Measurement of river bank and cliff erosion from sequential LIDAR and historical aerial photography

The methodology and errors involved in determining the meander migration rates and amount of sediment produced by river bank and cliff erosion over five decades along a 16- and 28-km reach of the Waipaoa River, New Zealand, are described. The reach average meander migration rates (0.22 and 0.12 m a–1, respectively) are low by international standards for rivers of comparable size, suggesting considerable stability of the river planform. The contribution of sediment from bank and cliff erosion (74.3 and 23.3 kt a–1, respectively) to suspended sediment load is also low (< 2%) because this river has a high specific load dominated by mass movement erosion sources in tributary watersheds. Cliff erosion is the dominant process accounting for 69–88% of sediment delivered from channel side processes. The average channel migration rates due to cliff erosion are broadly comparable with long-term rates of valley widening over the past 18 ka BP, suggesting there has been no appreciable change in rates of cliff erosion over this time. Bank and cliff erosion processes were likely relatively more important as a source of sediment before widespread land-use conversions from native forest cover to grasslands.