1. 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 APPROACH Using 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

14. LocationExistingProposed Fontron to Severn Segments of 15 and 18” CMP; swales Bioswales, 15” RCP Severn to 2 nd Swales, 12x15 and 18” CMP, sump at I-6 18” RCP 2 nd None2-18” RCPs 2 nd to Beach 2-12x18” CMP, swale (sump at I-1) 2-21” RCPs, enhance swale (deeper) Beach2-15x18 CMPsExtend swale and eliminate portion of pipe, headwalls and 3-18” RCP First15x20” CMPHeadwalls and 3-18” RCPs

15. QUESTIONS??