Effects of sedimentation on water-linked sectors in the Lusitu river catchment in southern Zambia.
The problem of sedimentation and drying-up of rivers is very pronounced globally, continentally, and nationally. In Southern Zambia and, Lusitu River Catchment in particular, sedimentation and eventual drying up of the river during most parts of the year punctuated diverse environmental and socioeconomic problems, which this study investigated to contribute to the ongoing epistemic debates around the problem. Lusitu River supports a large population of over 20,000 Gwembe Tonga People who were relocated into Lusitu Catchment in 1958, following the construction of Kariba Dam. The overall aim of the study was to assess how sedimentation affected water-linked sectors in the Lusitu River Catchment to formulate strategies for mitigation of negative effects. The objectives of the study were to: (i) investigate main drivers of sedimentation in the Lusitu River; (ii) determine the magnitude of sedimentation in the downstream section of the Lusitu River; (iii) to assess how sedimentation of Lusitu River affected water-linked sectors and (iv) to design an integrated restorative framework for the Lusitu River Catchment. The study was informed by analytic eclecticism paradigm and used mixed methodology, particularly concurrent design so that where applicable, both quantitative and qualitative data were collected. Data on objective one was collected using observation and semistructured interviews and was analysed using descriptive statistics namely, mean, standard deviation, coefficient of variation and thematic analysis. Data on objective two was collected using sediment coring method and was analysed using Inverse Distance Weighted (IDW) in ArcGIS10.4. Data on objective three was collected using semi-structured interviews and was analysed using thematic analysis. Data on objective four was gathered using Focus Group Discussions and was analysed using thematic analysis. The results showed that agricultural activities particularly, dry season crop field preparation prior to the onset of rainfall and intensive soil tillage farming practices were the major drivers of sediment. Sand mining was the least contributor. Geomorphic factors driving sedimentation of Lusitu River were gully erosion, loose soils (Leptosols), unstable riverbanks and weak sedimentary rock formations. There was large-scale siltation in the downstream section which measured 2,863,913.78m3 with mean sediment depth of 3.13m. Due to heavy sedimentation, the downstream of the Lusitu River was found to have lost 68.34% of its channel storage capacity. The intensity of riverbank gardening varied in relation to Lusitu River flow regime. The drying up of the Lusitu River led to water shortage for crop irrigation and livestock watering, but improved supply of drinking water. Small-scale crop farmers and livestock farmers experienced serious water shortage, with the former being the most hit. Time taken to draw water for domestic use increased in relation to the drying up of the river. The study found that local people adapted to water shortage by digging wells on the dry riverbed which were complimented by small sandy reservoirs dug by the local authority on the same for livestock watering. The study proposed river restoration framework, which constitutes nature-based solutions, engineering, conservation agriculture strategies, indigenous knowledge, and sediment business development model, among others. The study concluded that both soil erosion processes such as gully erosion, and upstream anthropogenic activities such as crop cultivation were the main drivers of sedimentation in the Lusitu River Catchment. Water shortage due to severe river sedimentation reduced income from crop farmers. It also reduced the number of livestock farmers reared thereby, perpetuating rural poverty. The study designed an integrated catchment restoration framework for Lusitu River Catchment to restore the river to perennial status, halt and reverse land degradation. The study recommends piloting of the framework for subsequent full-scale implementation.
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