Abstract
In many parts of South Africa, soil erosion rates are high, and likely
to be exacerbated by the longer droughts and more intense rainfall that
are predicted in long-term regional climate change scenarios. Suspended
sediment loads (SSL) and yields (SSY) are accepted means of expressing
and comparing sediment transport and soil erosion rates. Land care and
water security initiatives in South Africa require these data to provide
benchmarking, and trajectories of change. International researchers
began in the 1970s to investigate SSL estimation approaches. These
investigations typically used near-continuous turbidity data from
installed probes as a surrogate for sampled SS, and auto-samplers to
monitor SS concentration and develop sediment rating curves. Biophysical
and socio-economic conditions in South Africa differ markedly from the
northern hemisphere environments where foundational studies were
conducted. SSL estimations in South Africa are associated with extreme
hydrological regimes, remote study areas and lack the resources required
to collect and analyse representative SS data. There is a dearth of
measured SS data, and of observed SSL and SSY for South African
catchments. Using measured SS data from the Tsitsa River catchment
(Eastern Cape, South Africa) we found that a discharge-weighted
interpolation estimator was more appropriate than regression estimators,
and that SSY responses to biophysical factors were in some ways more
similar to northern hemisphere norms than expected. Lack of technical,
infrastructural, human and financial resources were our main constraints
to monitoring and estimating SSY. Our findings highlight the challenges
of, and provide some guidance for, estimating directly measured SSL in
the southern Africa region and inform future research in resource scarce
areas.