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.
