Design Case StudyDesign Case StudyReidsville Middle School Stormwater WetlandReidsville Middle School Stormwater Wetland

Kris Bass – NCSU BAECarol Patrick - PTCOG Jenn Johnson – NCSU BAE

Intro/BackgroundIntro/Background

•• Little Troublesome Creek Little Troublesome Creek –– 303(d) listed water303(d) listed water

•• PTCOG PTCOG –– Piedmont Triangle Council of Governments Piedmont Triangle Council of Governments ––EPA 319 grant to implement stormwater BMPEPA 319 grant to implement stormwater BMP’’s in the s in the watershed.watershed.

•• Site is at Reidsville Middle SchoolSite is at Reidsville Middle School

•• Retrofit an old sediment basin that has not been Retrofit an old sediment basin that has not been maintained into a stormwater wetland.maintained into a stormwater wetland.

Some PhotosSome Photos

WatershedWatershed

Watershed DataWatershed Data

•• Drainage Area = 24 acresDrainage Area = 24 acres

•• School, soccer field, parking lot, residential uses.School, soccer field, parking lot, residential uses.

•• Mostly clayey soils, Class C. Mostly clayey soils, Class C.

•• Composite Curve number = 84Composite Curve number = 84

•• Rational coefficient = 0.24, Tc = 5min.Rational coefficient = 0.24, Tc = 5min.

•• Design volume to store runoff from a 1Design volume to store runoff from a 1--1.51.5”” storm.storm.

•• Store runoff/design drawdown for 2Store runoff/design drawdown for 2--4 days.4 days.

Site PlanningSite Planning

Site Topo/ConstraintsSite Topo/Constraints

Storage CalculationsStorage CalculationsRequired Surface Area (sf)for Various Storms and Storage Depths

StormsStorage Depths (in) 1" 1.5" 2yr 10yr 25yr

6 25226 70166 334408 599355 68025912 12613 35083 167204 299677 34012918 8409 23389 111469 199785 22675324 6307 17541 83602 149839 17006530 5045 14033 66882 119871 13605236 4204 11694 55735 99892 113376

Available Area 7500

Drawdown CalculationsDrawdown CalculationsOrifice SizesOrifice Sizes Drawdown TimeDrawdown Time

0.50.5”” >3 days>3 days

0.750.75”” 2.25 days2.25 days

1.01.0”” 1.25 days1.25 days

Final Design SchematicFinal Design Schematic

Final Design SchematicFinal Design Schematic

Planting LayoutPlanting Layout

Wetland AreasWetland Areas Normal Water DepthNormal Water Depth ElevationsElevations

Deep PoolsDeep Pools 11--2.52.5’’ 9292’’--9494’’

Low Flow ChannelLow Flow Channel 11--1.51.5’’ 9393’’--9494’’

Shallow WaterShallow Water 00--66”” 9494’’--94.594.5’’

Shallow LandShallow Land 00--2.52.5’’** 94.594.5’’--9797’’

SlopesSlopes 2.52.5--55’’** 9797’’--102102’’

*Shallow Land and Slopes are above normal pool level

Plant List• Grass Mix – Carex species• Shrubs

• Clethra alnifolia• Ilex glabra• Hibiscus moscheutos• Rosa palustris• Cyrilla racemiflora• Lobelia cardinalis• Cephalanthus occidentalis

Herbaceous Plants• Shallow water

• Pontedaria cordata• Petlandria virginica• Sparganium americanum

• Shallow land• Saurus cernus• Juncus effusus• Scirpus validus

Site ConstructionSite Construction

Grad Student PlantingGrad Student Planting

1 month later1 month later

Looks a little dry?Looks a little dry?

Riser and Monitoring BoxRiser and Monitoring Box

Getting WetterGetting Wetter

Wetland Design CommentsWetland Design Comments

•• Design volume to store at least runoff from a 1Design volume to store at least runoff from a 1--1.51.5”” storm.storm.

•• Ideal storage depth 9Ideal storage depth 9””--1212””..

•• Design drawdown for 2Design drawdown for 2--4 days.4 days.

•• Consider peak discharges for inlets, outlets, bypass/spillways.Consider peak discharges for inlets, outlets, bypass/spillways.

•• Target a variety of water depths and habitat types. Flexibility!Target a variety of water depths and habitat types. Flexibility!

•• Pay attention to the construction!Pay attention to the construction!

•• Soils, soils, soils! Topsoil and tilling when possible!Soils, soils, soils! Topsoil and tilling when possible!

•• Manage water tables during first growing season.Manage water tables during first growing season.