SELBY%20STORM%20DRAIN%20IMPROVEMENT%20DESIGN

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SELBY STORM DRAIN IMPROVEMENT DESIGN

• Anne Arundel County
• Department of Public Works
• Presented by
• Shannon Lucas, P.E.
• Brightwater, Inc.

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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

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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
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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

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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

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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

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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

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LID APPROACHUsing bioswales

• Use Bioswales in upstream areas
• Infiltrate first few inches of runoff where soils
  will allow
• Use Swales with underdrains where soils wont
  infiltrate
• The swales will drain within 24 hours
• Swales support an attractive, functional
  landscape plan

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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

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Examples of BioSwales
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PROPOSED LAYOUT OF STORM DRAIN SYSTEM
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Location Existing Proposed
Fontron to Severn Segments of 15 and 18 CMP swales Bioswales, 15 RCP
Severn to 2nd Swales, 12x15 and 18 CMP, sump at I-6 18 RCP
2nd None 2-18 RCPs
2nd to Beach 2-12x18 CMP, swale (sump at I-1) 2-21 RCPs, enhance swale (deeper)
Beach 2-15x18 CMPs Extend swale and eliminate portion of pipe, headwalls and 3-18 RCP
First 15x20 CMP Headwalls and 3-18 RCPs
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QUESTIONS??