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BMP's for Developers

Johnson County requires developers to follow the Best Management Practices of the APWA/MARC BMP Manual (henceforth APWA/MARC).

This means that:

The basic goal for all developments is to maintain predevelopment peak flows, runoff volumes, and water quality. In other words, development should maintain the velocity and quantity of runoff and the amount of pollutants leaving the
site, unless the effects are fully considered and documented in the design or unless site conditions apply that require
more stringent measures. (APWA/MARC p. ES-1)

In addition to the APWA/MARC BMP Manual, guidance for countywide ordinances can be found on the JoCo Stormwater Management Program website for municipalities, and specific guidance is also given for unincorporated parts of
the county. Specific local ordinances, cost sharing, and other programs have been developed for the following municipalities:

De Soto
Leawood
Lenexa
Mission
Olathe
Overland Park
Prairie Village
Shawnee


Here we provide a brief overview of some of the more common BMP's that are used in JoCo to achieve these goals. You can also take a virtual tour of BMP's in Johnson County and of the Green Infrastructure in Lenexa.


BMP's for housing and retail developments

Pervious Pavements

Definition- Pervious Pavement: A type of pavement that allows water to infiltrate the surface layer and enter into a high-void, aggregate, sub-base layer. The captured water is stored in the sub-base layer until it either infiltrates the underlying soil strata or is routed through an underdrain system to a conventional stormwater conveyance system. (APWA/MARC p. 2-2)




Pervious pavements are an example of structural BMP's that reduce runoff at the source. There are many different kinds, including interlocking pavers that allow infiltration in spaces filled with pea gravel between the pavers; lattice work with vegetation; and concrete and asphalt that are made to allow water to seep through the surface. In all cases the pavement is underlain with several porous strata that can hold the water while it slowly moves out of the system. you can visit a demonstration project at the Coon Creek Trailhead in Lenexa and you can watch video demonstrations by clicking here.

Bioretention Basins

Definition- Bioretention: Small engineered and landscaped basins intended to provide water quality management by filtering stormwater runoff before release into stormdrain systems. (APWA/MARC p. 2-1)

Since commercial developments typically have a much higher proportion of impervious surfaces (large parking lots, "big box store" roofs, etc.) compared to housing developments, there is even more of a need to build structural BMP's into retail and business developments to manage runoff.

Bioretention basins are an example of a common structural BMP for commercial developments. They are ideal for use in median strips, parking lot islands, and landscaped swales, and are best distributed throughout the development to treat runoff as close to the source as possible. Bioretention basins are designed as vegetated depressions for the collection and treatment of runoff from areas of approximately 2.5 to 5 acres. The "treatment" component consist of an engineered matrix of soils and plant roots, which means that they not only retain water during a storm event, they also help to clean the runoff. This is done in two ways; through infiltration into the soil, where chemical and microbial processes filter nutrients and pollutants out of the water, and by rooted plants that are tolerant of high soil moisture, which reduce the volume of water through uptake by the roots, while removing nutrients and some pollutants. There are a couple of components used to regulate the volume of the water going into and out of the system; water velocity is first slowed and the volume of water is distributed throughout the bioretention basin, then the water is retained so that it can infiltrate into the soil and be taken up by plants, and finally water passing through the system is released either to surrounding soils, or is collected by an underdrain system that discharges to a sewer system or a water body. There is also typically an overflow to handle excessive runoff events. (APWA/MARC p. 8-14)

Effective bioretention cells typically are fairly small, taking up an area equal to about 5% of the total impervious surface of the development. They are easily designed and planned as part of the site’s required open space. In practice, these units are maintained in the same manner as decorative landscaping, which helps to minimize maintenance costs and increase value-added benefits. Implementing this one standardized practice in all developments can minimize design, inspection, and maintenance costs. (APWA/MARC p. 5-2)

Bioswales

Definition- Swale: A swale is a depressed area used for stormwater conveyance and/or short term storage (think of it as a modified ditch). The fact that runoff is conveyed through the system rather than being retained within it is what distinguishes a swale from a retention basin or rain garden.

There are several knds of swales used for stormwater runoff management. A Bioswale is an open vegetated channel with an engineered soil matrix and underdrain system designed to filter the runoff (see photo on left). A Native Vegetation Swale consists of Native grasses and forbes planted in a swale to reduce the velocity of the runoff and promote infiltration. A Turf Grass Swale is designed to convey stormwater planted with turf grass and are meant to be used as a substitute for closed drainage systems. Finally, a Wetland Swale is an open vegetated channel without underdrains or a soil matrix designed to filter runoff and remain wet between rain events. (APWA/MARC p. 2-3)

The main idea is that rather than routing stormwater runoff into a concrete channel or directly into a curb gutter system, you can use a channel that is designed to reduce the volume of water and pretreat the water to remove nutrients, sediment, and some pollutants. Bioswales are broad and shallow, with dense vegetation on the side slopes and channel bottom, and include an engineered soil matrix and an underdrain system. Because of their shape and the fact that they are vegetated, runoff is slowly conveyed down their length, promoting infiltration, reducing flow velocities, and pretreating the stormwater. You should make sure you select grass and plant species that tolerate low maintenance since minimizing the use of pesticides, fertilizers and herbicides is important in reducing pollution from runoff. (APWA/MARC p. 8-73)

Rain Gardens

Definition- Rain Garden: A small depression planted with native wetland and prairie vegetation, rather than a turfgrass lawn, where runoff collects and infiltrates. (APWA/MARC p. 2-3)

Rain Gardens are typically used for small areas (less than an acre), and are a good BMP to use for single family homes. They can help manage outflow from downspouts, or runoff from turfgrass lawns, patios, and driveways. Like Bioretention Basins and Bioswales, they are considered structural BMP's used for source control. Rain Gardens consist of a depression to retain the runoff, a deep layer of soil with good infiltration properties, and deep rooting plants that are tolerant of periodic high soil moisture. Rain Gardens can significantly reduce excess nutrients and sediment in runoff, and if they are sufficient in number they can be an important component of reducing runoff in a watershed. Normally the home owner will maintain Rain Gardens on their property. When they are first installed (the one on the left is newly planted), they should be weeded weekly; mulch can help reduce growth of unwanted plants until the garden is established. Don't use fertilizer in the Rain Garden, and avoid using fertilizer and lawn chemicals near the Rain Garden. After the plants are well established, you should leave the dead vegetation standing over winter to provide good bird habitat, but then remove the dead vegetation each spring by mowing or burning (if allowed). (APWA/MARC pp. 8-1 to 8-4)  You can visit the FOK Rain Garden at the De Soto Riverfest Park boat ramp. Click here for a video demonstration of Rain Gardens and Bioswales


Vegetated Wetlands

Definition- Extended Detention Wetland: A land area that is permanently wet or periodically flooded by surface or groundwater, and has developed hydric soil properties that support vegetation growth under saturated soil conditions. It may have been engineered with adequate capacity to detain large storm flows. (APWA/MARC p. 2-1)


A distinction must be made between using a constructed wetland for stormwater management and diverting stormwater into a natural wetland; natural wetlands and streams are protected by the Clean Water Act and activities that alter or fill them are regulated by state and federal agencies (for an overview go to the KDHE website). Natural wetlands should be protected because they are important for reducing flooding and improving water quality, as well as providing crucial habitat for many species of plants and animals. Constructed wetlands, in contrast, are used for receiving and pretreating stormwater runoff from developments.

An Extended Detention Wetland is a constructed basin that has a permanent pool of water throughout the growing season. Runoff is detained for a 40-hour period. They are relatively shallow (approximately 18 inches maximum depth) and are heavily vegetated. Both the rooted plants and microbial processes in the soil remove nutrients and many types of pollutants, resulting in a significant improvement in water quality. Extended Detention Wetlands are among the most effective stormwater practices in terms of pollutant removal, and they also offer aesthetic value, especially for their wildlife habitat. (APWA/MARC p. 8-40)

Riparian Corridors and Stream Buffers

Definition- Riparian Corridor: Strips of herbaceous and woody vegetation located parallel to perennial and intermittent streams and adjacent to open bodies of water. Riparian Buffers capture sediment and other pollutants in surface runoff water before these enter the adjoining surface waterbody.

Definition- Stream Buffer: An area defined by regulatory agencies or municipalities for the protection of riparian corridors and
floodplains. (APWA/MARC p. 2-3)



An undisturbed Riparian Corridor in northeastern Kansas will be heavily vegetated, typically with an under layer of grasses and forbs, an intermediate layer of bushes and young trees, and a mixed forest with trees of different ages and species several trees wide. Riparian Corridors are an integral part of the stream system. They provide shade which lowers water temperature; leaf fall and insects which form an important component of the stream food web; deep roots that hold the soil in place and absorb nutrients and other pollutants; and dense vegetation that slows the overland flow of runoff, allowing suspended sediment to settle out before reaching the stream. Riparian Corridors with native vegetation not only provide many important ecosystem services, they can also provide beautiful locations for recreational trails, as can be seen in Kill Creek Park and Mill Creek Streamway Park

Preserving existing vegetation along streambanks is a non-structural BMP that can be a very cost effective way of reducing both pollution from stormwater runoff and flood hazard to residential and commercial developments. APWA recommends creating community-wide stream buffer systems through the enactment of stream setback ordinances. For example, preserving a 100-foot riparian buffer in a watershed of 5,000 acres (less than 5% of the land in the watershed) can yield disproportionate benefits; not only does it reduce adverse impacts from stormwater runoff, it can also provide significant financial returns to communities by increasing home values through the aesthetic and recreational opportunities that it provides. (APWA/MARC pp. 7-12 to 7-14) You can find the EPA model setback ordinance as well as the ordinances adopted by the City of Lenexa and Overland Park on the MARC website.

Treatment Train

Definition- Treatment Train: The series of BMPs (or other treatments) used to achieve biological and physical treatment efficiencies necessary for removing pollutants from stormwater (or other wastewater flows). (APWA/MARC p. 2-3)

Mize Lake is an example of a complex series of structural BMPs used for managing runoff from a large area. It is a seven-acre lake with three sediment forebays, three wetlands, and two bioretention cells (click here for more information).

Many Treatment Trains combine both structural and non-structural BMP's to increase infiltration and successively treat the water as it passes through the system. Large scale systems like this are used to manage stormwater that is in excess of that which is captured and treated at the source by BMP's like the Bioswales or Bioretention Basins described above. (APWA/MARC 3-4)

The City of Lenexa has developed a Rain to Recreation program that utilizes stormwater management BMP's like Mize Lake and Lake Lenexa as parks and recreational facilities. By preserving Native vegetation, providing Riparian Buffers and other non-structural approaches these BMP Treatment Trains/recreational facilities maintain a natural character that provides both aesthetic value and important wildlife habitat.


Construction Site BMP's

Best Management Practices during construction not only significantly reduce the negative impacts of runoff during the construction phase, they can have long lasting positive effects on post-construction stormwater management. Obvious design elements, like minimizing impervious surfaces, incorporating effective BMP's for source control and pretreatment, and developing watershed-wide management practices are all important, but so is the way in which soil and vegetation are treated during the construction process. Plants that are Native to Kansas typically have deep roots that help stormwater penetrate deeply into the soil, and they are well adapted to the Kansas climate, allowing them to thrive without fertilizer, pesticides or regular watering. Maintaining Native vegetation, especially around waterways, can be a cost effective way to reduce runoff. Soil preservation and restoration measures are also important; compacted soils have poor infiltration capacity (a typical turf lawn with shallow, compacted top soil, shallow roots, and little above ground vegetation does little to slow runoff). In contrast, soils that have developed in areas with Native Kansas vegetation have deep, humus rich layers with excellent infiltration capacity. Wherever possible these soils should be preserved (or at least restored using techniques for saving and replacing the soil). Preserving the soil’s capacity to infiltrate precipitation is a relatively inexpensive non-structural measure that can be implemented as a preservation component of the site design; soil restoration, while potentially more challenging, is another way to improve infiltration. (APWA / MARC 5-39 to 5-40)