constructed wetlands presentation final

Botanical Gardens North Watershed

Richard HollanderArturo Huesca

Noah Posthuma

April 20, 2011

Unique Characteristics and Challenges of Catchment

• Long but narrow catchment area, with steeply sloped channel width, constrains size of treatment cells

– requires treatment train of pocket wetlands

• Allow for future residential and/or commercial development

• Handle pollutant loading from existing commercial and residential areas

• Provide amenity for residential areas in addition to a stormwater engineering solution

– design with high aesthetic values

• Manage for mosquitos, algal blooms and safety, given proximity to residential areas

Watershed Exploration

Dominos Farms Corporate Headquarters: Parking Lot Runoff

Dominos Farms Corporate Headquarters: Infiltration Pond

Stump sprouted deciduous forest

growing American Elms

Artificial pond surrounded by Scots Pine

Natural Riverine Forest (Poplars and Elms)

Across Plymouth Road

Across Plymouth Road – Permanent Water Flow

Pasture Land

Development at the lower end of the catchment

Catchment outlet pipe across Dixboro Road

Catchment Soil Hydrology

Catchment Land Use

TR-55 Inputs• Stormwater pocket wetland sized for 2-yr storm, 2.26 inches rainfall

• Channel Details• Total channel length of 7,547 feet• Manning coefficient ranging from top of catchment grassy

area of 0.41 to channel end of 0.022• Slope ranging from top of catchment of 0.001 to 0.043

through forested open areas to 0.016 through channels

• Total catchment area is 264 acres• Residential of 72 acres (density of 0.25 acre lot sizes)• Commercial (Domino’s corporate HQ buildings, parking lots,

private school) of 24 acres• Roads and Streets (including Plymouth Road and Dixboro

Road) of 19 acres• Open Space (primarily wooded forests) of 149 acres

TR-55 Results

•Total runoff of 0.453 inches

•Time of Concentration of 1.764 hours

•WQv of 10.01 acre-feet

• Pocket wetland system substantially dewatered within 48 hours, using 8 inch diameter pipe for outlet

HydrographHydrograph for 4-cell constructed stormwater pocket wetland, with 8 inch

diameter pipe for the outlet to allow for dewatering in 48 hours

Contaminant EstimatesLOADING

Land Use AcresPhosphoru

s Loading Nitrogen Loading TSS Loading

pounds per acre per year per land use

pounds per acre per year per land use

tons per acre per

year

pounds per year

pounds per year

tons per year

Residential 0.5 units/acre 0.8 6.2 0.09 1 units/acre 0.8 6.7 0.11 2 units/acre 0.9 7.7 0.14

10 units/acre** 72.144 1.5 108.216 12.1 872.942 0.27 19.479

Commercial 23.84 0.7 16.69 7.1 169.264 0.08 1.907

Industrial 0.7 9.5 0.15 Roads 19.17 0.8 15.336 7 134.19 0.14 2.684 Ag/Pasture 0.7 12.4 0.15

Forest 148.846 0.2 29.769 5.5 818.653 0.05 7.4423

Total 264.0 170.0 1,995.1 31.5

Sources for loading calculations: Claytor and Schueler (1996), Steuer et al. (1997), Bannerman 1993), Caraco (2001), Camp et al. (2004), Marsh (2010).** Note we estimate lot sizes for residential units as 0.25 acres/unit; thus, assuming 10 units/acre or 0.10 acre lot sizes is conservative (ie, overestimates contaminant loading for purposes of designing phytoremediating plant schedule).

Contaminant Estimates cont’d

REMOVAL

Phosphorus Nitrogen TSS

pounds per acre per yearpounds per acre per

year Tons per acre per year

96.9 877.8 18.0

(based upon Table 14.3 from Randolph (2004))

Constructed Wetland Placement

Unique Characteristics and Challenges of Catchment

Unique Characteristics and Challenges of Catchment

Pocket Wetland 1

Pocket Wetland 2

Pocket Wetland 3

Pocket Wetland 4

Plant Selection Criteria

• Enhance the use of native plants of Michigan to create an aesthetic riverine ecosystem

• Our catchment is in a rural environment

and constructed wetlands should provide food and cover for wildlife (waterfowl, pollinators, birds)

• Control of phosphorous – in our opinion, an excess of P in runoff is currently being discharged into ponds in the area, increasing the presence of algae and water eutrophication

Other design considerations

• For all forebay and micropools, use slope of no greater than 3:1

• Safety bench around all pools• Plant emergent vegetation on safety

bench to further deter people from entering pools

High Marsh (0-6 in)

Food and cover for wildlife

Peltandra virginicaSun/ShadeRhizomatous

Decodon verticillatusShallow waterGood for waterfowl

Eupatorium perfoliatumNative perennial, full sun

Iris versicolor

Aesthetic value

Low Marsh (6-18 in) and Micropool (>18 in)

Water Column AerationElodea canadensis

Phosphorous control to prevent eutrophication/Food and cover for wildlife

Nuphar lutea Lemna minor

Recommendations

• For control of algal bloom, plant floating water lilies which reduce sunlight for algae, as well as submerged oxygenating plants like Elodea which outcompete algae for nutrients, in addition to introducing tadpoles

• Vacuum decomposed algae from pond pools

• Implement city ordinances limiting or banning inorganic lawn fertilizer use, or institute impact fees, for residential units in catchment

• For mosquito control, introduce mosquito-eating Gambosia affinis fish to forebays and micropools; live well in Michigan

Recommendations cont’d

• Engage Huron River Watershed Council and City of Ann Arbor to coordinate volunteer teams to remove invasive plants (buckthorn, honeysuckle, phragmites)

• Remove sediment from forebays at least annually, disposing in landfill as needed