Northern Virginia Soil and Water Conservation District

Fairfax County, Virginia

CONTACT INFORMATION: Our office is open 9AM-5PM M-F

703-324-1460
TTY 711

12055 Government Center Parkway
Suite 905, Fairfax, VA 22035

Laura Grape,
Executive Director

Conservation Assistance (CAP) Project Options

Sustainable Landscapes. Energy Conservation. Community Incentives.

The Conservation Assistance Program (CAP/VCAP) provides incentives for community associations, places of worship, and homeowners to create more sustainable landscapes and energy efficient buildings. Here you will learn more about rain gardens, infiltration trenches, conservation landscaping and other project options that can help capture and absorb heavy runoff.

Rain Gardens

Rain Garden with rain

Bowl-shaped garden area that collects and absorbs runoff. Typical cost: $10-25 per square foot. Minimum size: 100 square feet.

A Rain Garden is Great for:

  • Capturing Heavy Runoff. The rain garden absorbs runoff and lets it soak into the soil below.
  • Flat Areas. Building a rain garden on a slope is a challenge best avoided if possible. (A rain garden can be incorporated into a terrace.) Try to find a nice flat area for your rain garden "bowl."
  • Well-Drained Soil. Got a great infiltration rate? Consider a rain garden! Conversely, a high water table or soggy area is usually not a good site for a rain garden. This option needs well-drained soil to absorb runoff quickly.
  • Areas Clear of Large Tree Roots. Most tree roots grow in the top 18 inches of soil, which would be excavated during rain garden construction.
  • Blending in with Garden Landscaping. A great rain garden design incorporates the plants into the broader landscape design.
  • Gardeners! Like any garden, a rain garden requires ongoing weeding and other maintenance. This project option works well when there are knowledgeable gardeners involved.

(!) Follow These Recommendations

  • Ponding depth should be six inches to one foot. Soil depth should be two to three feet.
  • Sizing: Most homeowner rain gardens are 150-300 square feet. Guidelines:
    • First, find the impervious area draining to the rain garden (length x width in feet).
    • Second, multiply that by a one-inch depth (0.08ft), a typical hard rain, to find the volume of runoff.
    • Third, decide your ponding depth (0.5 to 1 foot).
    • Finally, divide your volume by the ponding depth to find the recommended size for your rain garden.
  • Overflow: Extra water can leave the rain garden over a berm or through a overflow pipe
  • Rain garden plants should be both flood- and drought-tolerant. Native plants are required.
  • Ten Common Rain Garden Plants: Black-eyed Susan, Virginia Sweetspire, Winterberry Holly, Joe Pye Weed, Obedient Plant, Black or Red Chokeberry, Switchgrass, Elderberry, Arrowwood Viburnum, Ox-eye Sunflower.
  • Learn more: Rain Garden Design and Construction for Homeowners
  • Maintenance Recommendations: Water, weed (knowledgeably), prune, mulch, no fertilizer or pesticides, replace dead plants. Preserve ponding depth. Inspect after every major storm in first six months. Check the rate of infiltration once a year.

In the Picture

In 2015, the Loft Ridge community partnered with the Conservation Assistance Program to install a rain garden that captures and absorbs runoff from nearly 10,000 square feet. Click on the picture at right to see it in detail.

BayScaping or Conservation Landscaping

Conservation Landscaping

Incorporate native trees and shrubs, meadow or wetland plants into your landscape. Typical cost: $5-15 per square foot. Minimum size: 150 square feet.

Conservation Landscaping is Great for:

  • Hill Slopes with Erosion. (communities may want to consider light terracing with biologs and backfilling with soil amendments prior to planting)
  • Wet, Soggy Areas. Wetland plants can help soak up excess water (where rain gardens and infiltration trenches would not work because groundwater is too close to the surface)
  • Shady Areas with mature trees where grass does not grow well.
  • Converting Lawn Turf to a more natural state with meadows or reforestation
  • Riparian Stream Buffers or Chesapeake Bay Preservation/Resource Protection Areas

(!) Follow These Recommendations

  • CAP can help fund soil amendments with compost or leaf mulch and light terracing with biologs or wooden landscape ties. Unlike with rain gardens or infiltration trenches, CAP will not fund redirection of flow with french drains or catch basins and pipe into conservation landscaping.
  • Get permission for vegetation removal in RPA.
  • Plants must be native. Plants should tolerate shade and wet conditions.
  • Choose plant height carefully. Smaller sites benefit visually from fewer species. For a landscaped look, plugs or potted plants are more appropriate than seed mix.
  • Soil and Water staff can help with species recommendations or landscape plans if desired. Planting plan must be approved by Soil and Water staff prior to installation.
  • See Plant NoVa Natives and the Chesapeake Bay Native Plant Center for more information.
  • Maintenance Recommendations: Water, weed (knowledgeably), prune, mulch, no fertilizer or pesticides, replace dead plants.

In the Picture

Conservation landscaping is a great way to build community spirit and beautify the area.

Infiltration Trenches/Dry Wells

Labeled depiction of an infiltration trench

A gravel-filled area that collects and absorbs runoff. Typical cost: $5-15 per square foot. Minimum size: 100 square feet surface area or 300 cubic feet volume.

An Infiltration Trench is Great for:

  • Non-gardeners. Infiltration trenches only require watering and mowing.

(!) Follow These Recommendations

  • Underlying soils. Take into account the ability of the soil underneath the trench to retain water.
  • Capturing Heavy Runoff. The rain garden absorbs runoff and lets it soak into the soil below.
  • Flat Areas. Building an infiltration trench on a slope is a challenge best avoided if possible.
  • Areas Clear of Large Tree Roots. Most tree roots grow in the top 18 inches of soil, which would be excavated during rain garden construction.
  • Maintenance Recommendations: Turf top requires frequent watering.

In the Picture

 Learn more about infiltration practices in the Residential Low Impact Landscaping Workbook, then look under Filtering Practices.

Vegetated Swales

vegetated swale

A wide, shallow ditch with amended soil and dense vegetation or grass designed to slow and absorb rainwater runoff and/or filter pollutants. Typical cost: $5-25 per square foot. Minimum size: 150 square feet.

A Vegetated Swale is Great for:

  • Poorly graded sites.
  • Handling heavy runoff. Captures and redirects water within a property.
  • Flat or gentle slopes.

(!) Follow These Recommendations

  • Overflow: Extra water can leave the rain garden over a berm or through a overflow pipe
  • Vegetated swale plants should be both flood- and drought-tolerant. Native plants are required.
  • Ten Common Rain Garden Plants: Black-eyed Susan, Virginia Sweetspire, Winterberry Holly, Joe Pye Weed, Obedient Plant, Black or Red Chokeberry, Switchgrass, Elderberry, Arrowwood Viburnum, Ox-eye Sunflower.
  • Maintenance Recommendations: Water, weed (knowledgeably), prune, mulch, no fertilizer or pesticides, replace dead plants. Preserve depth. Inspect after every major storm in first six months. Mow to 6".

In the Picture

A completed vegetated swale installation. Vegetated swales can either be mowed grass or planted with perennials and taller grasses.

Porous Pavement/Pavers

Finished porous paver project

Replace impervious hard surfaces to allow water to pass through and absorbs into the ground below. Must be installed by certified professional. Typical cost: $10-35 per square foot. Minimum size: 300 square feet.

Porous Pavement/Pavers is Great for:

  • Parking Areas.
  • Converting Hardscape such as concrete, asphalt, and other paved surfaces.
  • Reducing Runoff.

(!) Follow These Recommendations

  • Use a certified contractor.
  • Ensure soils can handle infiltration and underdrain.

In the Picture

This porous paver diveway captures and absorbs both rainfall and runoff.

Other Project Options:

For all project types, see the Virginia Conservation Assistance Program webpage.