Stormwater management techniques have to be designed specifically for the types of effect that are wanted to be brought about. In general, following measures for management of rainwater are commonly used (Ferguson, 1998):

Use of rainwater / rainwater harvesting : Water harvesting is the direct capturing and use of runoff on-site. This can mean maintaining the water level in permanent ponds and wetlands or supplying water for irrigation and domestic purposes. For this the runoff either is stored and trickles away directly where the plants grow (runoff agriculture) or it is stored in tanks and reservoirs for later use.

Figure 1: Water Harvesting (Source: Ferguson, 1998)

Infiltration of rainwater: Infiltration is the soaking of rainwater into the ground via infiltration basins. Infiltration restores natural hydrologic processes and addresses in addition to flooding and erosion also water quality, groundwater and water supplies. Almost always the water quality is improved by the filtration and transformation processes in the soil.

Figure 2: Infiltration (Source: Ferguson, 1998)

Conveyance : This is the moving of surface runoff from one place to another where it is eventually discharged to streams, lakes or bays. The facilities for conveyances are pipes and channels draining one into another. Please refer to lesson B1 for further information on the collection and conveyance of water.

Figure 3: Conveyance (Source: Ferguson, 1998)

Detention : Detention aims at slowing down the rate of flow of surface runoff. The basic facility is a basin or storage reservoir with an outlet that temporarily stores storm runoff. Storage reservoirs, which delay the passage of water during storm events, reduce the peak flow rate and therefore decrease the risk of downstream flooding and erosion. Nevertheless, the total volume of flow is still allowed to run downstream, stretched out over time. Detention is a quantitative modification of conveyance. On its own it is inherently unable to address water quality, groundwater replenishment or water supplies. When water is stored in properly designed ponds and wetlands, suspended particles can settle out and the rainwater can be "treated". This is commonly called extended detention.

Figure 4: Detention (Source: Ferguson, 1998)

In this lesson the focus is on stormwater management techniques that are adapted to the natural hydrological cycle and that way help reduce the risk of flooding and erosion and improve the water availability. Therefore, stormwater infiltration (see section 3.2) as well as water harvesting techniques (See section 3.3) are illustrated in more detail.