Available Practices for LID

There are a range of different LID practices to deal with the increased volume and velocity of runoff waters from roofs, driveways, roads and other paved surfaces.  Scroll down for a short discussion of the following practices, or click on the title to be linked to a related extension fact sheet.

Riparian Corridors and Floodplains
Swales and Berms
Rain Gardens
Porous pavements
Rainwater harvesting: cisterns and rain barrels
Retention ponds
LID neighborhoods

Riparian Corridors and Floodplains

A flat area immediately adjacent to a stream and river channel is probably a floodplain. The trees that typically live in the floodplain are considered the riparian corridor.  Typically these areas are used for farming or left to native vegetation. When stream channels overflow, floodplains are inundated allowing floodwaters to slow down, drop their suspended sediment load.  When the water slows down, it can be infiltrated or absorbed into the soil and used by the riparian vegetation.  The water moving through the soil or groundwater reserves will have a slower release to the stream channel. 

When we fail to understand the benefits of flooding and restrict the floodwaters by constructing levees, roadways and other structures, undesirable changes occur in stream and river channels.  The increased runoff from urbanized areas typically exceeds the capacity of the downstream stream channel and floodplains. The extra energy from the water will deepen stream channel beds, and eventually widen the channel, and these changes often threaten adjacent land and structures including bridges.

Swales and Berms

Swales are slightly excavated areas which collect runoff. Berms are slightly elevated areas which channel runoff into swales. These are low cost, low maintenance approaches to improving runoff. Grass can be used as the only plant thereby allowing easy access for regular mowing. A clever landscaper can make use of the wetter than typical conditions in swales and the drier than usual conditions on top of berms to support plants that will do well under those moisture conditions.

Rain Gardens

If an attractive landscape element is desired which also collects, filters and allow some runoff to infiltrate the soil, then consider rain gardens. These are especially desirable to help with runoff from large roofs and parking areas.

The need for maintenance should be anticipated as plant material builds up over the years just as it does with any landscape planting. As plant root masses grow and surface leaf litter layers accumulate, infiltration may become restricted. Periodic removal of plants and replanting is typically needed.

Porous pavements

In areas where attractive pavements are desired and the extra cost is affordable, porous surfaces or special pavers which are set in sand instead of concrete can be used. Both types of porous surface must be underlain by a thick layer of gravel with a network of drainage pipes.  Entire surfaces can be paved with porous materials or just select areas to provide a visual impact.  Slightly concave surface drainageways, known as runnels, can be constructed in the same fashion so as to allow infiltration.

Rainwater harvesting: cisterns and rain barrels

In arid parts of the world, roof tops and other impervious surfaces have long been used to capture and divert rainfall into storage tanks usually known as cisterns. Such captured water can be used without treatment for many purposes. 

Rain barrels are a low cost, low tech way to capture rooftop runoff for minor uses like small vegetable gardens. It only takes ¼ of an inch of runoff from an average sized roof to fill a 55 gallon rain barrel. The modern rain barrel may look very much like the old fashioned rain barrel, but there are some important differences such as first flush diverters and mosquito exclusion screens.

Retention ponds

If you live in a neighborhood built after the late - 1980’s, chances are excellent that there is a pond nearby.  Just follow the slope downhill and you’ll find it. Oftentimes these ponds and their immediate surroundings are used for recreational purposes, but their true primary purpose is to capture runoff and release it slowly so as to lessen downstream flooding problems.  Unfortunately, some ponds may create thermal, biological, or erosional problems downstream.

LID neighborhoods

Although LID practices can be implemented on a home by home basis, neighborhood-wide applications are more desirable. LID neighborhoods use some or all of the practices discussed above to slow runoff waters so as to allow soil infiltration, evaporation and plant uptake. The expected intensity of rainfall (Figure 14), soil characteristics, slopes and other factors must be evaluated by engineers in designing LID practices tailored to work properly on a site. Beauty and environmental benefit make for added appeal for many homebuyers.

Mosquito control using chemicals is not desirable. Instead, LID measures should be designed to hold water for less than the time needed for mosquito larvae to hatch.

Authors:
Marley Beem, Department of Natural Resource Ecology and Management
Sharla Lovern, Department of Biosystems and Agricultural Engineering