anne arundel county department of public works presented by: shannon lucas, p.e. brightwater, inc
TRANSCRIPT
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