Building a Farm or Amenity Pond
(Conservation Currents, Northern Virginia Soil and Water Conservation District)
Ponds can be constructed for fishing, swimming, landscaping, animal and wildlife watering, or water quality management. The more diverse its intended use, the more complex are the factors to consider for its design and management. Farm/amenity ponds have less stringent standards and conditions governing their design and construction than do typical stormwater management ponds. They can vary considerably in size depending on the owners’ preferences, the purpose for which they are intended, and the available space. It is best to limit the number of expected uses.
Preliminary studies for locating, sizing, and designing the shape of a pond have a lot to do with the landform, soil type, impact on downstream properties vulnerable to water damage in case of dam failure, and the adequacy of water supply or the drainage area for the pond. A pond should be designed to blend well with existing ecological features. For those ponds that are not intended to trap nutrients or other pollutants, the location should not be in the path of runoff pollution.
The two main types of pond structures are excavated (dugout) ponds and embankment ponds (ponds constructed by damming a channel/depression). Excavated ponds generally are found in relatively flat areas with a high groundwater table, while embankment ponds are common in terrain with more defined relief.
The soil type of an area is important in determining the location for a pond during the feasibility studies. Sites with average to high clay content are ideal for ponds because they provide a tight base that reduces water loss, whereas those with sandy soil or shallow depth to bedrock do not. To minimize pond maintenance during the life of the pond, it is best to locate the pond off-line rather than in-line of a stream. Trained staff of the Northern Virginia Soil & Water Conservation District can provide assistance with pond feasibility studies.
Pond planning and design
Based on the physical features and the rainfall intensity of Fairfax County’s geographic region, ponds that depend on surface runoff as their main source of water supply must be sized such that there are at least two to three acres of drainage area for every acre-foot of pond storage. Pond storage capacity is measured in acre-feet. If a pond with a water surface of 1 acre is 6 feet deep at its deepest point, its storage capacity in acre-feet is calculated as 1 x 6 x 0.4 = 2.4 acre-feet (0.4 is a constant value based on the standard shape of pond bottoms). A pond with a small storage capacity is more vulnerable to the impacts of water pollution.
Constructed ponds must have adequate water and depths to sustain water losses due to seepage, evaporation, and lowered groundwater table especially during seasonal drought conditions. In this geographic region the recommended pond depth is 6-7 feet at the deepest area. This depth also guarantees survival of fish during freezing conditions of the winter months.
Call Miss Utility at 1-800-257-7777 to ensure that
there are no underground utility wires, pipes, or cables in the area for
the proposed pond site.
Ponds are best designed so that they can successfully pass a 100-year storm event through their riser and emergency spillway without overtopping the dam.
Request for permission to build a farm/amenity pond may be granted a “By Right” status (i.e., free of all requirements) if the plan meets the following conditions:
- The total area of clearing and disturbance for the purpose of building the pond is 2,500 square feet (232.25 square meters) or less.
- The proposed pond is located outside of a major floodplain, a Resource Protection Area (RPA), or a jurisdictional wetland (the latter being defined by applicable wetland permitting regulations).
- The pond poses little or no risk to life or downstream property, in case of dam failure or flooding.
- The proposed location is in an area with ideal soils and topographic features for constructing a pond.
- There are no proffers (associated with property rezoning) or development conditions (associated with special exceptions, special permits and/or variance) that would affect pond construction.
If any of the above conditions does not hold true, please see Pond Building Requirements.
to see some of the requirements that must be met before building a farm/amenity pond, unless these requirements are waived at the discretion of the appropriate permitting authorities.
After the site for a pond has been identified, the next step is to perform a detailed survey to plan and design the dam, the pond’s storage capacity, the emergency spillway, and the pipe water outlet.
One of the most critical structures of the pond is its dam. A mixture of coarse and finer textured soils makes a good foundation material. This combination of particle sizes provides enough bonding strength to keep the dam stable. Excessive seepage of water through the dam is prevented by proper compaction of the dam material, especially at the point of contact with existing land forms and around the horizontal outlet pipe that goes through the dam.
Important features of a dam are the water outlets that control the flow of water out of the pond. The primary outlet feature is the vertical pipe (riser) connected to a horizontal pipe (barrel) that actually passes through the dam. The primary outlet carries water during normal flows to maintain the pond water elevation. Pipes made of smooth metal, corrugated metal, or polyvinylchloride (PVC) plastic materials may be used.
The other important water outlet feature is the emergency spillway. During flood events this structure carries flood waters so that the water does not overtop the dam and wash it away. This feature can be designed and constructed in one of several ways. The basic criterion is that the structure should be large enough to adequately carry floodwaters. Its elevation must be set higher than the riser and about two feet lower than the top of the dam. If the emergency spillway is in the form of an open channel, a “rule of thumb” is that the bottom width of the spillway channel can be estimated by adding 15 feet to one-half of the total drainage area in acres. For instance, a pond with a 20-acre drainage area should have a spillway with a bottom-width of about 25 feet; one with a 50-acre drainage area should have a spillway with a bottom-width of about 40 feet.
Introduce the correct combination and species of fish to make a balanced pond ecosystem. In the Virginia area, a ratio of 1:1:3:7 of the following species are known to co-habit well: Largemouth Bass : Catfish : Sunfish : Bluegill, respectively. The catfish, sunfish and bluegill are best stocked in August or September. Bass are best stocked a year after the bluegill are stocked. Together, the bluegill and sunfish can be stocked at a rate of 500 per acre and the other species determined accordingly.
If you have questions about pond construction or maintenance, e-mail NVSWCD's Willie Woode or call him at 703-324-1430, TTY 711. For information about E&S permits for pond construction, call the Engineer-of-the-Day at 703-324-1575, TTY 711.
Requirements for Building a Farm/Amenity Pond if any of the conditions identified above are not met.
- Erosion control measures and small area grading permits: Chapter 104 (Erosion and Sediment Control) of the Fairfax County Code requires prior approval of an Erosion and Sediment (E&S) Control Plan before clearing, grading, filling or otherwise disturbing natural terrain on any area greater than 2,500 square feet (232.25 square meters). There is a minimum charge of $400 dollars for reviewing a “rough grading plan” for a potential pond that will be about 1/4 of an acre in size. The bigger the pond, the higher the fee.
- In like manner, section 2-601 of the Zoning Ordinance requires approval of E&S control and grading plans before the removal or addition of soil in excess of 18 inches (457.2mm) in an area exceeding 2,500 square feet (232.25 square meters).
- Article 2, part 7 of the Zoning Ordinance sets forth requirements that apply in common open space areas. Construction of ponds in common open space areas would be subject to the approval of the Department of Public Works and Environmental Services (DPWES)
- Submitted designs for all farm/amenity ponds must meet the minimum geotechnical design standards for structures with small dams classified in the Public Facilities Manual—Plate 64-4, as a “C” reservoir, unless waived by the Director of DPWES during the review and approval process.
- Under the Chesapeake Bay Preservation Ordinance, the Zoning Ordinance, and in the Public Facilities Manual (PFM), such ponds should not be located within a designated Resource Protection Area (RPA), major floodplain, or storm drainage easement. However, under certain conditions the Director of DPWES may permit such pond construction, at the recommendations of the Environmental and Facilities Review Division and Site Permits.
- If runoff from a 70-acre drainage area flows through the pond, a drainage study must be submitted together with grading plan details.
- For ponds that are planned to be located within a jurisdictional wetland or involve damming a continuously flowing stream, additional approval is required from both the Virginia Department of Environmental Quality (a state approval), and the US Army Corps of Engineers (a federal approval). A written waiver must be obtained if these agencies choose to waive this requirement.
- Ponds must be consistent with any proffers or development conditions that apply to the property(ies) in question.
- The Department of Conservation and Recreation must approve all dams of ponds that will store 15 acre-feet of water and are higher than 25 feet, as well as dams that store more than 50 acre-feet and are higher than 6 feet.