Sand Dam

Sand Dams are an excellent method for capturing seasonal rainfall and protecting it from evaporation and contamination at a local scale. With examples of this technology being found as early as 9,000 BC, it is nearly as old as agriculture itself, and exquisitely simple.  By building a barrier in seasonal rivers with sand beds, sediment is trapped when rains feed seasonal streams and rivers. Pore space between aggregate particles holds water that is stopped by the dam.  Only 1-3% of water flowing downstream will be retained by the dam, but 25-40% of the total volume of the dam will be filled with water.  This water remains long after the rains have stopped and raises the water table in the immediate vicinity of the dam.  By extending seasonal availably of water, vegetation in the surrounding area increases, which in turn retains water in the soil and slows ground water movement.  Increased moisture content and vegetation contribute to an increase in organic soil content and improve soil fertility in degraded areas. Minor irrigation, livestock and drinking water supply can all be supported with responsible management.  

This method has been used extensively in Kenya and is being deployed in many other parts of Africa where climate change and unsustainable management practices have left agricultural land desiccated and barren.  The potential for this technology to improve soil quality in drylands is not limited to Africa although perhaps the heightened sensitivity of some African ecosystems and their cultural components have spurred the first wave of a sand dam revolution.  Drylands with seasonal watercourses containing sandy beds and shallow bedrock exist all over the globe.  As climate change continues to affect seasonal weather patterns, more sand dams will likely be built as seasonal rains in some areas decrease, or as soil degradation causes decreased in soil moisture and organic content resulting in poor crop production and general vegetative cover.  

While this approach to soil restoration and ground water retention has many positives, it must be noted that the construction of a sand dam is no small task.  In the rural farming communities where this technology is most beneficial, funding for infrastructure is often extremely limited.  Communities must therefore be well organized to provide labor and posses knowledge of surveying and construction techniques to ensure the longevity of the dam; even then, if materials are not readily available, they may prove to be prohibitively expensive.  The process of constructing a sand dam takes a years, growing deeper with each season as an additional layer of sand are deposited, increasing the volume of the sand dam reservoir. 

This technology relies on the persistence of some seasonal rain, it is therefore not likely to help improve the soils in places where land degradation from drought is worst.  However, where seasonal storm severity has increased as well as reduced precipitation in the dry season, this may be an excellent way to improve the resilience of soils through increased perennial vegetative cover.  The multitude of benefits that result from that type of change are the sort that the regeneration of degraded soils offer only if accompanied by responsible land use.