In urban areas, rapid runoff during rain storms and spring thaw can result in flooding, erosion and the degradation of water quality as it carries debris and pollutants washed from impermeable surfaces of roofs and roads. Stormwater ponds are designed to collect stormwater during rain storms and spring thaw so contaminants settle as sediment, preventing them from reaching streams, rivers and lakes. Retention ponds store stormwater indefinitely and have no outlet. The water dissipates through infiltration, evaporation and transpiration. Detention ponds are more common in the Fox Cities. They store stormwater temporarily and have an outlet to discharge the water at a manageable rate to minimize flooding.
|City||Number of Ponds||First Pond||2014 Budget|
*Includes $7 million carried forward from 2013 for underground storage tanks at Appleton East High School.
Source: Municipal public works directors
Appleton owns and maintains 289 miles of storm sewers and 63 stormwater facilities: 39 wet ponds, seven dry ponds, 11 channels, four biofilters and two underground storage tanks. The city is removing 38 percent of the suspended solids and 28 percent of the phosphorus. Appleton’s goal for the removal of suspended solids in the Lower Fox River watersheds is 72 percent, but the city is removing only 29 percent from the downstream section and 18 percent from the upstream section, largely through street sweeping. Appleton spent $11.8 million on stormwater construction projects this year. The city also spends $250,000 annually for maintenance of stormwater ponds including management of the prairie grasses planted around the ponds, cleaning inlet and outlet grates, controlling pests like muskrats, and limiting algae growth through the use of aerators or chemicals.
Eventually stormwater ponds, by design, will become filled with sediment and will need to be dredged. Cities initially paid for stormwater projects through property taxes, but later established stormwater utilities to pay for the improvements through user fees, based on the area of impervious surface located on properties. A typical homeowner pays $155 a year.
Ponds may appear to be a cost-effective means of complying with state and federal water-quality standards because they are successful in removing impurities from the water, but once the water is treated the water often does not have a beneficial use. Greater use of Green Infrastructure (GI) and Low Impact Development (LID) that protects, restores, or enhances natural hydrolic conditions (soil absorption and infiltration, tree canopy capture, and vegetation capture) can play an important role.
Building codes that require rooftop drain be connected to storm sewers limit the use of stormwater harvesting practices (rooftop drains to rain barrels or planter boxes) or or infiltration practices (rooftop drains to rain gardens or infiltration swales). Additional green infrastructure (GI) like biofilters, permeable pavement and grass ditches also can play an important role.