Inferring mean rates of sediment yield and catchment erosion from reservoir siltation in the Kruger National Park, South Africa: An uncertainty assessment

摘要

Reservoir siltation surveys facilitate the quantification of the mean area-specific sediment yield (SSY) of catchments for decadal and longer time spans. This requires information on the volume (V-S) and dry bulk density (dBD) of reservoir deposits, the period of time (T-R) during which they were accumulated, the reservoir sediment trap efficiency (TE) and the catchment area (A). For the calculation of the catchment-wide average rate of erosion by water (E), the sediment delivery ratio (SDR) of the catchment needs to be estimated. Each step in this workflow represents a potential source of uncertainty. Here, we explore the extent to which individual error sources contribute to uncertainties in SSY and E values. Mean SSY and E values are inferred for small to medium-sized catchments (= 100 km(2)) of 15 small (= 350 x 10(3 )m(3)) intermittently dry reservoirs located in the southern Kruger National Park and observation periods of 30 to 65 yr. Mean relative uncertainties of resulting SSY and E values amount to +/- 21% and +/- 46% at the 95% confidence level, respectively. Uncertainties in SSY values arise mainly from the TE estimation (mean fractional uncertainty contribution of 64%), while the SDR estimation is the major cause (79%) for uncertain E values. Uncertainties in the determination of V(S )and dBD values are rather unimportant, contributing together 30% and 6% to the uncertainty of SSY and E values on average, respectively. Conclusions are drawn regarding reasonable surveying and sampling strategies. (C) 2018 The Authors. Published by Elsevier B.V.