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Vrije Universiteit Amsterdam (2007)

A study to up-scaling of the principle and sediment (transport) processes behind, sand storage dams, Kitui District, Kenya

Gijsbertsen Cedrick

Titre : A study to up-scaling of the principle and sediment (transport) processes behind, sand storage dams, Kitui District, Kenya

Auteur : Gijsbertsen Cedrick

Université de soutenance : Vrije Universiteit

Grade : Master thesis Hydrogeology 2007

The current study is the second component of the “Recharge Techniques and Water Conservation in East Africa – Up-scaling and Dissemination of the good practices with the Kitui sand storage dams” project. This project of the Acacia Institute and SASOL aims at using the experiences of the sand storage dams in Kitui to up-scale the construction of sand storage dams to other regions. Former research gave more insight in the hydrological processes around the sand storage dams. However, some questions remained unanswered. This second study (in combination with Hoogmoed and Jansen) is to provide an answer for the processes that remained unclear from the former research. This report describes a methodology for up-scaling of the sand storage dam principle combined with sedimentation processes in the surroundings of sand storage dams. The Kitui District is one of the arid and semi-arid lands (ASAL) of Kenya. For drinking water local people rely on the water supplied from riverbeds from ephemeral rivers. Local NGO SASOL builds sand storage dams in the Kitui District. A sand storage dam is a dam in the riverbed, funded on an impermeable layer, behind which sand accumulates. When groundwater is recharged, water is stored below the newly accumulated sand, reducing evaporative losses and health risks. Because the sand behind the dam has accumulated a larger aquifer is created from which water can be obtained. This extra ground water buffer can be used to bridge the dry periods. In October – December 2006 a fieldwork has been carried out in the Kitui District. Several catchment areas in the Kitui District, with both functioning and non-functioning sand storage dams, were visited. From each catchment site specific characteristics were observed and noted and from the surrounding area samples of the surface sediments were taken. These different conditions were compared to obtain criteria needed for good functioning of sand storage dams. In combination with available literature it appeared that sand availability in the riverbeds is one of the crucial components needed for the functioning of sand storage dams. Vegetation present in the riverbeds indicates that the sediments are less favourable in storing and subtracting water and therefore less favourable for the construction of sand storage dams. In the Kiindu catcment a sand storage dam was selected for measurements. The dam was modified for more accurate discharge measurements. Near the dam supended load and bedload measurements were combined with discharge measurements. For both beldoad and suspended load a discharge-sediment load a relation was obtained. In the Kiindu catchment the distribution of surface sediments was measured using sediment samples throughout the catchment area. All sediment samples, including bedload and suspended load, have been analysed on particle size.

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Page publiée le 23 mars 2015, mise à jour le 13 octobre 2018