4.6 Article

Runoff and suspended sediment yields from an unpaved road segment, St John, US Virgin Islands

Journal

HYDROLOGICAL PROCESSES
Volume 21, Issue 1, Pages 35-50

Publisher

WILEY
DOI: 10.1002/hyp.6175

Keywords

road erosion; runoff modelling; kinematic wave; unit hydrograph; eastern Caribbean

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Unpaved roads are believed to be the primary Source of terrigenous sediments being delivered to marine ecosystems around the island of St John in the eastern Caribbean. The objectives of this Study were to: (1) measure runoff and Suspended sediment yields from a road segment; (2) develop and test two event-based runoff and sediment prediction models and (3) compare the predicted sediment yields against measured Values from an empirical road erosion model and from a sediment trap. The runoff models use the Green-Ampt infiltration equation to predict excess precipitation and then use either in empirically derived unit hydrograph or a kinematic wave to generate runoff hydrographs. Precipitation, runoff, and Suspended sediment data were collected from a 230 in long mostly unpaved road segment over an 8-month period. Only 3-5 unit of rainfall was sufficient to initiate runoff front the road surface. Both models simulated similar hydrographs. Model performance was poor for storms with less than 1 cm of rainfall, but improved for larger events. The largest source of error was the inability to predict initial infiltration rates. The two runoff models were Coupled with empirical sediment rating curves, and the predicted sediment yields were approximately 0.11 kg per square meter of road Surface per centimetre of precipitation. The sediment trap data indicated a road erosion rate of 0.27 kg m(-2) cm(-1). The difference in sediment production between these two methods can be attributed to the fact that the suspended sediment samples were predominantly sand and silt, whereas the sediment trap yielded mostly or approximately sand and gravel. The combination of these data sets yields a road surface erosion rate of 0.31 kg m(-2) cm(-1) 36 kg m(-2) year(-1). This is four orders of magnitude higher than the measured erosion rate from undisturbed hillstopes. The results confirm the importance of unpaved roads in altering runoff and erosion rates in a tropical setting, provide insights into the controlling processes and provide guidance for predicting runoff and sediment yields at the road-segment scale. Copyright (c) 2006 John Wiley & Sons, Ltd.

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