Overview of the Woodland Ave Dam
Rich Guffanti
Overview of the Woodland Ave Dam
- Location: On Cobbs Creek, adjacent to the historic Blue Bell Inn (built 1766) and the site of Pennsylvania's first water-driven mill (built 1645 by Governor Johann Printz )
- The current dam was built in 1903 to create a pool of water for a nearby trolley system's power plant. It is 7 miles from the Delaware river
- Fish Migration: The dam is
currently the first major barrier on Cobbs Creek for migratory fish.
Biologists collected the four species in the tidal portions (below the dam)
Blueback herring (Alosa aestivalis)
American shad (A. sapidissima)
Striped bass (Morone saxatilis)
Gizzard shad (Dorosoma cepedianum)
White perch (M. americana) - Above the dam you will find 3 bait fish: Redbreast sunfish, Creek chub. Common shiner
Taking down a dam 7 miles from the Delaware River will transform the habitat from a quiet, lake-like impoundment (lentic) back into a fast-flowing, shallow, rocky, or sandy river system (lotic). This change generally benefits native, river-loving fish while displacing species that prefer slow, deep, or warmer water.
Based on typical fish responses to dam removals in Delaware River tributaries (such as the Paulins Kill or White Clay Creek), here is what would likely happen to those specific species:
1. Redbreast Sunfish
- Initial Shift: As the water level drops behind the former dam and becomes faster and shallower, the quiet, warm, deep-water habitat favored by sunfish will disappear.
- Result: They may initially decrease in numbers, but they will likely adapt and re-establish in quieter pools or side channels within the restored stream segment.
2. Creek Chub & Common Shiner
- Positive Impact: These species (minnows) prefer clear, moving water with gravelly substrates. The removal of the dam increases dissolved oxygen, cools the water, and restores a natural, free-flowing environment.
- Result: Their populations often thrive after dam removal because the new, faster-flowing conditions (riffles and runs) provide ideal spawning habitat and increased food availability, allowing them to recolonize the area.
General Ecological Changes Above the Dam
- Improved Connectivity: The fish will be able to move freely upstream and downstream to the Delaware River, reversing over a century of isolation.
- Sediment Release: Initially, fine sediment that was built up behind the dam will wash downstream, which may temporarily affect the water quality before the bank stabilizes.
- Return of Migratory Species: Migratory fish like American shad or American eel may return to the area, changing the overall fish community.
- Vegetation Growth: The exposed, muddy lake bed (formerly behind the dam) will quickly grow vegetation, becoming a healthy riparian buffer zone.
In summary, the Redbreast sunfish might decline slightly in the immediate area due to loss of deep water, while the Creek chub and Common shiner will likely thrive due to the restoration of preferred flowing, rocky habitat.
Key Impacts on Birds Above the Dam:
- Shift in Species Composition: Lake-dependent birds (such as ducks, geese, and swans) will likely move elsewhere, while "river-loving" species—such as Bald Eagles, Great Blue Herons, Belted Kingfishers, and various warblers—will move in to take advantage of the restored natural, forested riparian corridor.
- Increased Food Availability: The restoration of fish migration (such as shad and herring) from the Delaware River into the newly opened stream stretch provides a dramatic increase in food for birds of prey.
- Improved Breeding and Hunting Habitat: The reduction of the dam will expose sediment, allowing for the restoration of natural riverbanks, shallow marsh areas, and wetlands, which provide superior breeding, foraging, and roosting habitats.
- Short-Term Disturbance: In the short term, birders may stop seeing the specific, common species that were adapted to the artificial pond, but they will be replaced by a more diverse array of native, riparian-loving birds as the area matures.
Why the Change Occurs
The dam currently restricts the natural flow of the river, creating an
artificial environment that supports a narrow range of species. Removing it
reverses this process, allowing the river to return to its natural state, which
is generally more beneficial for biodiversity. This type of restoration is
already occurring in the Delaware River Basin, such as in the Paulins Kill and
Pequest River areas
Wayne
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