jbo@nve.no

Abstract The impact of erosion protection works on downstream sediment delivery was evaluated in a study of the River Gråelva in central Norway. Channel degradation and the associated undercutting of adjacent slopes have formerly uncovered pockets of quick clay and triggered major quick clay slides. To prevent further slides the river bed and banks have been reinforced with a layer of rock armouring. The stabilization work started in 1992. When conditions were still close to natural in 1992 and 1993, maximum sediment concentrations were in the range of 15 000–25 000 mg l^-1 and the calculated annual suspended sediment transport was 163 000 and 99 000 t year^-1, corresponding to sediment yields of 8150 and 4950 t km² year^-1. Maximum concentrations in 2000 and 2001 did not exceed 6000 mg l^-1 and the annual sediment transport had decreased enormously, to 11 800 and 18 500 t year^-1, giving sediment yields of only 590 and 925 t km² year^-1. However, a year-to-year variability controlled by climatic variables was still present.