4.1 The Need for Artificial Recharge – Setting the Scene
Namibia is the most arid country south of the Sahara, with scarce, unpredictable rainfall and perennial rivers only on its borders. Many Namibian settlements are situated in the coastal area of the arid Namib Desert (e.g., Walvis Bay, Swakopmund and Henties Bay) and depend on groundwater stored in the coastal aquifers of the ephemeral Kuiseb, Swakop and Omaruru Rivers that originate more than 300 km inland at altitudes near 2,000 m and rarely flow to the ocean. Table 3 summarizes salient features of the Omaruru Delta system.
Table 3 – Omaruru Delta (OmDel) Scheme.
| Name of scheme | Omaruru Delta (OmDel) Scheme |
| Location | West coast area of Namibia |
| Mean annual rainfall | < 50 mm/year |
| Source of water | Regulated flood water |
| Type of aquifer | Alluvial aquifer |
| End use of water | Domestic and mining use |
| Type of managed aquifer recharge | Infiltration ponds |
| Current average volume of water recharged | 7.9 Mm3/year |
| Volume of water recovered | 4.6 Mm3/year |
| Year commenced | 1991-1995 |
| Owner/management of scheme | Namibia Water Corporation (NamWater) |
| Unique attributes of this MAR scheme | Storage and slow release of flood waters to significantly increase recharge of downstream alluvial aquifer |
In the mid-1970s, the rapidly growing water demand associated with these coastal settlements and a large uranium mine increased to 8.4 Mm3/year. This is 15 to 20 percent more than the mean annual exploitable recharge of the three aquifers combined. The situation had been further exacerbated by a series of very dry years (Water Scarcity Solutions, 2015). In the existing wellfield in the delta aquifer of the Omaruru River (an area with less than 50 mm/year precipitation extending 35 km inland up to the Namib Plain) abstraction had become almost twice the safe yield and groundwater levels had dropped tens of meters (Zeelie, 2004).
To reverse the negative trend, a research project was initiated in 1988 with the aim of investigating whether the sustainable yield of the aquifer could be increased by artificial recharge. The Omdel scheme was subsequently constructed during the period from 1991 to 1995. It consists of a dam with a storage capacity of 41 Mm3 and a series of infiltration basins in the riverbed 6 km downstream, where the present river channel crosses deep paleo river channels (Zeelie, 2004; Murray, 2009; Christelis, 2019).