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CHARACTERIZATION OF SEDIMENT STORAGE
AND REMOBILIZATION IN
VALLEY FORGE NATIONAL HISTORICAL PARK
Technical Report NPS/NER/NRTR—2007/095
Lisa M. Fraley, Andrew J. Miller, and Claire Welty
University of Maryland Baltimore County
Center for Urban Environmental Research and Education
1000 Hilltop Circle, Technology Research Center
Baltimore, Maryland 21250
September 2007
U.S. Department of the Interior
National Park Service
Northeast Region
Philadelphia, Pennsylvania
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Abstract
National Park Service managers have been concerned for several years about potential impacts of sediment associated with upstream urban development on the 3.7-km (2.3-mi) portion of Valley Creek that runs through Valley Forge National Historical Park (VAFO) upstream of its confluence with the Schuylkill River. A study was conducted between September 2003 and September 2006 to obtain baseline inventories and to monitor suspended sediment and the distribution of sediment storage, bank erosion, and channel instability. Field investigations included a total-station survey of the longitudinal profile of Valley Creek, cross-section and bankline surveys after significant storm events (including the second highest discharge on record for Valley Creek), pebble counts and volumetric barrel samples to measure particle size distribution of the streambed, and use of tracer gravels to determine the sediment particle sizes mobilized during storm events. Sediment load estimates were compiled using turbidity data collected at 15-minute intervals at the USGS Valley Creek stream gage between July 2005 and September 2006 and preliminary USGS unit flow value records for the same period. Estimated suspended sediment yield for the watershed for the 2006 water year was 41.4 metric tons/km2/yr—much lower than historical sediment yields from watersheds in areas of agricultural land use or in early phases of urban development, but comparable with an area of mixed development in suburban Maryland. Results of field surveys suggest that bank erosion may be a dominant source of sediment, but also indicate that fine sediment stored in and remobilized from the bed may be a significant fraction of annual sediment yield in Valley Creek.
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