PROPOSED WATERSHED MANAGEMENT STRATEGIES FOR A CANAL-LINKED WATERSHED IN PENNSYLVANIA
The Delaware Canal is a unique watershed since it is a linear system with many different stream inputs along its 60-mile length. The watershed crosses 18 township and two county jurisdictional boundaries. The canal is 167-year-old man-made waterway which was built and operated commercially to haul coal and other goods from Bristol, Pennsylvania to Easton, Pennsylvania. The canal is now owned by the Commonwealth of Pennsylvania and is managed by the Pennsylvania Department of Conservation and Natural Resources as the Delaware Canal State Park. The park is an important recreational resource for eastern Pennsylvania and is used by residents and tourists for walking/hiking, running, fishing, canoeing, and horseback riding. The Delaware Canal and park system have been recognized nationally on the National Register of Historic Places (1974), as a National Historic Landmark (1978), and as a National Recreation Trail (1990). The Delaware Canal State Park is also part of the Delaware and Lehigh National Heritage Corridor and a State Heritage Park.
In 1998, Environmental Liability Management, Inc. (ELM) was retained by a non-profit organization, the Friends of the Delaware Canal (Friends), to prepare a map of the Delaware Canal Watershed and to analyze potential strategies to reduce accelerated erosion and sedimentation in the canal watershed. The report was intended to educate local residents and township and county officials on land use/management practices that can be incorporated into local ordinance to reduce the excessive sedimentation in the canal.
The findings of the watershed evaluation were presented along with suggestions for municipalities to consider in developing protective ordinances for the watersheds feeding the Delaware Canal. Comments and suggestions from the municipalities and any other stakeholders regarding the project goals, methods, or strategies were strongly encouraged. To date, two of the 18 municipalities along the Delaware Canal have shown interest in incorporating the suggested land use/mangement practices at the municipal level. One Township has incorporated the report suggestions into their draft Comprehensive Plan.
II. STATEMENT OF THE PROBLEM
During its commercial operation, the canal was constantly dredged to remove accumulated sediment. Since becoming a park system, maintenance has been limited to localized sand bar removal near stream inputs. Silt- and clay-sized particles have accumulated along the length of the canal and can only be removed by costly dredging operations. The dredging operation costs between 100,000 and 400,000 per mile, depending on sediment disposal and restoration costs. Such dredging programs remove sediment for the short-term, but long-term strategies must be developed to lower the sedimentation rate so that the frequency and magnitude of future dredging activities can be reduced. This paper presents some of the management options that should be adopted in an integrated manner.
III. PROJECT DESCRIPTION & FINDINGS
ELM made a preliminary determination of the watersheds that discharge water into the canal using existing topographic maps and a 1977 field survey completed by the Pennsylvania Department of Forests and Waters. ELM field-verified surface water inputs along the canal and mapped the associated watersheds. An analysis of the sediment particle size distribution was completed which confirmed that the relatively abundant sand-sized particles dropped out of the water close to the discharge area while silt and clay-sized particles were carried and deposited further downstream. These smaller-sized particles sediments are removed by major dredging operations which are completed infrequently (once every 10 to 30 years) due to the high cost.
IV. POTENTIAL STRATEGIES FOR WATERSHED MANAGEMENT & SEDIMENTATION CONTROL IN THE DELAWARE CANAL WATERSHEDS
The Friends and ELM presented the preliminary results of the mapping and sediment analysis to various parties including the Pennsylvania Department of Environmental Protection (PADEP), Bucks County Soil Conservation District, and the Delaware Canal State Park. These meetings were conducted to inform the parties of the project goals and watershed study results in an effort to gain feedback and suggestions for the development of a management strategy for the Delaware Canal Watershed. In developing the following strategies, ELM consulted various PADEP manuals and guidance, including the Pennsylvania Erosion and Sediment Control Manual, the Pennsylvania Best Management Practices Manual, and the Federal Interagency Stream Restoration Working Group Stream Corridor Management Manual. The result was the following suggested storm water management and sediment control practices for consideration by municipalities along the Delaware Canal. These strategies are intended to meet and develop further the current recreational activities associated with the canal while still maintaining the relevant scenic and historic resources.
A. Potential Storm Water Management and Sediment Control Practices
1. Limit the Change in Runoff with Change in Land Use
Post-development runoff volume should remain within 10% of the pre-development condition to prevent streambank erosion and the transport of large amounts of gravel, sand, and silt into the canal. Controlling the hydrograph peak flow rate is not sufficient to control the total storm water volume, which accelerates bank erosion when increased more than 10% at one location or in combination with other development areas in close proximity. Cumulative effects of increased runoff volumes in a watershed cause accelerated erosion, resulting in increased sediment loading to the canal. Post-development flows can be readily evaluated in the planning stages through an emphasis on maintaining the average area-weighted runoff coefficient in storm water runoff pre- and post-development calculations. The area-weighted storm water runoff coefficient should be within 10% of the predevelopment runoff coefficient.
2. Encourage Silt and Clay Erosion Control Practices
Within the Delaware Canal Watershed, a series or combination of BMPs, known as BMP trains, should be encouraged to aggressively prevent entrainment of fine soil particles in storm water (silt and clay); and to trap silt-sized particles on-site to the extent practicable, especially by designing improved sediment traps to capture silt-sized particles. The use of several appropriately integrated BMPs (sediment traps, silt fencing) is not a cost-prohibitive requirement. If factored into the design and construction process at the start of a project, the cost to employ a combination of effective BMPs is comparable to the cost to employ the traditional practice of emphasizing one or two types of control.
3. Establish a Riparian Buffer Zone
Consistent with the Federal Interagency Stream Restoration Group Stream Corridor Restoration Manual, a minimum undisturbed buffer zone should be maintained along streams draining to the canal. A buffer zone of 15 feet of larger would protect steep slope areas adjacent to the stream, reduce runoff flow velocities, and reduce sediment loading to the canal. Some municipalities in Pennsylvania have already adopted riparian zone protection ordinances.
4. Conduct Dredging in a Manner that Limits Widespread Distribution of Sediment and Enhances Wildlife Habitat Associated with the Canal
Through limited localized changes in the canal depth and configuration, more sediment can be trapped near points of entry reducing long-term dredging costs. These deeper areas can also serve as fish refuge areas when ice covers the canal during winter months. Other dredging modifications that can be employed to enhance wildlife use include the establishment of areas with moderately sloping banks and flat bottom profiles near the banks.
B. Enforceability of Suggested Management and Control Strategies
The suggested management strategies will be more effective if they can be adopted in the form of ordinances. Several options are available to municipalities including:
Establish an overlay canal watershed zone, based on the watersheds preliminarily determined by ELM, state-adopted watershed boundary lines for neighboring streams, and other available site-specific data. More specific erosion and sediment control requirements can be established, such as those suggested above for these watersheds;
Establish the Delaware Canal as an exceptional value or high quality waterway under state regulations. Such a designation would increase the requirements for erosion prevention and control measures along the streams feeding the canal.
Two municipalities have already expressed interest in incorporating the suggested practices into their local land use/management strategies as an overlay zone. More comments and suggestions from local and county stakeholders are expected.
Document Type: Research Article
Publication date: 2000-01-01
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