecosystems is important to both private and public regulatory agencies. The Watershed Erosion Prediction Project (WEPP) model represents the most current erosion prediction technology. WEPP has been applied to the problems of logging road erosion in more mesic forests but has not been tested or evaluated on roadways located in semiarid mountainous ecosystems.

Six rainfall simulation experiments were conducted to measure runoff and sediment yield off three separate plots located on Tickville Road, located on Camp W.G. Williams, a National Guard Training Center in Utah . These data were compared with runoff and erosion estimates produced by the WEPP model. WEPP cropland and rangeland erodibility equations were used to predict rill erodibility (Kr), interrill erodibility (Ki), and critical shear (TAUc). These were tested for their effectiveness in predicting road erodibilities in these environments. A sensitivity analysis was performed on those parameters that were suspected of having a substantial impact on model output and accuracy.

There was an excellent correlation between predicted and observed total runoff volumes for all simulations (R2= 0.96). The differences were greater than 10% only for plot 2 wet; otherwise, the average difference for all six simulations was 4.9%. When using Kr, K.i , and TAUc as predicted by rangeland methods, predicted sediment yields differed from those measured, on average, by 82%. Predicted sediment yields differed by only 22% compared to calculated sediment yields, when using the cropland erodibility equations to predict Kr, K.i , and TAUc. A sensitivity analysis showed that percent slope, slope length, days since last tillage, and ridge roughness all had a significant impact on WEPP predicted sediment yields. Results show the effectiveness of the WEPP model in predicting runoff and erosion off native surfaced roads in these semiarid mountainous regions.

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