Plumtree and Tiber Watersheds

Plumtree Branch Watershed and Tiber Branch Watershed Stormwater Retrofit Studies

Howard County Department of Public Works completed stormwater retrofit studies in the Plumtree Branch Watershed and Tiber Branch Watershed in the Ellicott City area. The studies included drainage assessments and improvement studies of:

  • Existing stormwater infrastructure (inlets, pipes, manholes, outlets, swales)
  • Opportunities for improved stormwater infrastructure and management
  • Opportunities for water quality improvement

Watersheds were divided into assessment areas and categorized for improved stormwater infrastructure and management and water quality opportunities:

  • Potential Capital Improvement Projects
  • Potential Repair and Maintenance Projects
  • Potential On-Lot Improvements

Potential work in these areas depends upon further analysis, future funding, and each project’s prioritization relative to each other and to additional priorities throughout the County. Homeowners can also reduce runoff on their own properties by installing rain gardens and rain barrels, taking advantage of existing County cost-sharing, credit and reimbursement programs. See for more information on water quality programs for residential properties.

The final studies are available for viewing. Comments and questions can be sent to

Valley Mede Drainage Study

A comprehensive hydrologic and hydraulic analysis of the July 30, 2016 flooding event in the Valley Mede, Chatham and Nob Hill areas of the Plumtree Branch and Little Plumtree Branch watersheds of Ellicott City was completed in 2017. This analysis also modeled how certain water retention controls, stream channel enhancements and local drainage improvements may reduce the amount of flooding for various storm conditions. A formal presentation explaining the results of the drainage study took place at a public meeting on Wednesday November 15, 2017 starting at 7:00 PM in the George Howard Building’s Banneker Room at 3430 Court House Drive in Ellicott City. Presentation materials can be downloaded below.

PDF Presentation

The final hydrologic and hydraulic analysis report is available for viewing. Comments and questions can be sent to

Valley Mede Storm Drain Inspection

An inspection of the storm drain system that serves as a conduit for Little Plumtree Branch drainage under MD Route 40 in the vicinity of St. John's Plaza in Ellicott City was completed in March 2018. The inspection report can be found here.

Downtown Ellicott City Flood Study

A detailed floodplain analysis using both one-dimensional and two-dimensional hydraulic modeling is available for viewing. The floodplain study, which was completed in July 2013, considered several standard rainfall events as well as the rainfall event that resulted from the remnants of Tropical Storm Lee on September 7, 2011. The study also included a conceptual assessment of potential flood mitigation options.

  • Floodplain Study Report
  • Inflow Hydrograph Comparison
  • Rainfall Intensity Distribution Comparison
  • Cumulative Rainfall Distribution Comparison
  • Flooding Depth and Limits – Multiple Storm Events
  • Conceptual Mitigation Options
  • Appendix A - Existing Hydrology and Hydraulics
  • Appendix B - Concept Designs
  • Appendix C - Proposed Hydrology and Hydraulics
  • Appendix D - 1-D Hydraulic Modeling (HEC-RAS)
  • Appendix E - 2-D Hydraulic Modeling (TUFLOW)
  • Appendix F - Center for Watershed Protection SWM Concept Analysis

    The Howard County Flood Mitigation Plan 2013 Progress report is available for viewing here.

    The Tiber-Hudson and Plumtree Branch Stream Corridor Assessment is a visual survey of the stream corridor to document conditions that potentially affect flood conditions. Also see the supplemental Case Study: Valley Mede-Ellicott City Tropical Storm Lee Flood Event


    Ellicott City Retaining Walls Inspection Report (May 2016) – Stream Walls

    An above-water visual condition inspection of all the retaining walls located along the Hudson Branch and Tiber Branch in Old Ellicott City, MD was conducted in Spring of 2016. The purpose of this inspection was to assess the current condition of the walls and provide a tool for prioritizing the repair of the inspected walls.

    Ellicott City Retaining Walls Inspection Report – Stream Walls