Green Infrastructure

Stormwater green infrastructure reduces and treats runoff before it reaches creeks, streams and lakes. This is particularly important during the first few inches of rainfall (typically, the first 1.37 inches in Lenexa), known as the first flush. The first flush creates runoff with a concentrated pollutant load because pollutants have built up on surfaces during the dry period since the last rain event.  

Green infrastructure mimics natural systems and promotes stormwater runoff to be absorbed into the ground. This reduces need for gray infrastructure, saving money in maintenance and replacement costs. It also provides wildlife habitat, areas for recreation and green space.  

Stormwater best management practices 

Stormwater Best Management Practices (BMPs) are an effective, flexible and environmentally sound way to control the volume and quality of stormwater that leaves a developed site. They protect downstream water bodies by using landscaping techniques and native plantings while improving aesthetics and adding amenities to a wide variety of developed projects. 

  • Stormwater BMP manual: We adopted this manual, created by the Mid-America Regional Council and the American Public Works Association, to provide guidance to developers using BMPs in Lenexa. 

Green infrastructure examples

bioretention cellExtended Detention WetlandExtended Dry Detention BasinExtended Wet Detention BasinNative Preservation AreaNative Vegetation SwalePervious PavementProprietary Stormwater Treatment UnitRain Garden

Bioretention Cell

Extended Detention Wetland

Extended Dry Detention Basin

Extended Wet Detention Basin

Native Preservation Area

Native Vegetation Swale

Pervious Pavement

Proprietary Stormwater Treatment Unit

Rain Garden

Bioretention Cell

A bioretention cell uses native vegetation and a carefully engineered soil mixture to filter, uptake and infiltrate stormwater by natural processes. After filtering through the engineered soil matrix, stormwater that is not absorbed by the plants or passed through to the native soil below is collected by an underdrain system that will discharge into a nearby storm sewer.

Extended detention wetland

An extended detention wetland has a permanent pool that is approximately 18 inches deep. As stormwater runoff flows through the area, pollutants are removed through settling and biological activities. Extended detention wetlands are among the most effective stormwater BMPs for pollutant removal and are often aesthetically pleasing.

Extended dry detention basin

Extended dry detention basins are designed to detain stormwater runoff for approximately 40 hours, but they do not maintain a permanent pool of water between rain events. They are often times built early in the site development process and used to capture sediment from construction activities within the basin drainage area.

Extended wet detention basin

An extended wet detention basin is commonly known as a detention pond and has a water depth of typically 6 to 12 feet. They detain stormwater runoff above a pond’s typical water level for up to 40 hours after a storm and maintain a permanent pool of water between rain events. Extended wet detention basins are often times built early in the site development process and are also used to capture sediment from construction activities within the basin drainage area.

Native preservation area

A native preservation area minimizes site disturbance and maintains natural conditions through retaining, restoring and conserving the existing soils, plants and water found there before development. Impervious areas are minimized, and native vegetation slows surface runoff, filters out sediment and pollutants and aids with infiltration.

Native vegetation swale

Native vegetation swales are broad, shallow channels with dense native plants covering the sides and bottom. The runoff is directed into these swales, and the native plants promote infiltration and reduce water flow velocity while pretreating the stormwater.

Pervious pavement

Pervious pavement has more air space than traditional pavement, which allows stormwater to move through the surface into a reservoir base of crushed aggregate and then into the ground via infiltration. This helps improve water quality by controlling stormwater at the source and reducing runoff. Pervious pavement comes in the form of concrete, asphalt, paving stones and plastic-based pavers, among others.

Proprietary stormwater treatment unit

Proprietary stormwater treatment remove pollutants by directing the stormwater flow through a filter media. These units are available from a variety of manufacturers and can be designed to address most of the common pollutants associated with stormwater runoff.

Rain Gardens

A rain garden is a shallow depression planted with a diverse variety of native wetland and prairie vegetation. Using native plants with deep root systems in a rain garden helps absorb water and filter pollutants.