Retention Ponds

Retention ponds have become increasingly common in jurisdictions requiring that storm water be contained and made use of on-site, as opposed to being directed off-site via a storm water system. The ponds are designed to maintain a certain level of water, as shown in Figures 14.25-A and 14.25-B. Additional water-holding capacity is provided based on assumed storm water events. The canal-like basin shown in Figures 14.25-A was designed to allow the upper area of the basin to serve some purpose such as passive, or in some cases active, recreation uses. The upper slopes (14.25-B) are planted to hold the soil and to serve as a surface for passive uses such as picnicking or field sports. In the case of Figures 14.25-A, the upper slopes provide wildlife habitat and serve nature study purposes, while the area in Figures 14.25-B provides for valuable park and recreation uses, serving adjacent residential neighborhoods.

The example in Figure 14.26 of a retention basin and surrounding grassy slopes was designed to serve a diverse range of active and passive park uses for surrounding neighborhoods. A sandy beach was

Figure 14.25-a Retention pond with upper slopes supporting native plants in a residential neighborhood in Voorhof, the Netherlands Figure 14.25-B Retention canal located in a more dense residential neighborhood in Voorhof, the Netherlands

created for sunbathing and access for wading. The steep slopes forming a basin were designed as a visual amenity while providing excess-water-holding capacity in the event of heavy rains.

The slopes of the retention basin at Sud Park in Rotterdam, shown in Figure 14.26, were planted in grass, most likely to reinforce the parklike nature of the area in what is a dense, highly populated mixed cultural residential area. In the examples in Figures 14.27-A and 14.27-B, the edges are treated to provide biodiversity, to support wildlife as well as to improve water quality. In both examples the narrow greenways serve as a visual buffer between two adjoining residential areas that line the waterways. Even though both situations are located in dense residential areas, one can enjoy walking along the greenways surrounded by vegetation, with minor visual intrusion of the adjacent townhouses or office complex.

Figure 14.27-a Greenway with retention canal in Voorhof, the Netherlands Figure 14.26 Retention lake in Sud Park, Rotterdam, the Netherlands

Figure 14.27-B Narrow retention canal with diverse planting to filter water and stabilize steep side slopes adjacent to road and parking lot in Voorhof, the Netherlands