Surface water harvesting requires runoff producing areas with sufficiently high runoff coefficients and runoff receiving areas, where the water is utilised. The differences between the different harvesting methods lie mainly in the size of the systems.

Figure 9 Examples of micro-catchment water harvesting (contour bench terrace, bunds, Negarim system) (Source: FAO, 1999)

“Rainwater harvestingâ€? is the collection and concentration of rainfall either from roofs and courtyards, from micro-catchments, or from macro-catchments. Water collected from paved, compacted or otherwise treated surfaces like rooftops is mainly used for domestic purposes and livestock watering. “Micro-catchment water harvestingâ€? (see figure 9) stands for the collection of surface runoff from a relatively small catchment area (less than 1000 m²). The water is stored in the root zone of an adjacent infiltration basin, that is planted with a single tree or bush or with annual crops. “Medium-sizedâ€? or “macro-catchment water harvestingâ€? (figure 10) is the collection of water in larger catchment areas (1000 m² – 200 ha), that are located outside the cultivated areas. From there the runoff is conveyed to the cropping areas (Prinz, 1996).

Figure 10: Example of macro-catchment water harvesting (hillside conduit, photo: Klemm)

“Floodwater harvesting� is also referred to as large catchment water harvesting with catchments being many square kilometres in size. It includes the harvesting of water within the streambeds of ephemeral or seasonal rivers (“wadis�) and the diversion of the wadi water. For this dams can be constructed within the riverbed, that block the water flow leading to an inundation of the valley bottom of the flood plain. Thus the water infiltrates and allows the use of the wetted area as cropping zone (See figure 15). “Floodwater diversion� (Figure 11) is the con­struction of dikes or other diversion structures forcing a part of the wadi water to leave its natural course and conveying it to nearby cropping areas. Since “floodwater harvesting systems� include a more complex structure of dams and distribution networks, relatively high technical input is required (Prinz, 1996).

Figure 11: Examples of floodwater diversion (Source: FAO, 1999)