Abstract
Sand dams, a water-harvesting structure employed by rural communities in drylands have an inconsistent record of effectiveness. While many sand dams are highly functioning, improper siting, siltation, seepage, and high rates of evaporation from shallow sand reservoirs inhibit the water storage capacity of some sand dams. This study examines large-scale drivers of sand dam storage potential through analysis of an integrated surface and subsurface flow model. Multiple simulations were run, and comparative simulation analyses consider the effect of geomorphological factors, intraseasonal rainfall variability, and future climate conditions on sand dam performance criteria. The analyses revealed that a watershed highly cultivated with low water crops actually reduces evapotranspiration below that of natural vegetation and supports higher groundwater recharge. Additionally, intraseasonal variation and volume of rainfall impact sand dam performance less than the prevailing pattern and duration of dry and rainy seasons. Sand dams constructed in watersheds with sandier soils may experience greater connectivity with the stream margins and thus provide additional groundwater recharge. Lastly, climate change may improve some conditions desirable for sand dam performance, such as extending the duration of the rainy season and reducing overall evapotranspiration. However, the interactions between the expected climate change conditions and other geomorphological factors may result in a net decline in sand dam performance. The results of this study may help identify watersheds that are likely to support a sand dam with high potential for capturing and storing water throughout the dry season.
Highlights
Billions of dollars are invested into international development projects in Africa every year (Rhode and Stitteneder, 2020), and yet many donor-funded projects fail—up to 64% by some estimates (Hekala, 2012; Mikovicet al., 2020)
Many challenging circumstances contribute to the high failure rate (Ika, 2012), but improved design procedure and decision-making may avert problems related to geographical mismatch in international development projects (Youker, 2003)
Water that remains in the vadose zone after ET requirements are met, is percolated to the groundwater as recharge at a rate based on the moisture content, suction head, and depth of the vadose zone (Streamline Technologies, 2018; Saksena et al, 2019)
Summary
Billions of dollars are invested into international development projects in Africa every year (Rhode and Stitteneder, 2020), and yet many donor-funded projects fail—up to 64% by some estimates (Hekala, 2012; Mikovicet al., 2020). Many challenging circumstances contribute to the high failure rate (Ika, 2012), but improved design procedure and decision-making may avert problems related to geographical mismatch in international development projects (Youker, 2003). A water-harvesting technology, offer an excellent example of an international development initiative. The sand reservoir fills with water during subsequent high-intensity rains and flash floods (Borst and de Haas, 2006; Hut et al, 2008). Rural communities draw water from the sand dam for domestic and agricultural use (Lasage et al, 2008; Eisma and Merwade, 2020). Sand dams are essentially a type of artificial perched aquifer (Lasage et al, 2008) that may occasionally become connected to groundwater via leakage from the sand reservoir or lateral seepage into the sand reservoir (Quinn et al, 2019)
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