Abstract. Sediment delivery into water sources and bodies results in the reduction of water quantity and quality, increasing costs of water purification whilst reducing the available water for various other uses. The paper gives an analysis of sedimentation in one of Zimbabwe's seven rivers, the Mazowe Catchment, and its impact on water quality. The Revised Universal Soil Loss Equation (RUSLE) model was used to compute soil lost from the catchment as a result of soil erosion. The model was used in conjunction with GIS remotely sensed data and limited ground observations. The estimated annual soil loss in the catchment indicates soil loss ranging from 0 to 65 t ha yr−1. Bathymetric survey at Chimhanda Dam showed that the capacity of the dam had reduced by 39 % as a result of sedimentation and the annual sediment deposition into Chimhanda Dam was estimated to be 330 t with a specific yield of 226 t km−2 yr−1. Relationship between selected water quality parameters, TSS, DO, NO3, pH, TDS, turbidity and sediment yield for selected water sampling points and Chimhanda Dam was analyzed. It was established that there is a strong positive relationship between the sediment yield and the water quality parameters. Sediment yield showed high positive correlation with turbidity (0.63) and TDS (0.64). Water quality data from Chimhanda treatment plant water works revealed that the quality of water is deteriorating as a result of increase in sediment accumulation in the dam. The study concluded that sedimentation can affect the water quality of water sources.
PurposeThe purpose of this paper is to communicate and share experiences with stakeholders on how the sustainability threats and challenges associated with managing Lake Kariba and the Kariba Dam wall are being managed by the Zambezi River Authority (ZRA).Design/methodology/approachThe case study area is Lake Kariba and Kariba Dam wall located in the mid‐Zambezi river basin. The data and information for the case study is from ZRAs own records.FindingsThe case study concludes that the threats and challenges so far experienced have been mitigated adequately with management programmes and tools having been put in place. However, a lot still needs to be done to improve the socio‐economic living conditions of the displaced Tonga/Korekore people.Originality/valueLake Kariba was created in the late 1950s to provide water primarily for hydro‐power production. However, this water resource now serves many users and has its sustainability threats; invasive weeds, water pollution, cyclic drought and flood events, the competing uses and multiple legislative provisions. The Kariba Dam wall, as an engineering structure, has its own sustainability challenges; effects of alkaline aggregate reaction, the spillway plunge pool stability and the general ageing of the dam structure. The Tonga/Korekore people, who were displaced on both banks of the Zambezi River when Kariba Dam was built, still feel short‐changed. Stakeholders will be able to associate and relate to similar threats, challenges and experiences and use the management solutions being applied at Kariba. The opinions and conclusions drawn in this case study are those of the author.
PurposeThere has been a general promotion of small and medium sized dams as the solution to supply water for domestic, sanitation and other livelihood purposes in the less industrialised countries of the world. This paper aims to communicate and share ideas and experiences with policy makers and other engineering practitioners in issues related to the sedimentation of, and the development of small and medium sized dams so that relevant issues are taken into account in the planning, design and implementation of such small and medium sized dams.Design/methodology/approachThis paper, which is a viewpoint, utilises the findings of various research work carried out in Zimbabwe and findings from other regional and international literature as a basis for discussion and arriving at some engineering and other developmental policy recommendations. The research work utilised and analysed in this paper is based on actual field work carried out by others as cited.FindingsThe paper concludes that the following policy and technical issues should always be borne in mind in the promotion of small and medium sized dams: the predicted increase in rainfall intensities due to climate change/variability requires the review of existing small and medium sized dam spillway capacity designs; an increase in the minimum storage ratios of small and medium sized dams should be made from the current recommended 0.1‐0.3; further research work is required to validate the postulation that rainfall intensities are increasing due to the effects of climate change/variability resulting in increased sedimentation of reservoirs; whilst sediments are required for ecosystem sustenance, they can also be viewed as a pollutant in respect of certain other human water supply needs; do not build small dams on large catchments as such small dams will silt‐up quickly and thereafter pose challenges in the management and disposal of the accumulated sediments and nutrients when decommissioning/rehabilitating them; every dam site, irrespective of the resultant dam size, should be developed to its maximum potential in respect of the dam site's water yield and/or prevailing topography; WHO predicts that road traffic injuries will rise to become the fifth leading cause of death by 2030. The “vulnerable road users” and/or their estates should also receive like attention and timely compensation benefits as advocated for the large dam's “disadvantaged and vulnerable” people.Originality/valueEvery year, about 1 per cent of the world's reservoir capacities are lost to sedimentation. Most researchers postulate that an increase in the intensity of rainfall due to climate change/variability is imminent and will result in increased sediment loads with resultant negative impacts on dam reservoir life‐spans and usefulness. This paper discusses the advantages, disadvantages and efficiency of small and medium sized dams in satisfying the various beneficiary needs in the less industrialised countries of the world. The technical issues that have to be considered in the design and con...
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