## 4 Conclusions  
This study conducted flume tests on wave erosion of slope models, utilizing various wave frequencies and heights for the tests. The data measured during the experiments included wave water levels, seismic and acoustic signals, and pore pressure. We also analyzed the slope model's erosion ratio, slope retreat, and the run-up height of the wave (H\({}_{\rm w}\)) through image analysis. The study found that at least three factors influence the seismic and acoustic energy of wave erosion, including (1) wave height, (2) waves swashing and impacting the slope, and (3) the run-up height of the wave. This phenomenon could be applied and is promising for issuing near-shore slope failure warnings. The main conclusions are as follows:  
1. Piezometers and seismic sensors should be installed as close to the slope surface as possible but also positioned to avoid exposure by erosion. This placement allows for the measurement of more significant signals. The variation in wave height strongly affects the amplitude of pore pressure near the slope surface. The higher the wave height, the greater the amplitude of the pore pressure, indicating stronger wave erosion forces. Therefore, sensors should be placed as close to the slope face as possible in applications to assess changes in wave height and the condition of wave erosion. 2. As the run-up height of the wave (H\({}_{\rm w}\)) rises, the pore pressure generally also increases, even if the piezometers are installed a bit away from the slope surface. The increase in pore pressure can be used as an indicator of the increase in the H\({}_{\rm w}\), reflecting the enlargement of wave erosion on slopes. As waves gradually erode the slope surface, the amplitude variation in pore pressure increases, serving as an indicator that the slope has undergone further erosion. 3. When waves backwash cyclically, the rapid drawdown phenomenon may induce sliding of the slope. 4. Generally, when waves intensely swash and impact the slope surface, seismic and acoustic energy traces in the time-frequency spectrum will be very obvious. If a collapse occurs while the wave impacts the slope, the energy traces of the collapse in the time-frequency spectrum can easily be masked by the energy traces of the impacting waves. * With the transition of erosion from swash to impact, a marked rise in both the spectral magnitude and Power Spectral Density (PSD) of seismic and acoustic signals was observed. The impact mode of wave erosion generated louder sounds and more significant seismic energy compared to that from swash erosion. * Sometimes, even when H\({}_{\text{w}}\) and the erosion ratio increase, the spectral values and PSD of the seismic and acoustic signals may not increase correspondingly. This is due to previously slid loose soils being swashed without being impacted. Even though the H\({}_{\text{w}}\) gradually increased, the erosion rate remained roughly the same; that is, the erosion rate did not increase correspondingly with H\({}_{\text{w}}\). As the H\({}_{\text{w}}\) decreased, the turning point where seismic and acoustic energy declined indicates that the force of wave erosion on the slope began to diminish gradually. * Wave height has a greater influence on erosion and retreat compared to wave frequency, based on the R\({}^{2}\) values from the linear regression. * Arias Intensity (I\({}_{\text{A}}\)) and erosion ratio increased exponentially. Therefore, when I\({}_{\text{A}}\) due to wave action can be obtained for a slope, there is great potential for I\({}_{\text{A}}\) to be applied in estimating the erosion ratio for that slope. Due to the small scale of the tests, all seismic signals generated during the small-scale model tests can be easily recorded. However, if significant human or environmental noise is present and the source of this noise is close to the sensors, the seismic signals we intend to monitor may be easily obscured.