Each municipality should develop a stormwater management plan if it has not already done so. It is recommended that all municipalities adopt a stormwater control ordinance to address both water quality and quantity control.
Ordinances adhere to the requirements of the Natural Resources (NR) codes as well as the MMSD requirements. Municipalities not currently under a WPDES Municipal Stormwater Discharge Permit should begin development of an ordinance in advance of the permit issuance. The NR codes outline the permit requirements as well as the performance standards for stormwater management practices.
Increases in stormwater runoff rates and volume have been shown to have a detrimental effect on stream quality and habitat. While many measures exist to reduce peak flow rates, there are not many practical ways to reduce runoff volumes unless soil conditions permit. With the predominantly clay soils present throughout the Milwaukee River Basin, there is not much chance to reduce runoff volume through infiltration unless it is in small areas like rain gardens. Volume controls such as collecting rooftop runoff in rain barrels or rain gardens help reduce runoff from residential areas but such techniques are often not feasible in commercial or industrial areas where the percentage of impervious surface is high.
Many municipalities in the basin have adopted stormwater ordinances that address the issue of peak flow reduction. The Milwaukee Metropolitan Sewerage District (MMSD) has also implemented peak flow reduction requirements (Chapter 13 Surface Water and Storm Water guidelines) that further limit the allowable peak flow rate from a development within their service area. In addition, many municipalities have been issued a WPDES stormwater discharge permit from the WDNR that requires treatment of stormwater runoff prior to discharge into receiving waters.
The WDNR has created several administrative rules that apply to stormwater management. Administrative Code Chapter NR216 deals with stormwater discharge permits for municipalities as well as from private industry and construction sites. NR216 and the proposed Chapter NR151 of the Wisconsin Administrative Code establishes runoff pollution performance standards for new development, existing urban areas, transportation facilities and agricultural operations.
Quantity Control Requirements -- Back
Because infiltration is typically limited in the basin, detention basins are widely used to achieve required levels of peak flow reduction. To learn more about the infiltration and detention basins follow the link here. In situations where the required reduction is small, it may be possible to oversize the site storm sewer or use a grassed swale system with check dams to temporarily store runoff.
Wet Detention Basins
Devices -- Back
Dry detention basins that are designed to function as infiltration basins have the added benefits of providing some pollutant removal and reducing the volume of stormwater released from the basin.
Pollutants contained in the infiltrated runoff are absorbed by the soil particles and are considered permanently removed from the water. Infiltration basins also provide for some groundwater recharge if the soil conditions permit.
Infiltration trenches and grass swales can also be constructed to infiltrate stormwater. Porous media such as sand and washed gravel are placed in the bottom of the trench or swale. Loosely placed sandy topsoil can also be placed if the trench or swale will become vegetated. The runoff draining to these trenches and swales has the opportunity to infiltrate rather than discharge into waterways. Ditch checks (also referred to as check dams) can also be installed to slow or temporarily store the runoff to allow it to infiltrate.
Gardens -- Back
Visit the WDNR rain garden site.
Structural BMPs -- Back
Some manufacturers claim to also get adequate treatment for large areas through combined use of several large structures installed in series. Treatment is achieved through confining the “first flush” of stormwater to a chamber where suspended solids can settle out of the water. Oil, grease, and other floatables are also trapped in the chamber. Higher flow rates bypass the treatment chamber and are discharged into the downstream storm sewer system as normal. It should be noted that these devices do not provide any reduction in peak flow rates or runoff volume. In-pipe treatment devices require periodic removal of accumulated sediment and floatables by a vacuum truck to maintain specified performance. The frequency of cleaning is dependent on the rate sediment and floatables accumulate.
Sand filters are devices that allow runoff to infiltrate through a deep sand media that filters most pollutants from the runoff. The filters typically have a drain system that conveys the filtered runoff to a storm sewer or drainage swale. In areas where soils have higher infiltration rates, these devices may also reduce runoff volume and further reduce pollutants by allowing runoff to infiltrate beyond the constructed filter. Routine maintenance consists of removing visible sediments and debris accumulated on the filter surface and periodic raking or replacement of the top layer of sand. Long-term use of the sand filter may require complete replacement of the sand media if the accumulated sediment plugs the filter and reduces performance.
Source for text in oval:
Streets and Roads
| Buffers | Detention
and Infiltration Basins | Street Trees
This page was created on March 26, 2003.