Project Scope and Design
The purpose of the project is to improve the water quality and reduce the stream flow into the downstream creeks, rivers, and eventually the Chesapeake Bay. The way to do this is to stabilize the streambed and improve the connection between the streambed and the floodplain. The extent of this project is for the entire length of the streambed upstream of the crossing under Wakefield Drive.
In addition to the main streambed, several stormwater outfalls that feed side streams joining the main stream will also be part of the project. The most visible of these tributary streams are now crossed by Golden Gate, Natural, and Tappan Zee bridges.
The project is designed to preserve the natural ambiance of the parkland. There are several side benefits to a project such as this. The renovated streambanks are better vegetated with native plant species. Fish and other aquatic animals can have improved habitat and repopulate restored streams fairly rapidly after the construction is complete.
Several remediation concepts have been applied to this project, including:
- The areas immediately downstream of the stormwater outfalls will be reshaped to dissipate some of the flow energy.
- The streambed will be substantially raised using large rocks and fill and the remaining smaller streambanks will have a much more gradual slope so that significant stormwater will overflow the streambanks into the natural floodplain.
- Native species will be planted along the gradually sloped streambanks. Biodegradable matting is applied to stabilize the streambanks for the first year until the vegetation takes hold.
- A series of riffles (shallow areas with turbulent water flowing over rocks) and pools will be created in the main stream.
Other features of the design include:
- Minimize loss of healthy mature trees Extensive surveys have been made of the condition and location of the trees in the project area. Both the final design and the construction access have been designed to preserve as many healthy, mature trees as possible.
- Upgrade bridges All of the existing bridges in the project area will be removed. All but one will be replaced with a different standard bridge design and situated to be above the level of the 100-year flood plain and have more gradual approaches. One bridge, Golden Gate, will be eliminated by a redesign of the adjacent outfall.
- Minimize impact of construction access The location and width of the swath necessary for construction equipment access is carefully planned and minimized. Three points of access into the project area will be near the tennis court gazebo, off Elizabeth Lane, below Mary Lee Lane, and off Wakefield Dr, near the stream crossing.
- Restore asphalt paths All existing asphalt paths in areas used for construction access will be replaced with new 6-foot wide asphalt paths. That will refurbish about 40% of all the asphalt paths in the parkland. THA plans to refurbish the remaining 60% of the parkland’s paths immediately after completion of the stream restoration project.