Natural and Engineered Wetlands for Stormwater Management Dan Hitchcock, Ph.D., P. E. Baruch Institute of Coastal Ecology and Forest Science Clemson University Georgetown, SC
Prominence and Diversity of Coastal Wetland Habitats Clemson University Baruch Institute
Prominence and Diversity of Coastal Wetland Habitats
Prominence and Diversity of Coastal Wetland Habitats
Wetland Biogeochemistry Highly productive ecosystems Partially versus fully inundated systems Aerobic vs. anaerobic conditions Nutrient cycling redox chemistry Carbon sequestration Water quality benefits
HYDROLOGY VEGETATION SOILS WETLAND SYSTEM DYNAMICS
HYDROLOGY VEGETATION SERVICES: FLOOD CONTROL STORM PROTECTION AIR/SOIL/WATER QUALITY NATURAL RESOURCE PRODUCTS CLIMATE REGULATION HABITAT/CORRIDORS NUTRIENT CYCLING CARBON STORAGE BIODIVERSITY RECREATION AESTHETICS HEALTH PLANT SUCCESSION PRODUCTIVITY WATER/NUTRIENT UPTAKE SOILS ORGANIC LOADING TEMPERATURE REGULATION SOIL STABILIZATION Landscape parameters, their interactive complex processes & ecosystem services = GREEN INFRASTRUCTURE (Modified from Ge Sun, Southern Global Climate Program, USDA Forest Service)
Zoning for Future Land Uses? Waccamaw Neck, Coastal Georgetown County, SC Land Use Map Commercial Conservation Public/Semi-public Private Recreational Public Recreational High Density Residential Low Density Residential Medium Density Residential Map courtesy of Georgetown County, SC
Bannockburn Plantation
(from Buol, 1978) Surface and Groundwater Interaction
Upper Debidue Creek (UDC) PIEZOMETER MET STATION STREAM STATION Weather Station Piezometer Sample well / rain gage / soil moisture sensor Stream monitoring Pond monitoring From Dr. Tom Williams, Clemson
2008 2009 2010 Upper Debidue Creek Rainfall and Stage 2009: P = 1031 mm 2010: P = 1247 mm
Seasonal Runoff Variability UDC WS80 Epps, T. H., D. R. Hitchcock, A. D. Jayakaran, D. R. Loflin, T. M. Williams, and D. M. Amatya, 2013. Characterization of Storm Flow Dynamics of Headwater Streams in Lower Coastal Plain South Carolina. Journal of American Water Resources Association 49:76-89.
What drives the water table??
Wetland Water Budget EVAPOTRANSPIRATION INFLOW PRECIPITATION BANK RUNOFF INFLOW OUTFLOW GROUNDWATER Modified from Kadlec and Knight, 1996
Upper Debidue Creek Stand Inventory
N 5 mi. Online Community Resource Inventory: www.cri-sc.org State protected lands Private protected lands Open water Parcels Major roads Excessively well-drained sand Poorly-drained sand Very poorly-drained sand Well-drained sandy loam Poorly-drained sandy loam Poorly-drained sandy clay loam Well-drained sandy clay clay loam Somewhat poorly drained clay
The Systems Approach HYDROLOGY VEGETATION SOILS IMPERVIOUS SURFACE FOREST AND WETLAND COVER
Water Quantity and Quality QUANTITY: Flood control Conveyance Storage Salt water intrusion Sea level rise / climate change QUALITY: Harmful bacteria and viruses Nuisance algal blooms Low dissolved oxygen (DO) Fish kills Sediment and chemicals Invasive species Downstream ecological health
Wetlands for Stormwater Management!!!
Stormwater Wetland Pollutant Removal Total N = 28-39% Total P = 42-53% Metals = 14-72% Copper = 29-50% Zinc = 32-52% Lead = 62-76% Hydrocarbons = 80% Pathogens = 58-78% Total Suspended Solids = 66-78% (SCDHEC BMP Manual and based on data from the Center for Watershed Protection)
Pollutant Removal (for NC Regulatory Credits) Total Suspended Solids = 85% Total N = 40% Total P = 40% (From the NCDENR Stormwater BMP Manual)
General Stormwater Wetland Design Criteria in GA Minimum drainage area = 25 acres Minimum dry weather flow path of 2:1 (L:W) Minimum of 35% area has depth of <= 6 inches Minimum of 10-20% area has deep pool (1.5-6 ft) All wetland designs should include a forebay (From the Georgia Stormwater Management Manual)
Basic H&H Considerations Base flow critical for plant survival Stormwater flow prediction from drainage area Working with given topography Retrofitting stormwater infrastructure Consider groundwater!
Engineered Wetlands in Coastal Landscapes the right practice for the right place?
Wetland Design A Six-Step Process 1. Understand basic layout concepts 2. Determine what volume of water to treat 3. Determine surface area and depth of each wetland zone 4. Select the soil media type 5. Select the appropriate outlet structure 6. Select plants (From the NCDENR Stormwater BMP Manual)
Basic Wetland System Components Inlet swale, pipe, diverter, sheet flow, must be stabilized Deep pool forebay (required) + non-forebay pools (PPE) Shallow water depth = 3-6 Shallow land only wet after a rain event, top of land is top of the temporary pool elevation Upland natural amenity with access for maintenance Outlet weir overflow + drawdown + access + stabilized (From the NCDENR Stormwater BMP Manual)
Basic Wetland System Components (From the NCDENR Stormwater BMP Manual)
Basic Wetland System Components (From the NCDENR Stormwater BMP Manual and the NCSU Stormwater Group)
Major Design Elements - Sizing Wetland sized to treat the first flush (1-1.5 ) of design storm Minimum treatment volume shall be 3,630 ft 3 Minimum length-width ratio of 1.5:1, but 3:1 is preferred Max shallow land depth (TPE) shall be 1 ft. Vegetated side slopes no steeper than 3:1 Drawdown must occur in 2-5 days (From the NCDENR Stormwater BMP Manual)
Recommended Plants Deep pool Floating aquatics Submerged aquatics Shallow pool Herbaceous plants Upland soil characteristics Herbaceous plants Shrubs No cattails! Only native species (From the NCDENR Stormwater BMP Manual)
Plant Selection and Planting Strategies Pondscaping have a plan with planting zones Minimum of 10 different species with at least 5 of these as emergent plants Shallow water area: minimum of 50 herbaceous plants of 4 cubic inch container per 200 ft 2, planted max. of 2 ft on center OR 8 shrubs in 1 gal. container, max. 5 ft on center OR 1 tree at least 3 gal. container and 40 grass-like plants of 4 cubic inch (From the NCDENR Stormwater BMP Manual)
Plant Selection and Planting Strategies Shallow land area: minimum of 50 herbaceous plants of 4 cubic inch container per 200 ft 2, planted minimum of 2 ft on center Centipede grass as buffer Specific supplementary plantings for any losses Water plants frequently until established At least 4 in. of topsoil must be added to liner for plant growth (From the NCDENR Stormwater BMP Manual)
Maintenance Requirements Have a clear and specific approved maintenance agreement Monitor sediment (especially in forebay) and selectively remove at specified depth of accumulation(s) Inspect for erosion and repair and stabilize as needed Inspect inlets and outlets for debris and clean as needed Replace wetland vegetation to maintain >= 70%, 90-95% desired Remove invasive vegetation (From the NCDENR Stormwater BMP Manual)
BMPs in Series or Treatment Train Rainwater Harvesting Buffer Some BMPs are better than others for certain pollutants Consider the connectivity of BMPs Front-end sediment collection; i.e., forebays or traps Vegetated BMPs can be overloaded so should be toward the end of train Rain Garden/ Bioretention Pond (w/ Forebay) Wetland Receiving Waters 37
??? Questions??? For more info, please contact: Dr. Dan Hitchcock, P.E. dhitchc@clemson.edu