From: The Dark Side of Stormwater Runoff Management: Disease Vectors Associated With Structural BMPs
Designing and Building a Better BMP
Times are changing rapidly in the field of vector prevention and control. The number of pesticides available for mosquito control are dwindling fast, and biological-control agents (e.g., mosquito fish) often have limited application. Neither approach generally provides a long-term solution. The best solution to minimizing vector production is through prevention, by "engineering them out" of structural devices and enforcing proper and regular maintenance. The following criteria should be considered in the design of all structural BMPs to reduce the probability of mosquito breeding and allow for routine vector surveillance (or abatement if necessary) and maintenance.
Dry Systems
1. Structures should be designed such that they do not hold standing water for more than 72 hours to prevent mosquito development. Provisions to prevent or reduce the possibility of clogged discharge orifices (e.g., debris screens) should be incorporated into the design. The use of weep holes is not recommended due to rapid clogging.
2. The hydraulic grade line of each site should be a primary factor in determining the appropriate BMP that will allow water to flow by gravity through the structure. Pumps are not recommended because they are subject to failure and often require sumps that hold water. Structures that do not require pumping should be favored over those that have this requirement.
3. Designs should avoid the use of loose riprap or concrete depressions that can hold standing water.
4. Distribution piping and containment basins should be designed with adequate slopes to drain fully and prevent standing water. The design slope should take into consideration buildup of sediment between maintenance periods.
5. The use of barriers or diversions that results in standing water should be avoided.
Systems With Sumps or Basins
1. Structures designed with sumps or basins that retain water permanently or longer than 72 hours (e.g., CDS, Delaware-type sand media filters) should be sealed completely to prevent entry of adult mosquitoes. Adult female mosquitoes can use openings as small as 1/16 in. to access water for egg laying. Screening can be used to exclude mosquitoes but is subject to damage and is not a method of choice.
2. Structures should be designed with the appropriate pumping, piping, valves, or other necessary equipment to allow for easy dewatering of the unit if necessary.
3. If the sump or basin is completely sealed, with the exception of the inlet and outlet, the inlet and outlet should be fully submerged to reduce the available surface area of water for mosquitoes to lay eggs (female mosquitoes can fly through pipes).
Permanent Ponds
1. Permanent ponds should maintain water quality sufficient to support surface-feeding fish such as mosquito fish (Gambusia affinis), which feed on mosquito larvae.
2. Permanent pond shorelines should be accessible to both maintenance and vector-control crews for (1) periodic maintenance and/or control of emergent and pond-edge vegetation and (2) routine monitoring of mosquito immatures and abatement procedures if necessary. Emergent plant density should be controlled so that mosquito predators are not inhibited or excluded from pond edges (i.e., fish should be able to swim between plant bases).
3. If possible, permanent ponds should be maintained with depths in excess of 4 ft. to preclude invasive emergent vegetation such as cattails. Emergent vegetation provides mosquito larvae with refuge from predators and increases nutrient availability. The pond edges below the water surface should be as steep as practicable and uniform to discourage dense plant growth and reduce favorable mosquito habitat.
4. Concrete or liners should be used in areas where vegetation is not necessary to prevent unwanted plant growth.
5. Permanent ponds should be designed to allow for easy dewatering of the basin when needed.
General-Access Requirements
1. All BMP structures should be easily and safely accessible, without the need for special requirements (e.g., Occupational Safety & Health Administration requirements for "confined space"). This will allow vector-control personnel to effectively monitor and, if necessary, abate vectors.
2. If covers are used, the design should include spring-loaded or lightweight access hatches that can be opened easily. Covers should seal completely.
3. All-weather road access (with provisions for turning a full-size work vehicle) should be provided along at least one side of large aboveground BMPs that are less than 7 m wide. BMPs that have shoreline-to-shoreline distances in excess of 7 m should have a perimeter road for access to both sides. (Mosquito larvicides are applied with handheld equipment at small sites and with backpack or truck-mounted high-pressure sprayers at large sites. The effective swath width of most backpack or truck-mounted larvicide sprayers is approximately 7 m on a windless day.)
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4. Access roads should be built as close to the shoreline as possible. It is important to not have vegetation or other obstacles between the access road and the BMP that might obstruct the path of larvicides to the water.
5. Vegetation should be controlled (removal, thinning, or mowing) periodically to prevent access barriers.
March-April 2002
From: The Dark Side of Stormwater Runoff Management: Disease Vectors Associated With Structural BMPs
Designing and Building a Better BMP
Times are changing rapidly in the field of vector prevention and control. The number of pesticides available for mosquito control are dwindling fast, and biological-control agents (e.g., mosquito fish) often have limited application. Neither approach generally provides a long-term solution. The best solution to minimizing vector production is through prevention, by "engineering them out" of structural devices and enforcing proper and regular maintenance. The following criteria should be considered in the design of all structural BMPs to reduce the probability of mosquito breeding and allow for routine vector surveillance (or abatement if necessary) and maintenance.Dry Systems
1. Structures should be designed such that they do not hold standing water for more than 72 hours to prevent mosquito development. Provisions to prevent or reduce the possibility of clogged discharge orifices (e.g., debris screens) should be incorporated into the design. The use of weep holes is not recommended due to rapid clogging.
2. The hydraulic grade line of each site should be a primary factor in determining the appropriate BMP that will allow water to flow by gravity through the structure. Pumps are not recommended because they are subject to failure and often require sumps that hold water. Structures that do not require pumping should be favored over those that have this requirement.
3. Designs should avoid the use of loose riprap or concrete depressions that can hold standing water.
4. Distribution piping and containment basins should be designed with adequate slopes to drain fully and prevent standing water. The design slope should take into consideration buildup of sediment between maintenance periods.
5. The use of barriers or diversions that results in standing water should be avoided.
Systems With Sumps or Basins
1. Structures designed with sumps or basins that retain water permanently or longer than 72 hours (e.g., CDS, Delaware-type sand media filters) should be sealed completely to prevent entry of adult mosquitoes. Adult female mosquitoes can use openings as small as 1/16 in. to access water for egg laying. Screening can be used to exclude mosquitoes but is subject to damage and is not a method of choice.
2. Structures should be designed with the appropriate pumping, piping, valves, or other necessary equipment to allow for easy dewatering of the unit if necessary.
3. If the sump or basin is completely sealed, with the exception of the inlet and outlet, the inlet and outlet should be fully submerged to reduce the available surface area of water for mosquitoes to lay eggs (female mosquitoes can fly through pipes).
Permanent Ponds
1. Permanent ponds should maintain water quality sufficient to support surface-feeding fish such as mosquito fish (Gambusia affinis), which feed on mosquito larvae.
2. Permanent pond shorelines should be accessible to both maintenance and vector-control crews for (1) periodic maintenance and/or control of emergent and pond-edge vegetation and (2) routine monitoring of mosquito immatures and abatement procedures if necessary. Emergent plant density should be controlled so that mosquito predators are not inhibited or excluded from pond edges (i.e., fish should be able to swim between plant bases).
3. If possible, permanent ponds should be maintained with depths in excess of 4 ft. to preclude invasive emergent vegetation such as cattails. Emergent vegetation provides mosquito larvae with refuge from predators and increases nutrient availability. The pond edges below the water surface should be as steep as practicable and uniform to discourage dense plant growth and reduce favorable mosquito habitat.
4. Concrete or liners should be used in areas where vegetation is not necessary to prevent unwanted plant growth.
5. Permanent ponds should be designed to allow for easy dewatering of the basin when needed.
General-Access Requirements
1. All BMP structures should be easily and safely accessible, without the need for special requirements (e.g., Occupational Safety & Health Administration requirements for "confined space"). This will allow vector-control personnel to effectively monitor and, if necessary, abate vectors.
2. If covers are used, the design should include spring-loaded or lightweight access hatches that can be opened easily. Covers should seal completely.
3. All-weather road access (with provisions for turning a full-size work vehicle) should be provided along at least one side of large aboveground BMPs that are less than 7 m wide. BMPs that have shoreline-to-shoreline distances in excess of 7 m should have a perimeter road for access to both sides. (Mosquito larvicides are applied with handheld equipment at small sites and with backpack or truck-mounted high-pressure sprayers at large sites. The effective swath width of most backpack or truck-mounted larvicide sprayers is approximately 7 m on a windless day.)
4. Access roads should be built as close to the shoreline as possible. It is important to not have vegetation or other obstacles between the access road and the BMP that might obstruct the path of larvicides to the water.
5. Vegetation should be controlled (removal, thinning, or mowing) periodically to prevent access barriers.