Water Detention Swale

The examples shown in Figures 14.28-A and 14.28-B present the range of landscape and slope design treatment of two drainage canal and water retention systems. The canal example 14.28-A is concrete lined, primarily treated with a hard, smooth surface to allow a swift flushing of the canal and reduce maintenance (area A). The upper slopes are planted with grass, allowing for informal recreation use (area B). The grass is easy to maintain but provides little in the way of visual variety or biodiversity. The canal example in Figure 14.28-B serves similar storm water conveyance and park functions but is more of an amenity, given the lush and diverse plantings. The canal in 14.28-B was designed to retain water at a prescribed level year-round, whereas the canal in 14.28-A is allowed to dry out during low-rainfall months.

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Figure 14.28-a Drainage canal also provides valuable park and greenway functions in Shreveport, Louisiana Figure 14.28-B Retention canal and greenway in Voorhof, the Netherlands

Water detention Swale

Water detention ponds or swales can serve to slow down storm water and store it for later use, or function as a site design feature. In the examples shown in Figures 14.29-A, 14.29-B, and 14.30, a wide drainage swale was created in two parks, allowing for the detention of extreme storm water during heavy rains. Both were designed to accommodate a large quantity of water with a minimum slope that would slow the water, to let it penetrate into the soil, and would eventually become dry, allowing

for informal park uses. A rock trail, seen in Figures 14.29-A and B, provides passage across the swale during low-water events and C connects to a paved walking trail on the higher ground. A narrower B and deeper swale could have been constructed, providing for a similar flood capacity, but that would A limit the use of the area for recreation, at the same time creating a physical and visual barrier that Figure 14.29-a Stepping stone would unnecessarily divide the trail traversing drainage retention park. A bridge would be required swale, Rotterdam’s Sud Park for passage across the deeper and narrower swale, potentially a more costly solution. In cases where open space is limited, the narrower swale would be an appropriate solution. An example of the bridge and swale solution is shown in Figure 14.30. Figure 14.31 provides an example where a bridge (A) solution was designed over a narrow and deep canal (B) to accommodate a tight space. The bridge in this example is a less visually integrated approach, but with straightforward functional advantages.

C B A B Figure 14.29-B Stepping stone trail traversing drainage retention swale connecting to upper asphalt paved walkway, Rotterdam’s Sud Park

Figure 14.30 Manzanaras Park, Madrid, designed by West 8 landscape architects

West 8 lAndsCApe ArChiteCts, MAdrid, spAin

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Figure 14.31 Pedestrian bridge over canal solution, Delft, the Netherlands

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Figures 14.32-a and 14.32-B An example of water retention and storage for later use to irrigate urban gardens. Item A is for water retention, and B is a flower and vegetable garden. Amersfoort, the Netherlands.

Figure 14.33 A dry stream channel in Almere, the Netherlands The extensive urban garden shown in photographs in Figures 14.32-A and 14.32-B serves a second and important purpose as a water retention strategy. The gardens are primarily planted with seasonal flowers, herbs, and vegetables. The canal in the same picture adds interest as only a water feature can in a dense urban setting. The area, which is essentially a large basin or vessel, has been designed with a capacity for detaining water during heavy storms. Eventually the water is absorbed in the soil or evaporates. Some of the water stored in the concrete canal is used to supplement irrigation of adjacent planting. Item A in figure 14.32-B is the same canal as in Figure 14.32-A. The area marked B shows the variety of plants including perennials and herbs to add visual interest at the same time can detain water overflow from the canal during heavy rains. A dry stream was created in the dense urban commercial area shown in Figure 14.33. When not containing water, the dry streambed can serve a variety of creative functions such as a skateboarding park or a site for programmed uses and events hosted by the city or merchants.