4.11 Water-spreading weir, Ethiopia

to store and retain shallow groundwater is highly relevant in arid regions and improves water access and availability. Chapter 9 provides a detailed description of the use of road drifts and similar approaches. a closely related technique is to use water-spreading weirs combined with river road crossings. These structures have been developed with considerable success in several Sahelian countries, including niger (photo 4.11). Waterspreading weirs route temporary floods out of dry riverbeds to inundate surrounding areas. The water-spreading weir serves as the main river crossing; roads connecting to the weir or river crossing further spread the floodwater. In this way, the combination of the river crossing with embanked roads leading to it acts as a large flood spreader (figure 4.6). drop structures and cross drainage are added to the water-spreading weirs to ensure their stability. arid and semiarid environments are thus regreened with forest and grass species (GIZ and KfW 2013). embankments without safety barriers (and without a water body below the slope) should have trafficable slopes to allow for an errant vehicle leaving the carriageway. embankment side slopes should not be steeper than two units horizontal to one unit vertical.

PHOTO 4.11

Water-spreading weir, Ethiopia

Source: © GIZ-SDR Project (Heinz Bender). Used with the permission of GIZ-SDR Project. Further permission required for reuse.