Towards a universal optimization of the performance of sand storage dams in arid and semi-arid areas by systematically minimizing vulnerability to siltation: A case study in Makueni, Kenya

Abstract

Sand storage dams are hydraulic retention structures that increase the volume of coarse sediments in seasonal sandy streams by exclusively blocking the bedload transport during runoff events. However, siltation of fine grain particles, which are transported as part of the suspended load, is a major factor causing sand storage dams to perform poorly. Therefore, this study aimed to evaluate the hydrological performance and cost-efficiency of 30 sand storage dams. This study also aimed to increase the understanding of critical factors which may affect the performance and lead to siltation of sand storage reservoirs. The analysis was based on a physical survey of 30 sand storage dams that were built in onestage in southeastern Kenya. Most of the study sites had the capacity to produce sand. However, the reservoirs suffered from severe siltation, which caused generalized low annual yields, reduced supply capacities, and low cost-efficiency. It is argued that the main factors for the poor performance were the high inter-and intra-annual variability of bedload transport, which coupled with the construction of onestage spillways, led to siltation of the reservoirs. Thus, large volumes of fine grain particles accumulated in the reservoirs during runoff events with bedload layer heights lower than the height of the one-stage spillways. To systematically maximize the robustness to the inherent variability of bedload transport, and ensure optimal performance levels by systematically minimizing siltation, spillways should be built in stages of reduced height. Thus, the lower the stage height, the higher the probability of maximizing the accumulation of coarse sediment. It is estimated that a multi-stage construction process with stage heights of 20 cm would have produced a performance 26 times higher. This implies that the 30 reservoirs would have had the capacity to supply 8516 people as compared to the current supply capacity of 330 people. Improvements in the performance of sand storage dams can greatly assist attempts to link this technology with income-generating activities for agropastoralists in arid and semi-arid areas.

Investigating the environmental response to water harvesting structures: a field study in Tanzania

“…To make this distinction, further studies are needed to compare macroinvertebrate assemblages in undammed sandy streambeds with those in sand dams. Of all substrates studied, Duan et al (2008) identified sandy substrate as having the lowest taxa richness and as being the least suitable for macroinvertebrates and benthic fauna, causing sandy substrates to be fairly homogeneous. Sandy substrate also has small interstice dimensions that provide only very small living spaces for macroinvertebrates (Duan et al, 2008).…”

“…Of all substrates studied, Duan et al (2008) identified sandy substrate as having the lowest taxa richness and as being the least suitable for macroinvertebrates and benthic fauna, causing sandy substrates to be fairly homogeneous. Sandy substrate also has small interstice dimensions that provide only very small living spaces for macroinvertebrates (Duan et al, 2008). Homogeneous bed material suggests that there are few, or no, structures available for macroinvertebrates to use as refugia during high streamflow (Taniguchi and Tokeshi, 2004) and few niches for different species to utilize during various stages of their life cycle (Salant et al, 2012).…”

“…Holes drilled in the bucket's lid were plugged with cotton to prevent transfer of macroinvertebrates into or out of the sample (Stubbington et al, 2009). The samples were transported to the research base and rehydrated with de-chlorinated water to encourage re-emergence of desiccation-tolerant life stages (Boulton et al, 1992;Stubbington et al, 2009). For a 28 d period, the samples were checked daily for macroinvertebrates.…”

“…This has been the case with sand dams in sub-Saharan Africa. Sub-Saharan Africa is home to over 3000 sand dams, yet approximately 50 % of the sand dams are essentially non-functioning (de Trincheria et al, 2018;Viducich, 2015).…”

“…Other studies used modelling to further explore the seepage of sand dam water through streambanks (Hut et al, 2008) and the potential of sand dams to increase water security in Ethiopia (Lasage et al, 2015). The socioeconomic benefits of sand dams have also been explored (Lasage et al, 2008) along with the negative effects of sand dam siltation and/or seepage due to poor construction and or siting (Nissen-Petersen, 2006;de Trincheria et al, 2015;Viducich, 2015). Except for the Borst and de Haas (2006) study and the Quinn et al (2018bQuinn et al ( , 2019) studies on highfunctioning sand dams, most published sand dam studies are based on survey data or modelling efforts.…”