Minimum and maximum annual flow (m3 x 106) and concentrations (mg/l) of aluminium, iron, manganese and zinc (input) used in a Monte Carlo analysis (10 000 iterations) to estimate annual metal loads (kg/year) originating from the Klipspruit and Steenkoolspruit rivers. Results are reported as average annual loads and the average, 10th, 50th and 90th percentile ratios of Klipspruit to Steenkoolspruit loads (output).