Natural Stream Channel Design Enhances Dam Removal Project
by F. X. Browne, Inc. Senior Project Scientist/Fluvial Geomorphologist Deborah Slawson, Ph.D., and Sustainable Environments Editor Rebecca Buerkett
The Huntingdon Pike Dam Removal and Natural Channel Design Stream Restoration Project on the Pennypack Creek was designed by F. X. Browne, Inc. and sponsored by the Southeastern Montgomery County Trout Unlimited. The goal of the project was to restore natural flows and reduce sediment deposition in the stream at the same time as reconnecting the stream to its floodplain, thereby enhancing the habitat naturalization of the stream and long-term stability of the restoration.
The Pennypack Creek is designated as a Warm Water Fishery, Trout Stocking Fishery, and Migratory Fish Stream. The stream is listed on the Pennsylvania 303(d) list of impaired waters due to urban and small residential stormwater flows, flow alterations, and water flow variability. The impacts of stormwater flows on the Pennypack Creek are exacerbated by numerous road crossings, bridge abutments, and six dams, which alter natural stream morphology and sediment transport. The dams have a particularly negative affect on the water quality of the stream by impeding downstream flow, increasing sedimentation, decreasing dissolved oxygen upstream of the dams, increasing water temperature, and promoting downstream erosion. Stream conditions downstream of dams are subject to increased erosive forces. In addition to these impacts, the dams also present a barrier to fish migration and degrade in-stream aquatic habitat.
Natural sediment transport in this section of stream was affected by the bridge crossing of State Route 232 (Huntingdon Pike) immediately upstream of the dam and an abandoned bridge immediately downstream of the dam. This bridge contributed to upstream sedimentation of the creek and promoted erosive forces downstream of the dam. Pooling of water behind the dam increased water temperature in this trout stocked stream and served to concentrate nutrient-laden fine sediments that are often preferentially washed over the dam in heavy rainfalls. This complex of dam and bridges had obvious detrimental effects on stream water quality and aquatic habitat in the Pennypack Creek within the park.
The project consisted of removing the existing dam and redesigning the stream channel and floodplain geometry using natural channel stream design methods to more effectively handle the flow and sediment transport regime in Pennypack Creek after dam and bridge removal. This redesign of the stream channel included regrading streambank slopes to restore hydraulic connectivity with the adjacent floodplain. The project was completed in December 2007. Removal of the Huntington Pike Dam promoted water quality by restoring natural stream sediment transport and allowing the stream to reconnect with its floodplain. The dam removal had beneficial effects on the temperature profile of the stream, as well as allowing for the restoration of unimpeded flow and pool, riffle, and run features, and a natural stream profile. Follow-up stream channel restoration activities reduced sediment loading to the stream from eroding banks, reconnected the stream to its floodplain, and created critical habitat for aquatic organisms.
This dam removal and restoration project is part of a greater effort to remove dams from the Pennypack Creek, restore a more natural flow regime, improve in-stream habitat and fish passage, and improve the feasibility of reintroducing breeding populations of native Hickory Shad to the Pennypack Creek. Funding was provided by a Pennsylvania Department of Environmental Protection (PADEP) Growing Greener Grant and a grant from American Rivers. Watershed partners involved in this regional effort include the Fairmount Park Commission, Montgomery County Department of Parks and Recreation, PA Fish and Boat Commission, Pennypack Ecological Restoration Trust, and the Southeastern Montgomery County Trout Unlimited.
