Background  The bank slopes of the reservoirs or lakes suffer from severe erosion owing to the appearance of water-level-fluctuating zone. However, the processes and quantified impacts of wave-induced erosion on slopes remain unclear. This paper focuses on the characteristics of wave-induced slope erosion under three water level-fluctuation conditions:dropping (WLD), fixed (WLF) and rising (WLR), to provide a scientific reference for predicting the soil loss and protecting the bank.

Methods  A steel tank with glass pane was used to simulate the wave-induced slope erosion in the three treatments. The slope elevation data were collected by using the method of the pin meter for every 15 minutes from the beginning to the end, a total of 5 times during all treatments. These data were processed by using software (Surfer 9.0) to get the slope micro-topography and the erosion volume. Then the temporal and spatial change of slope erosion-deposition can be analyzed according to the erosion amount or erosion rate calculated based on bulk density of slope soil.

Results  1) The micro-topography of slope was dramatically different among three treatments. Two layers of wave-cut notch was formed on the slope for the WLD, while a layer of wave-cut notch was formed and then disappeared later in the WLF and WLR, but the processes of disappearance were different between them. 2)The erosion amounts in the WLR and WLD were similar, and its value was about 1.5 times larger than that of the WLF. The erosion primarily happened in the first 30 minutes for the WLR. The erosion rates were gradually decreased for both the WLF and WLD, but the decreasing rate of the WLF was larger than the WLD. 3)For the spatial variation of erosion-deposition, the middle part of slope was the major source of sediment for the WLD. The upper part of slope was the major source of sediment in the WLF and WLR, and partial sediment deposited in the lower part for the WLF.

Conclusions  Wave is one of the important external forces to cause bank slope erosion, while the extent of wave fallback affects sediment transport and the extent of sedimentation. The time-spatial variations of slope erosion-deposition vary, mainly as a result of the combined effects of the movement of wave breaking point caused by water level fluctuation and the change in the injection angle of the wave caused by topographic variation. Moreover, the fluctuation of water level may raise the impact of the waves on the slope, which thus increases the erosion. Therefore, water level fluctuation should be taken into consideration, and the damage effect of wave breaking on bank slopes should be reduced in the prevention of the soil erosion on reservoir bank.