## 3 Experimental Results and Analysis
### Hydrodynamic Pressure
#### 3.3.2 Fluctuating Pressure  
The mean hydrodynamic pressure represents the average falling jet force on the floor slab of the plunge pool over a period of time, and the fluctuating pressure caused by turbulence represents the degree of turbulence at every point tested. The pressure fluctuation on the center line of the plunge pool was measured by transducers and the root mean squares (RMS) of the fluctuating pressure were determined by  
\[\sigma=\sqrt{\frac{1}{N}\sum_{i=1}^{N}\left(P_{i}-\overline{P}\right)^{2}} \tag{3}\]  
where,  
\[\overline{P}=\frac{1}{N}\sum_{i=1}^{N}P_{i} \tag{4}\]  
in which \(\sigma\) is the RMS fluctuating pressure, \(P_{i}\) is the instantaneous pressure at a given point, \(i\) is the test number, \(\overline{P}\) is the mean value of pressure at all test points, and \(N\) is total number of tests. As shown in Figure 8a-c, the experimental results indicate that the RMS fluctuating pressures remain stable at the beginning of the plunge pool, then increase sharply, exhibiting a peak before returning to a stable value at the end. For sediment-laden flow, the maximum values of the RMS pressure increased with increasing sediment concentration from 0 kg/m\({}^{3}\) to 250 kg/m\({}^{3}\) for a given upstream water head. The increasing concentration of sediment causes an increase in the viscosity of the flow, resulting in a decreased turbulence intensity [35] and an increased fluctuation in turbulence, which is consistent with the turbulence characteristics of sediment-laden flows in open channels [34].  
Figure 8d shows that the maximum RMS increased with increasing upstream water head at a given concentration of sediment, and shows that the location of the maximum RMS moved downstream with the length of the region following the peak increasing with increasing water head. This indicates that the higher the upstream water head, the more energy carried by the jet and then applied to the slab, and the larger \"hill\" region following the peak of the RMS indicates that the main stream impact region is larger. Figure 8d, in which same color lines represent the RMS measured for different sediment concentrations at the same upstream water head, further demonstrates this relationship: The differences between the maximum RMS at different concentrations are similar, regardless of the upstream water head.  
Figure 9 depicts the maximum time-averaged pressure and the maximum fluctuating pressure for different sediment concentrations at different upstream water heads. The maximum time-averaged pressure can be seen to increase with both sediment concentration and water head, but the slopes at which the pressure increases with sediment concentration for all three water heads are nearly identical. The same trends are exhibited for the maximum fluctuating pressure. The results demonstrate that the pressure increases in a stable manner with the increasing sediment concentrations regardless of the upstream water head owing to the viscosity of the suspension and the accompanying flow resistance. [PERSON] et al. [40] conducted experiments studying a submerged hydraulic jump with sediment-laden flow and determined that suspended sediment increased the flow resistance as a result of the decreased maximum flow velocity, which likely further confirms the presently observed effects of sediment in the flow.