DETERMINATION OF SEDIMENT EROSION AND DEPOSITION RATES FOR VALLEY CREEK IN VALLEY FORGE NATIONAL HISTORICAL PARK
PIs: C. Welty (UMBC), Andrew J. Miller (UMBC), Robert J. Ryan (Drexel University)
Funding Source: National Park Service
The objective of this study is to measure sediment erosion and deposition volumes and rates in the 2.1-mile portion of Valley Creek that runs through Valley Forge National Historical Park in Chester County, Pennsylvania. The study will provide baseline data for the National Park Service to utilize in assessing future perturbations to the stream affecting erosion and sedimentation rates. Multiple within the 2.1-mile stretch of Valley Creek over a period of two years, using a system of surveying and sediment sampling at multiple transects within each reach. The work will be carried out by one masters student at University of Maryland, Baltimore County (UMBC) under supervision of a PhD student at Drexel University (Rob Ryan) and two UMBC faculty members. The PIs have expertise in the areas of hydrology, geomorphology, and environmental engineering.
|Lisa Fraley, MEES MS student at UMBC, using a SET510 Total Station to measure water surface profile.||Introduction
In observing stormwater runoff from parking lots, lawns, and forested areas into detention basins and then into Valley Creek, our research team has noted that overland flow is typically clear and shows very little turbidity. However, as Valley Creek swells from storm runoff, it quickly becomes a reddish-brown color, and stream banks slough off from the action of fast channel flow. Empirical evidence points to high water velocities and consequent in-stream bank erosion as the principal cause of the mud-brown color of Valley Creek during storm flows, as opposed to entrainment of sediment during overland flow. Our working hypothesis is therefore that in-stream channel erosion is the dominant source of sediment to Valley Creek. This is consistent with quantitative studies that have been carried out and have documented in-stream erosion as being the most significant source of both fine and coarse sediment in urbanizing watersheds (e.g., Trimble, 1997; Nelson and Booth, 2002). The purpose of the proposed study is to test our hypothesis by carrying out a field sampling campaign for two years to document sediment sources, transport rates, and net deposition rates in Valley Creek within Valley Forge National Historical Park. This study could serve as a prototype for determining a sediment budget for the entire watershed and other watersheds in similar urbanizing areas.
The area was first settled in the mid-1600s and has undergone numerous land-use changes that have affected the watershed's hydrology. Clear-cutting from settlement and agriculture, mining of limestone quarries beginning in the industrial period, and development responsible for 17% impervious land cover, have all contributed to the present hydrologic condition of the watershed. The pattern of land-use development in Valley Creek watershed is unusual for an urbanizing area in that the most developed sections are in the headwaters, whereas the mouth of the creek is surrounded by a national park composed of forest and grassland. This means that the park is on the receiving end of all upstream development that affects the creek. Despite degradation from development, Valley Creek is designated as an Exceptional Value stream by the Commonwealth of Pennsylvania in part due to its population of reproducing Brown Trout.
Owing to the presence of the Park, the EV rating, and the cultural resources in the area, an extensive data base exists on the physical, biological, and chemical characteristics of the watershed. C. Welty is in the process of completing a large study sponsored by National Science Foundation to quantify the effects of anthropogenic activities on the hydrology and ecology of the watershed.
|Jane Diehl, MEES MS student at UMBC, working with Lisa (above) to record water surface elevations of Valley Creek.|
|Matt Young, BS student in Computer Science at Drexel University, assisting Lisa and Jane with water surface profile measurements.||
Recently-completed hydrological modeling of over 100 detention basins operating simultaneously in Valley Creek watershed indicates that the stormwater management system in place actually exacerbates flooding from the typical small storms (1-yr or 2-yr return periods) that comprise most of the rainfall of this region (Emerson et al., 2003). It is well known that stormwater detention basins are designed on an individual basis to reduce peak flow rates and not to reduce the increased volumes of runoff resulting from subbasin development. This increased runoff volume generated from many subbasins operating simultaneously, coupled with frequent events not being detained at all, contributes to observed high stream velocities and resulting in-stream erosion during storms. Related studies in other urbanizing watersheds have noted similar patterns. Moglen and McCuen (1988) have demonstrated quantitatively that detention basins designed for peak-flow stormwater control in fact have contributed to channel erosion.
Because Valley Forge National Historical Park is located at the mouth of Valley Creek watershed, a significant portion of the sediment load generated by a storm from upstream sources watershed may reach the park before exiting to the Schuylkill River. It is not known quantitatively to what extent the watershed sediment load passes through the park or is deposited to the streambed in the park or upstream of the park. Quantification of this process is important, because fine-sediment deposition can reduce the permeability of spawning gravels and result in smothering fish embryos by impeding the flow of oxygen to gravel layers where the eggs are laid. Because stormwater flows and resulting sedimentation can adversely affect the ability of Brown Trout to reproduce, a fundamental reason for the EV ranking of this stream could be threatened by excessive sedimentation problems. In addition to concerns related to fine sediment, coarse sediment deposition can have
a harmful impact by reducing the cross-sectional area and the channel-carrying capacity of the stream, contributing to flooding and channel instability. For this reason, determination of all size classes of sediment deposition in the park is of interest.
Owing to the location of the park in the lower reaches of the watershed, Valley Creek in this location also receives the highest volumetric flowrates in the channel during storms. The resulting bank erosion affects the aesthetic and recreational value of the creek because roads and trails running alongside of the creek can be damaged by the erosion process. Quantification of the rates of sidebank erosion in the creek would enable the Park to provide justification for improved stormwater management or shared remediation costs with upstream parties contributing to the stream condition.
Science Questions to be Answered
(1) What are the volumes and rates of sediment accumulation
and scour on the bed of Valley Creek within the park? What
are the grain size distributions of the sediment deposits? How
do these vary over time and space?
(2) What is the spatial distribution of bank erosion rates along Valley Creek within the park and how much sediment is derived from bank erosion?
(3) Within the budget constraints of this project and technical limitations of available measurement techniques, what approximations can be made for estimating transport rates of bed-load sediment and suspended sediment in Valley Creek at the VFNHP upstream boundary? How do bed-material transport rates at intermediate locations within the park compare with the influx at the upstream boundary?
(4) How do natural geologic controls and anthropogenic controls (such as dams, bridges, etc.) affect the spatial pattern of sediment storage along Valley Creek within VFNHP? How do flow events of different magnitudes affect the pattern of storage?
Management Questions to be Answered
(1) To what extent is an influx of sediment from the upstream watershed likely to influence bed composition, bed topography, and habitat conditions along the reach of Valley Creek within the park? To what extent can that influx and resulting changes in bed conditions be quantified? What is the spatial pattern of sediment storage along the channel bed and how does it change over time?
(2) What is the extent and spatial pattern of bank erosion and channel instability along Valley Creek within Valley Forge National Historical Park, and to what extent can this be related to sediment influx and upstream urbanization?
(3) What are low-cost methodologies that can be used by VFNHP personnel that would allow them to easily continue to monitor changes in erosion, deposition, and grain-size distributions in Valley Creek within the park over time?
(4) What management recommendations can be provided that could
aid VFNHP in addressing any negative impacts of the sediment load
on Valley Creek?
Literature Review on Methods of Measuring FLuvial Sediment, by Lisa Fraley, January 2004
References and Selected Bibliography
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Hilton, S. and T.E. Lisle, 1993. Measuring the fraction of pool volume filled with fine sediment. USDA Forest Service Research Note PSW-RN-414, 11 pp.
Lisle, T.E., 1995. Particle size variations between bed load and bed material load in natural gravel bed channels. Water Resources Research, 31(4), 1107-1118.
Lisle, T.E. and S. Hiilton, 1992. The volume of fine sediment in pools: an index of sediment supply in gravel-bed streams. Water Resources Bulletin 28(2), 371-383.
Lisle, T. E. and Sue Hilton, 1999. Fine bed materials in pools and natural channel gravel beds. Water Resources Research, 35(4), 1291- 1304.
Lisle, T. E. and R.E. Eads, 1991. Methods to measure sedimentation of spawning gravels. USDA Forest Service Research Note PSW-411, 7 pp.
Martinez, M.H. and S.E. Ryan, 2000. Constructing temporary sampling platforms for hydrologic studies. USDA, Forest Service, Rocky Mountain Research Station, General Technical Report RMRS-GTR-64, 10 pp.
Moglen, G. E. and R.H. McCuen, 1988. Effects of detention basins on in-stream sediment movement, Journal of Hydrology, Volume 104, Issues 1-4, Pages 129-139, December 30, 1988.
Nelson, E.J. and Booth, D.B., 2002. Sediment sources in an urbanizing, mixed land-use watershed, J. of Hydrology, 264, 51- 68, 2002.
Pizzuto, J. E., W. C. Hession and M. McBride, 2000. Comparing gravel-bed rivers in paired urban and rural catchments of southeastern Pennsylvania, Geology, Vol. 28(1) 79-82.
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Sterling, S.M. and M. Church, 2002. Sediment trapping characteristics of a pit trap and the Helley-Smith sampler in a cobble gravel-bed river, Water Resources Research, 38(6), 10.1029/2000WR000052.
Trimble, S.W., 1997. Contribution of in-stream channel erosion to sediment yield from an urbanizing watershed. Science, 278, 1442-1444.
Wilcock, P.R., 2001. Toward a practical method for estimating sediment-transport rates ingravel-bed rivers, Earth Surface Processes and Landforms, Earth Surf. Process. Landforms, 26 (13) 1395-1408.
Wolman, M.G., 1954, A method of sampling coarse river-bed material:
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