Watershed Information Site

Indiana Ordinance

Stormwater Center

Many impermeable surfaces such as streets, driveways, sidewalks, walkways, and roofs are in residential subdivisions. Retention ponds capture diverted stormwater runoff from these surfaces. The ponds provide two primary services. First, they retain the runoff before releasing it into streams. They release the water at flow rates and frequencies similar to those that existed under natural conditions. The flood volume held in a retaining pond reduces the impact on downstream stormwater systems.

The second benefit of the retaining ponds is that they provide pollutant removal through settling and biological uptake.

Retention ponds are ideal partners for residential areas within a watershed, since the pollutant most commonly and successfully removed from stormwater is sediments.

Subdivisions include impermeable surfaces such as streets, driveways, sidewalks, walkways, and roofs. Residential areas are prone to flooding and must deal with stormwater runoff as do large commercial sites such as grocery stores, restaurants, and retail stores. The stormwater systems in subdivisions are just as important as commercial areas. The stormwater systems flush rainwater quickly from streets and gutters and into the nearest waterway (EPA Victoria 2001). Unfortunately, stormwater is not treated and often contains many pollutants including car fuel, oil, and sediments. The use of ponds as BMP’s with stormwater systems in urban areas is becoming more widespread. It is already common to see retention ponds in commercial areas.

Retention ponds capture the diverted stormwater runoff from streets and gutters. These ponds provide two primary services. First, they retain the runoff before releasing it into streams. They release the water at flow rates and frequencies similar to those that existed under natural conditions. The flood volume held in a retaining pond reduces the impact on downstream stormwater systems (England 2001).

The second benefit of the retaining ponds is that they provide pollutant removal through settling and biological uptake (Idaho DEQ 2001). Ponds remove 30-80% of certain pollutants from water before it enters nearby streams. Common pollutants reduced are sediments, bacteria, greases, oils, metals, total suspended solids, phosphorous, nitrogen, and trash (England 2001). Ponds are one of the most effective tools at providing channel protection and pollutant removal in urban streams (www.stormwatercenter.net 2001). Essentially, retention ponds provide water quality and quantity control (EPA 2001).

Two common classifications of retaining ponds are either “wet” or “dry.” Wet ponds, known as retention ponds, continually have a pool of water in them called dead storage. Dry ponds, detention ponds, do not have dead storage and dry out between storms (EPA 2001). Retention ponds are more effective than dry ponds. The permanent pool of water found in the wet ponds is more efficient at removing particle pollutants. It does this by absorbing energy from inflow of the stormwater as it enters the pond, preventing scour material from settling to the bottom, and exchanging new incoming stormwater with previously captured water. This provides extra time between storms for pollution to settle (Idaho DEQ 2001). Aquatic vegetation is often associated with wet ponds. Vegetation such as grasses and plants are able to establish themselves in the permanent pool of wet ponds thus providing extra pollutant removal. The aquatic plants and grasses serve as an extra filter in the pond. They assimilate dissolved pollutants and, by biological uptake, transform pollutants into less toxic materials. Microorganisms often establish themselves in wet ponds and aid in the breakdown of pollutants (EPA 2001).

Turbidity, pH, and total hardness are tested at the retention ponds. Water samples are collected at the inflow area and outflow area of each pond. A LaMotte 2020 Turbidimeter tests water samples to determine turbidity.

A water quality test kit is used to chemically test pH and total hardness. Research results show a substantial decrease in turbidity between the inflow water and outflow water of the retention ponds.

There are ongoing activities within a residential setting. Common activities are things such as clearing lots, building houses and additions, landscaping, and the installation of swimming pools. These activities may appear minimal when compared to commercial building, but the same idea of impact should be considered. These activities increase the possibility of sediments and other pollutants entering nearby streams. Residential areas also pose an added threat to the stormwater system and nearby stream with common activities such as fertilizing and watering lawns, washing cars, and painting houses. The ongoing activities within a residential area provide diverse challenges for a retention pond.