The Impact of Dam Construction on Downstream Water Resources: A case of Nandoni Dam in Luvuvhu quaternary catchment A91F, North-Eastern South Africa.

Abstract

Globally, there is increasing concern over the increased damming of rivers, as this has led to a change in the hydrological regime and transformation of river runoff. There are varying impacts of dams on river flow regimes depending on how these dams are operated. Damming of rivers has altered the hydrologic cycle globally, causing severe consequences for streams' ecological and morphological equilibrium. Reservoir use and its impact on flow regimes have not yet been linked in a recognizable way. This study assessed Nandoni Dam water resources in relation to inflow and outflow, and the amount of streamflow required to maintain the ecological integrity. The inflows and outflows in dam were determined using the traditional water balance approach. Streamflow data collected at Mhinga station A9H012 downstream of Nandoni Dam before dam construction was used to calculate environmental flows using the IHA/RVA methodologies. Inflows trends over the study period were found to be on a downward trend. Peaks in computed inflow occur during periods of heavy rainfall as excepted for rainfallrunoff relationships. Abstraction of water from the Nandoni Dam for domestic purposes (i.e., to water treatment plants) increases over the study period despite increases or decreases in dam water storage. The downstream flow of the dam is impacted both positively and negatively, despite quantitative suggestions regarding streamflow required to maintain ecological integrity. A range of environmental flow requirements was presented in this study downstream of the Nandoni dam. Values for selected Environmental Flow Components (EFCs) parameters are presented as percentiles between 10% and 90%. Different durations of analysis show significant variations in minimum and maximum flows. High pulse numbers, as well as the rate at which they rise and fall, have changed significantly. Hydrologic regime downstream was disturbed, and streamflow variations were directly affected by the construction of the dam. It is crucial to build a detailed water budget model that considers climatic, hydrological, and stakeholder interests to optimize dam operation rules. Reservoir operations must be developed with the participation of riparian communities, engineers, hydrologists, physical geographers and climatologists and general environmentalists to be socially, economically, and environmentally sustainable.