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SELBY STORM DRAIN IMPROVEMENT DESIGN

SELBY STORM DRAIN IMPROVEMENT DESIGN. Anne Arundel County Department of Public Works Presented by: Shannon Lucas, P.E. Brightwater, Inc. OBJECTIVE. MINIMIZE OR ELIMIINATE FLOODING FROM FREQUENT SMALL STORMS Storms of 1- to 2-year frequency are causing flooding in the community

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SELBY STORM DRAIN IMPROVEMENT DESIGN

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  1. SELBY STORM DRAIN IMPROVEMENT DESIGN Anne Arundel County Department of Public Works Presented by: Shannon Lucas, P.E. Brightwater, Inc.

  2. OBJECTIVE • MINIMIZE OR ELIMIINATE FLOODING FROM FREQUENT SMALL STORMS • Storms of 1- to 2-year frequency are causing flooding in the community • 1-year storm = 2.7 inches in 24 hours • 2-year storm = 3.2 inches in 24 hours • IMPROVE WATER QUALITY OF STORMWATER RUNOFF • Use Low Impact Development SWMgt approaches • MINIMIZE PRIVATE PROPERTY and UTILITY ENCROACHMENTS

  3. Responsibility • Residents of Chesapeake Bay Watershed • Residents of the South River Watershed • Impairments • Nutrients (Phosphorous and Nitrogen) • Total Suspended Sediment • Fecal Bacteria • Fish and Benthic Bio-assessment • Doing our part – taking the opportunity Photo from southriverfederation.net

  4. CHALLENGES • Selby Community has no adequate storm drain system • Low vertical relief (flat slopes) make it difficult to move stormwater runoff • High water table further impedes the management of stormwater runoff • Jurisdictional wetlands limit management options • Annual cleanout of existing stream channels and wetlands is prohibited by regulations • Sanitary Sewer System constrains area for retrofits

  5. PREVIOUS EFFORTS BY COUNTY • Earlier Effort by County resulted in design with very large multiple pipes that required raising roads. • Interference with existing Sanitary Sewer System became prohibitive. • There was no water quality improvement with the earlier design. • Large pipes required substantial encroachment on private property

  6. Old School Approach • Get the water off the roads and into pipes as quickly as possible • Size pipes to carry large storm events • Concentrates runoff and moves it quickly to downstream • Exacerbates problems downstream • more water all at once • erosive velocities

  7. CURRENT APPROACH • Design for the frequent flooding events (2-year storm) • Use Low Impact Development (LID) or Environmental Site Design approach to reduce runoff volume to downstream areas • Improve water quality of runoff using LID techniques • Light touch • Minimize conflicts with private property and utilities

  8. LID APPROACHUsing bioswales • Use Bioswales in upstream areas • Infiltrate first few inches of runoff where soils will allow • Use Swales with underdrains where soils won’t infiltrate • The swales will drain within 24 hours • Swales support an attractive, functional landscape plan

  9. LID APPROACH (continued) • Swales slow the runoff enough to reduce downstream flows in two ways • Storing runoff temporarily in swales and underground in the soils actually reduces total volume of runoff • Increasing the time for runoff to concentrate reduces the magnitude of peak flows • Bioswales treat runoff and improve water quality

  10. Examples of BioSwales

  11. PROPOSED LAYOUT OF STORM DRAIN SYSTEM

  12. QUESTIONS??

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