(PRIDE - Protecting Resources in Delicate Environments, the educational component of James City County's water quality program will perform a demonstration project at the King of Glory Church on Longhill Road on Saturday October 18, 2003, from 10 a.m. to 12 noon. Volunteers from the King of Glory Church, AES Consulting Engineers, Henderson, Inc., and James City County will cooperatively participate in constructing a 300-square foot rain garden to demonstrate water quality and drainage improvement in an existing parking lot area.)

Project Introduction

During close-out procedures for a recent expansion of the King of Glory Lutheran Church Community Center (County Plan SP-118-00), County Environmental Division staff and representatives of the King of Glory Church discussed actions taken by Church personnel to improve a drainage situation at the south end of the expanded parking area.

Due to parking lot grading and overland sheet flow across paved parking areas, runoff was concentrating at the southeast corner of the new parking area. As runoff ponded in this corner, overflow was being directed to the interior side slope of the existing onsite pond in an erosive manner. In an effort to correct the drainage situation, church maintenance volunteers installed a stone diaphragm, two small plastic drainage inlets and plastic storm drain pipe in this corner of the parking lot. The intent of the small drainage system was to convey drainage from the existing parking lot area to an existing onsite stormwater conveyance channel.

Meanwhile, County PRIDE staff was concurrently in search of a feasible location to perform a rain garden demonstration project within the Powhatan Creek watershed. Based on some preliminary research, field visits and coordination with King of Glory Church, County PRIDE staff decided to pursue this site for the rain garden demonstration, which would also help to resolve the persistent drainage situation experienced by the Church. The basis of the demonstration project idea was to convert an existing grass and tree landscaped area situated at this corner of the site into a rain garden, which is a small bioretention type stormwater management/Best Management Practice (BMP).

The rain garden will accept and provide water quality treatment for this corner of the parking lot and will demonstrate how existing sites such as churches, businesses and even individual single-family lots can convert existing areas into acceptable water quality treatment devices.

The church site and the project area are situated within identified Subwatershed 207 (Upper Chisel Run) and Catchment 207-201-1 of the Powhatan Creek Watershed Management and Stormwater Master Plans, respectively. Specific stormwater strategies for this subwatershed and catchment include encouraging stormwater retrofitting.

Project Area

The project area is approximately 20 ft. long and 15 feet wide or roughly about 300 square feet in size and services about ¼ acre of drainage area. Concept work plans were presented to the King of Glory Church and subsequently approved by its Board of Trustees. Following approval, representatives of the County's PRIDE program worked with Church maintenance and grounds personnel and other volunteers to present a final plan and to establish a date and time for the event.

What is a Rain Garden?

A rain garden, or bioretention basin, is a low impact water quality practice which removes pollutants from stormwater runoff associated with impervious areas such as roofs, parking lots, driveways, etc. Rain gardens are created in low-lying areas where flow and velocity are within reasonable tolerances. Bioretention basins are typically located beneath landscaped areas but are depressed (bowl-shaped), rather than raised (bermed) like typical landscape islands that are routinely visible in most residential, commercial and business areas. Rain gardens generally consist of the following components, from the surface downward:

Native tree, shrub, ground cover and flower landscaping; A mulch layer about 3 inches deep; An underlying planting soil layer which consists of a specialized mixture of sand, topsoil and organic material ranging from 2 to 4 ft. deep; Geotextile fabric to provide separation between soil and stone layers; A stone layer with perforated underdrains; An overflow device within the basin; A safe surface overflow path from the basin.

Runoff which flows into the rain garden will temporarily pond in shallow depths of 6 to 9 inches and over the next few hours the mulch, planting soil and under drain layers store, absorb and filter rainwater. Although the device acts as a filter, stormwater is also infiltrated into natural soils surrounding and below the basin, thus providing for infiltration and recharge of groundwater sources. If there is an excessive amount of water, stormwater will discharge through the bedding stone layer, the subsurface perforated under drain pipe, the overflow device, and an emergency spillway into a downstream stormwater conveyance channel.

Rain Garden Design

A landscape plan was prepared by County staff with the assistance of Harmony Design of Williamsburg, Va. Usually a wide variety of native landscape plants are specifically selected and planted within the surface layer of rain gardens. Plants specifically selected for this rain garden included blueflag iris, cinnamon fern and elderberry. Final design of the stone and under drain pipe and the overflow system was performed by County Environmental Division staff.

Rain Garden Construction

Construction of the rain garden was divided into two parts. On Saturday October 11th volunteers from AES Consulting Engineers and Henderson, Inc., both of Williamsburg, Virginia, were present to excavate the basin and install the stone and under drain pipe systems. The second part of the project will be performed on Saturday October 18 to coincide with a designated clean-up day at the King of Glory Church. Church and PRIDE volunteers will place geotextile fabric over the stone layer and proceed with placement of planting soil and trees, shrubs, ground cover and mulch.

Geotextile fabric was purchased from ACF Environmental of Richmond, Virginia and landscaping plants were purchased from Pinelands Nursery of Columbus, New Jersey, which has a local greenhouse here in James City County. An existing larger infiltration pond, which is in close proximity of the rain garden, will also be planted with wetland plants including soft-stem bulrush and swamp hibiscus.

Rain Garden Maintenance

Long-term maintenance of the rain garden will be minimal and no more difficult to maintain than that required for normal landscaped areas. The basin would be well-drained due to the underlying stone, under drain pipe and planting soil layers. Once plants are established, occasional inspection, weeding and mulch replacement is all that will be typically necessary. Future maintenance would be by the Church, although County PRIDE staff will provide follow-up monitoring and guidance as necessary.

Rain Garden Cost

The total cost to plan, design and construct the rain garden was approximately $3,000 or about $10 per square foot. Donated design, labor and equipment services saved the project approximately $1,500.

Remarks

Once constructed, the landscaped area will look the same, if not better, than existing conditions and the plants will be much more tolerant of extreme wet or prolonged drought conditions. The rain garden will help solve a persistent drainage issue present in this corner of the existing parking lot. The project will provide a distinct stormwater management and water quality benefit, consistent with the initiatives of the Powhatan Creek Watershed Management Plan and the Chesapeake Bay Preservation ordinance of James City County. The project will be utilized by County staff as a great educational tool and demonstration site for the use of better site design and low-impact development stormwater management techniques.