Howard County, Md., has recently taken on an ambitious Woodcrest Drive Stream Rehabilitation Project that began in June 2022 and is projected to be completed in March 2023. The project involves restoring approximately 3,637 linear feet of stream along four unnamed tributaries to Deep Run, which is located within the Lower North Branch Patapsco River watershed. The location of the project site was identified during the Patapsco River Watershed Study done in 2016.
Through a combination of county funding and a Chesapeake and Atlantic Coastal Bays 2010 Trust Fund Grant, the restoration project construction costs are estimated to total approximately $1,204,000.
“The primary focus of the project is channel stability, specifically ensuring vertical and lateral stability in areas where there is a risk of sewer infrastructure instability, severe channel incision or headcut migration,” Mark Richmond, Howard County stormwater management division chief, explained. “Channel bed structures are intended to increase the overall stability of the site by providing grade control through the project reach to reduce further bed and bank degradation. The project also focuses on enhanced ecological function through increased floodplain connectivity and in-stream habitat.”
He continued, “To accomplish these goals and ensure the project remains stable across a range of flows, a variety of restoration and stabilization measures will be installed. Restoration methods include channel planform modifications, installation of a mixture of channel bed structures, including riffle grade controls, cascades and step pools, stream bank and floodplain grading and nutrient processing features. The channel will be modified to a more stable planform that can accommodate the steep valley slope and increase floodplain connection.
“Floodplain benches will be constructed to provide more frequent flood relief while promoting additional hyporheic exchange and nutrient processing. Woody material will be incorporated into the riffles and pools to improve in-stream habitat and provide a greater differentiation of bed materials. Water quality improvement through the site and downstream waters is expected through the reduction of total suspended solids, nitrogen and phosphorus. The stream restoration project will ultimately create a stable stream system with enhancements to in-stream and riparian habitat.”
An additional pilot approach to the project spotlights nutrient processing features, including recent research specializing in the design and increased effectiveness of trapping and processing nutrients.
“These features are small floodplain benches constructed of a mix of organic materials, including woody debris and frequently accessed during the one- and two-year storm events,” Richmond explained. “Nutrient processing windows are designed to trap nutrients and sediment being transported through the system so that they may be stored and removed by plants and microorganisms, such as bacteria and fungi.”
The timeline for this project was specifically chosen based on two conditions. One took into consideration the stream closure period since in-stream construction activities are prohibited between March 1 and June 15 by the Maryland Department of the Environment. This regulation aims to minimize impact to aquatic habitats. The second condition considered the end of the school year to ensure construction did not interfere with students reaching school. The project involves the use of pedestrian walkways, which are traveled by students to reach the local school.
According to Richmond, the first phase of the rehabilitation project was mobilizing the contractor. “During this phase, the contractor installed orange construction fencing around the perimeter of the project site. This fencing outlines the area that the contractor may work and store equipment, as well as provides a visible barrier for the public not to enter,” Richmond illustrated. “The contractor walked the site and installed any necessary tree protection; identified trees that need to be removed; and installed stabilized construction entrance and pathways so that construction equipment could be brought into the site. The erosion and sediment control features were then installed to minimize erosion from the construction site, causing sediment pollution in the streams.”
Currently, the contractor has completed mobilization and has begun the installation of cascade structures, riffle structures and step pools along the stream. The contractor has begun the process of grading the stream, streambanks and installing in-stream structures with multiple crews on separate branches of the stream since the same process is followed on all the tributaries in the project and many of these tributaries are independently located.
“This project also includes a replacement of an existing culvert in the northern branch of the project,” Richmond described. “The existing culvert is undersized, which frequently causes the pathway to be flooded. The larger size culvert should eliminate this from happening as frequently. We are also replacing an existing pedestrian bridge, which children use to cross the stream to reach the school. The existing bridge is starting to deteriorate with age and needed to be replaced. Since this project would already involve stream work in the vicinity of the bridge, it provided an opportunity to incorporate a new bridge into the design with minimal disruptions to the design or schedule.” Some trees will also need to be removed during the project. The county works with the contractor in order to focus on the removal of primarily already dead trees, trees that pose safety hazards or trees that are impeding the progress of construction. The final phase of the rehabilitation project includes planting an estimated 1,500 native trees, shrubs and live stakes within the site.