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Winter 2005


West Nile virus -- Oregon, Mosquitoes -- Control -- Oregon, West Nile virus -- Oregon -- Statistics, West Nile virus -- Prevention, Urban runoff management -- Oregon, Storm water retention basins -- Oregon -- Evaluation


From the Roman aqueducts to Bonneville Dam, humans have built structures to moderate the extremes of natural water flow. Some of these structures, from Roman cisterns to the catch basins under modern city streets, have inadvertently supplied mosquitoes with the standing water in which they thrive and multiply. Even more mosquito habitat may have been created in the last decade by a change in the Clean Water Act. The original drive behind the Act, in 1972, was the elimination of point-source pollution: sewage and industrial discharge into waterways. In the 1990s new regulations aimed to prevent non-point-source pollution, due to urban stormwater runoff. There are two basic methods of cleaning stormwater: filtering, through earth, vegetation or manufactured filters; and settling, retaining the water behind a barrier to let particulates sink to the bottom. New studies show that water retention methods, such as the familiar catch basin, may breed mosquitoes. Even if retention structures are designed to minimize mosquito habitat by draining quickly, they may clog and accumulate standing water without regular maintenance.


Originally appeared in the Winter 2005 edition of Metroscape, published by the Institute of Portland Metropolitan Studies, Portland State University.

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