Prediction of suspended-sediment transport and identification of sediment source areas in the Fountain Creek watershed

The Fountain Creek drainage network currently is in a precarious geomorphic situation. This situation arises because:

1. the Palmer Divide and the Rampart Range have the potential to cause very high orographically induced rainfall rates
2. east of the foothills, streams within the watershed flow through valley bottoms filled with easily eroded alluvial sediments
3. there is rapid development in the drainage basin that has the potential to exacerbate the rainfall runoff rates, increase flood peaks, and undermine the natural geomorphic protections against uncontrolled incision provided by bed armoring and floodplain vegetation. 

Bedload transport in Fountain Creek has been studied in detail by the US Corps of Engineers.

Relatively little work has been done to evaluate, by particle size range, the much larger transport of suspended sediment throughout the basin, despite the fact that parts of the Fountain Creek network have the potential to export large volumes of suspended sediment during high flows.  Unfortunately, the high cost of making suspended-sediment measurements previously has been a barrier to addressing this important component of the sediment transport problem in the Fountain Creek watershed. 

OBJECTIVES:

The major objective of this study was to test a computational method to predict local suspended-sediment loads at two sites with different geomorphic characteristics in order to evaluate the feasibility of using such an approach to predict local suspended-sediment loads throughout the entire watershed.

Detailed topographic surveys, particle-size data, and suspended-sediment samples were collected at two gaged sites:

• Monument Creek above Woodmen Road at Colorado Springs, Colorado (USGS gage 07103970)
• Sand Creek above mouth at Colorado Springs, Colorado (USGS gage 07105600)

These data were used to construct three-dimensional computational models of relatively short channel reaches at each site.  The streamflow component of these models predicted a spatially distributed field of water-surface elevation, water velocity, and bed shear stress for a range of stream discharges. Using the model predictions, along with measured particle sizes, the sediment-transport component of the model predicted the suspended-sediment concentration throughout the reach of interest. These computed concentrations were used with predicted flow patterns and channel morphology to determine fluxes of suspended sediment for the median particle size and for the measured range of particle sizes in the channel.