2.5 Traditional Water Conservation Techniques
Traditional water conservation techniques have been practiced in dry areas under a wide range of ecological conditions over millennia. Besides domestic water use, early populations used water mainly for small-scale agriculture involving raising crops, or livestock, or a mixture of the two. Minimization of runoff losses (in combination with increased infiltration) and the collection and concentration of rainfall (including storage) are the most important approaches for making better use of scanty rainfall in dry regions. Typical approaches included small pits with worked soil and stone lines across fields for in-situ moisture conservation (Mali, Burkina Faso), runoff harvesting in excavated shallow natural depressions (Namibia, Angola) and wells dug in the sands of dry riverbeds (Kenya, Namibia) as documented by Postel (1992) and Braune (2007).
Runoff harvesting, for example via excavation dams and pump-storage dams (Figure 4), was systematically introduced by the government in central-northern Namibia (former Ovamboland) during the 1950s and 1960s. Effectiveness was increased by building a fully enclosed dam, several meters high, around the depression with the excavated material. Water is pumped into these pump-storage dams (capacity between 23,000 and 105,000 m³) during the short flooding period of the Cuvelai River in Namibia. To prevent evaporation of this very expensive water, the surface of the dam was often covered with floating material (Stengel, 1963). A German cooperative research project, from 2006 to 2015, aimed to bolster the region’s water resources. The project combined new and adapted technologies (rainwater harvesting; small-scale, decentralized groundwater desalination; subsurface water storage; as well as sanitation and water reuse) in a multi-resource mix for water supply and sanitation (CuveWaters, 2015).
Figure 4 – Satellite image of Onandjokwe pump-storage dam in Northern Namibia (Drießen and Jokisch, 2011).
The practice of water storage in sandy river beds in Namibia has a long history. It was advanced from the beginning of the 20th century by the then German colonial administration and again from the 1950s onwards by the South West Africa Administration. The key proponent was Otto Wipplinger, director of the Department of Water Affairs in the former South West Africa. His study of various types of sand storage dams, “The Storage of Water in Sand”, focused on the artificial creation of sand basins by building low walls in river basins (Wipplinger, 1953). The innovation was to build a wall just high enough to break the flow of the water and allow the deposition of coarse sediments, while the very fine material (clay) passes over the wall with the flood. Once the basin fills up, the wall is raised and the process of building the sand dam carries on (Figure 5). A sand basin can take from 10 to 20 years to reach full capacity and can be synchronized with a rising demand for water. Such dams are now widely used in Namibia, especially by the farming community, but also for large-scale use. The key benefit is that water stored in the sand is largely protected from evaporation, which can be up to 2000 mm/year from an open water surface in the area. It is also a major conservation measure through which groundwater levels and groundwater quality have been restored to their original levels (Lau and Stern, 1990).
Figure 5 – Sand-storage dam built in stages (Sauermann, 1966).
Various small-scale groundwater damming techniques have also been developed and applied in many other parts of the world, notably in Southern and East Africa, and in India (Nilsson, 1988). The first Kenyan dams were built in the 1950s. There was a significant increase in the number of sand dams built in Kenya between 1980 and 2010, driven predominantly by the work of the Utooni Development Project (UDO) and Sahelian Solution (SASOL). In the early 2020s, approximately 150 dams were built each year, of which 100 are in Kenya. Sand dams have also recently been introduced into Mozambique, Ethiopia and Sudan (Excellent, 2012).
The Namibia experience showed that the small-scale appropriate technologies and their various improvements are generally not known to the farmers, nor the agricultural agencies whose forte is crop production, nor the water agencies whose main focus is bulk water supply. The particular focus and international leadership of the former South West Africa in small-scale water supply options throughout the 1950s and 1960s came about through the initiative of a small number of highly knowledgeable and dedicated individuals in the right place at the right time (Stengel, 1963). Under their successors, in a period of renewed focus on bulk water supply (mines and larger towns), the small-scale approaches and technologies were virtually forgotten within a period of 20 years (Lau and Stern, 1990).