Measuring and modeling hydrological processes of sand-storage dams on different spatial scales

Sand-storage dams are a successful water harvesting technology in Kenya and a promising solution to ensure water and food security in other semi-arid regions. Assessing the suitability of sand-storage dams for other semi-arid regions requires both a good understanding of the hydrological factors for success of a single dam and the regional effects of a network of dams. Results from a measurement campaign on hydrological processes in the surroundings of a single dam in the Kitui District in Kenya indicated that groundwater levels increase quickly after precipitation. Recession of groundwater levels during the dry season following the rains was more gradual. Based on these results, a groundwater model for a single sand-storage storage dam was developed. As the river banks are important recharge areas for the groundwater stored upstream of the dam, the model showed high sensitivity for parameters like thickness and hydraulic conductivity of the shallow aquifer on the riverbanks and thickness of the sand layer in the riverbed. Parallel to the single dam model, a model for a series of dams was developed. This second model indicated that the inter-darn distance is an important parameter. The distance between dams determined whether influence areas did overlap or that dams behaved as individual structures. When the influence areas did overlap, stored water volume per dam decreased. The results from measurements and modeling confirm that sand-storage darns can effectively increase water availability throughout the dry season. Since measurements and models explain how sand-storage dams successfully modify hydrological systems in semi-arid Kenya, the results can assist in planning introduction of the technology in other regions. (C) 2008 Elsevier Ltd. All rights reserved.