Steepland erosion measured from historical aerial photographs

A method is presented for quantifying erosion in mountainous catchments. Historical aerial photographs were used to measure elevation changes on all potential areas of erosion and deposition within a catchment. Total catchment erosion volume and the ensuing sediment supply rate were then calculated. The upper basin of the Waipawa River. Ruahine Range, New Zealand, is used as a case study area to demonstrate the method. There, the average annual specific sediment yield was 7,200 (± 2.000) m3/km2/year. The accuracies of measured elevations from common aerial survey scales are of the order of ± 1 m. Thus, the method can be applied successfully only in mountainous catchments that include areas prone to high erosion rates.