March-April 2011

How One County Health District Deals With Mosquitoes in the Urban Infrastructure

Water found in the urban infrastructure engineered to handle stormwater and nuisance water has been exploited by the adult female mosquito. To combat mosquito breeding and viruses caused by mosquitoes, the Washoe County (Nevada) Health District Vector-Borne Diseases Prevention Program has developed regulations along with designs that have given us the authority to review new residential, commercial, and industrial development and redevelopment projects. This program minimizes the mosquitoes in the public infrastructure. As the project moves through the public review process for approval, building plans are forwarded to our program (Denise Cona) to ensure the design detail meets our program approval. The proactive approach of working with the Community Development Departments of Washoe County and with the cities of Reno and Sparks, NV, allows us to require designs in detention basins, retention basins, channels, landscape improvements, ponds, wetlands, and catch basins to reduce the impact of these insects. Instead of reacting to the buildout of infrastructure through pesticide use, as many vector control districts do, our approach is to collaboratively work with planners and civil engineers through better design, based on our regulations, to minimize the nuisance and public health risks associated with adult female mosquitoes.

Over the past eight years, the Vector-Borne Diseases Prevention Program of Washoe County Health District has required a low-flow channel design in detention, retention basins, and channels, which allows for the channelization of stormwater and nuisance water runoff without reducing the capacities of these facilities to handle large storm events. We are also a strong proponent of low-impact development (LID) design, such as bioswales, rain gardens, and other features that capture and infiltrate runoff, reducing the runoff that enters the hard infrastructure system. In new landscape design, we have developed LID designs to reduce water runoff from impervious surfaces due to overwatering of lawns in common areas and residential lots.

Ponds constructed in our urban environment provide an aesthetic feature and habitat for midges. Midges are mosquito look-alikes that do not bite, although they are a nuisance to residents. The Vector-Borne Diseases Prevention Program has no pesticide material to combat this insect. As a result, when ponds are constructed, we require a fountain aerator placed in the pond that is operated daily for two hours in the morning and evening from April though October. We also require cobble rock placed 2 feet below and 2 feet above the mean water line. This reduces mosquito habitat such as weed growth from occurring on the shoreline and helps reduce the burrowing of rodents. 

In addition, we developed a wetland model design using meandering low-flow channels and forebays, which captures sediment as well as debris and trash from entering the wetlands through urban outfall pipes, and a plant list with native vegetation associated with our high-desert environment. Our experience in wetlands has led us to the conclusion than if a monoculture environment, such as Hoary cress (white top) or cattails, is allowed to exist unchecked, it creates an environment conducive to mosquito breeding and at the same time outcompetes other desirable plant species. 

For the past two years, the Vector-Borne Diseases Prevention Program has collaboratively been working with Washoe County engineers such as Norm Lindeman, and engineer with the Washoe County Department of Public Works, to design as well as retrofit catch basins to improve water-quality benefits and at the same time prevent the colonization of adult female mosquitoes. The design used involves impervious pavers with a Xeripave tray placed above the sump but below the grate to capture floatable materials such as debris, trash, and large sediment from entering the storm drain system. This design improves water quality while preventing the adult female from depositing her eggs in the sump, which ponds water.

Today, vector control agencies throughout the Untied States rely heavily on chemical control methods to combat mosquito problems in the urban as well as agricultural environments. The “prevention through design” approach the Washoe County Health District Vector-Borne Diseases Prevention Program has taken has removed our reliance on the use of pesticides for insect control and allowed us to become proactive through the community development planning process. As a result of this collaborative approach, “non-vector-friendly” urban infrastructures have been designed in new development and redevelopment projects in Washoe County.

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