Anne Arundel County Department of Public Works

Presented by:Shannon Lucas, P.E.

Brightwater, Inc.

OBJECTIVEMINIMIZE OR ELIMIINATE FLOODING

FROM FREQUENT SMALL STORMSStorms of 1- to 2-year frequency are causing

flooding in the community1-year storm = 2.7 inches in 24 hours2-year storm = 3.2 inches in 24 hours

IMPROVE WATER QUALITY OF STORMWATER RUNOFFUse Low Impact Development SWMgt

approachesMINIMIZE PRIVATE PROPERTY and UTILITY

ENCROACHMENTS

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

CHALLENGESSelby Community has no adequate storm drain

systemLow vertical relief (flat slopes) make it difficult to

move stormwater runoffHigh water table further impedes the

management of stormwater runoffJurisdictional wetlands limit management options

Annual cleanout of existing stream channels and wetlands is prohibited by regulations

Sanitary Sewer System constrains area for retrofits

PREVIOUS EFFORTS BY COUNTYEarlier 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

Old School ApproachGet the water off the roads and

into pipes as quickly as possibleSize pipes to carry large storm

events

Concentrates runoff and moves it quickly to downstream

Exacerbates problems downstreammore water all at onceerosive velocities

CURRENT APPROACHDesign 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 touchMinimize conflicts with private property and

utilities

LID APPROACHUsing bioswales

Use Bioswales in upstream areas Infiltrate first few inches of runoff where soils

will allowUse Swales with underdrains where soils won’t

infiltrateThe swales will drain within 24 hoursSwales support an attractive, functional

landscape plan

LID APPROACH (continued)Swales slow the runoff enough to reduce

downstream flows in two waysStoring 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

Examples of BioSwales

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