Background Wave erosion is the main type of soil erosion in the water-level-fluctuating zone (WLFZ) of the Three Gorges Reservoir (TGR), the disasters such as soil erosion and landslide caused by wave erosion are becoming more and more serious, which have seriously threatened the local economic development and ecological environment construction around the reservoir area. In addition, vegetation restoration can meet the goals of soil and water conservation and soil erosion and enhancing the slope stability in the WLFZ. However, the effects of plants on the wave pressure, pore water pressure and erosion caused by waves and their relationships remains largely unexplored.

Methods The typical plant and soil of Cynodon dactylon and purple soil in the WLFZ of the TGR was used as the research object. Three slope conditions with bare as CK, coverage of 30% by C. dactylon and coverage of 60% by C. dactylon were formed for simulated wave test with wave heights of 4, 6 and 8 cm. The wave pressure, pore water pressure was monitored by mechanical sensors on the surface of the slope and within the slope during the test. And the wave erosion for each test was also measured by drying method. Then the influence of C. Dactylon cover on the wave pressure, pore water pressure and wave erosion of purple soil in the WLFZ were evaluated by statistical analysis.

Results The wave pressure, pore water pressure and wave erosion affected by the cover rate of C. dactylon and the wave height. The wave pressure, pore water pressure and wave erosion increased by 3.80%-48.62%, 13.12%-50.44% and 0.88%-8.08% with the increase of wave height when the slope condition was bare, respectively. And the wave pressure, pore water pressure and wave erosion decreased by 2.98%-220.17%, 15.47%-75.64% and 29.31%-80.83% with the cover of C. Dactylon, respectively, when compared with the bare condition. Correlation analysis showed that the wave erosion was significantly negatively correlated with the C. dactylon coverage (P < 0.01), and was significantly positively correlated with sensor 4# and 5# wave pressure, sensor 1# and 3# pore water pressure (P < 0.05), while not significantly correlated with wave height, sensor 6# wave pressure, and sensor 2# pore water pressure.

Conclusions The result indicated that the cover of C. dactylon on the WLFZ effectively reduced the wave pressure and pore water pressure caused by wave effect, and resulting in reduction of the wave erosion. The resistance to wave erosion on slope of the WLFZ was enhanced due the combined action of the above-ground and underground parts of C. dactylon. This study deepens the understanding on the relationship between the wave force and erosion in the WLFZ under the cover of C. dactylon, and provide a reference basis for the vegetation restoration and soil water conservation in the WLFZ.