Karst Initiatives/Storm Water Management in Berkeley County

Brian Hopkins, Ph.D., P.E.

Berkeley County Engineering Department

Issues for stormwater management

The Water BalanceWater Quantity ControlWater Quality ControlKarst

Maintaining water balance as impervious covers the Karst features and other recharge receptors

Good quality recharge Structural issues

Nuisances Issues

Measures and Ordinance based on WV DEP/US EPA/Center For Watershed Protection Guidelines

Water Quality Volume( WQv) (0.9” in. Precipitation) Capture and TREAT 90% of average rainfall (0.9” rainfall)

Recharge Volume (Rev) Maintain dry weather hydrology Based upon the USDA hydrologic soil groups

Channel Protection Volume (Cpv) Protection from erosive events caused by bankful flows due to urbanization

Overbank Flood Protection (Qp25) Protect infrastructure from flooding from increased PEAK flows zero discharge of 10 yr event in flood hazard areas

Extreme Flood Protection (Qf) Protect infrastructure from flooding during extreme flood events Restrict development in flood plains

Water Quantity Control

Channel Protection Volume – detention of 1 yr event over 24 hours – lower peak discharges and provides a buffering effect

Over Bank Protection Volume - Manage the 25 yr storm peak flow rates to pre-existing peak discharge conditions – not volume

Extreme Flood Event – Safely pass the 100 yr event

Flood prone areas – additional storage required – zero discharge of the 10 yr event

Down stream analysis required

Quality

Goal is to protect surface and sub surface aquatic systems.

Reduction of pollutants. TREATMENT through BMP’s – (Water Quality

Volume) Filtering Chemical processes (oxidation) and adsorption Biological processing – microbes, plants, etc. Plants – filter, uptake, and provide substrate. Residence time for treatment.

Effective SWM Practices

Ponds Micro-pool ED pond Wet Pond Wet ED pond Pocket pond

Wetlands Shallow Marsh ED wetland Pond/marsh system Pocket Wetland

Commercial Contech Storm Filter Aquaswirl

Filtering Sand filter

Underground Surface Perimeter

Organic Filter/Bioretention Infiltration

Infiltration trench Infiltration basin

Open Channels Dry/Wet Swales

Recharge

Discrete vs. Diffuse Recharge: Treatment required for pure groundwater

Maintain a Water BalanceExfiltration or Recharge Augmentation:

More impervious and more abstraction means less ground water in general thus methodology to make up for what is lost is required.

Understanding the dynamics of recharge: Studies, field investigations, and modeling required to understand total

implications

Nuisances Ponded Water SWM and Mosquito abatement

Pretreatment – remove nutrient and organics loadings Small, Deep pools – “micro pools” promote mixing, reduce stagnation,

provide habitat for predators and inhibit invasive emergent vegetation Predators in properly designed facility

Mosquito fish, dragon flies, aquatic beetles, and amphibians. Fluctuating water surface elevation Vegetation - Some types of vegetation help with mosquito control, while

others exacerbate mosquito problems Spatterdock, Arrowhead, etc. recommended

Chemical - Mosquito dunk and other treatments in maintenance schedules

Flexibility - Other filtering options (bioretention, sand filters, channels, etc. do not include standing water (designed for 48 hour drain down time)

Initiatives More geotechnical testing requirements.

Requirements of “Geotechnical methods for Karst feasibility testing” specifically added to SWM Ordinance Karst study, borings, geophysical investigations Monitoring systems, Maintenance and repair of sinkholes

Recommendations for providing Phase I environmental assessments and phase II where required prior to site plan approval

Increased field inspections at review time and coordination with WV DEP on Karst areas and features

Initiatives Continued

Comprehensive plan for county and zoning to proposed to preserve recharge zones and limit development in more sensitive areas

County wide comprehensive topographic data Potential for Master SWM Plan – Storm Water

Utility being plannedLID options - 2 acre lots, 18’ pavement

open street sections

Future/GoalsContinued Identification and Studies of

Karst Features within the countyComputer and GIS based stormwater

quantity and/or quality modelsWater quality testing

References

WVDEP Storm Water Management – Ground Water Protection Plan Guidance Document 2000 MD SWM Design Manual Vol. I&II– MD DEP, Center for Watershed Protection, et.al. USDA Natural Resources Conservation Service Maryland Conservation Practice Standard Pond

Code 378 (January 2000) “Managing Mosquitoes in Stormwater Treatment Devices” 2004, University of California,

Department of agriculture and natural resources. HydroGIS ’96: Application of Geographic Information Systems in Hydrology and Water

Resources Management. Brown, W. and T. Schueler, 1997. National Pollutant Removal Performance Database for

Stormwater BMPs. Center for Watershed Protection. Chesapeake Research Consortium. Meyer, S.P., Salem, T.H., and Labadie, J.W. (1993) Geographic Information Systems in Urban

Storm-Water Management, Journal of Water Resources Planning and Management, 119 (2): 206-228.

Chesapeake Bay Program Recommendations for Refinement of a Spatially Representative Non-tidal Water Quality

Monitoring Network for the Chesapeake Bay Watershed August 2005, Report of the Task Force on Non-tidal Water Quality Monitoring Network Design Scientific and Technical Advisory Committee, STAC Publication 05-006