Dumont Oaks Stream Restoration and Stormwater Pond Retrofit

Reference

Daniel Harper (240) 777-7709

Project Highlights

  • Geomorphic Assessment
  • Rosgen Stream Classification
  • Stream Restoration & Bioengineering Design
  • GIS Analysis & Construction Inspection
  • Forest Conservation

Project Details

CRI was selected to conduct a comprehensive field investigation along 1,800 feet of Dumont Oaks Tributary in order to assess stream stability problems and prioritize stream restoration needs. We conducted a review of the available mapping resources using GIS to determine drainage areas for various points on Dumont Oaks Tributary and basin composition with regard to land use, utility conflicts, soils, and geology. This review was followed by a preliminary field reconnaissance to determine the geographic limits of the stream reaches that would receive detailed field investigation and 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.

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. We determined the median particle size of the channel substrate using a modified Wolman pebble count. We established bank erosion pins on left and right banks at each cross section using .25 inch rebar. We also surveyed a longitudinal profile of the channel bed and water surface along the entire study area in order to determine channel slope.

We calculated channel geometry and generated a graphical representation of each cross section. Bankfull discharges at the cross sections were calculated using Manning’s equation. Using these parameters, we derived the Rosgen Steam Classification for each reach. CRI completed a Natural Resources Inventory 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, CRI evaluated the potential for stabilization or restoration of specific stream reaches. 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.

Proposed stream improvements at Dumont Oaks Tributary include localized stabilization and in-channel improvements as well as significant channel geometry adjustments. The major types of measures being proposed include:

  • Instream grade control structures (i.e., Cross Vanes, Rock Weirs) to prevent further entrenchment of channel.
  • Grading banks to a stable angle providing increased floodplain access coupled with bioengineering techniques like live fascines, branch layering and vegetated matting for stabilization.
  • Raising the channel invert to allow flood flows greater access to the floodplain and reduce shear stress on banks.
  • Installing rock toe protection coupled with minor grading of severely eroded banks above bankfull and supplemental plantings.
  • Stabilization or removal of trees that are severely undermined and in danger of toppling into channel.
  • Removal of in-channel debris.

A Joint Federal/State Permit Application was submitted and approved for construction in wetlands and waters of the US. CRI provided construction inspection. In addition, CRI participated in public meetings where conceptual designs were presented and questions answered. The community was very supportive of the project.