DETERMINATION OF SPATIAL PATTERNS OF SEDIMENT STORAGE AND TRANSPORT IN VALLEY CREEK, VALLEY FORGE NATIONAL HISTORICAL PARK

Urbanization has altered the hydrologic regime of Valley Creek, a tributary of the Schuylkill River west of Philadelphia, PA. Increased peak flows from growing percentages of impervious surface in the watershed have resulted in an increased flux of sediment through the 2.3 mile portion of Valley Creek that runs through Valley Forge National Historical Park (VFNHP), directly upstream of the Schuylkill confluence. With support from the National Park Service, and in cooperation with the U.S. Geological Survey, a study is currently underway to conduct baseline inventories and monitoring of sediment transport and storage. Based on an extensive channel characterization, 12 transport and storage reaches have been designated. During the summer of 2004, 36 cross-sections within VFNHP were benchmarked with steel bars and surveyed (3 per reach) with a total station. Eroding stream banks at several locations were also surveyed to determine the amount of sediment entering the channel due to bank instability. These bank lines and cross-sections continue to be resurveyed after significant storm events, one of which included the second highest discharge on record for Valley Creek (77.3 m³ on September 14, 2004). In addition to these surveys, several methods are being utilized along each cross-section to determine the spatial pattern of particle-size distributions, the depth of the mobile layer, and the sediment particle sizes mobilized as a function of discharge. Field monitoring is continuing through the summer of 2005. Work is also in progress to monitor suspended-sediment concentrations transported across the park boundary, using a turbidity probe calibrated to suspended-sediment concentrations collected by an automatic sampler. Interpretations from this study will determine whether the dominant sediment input is from bank erosion within VFNHP or from upstream sources. In addition, the spatial pattern of sediment transport and storage will be determined, and the resulting channel morphology of the portion of Valley Creek that runs through VFNHP will be documented.