Fish Passage Design at the Adam T. Bower Memorial Dam

STATE-OF-THE-ART NATURE-LIKE FISHWAY BOLSTERS THE FUTURE OF FISH AND AQUATIC MOVEMENT IN THE SUSQUEHANNA RIVER

Our Client’s Challenge

Approximately two miles downstream of the Susquehanna River’s west and north branch confluence lies the Adam T. Bower Memorial Dam. Spanning the river’s width between the towns of Shamokin Dam and Sunbury, the dam is over 2,700 feet long and includes more than 2,000 feet of inflatable bags, making it the longest inflatable dam in the world.

When fully inflated for the May through October recreational season, the dam forms the 3,000-acre Lake Augusta, which is up to 10 feet deep and extends upstream for approximately 6.5 miles along both river branches. Lake Augusta is the focal point of the Shikellamy State Park and has provided anglers, boaters, water-skiers, and other day-trippers open-water recreational opportunities since the dam’s construction in 1970.

Industrial development throughout the 1900s restricted migratory fishes’ movement into the river’s headwaters, resulting in declining anadromous fish and catadromous eel populations. So, as a condition of the dam’s original permit, fish passage was required once other downstream dams on the river, including four hydropower dams, had fish passage facilities in place.

Once the downstream fish passages were added, American shad were observed near the base of the inflatable dam, demonstrating downstream migratory fish passage. This triggered the Pennsylvania Department of Conservation and Natural Resources (DCNR), the owner and operator of the Shikellamy State Park and the inflatable dam, to provide fish passage to satisfy the permit conditions and continue restoring the migration passage routes of the Susquehanna River.

With a drainage area of over 18,000 square miles, the inflatable dam and surrounding features create fish passage challenges. Operating the dam changes the seasonal headpond elevation by more than eight feet. Raising and lowering the dam during high water events creates unique hydraulic conditions that must be accounted for to provide ideal conditions for attracting and passing aquatic species through the fishway.

Limited space and the proximity of a U.S. Army Corps of Engineers levee system on the east riverbank also provided challenges. The fishway needed to be sited so that it would not adversely impact the levee system or the dam’s performance. It also could not increase upstream water elevations or adversely impact flooding. Creating a fishway that minimized maintenance activities was also critical to DCNR to not overtax the park staff’s limited resources.

Our Solution

In partnership with Kleinschmidt Associates, Gannett Fleming provided the fishway’s preliminary and final design and construction-phase services.

We conducted topographic and bathymetric surveys to establish base mapping and horizontal and vertical controls. The project team performed fishway layout and hydraulic modeling, established staging area and erosion control measures, and developed a conceptual water diversion plan and construction cost estimates. Our detailed wetlands and waterway investigations and threatened and endangered species coordination supported DCNR’s permit applications.

Coordination with DCNR assisted in understanding the operating procedures associated with the inflatable dam. The project team reviewed historic river flows and established sound design criteria by holding design workshops with key stakeholders, including the U.S. Fish and Wildlife Service and the Pennsylvania Fish and Boat Commission, and developed a two-dimensional hydraulic model to analyze and support conceptual designs and cost estimates.

On the left, an aerial view of the project site before construction. On the right, the same aerial view after project completion.

The 900-foot-long fishway is located immediately downstream of a fixed crest weir that forms the western end of the inflatable dam. The weir was modified to pass the fishway through the dam. The fishway consists of four resting pools and five riffles in a 36-foot-wide main channel and a 70- to 100-foot-wide floodplain area constructed of riprap and boulders to mimic a natural channel.

The design allows floating woody material like tree branches to pass through the fishway. Woody material that becomes captured within the fishway but does not adversely impact hydraulics may be left in place to provide additional habitat and support the biological growth in natural channels.

Walking paths and access roads improve emergency access to the river, promote pedestrian access for recreation, and facilitate future dam maintenance like replacing inflatable bags. Providing permanent dam access will reduce the need for temporary causeways and, in turn, potential environmental impacts.

The fishway restores migratory passage to over 18,000 square miles of the Susquehanna River basin, making it one of the largest nature-like fishways on the East Coast of the U.S. Its cutting-edge design provides passage for a wide range of aquatic species, unlike historic technical fishway designs like vertical slot fishways involving concrete that often limit passing to just the target species.

While the target species are American shad, river herring, and American eel, the channel and floodplain provide a range of flow depths and velocities, allowing a diverse array of aquatic species to use the fishway.

Aerial images provided courtesy of KC Construction.

Water moves around the west side of the dam then continues through the 900-foot-long fish passage, creating riffles as it passes over rocks and pools.

Key Features

The fishway channel, floodplain, and strategically placed boulders produce varying flow conditions, allowing a wide range of aquatic species to pass through the fishway.
Natural materials, like rock and boulders, minimize manufactured materials and better mimic the natural environment.
The fishway’s rocky substrate resembles a natural streambed and creates a permanent riverine habitat while the fishway is in operation.

Outcomes

Remediates the inflatable dam’s ecological impact on migratory fish by allowing aquatic species to pass the dam and continue to their historic spawning grounds in the headwaters of the Susquehanna River, contributing to migratory fish restoration.
Facilitates recreation opportunities in Shikellamy State Park, attracting tourists and boosting the local economy.
Provides quality aquatic habitat for macroinvertebrates and wading birds and provides upstream and downstream movement of resident and migrating species.