Sediment-Trap Efficiency of a Multiple-Purpose Impoundment, North Branch Rock Creek basin, Montgomery County, Maryland, 1968-76
Herb WJ. 1980. Sediment-Trap Efficiency of a Multiple-Purpose Impoundment, North Branch Rock Creek basin, Montgomery County, Maryland, 1968-76. U.S. Geological Survey (USGS) Water Supply Paper. 2071. USGS. Reston, VA
Lake Bernard Frank, a multiple-purpose reservoir in Montgomery County, Md., impounds runoff and sediment from 12.5 square miles of the upper North Branch Rock Creek basin. Sediment-trap efficiency was studied by the U.S. Geological Survey between 1967 and 1976. Suspended-sediment inflow to the impoundment for unmeasured storm periods in 1968-76 was estimated from daily suspended-sediment transport curves. Bedload contribution was estimated by the Schoklitsch and Meyer-Peter and Muller bedload-transport equations. The sediment contribution for the 1.76-square-mile ungaged part of the basin was estimated from land use and land cover determinations derived from aerial photographs taken annually and land use and land cover sediment-yield relations. The impoundment attenuated both streamflow peaks and instantaneous sediment loads. An instantaneous streamflow peak on North Branch Rock Creek was measured at 207 cubic feet per second per square mile above the impoundment, but, for the same storm, the peak downstream from the impoundment was only 7.0 cubic feet per second per square mile. For one storm, the maximum instantaneous suspended-sediment load was measured at 4,880 tons per day on North Branch Rock Creek upstream from the impoundment, while the maximum instantaneous suspended-sediment load below the reservoir was 33 tons per day. Discharge-weighted percentages of sand, silt, and clay averaged 16,50, and 34 for locations upstream from the impoundment and were zero, 16, and 84 below the reservoir. From 1968 through 1976, about 136,000 tons of sediment was estimated to have entered the impoundment. Over the same years, 5,910 tons of sediment was measured to have left the impoundment. The measured trap efficiency was 96 percent, which closely agrees with the trap efficiency computed from the impoundment’s capacity-inflow ratio.
- Type
- Published Report
- Authors
- Herb, W
- Date of Issue
- 1980
- Publisher
- USGS
- Units
- CHOH
- Keywords
- Drainage Basins, Eastern U.S., Geology, Hydrogeology, Hydrology, Lake Bernard Frank, Lakes, Land Use, Maryland, Montgomery County, North Branch Rock Creek, Reservoirs, Rock Creek, Rock Creek basin, sediment yield, Sedimentation, Sediments, stream transport, surface reservoirs, Surveys, Transport