Reference

Andy Frank, 301-585-1921

Maryland-National Capital Park and Planning Commission (M-NCPPC)

Project Highlights

  • Geomorphic Assessment
  • Rosgen Stream Classification
  • Natural Resources Inventory/Forest Stand Delineation
  • H&H Analysis
  • Wetland Delineation
  • Stream Restoration & Bioengineering Design
  • Permitting
  • Construction Inspection

Project Details

Before Restoration

Before Restoration

Comprehensive field investigations were conducted along the two project areas; an unnamed tributary to Sligo Creek flowing through the Sligo Creek Golf Course (approximately 1260 feet in length) and Batchellor’s Forest, a tributary to Northwest Branch of the Anacostia River.  The investigations were undertaken to assess stream stability problems and prioritize stream restoration needs.   A review of the available mapping and natural resources was conducted using GIS to determine drainage areas for various points along the study lengths and basin composition with regard to land use, utility conflicts, soils, and geology. This was followed by a preliminary field reconnaissance to determine the geographic limits of the stream reaches that would receive detailed field investigation and the specific locations for data collection. The quantitative portion of the assessment of stream channel conditions used the Rosgen Stream Classification System.  Data regarding existing conditions of the riparian zone, stream channel, and streambanks within each reach were noted.  Care was taken to detect potential public safety issues, infrastructure conflicts, and property damage resulting from stream conditions.

During Construction

During Construction

Cross-sections were established at points that typified the reach. Channel dimensions including top of bank, bankfull, toe of slope, edge of water, thalweg, bankfull width, slope, and floodprone width were measured using a laser level and survey rod. Pebble counts were conducted throughout each reach to augment the Rosgen classification for each of the study reaches. Additional pebble counts were conducted at each of the classification riffles and boundary pebble counts at the pool cross section and non-classification riffle in each reach.  A longitudinal profile that included (at minimum) the thalweg, water surface and bankfull at each facet change were also surveyed along the entire study area in order to determine thalweg length and the water surface and bankfull slopes.

Right After Construction

Right After Construction

Channel geometry was calculated and a graphical representation of each cross section was generated.  Bankfull discharges at the cross sections were calculated using Manning’s equation.  Using these parameters, the Rosgen Steam Classification was derived for each reach.  A Natural Resources Inventory was completed and a Forest Stand Delineation was prepared, submitted and approved.  Non-tidal wetland boundaries were delineated according to the 1987 Corps of Engineers Manual.

Following the assessment of existing conditions, the potential for stabilization or restoration of specific stream reaches was evaluated.  The relative size of the proposed project, construction access, impacts to wetlands or forests, potential utility conflicts, and distance to the closest pedestrian areas were evaluated.

After Restoration

After Restoration

Stream improvements proposed for the unnamed tributary at Sligo Creek Golf Course included localized stabilization and in–channel improvements as well as significant bank grading and channel geometry adjustments. The major types of stream restoration techniques utilized for the project include:

  • In stream log step pool grade control structures were installed to prevent further entrenchment of channel.
  • Grading of bankfull benches to provide increased floodplain access coupled with bioengineering techniques like vegetated matting for stabilization.
  • Replaced undersized culverts with oversized ached culvert to reduce backwatering at cart path crossings.
  • Created no mow zone to maintain vegetative buffer along the study area take the stream out of play.

Stream improvements proposed for Batchellor’s Forest Run at the Northwest Park Golf Course included localized stabilization and in–channel improvements as well as significant bank grading and channel geometry adjustments. The major types of stream restoration techniques utilized for the project include:

  • In stream control structures and near bank stress relieving structures (rock cross vanes and log vanes) were installed to prevent further entrenchment of channel and reduce bank erosion contributing to sediment load.
  • Grading of bankfull benches to provide increased floodplain access coupled with bioengineering techniques like vegetated matting for stabilization.

CRI also completed a Section 404 Joint Permit Application for both projects and obtained approval for construction in wetlands and waters of the US.  CRI provided construction inspection services to assist the contractor with maintaining design objectives throughout construction. In addition, CRI participated in public meetings where conceptual designs were presented and questions answered.  The community was very supportive of the projects and they have been viewed by M-NCPPC as successful stream restoration projects.