## 2 Experimental Setup  
The experiments were conducted using a re-circulating flume, shown schematically in Figure 1a. The flume mainly consisted of an upstream tank with a water level indicator supporting a stabilized water head, a plunge pool, and a pump with a flow meter. The upstream tank was 1 m wide, 1.3 m long and 2.6 m high. The 0.61 m deep plunge pool was 4 m long and of a trapezoidal cross-section, 0.8 m and 0.4 m wide at the top and bottom, respectively. A deep outlet was fixed at the upstream tank 1.28 m above the bottom plate of the plunge pool, as shown in the schematic diagram in Figure 1b. The tank and the plunge pool were connected by 12 cm diameter pipes and a mud pump.  
The tests were conducted in a room-temperature environment of about 20 \(\pm\) 2 \({}^{\circ}\)C. Upstream and downstream water levels were controlled within an experimental error of \(\pm\) 1 mm. The flow discharge was measured by a flow meter, and each experiment case was conducted three times to determine the average discharge. Diaphragm-type TS202 pressure transducers (Beijing Tiantai Xingye Technology co. Ltd, Beijing, China)with a diameter of 20 mm were spaced at 0.1 m intervals along the centerline of the plunge pool to measure the hydrodynamic pressure. A DASP data collection system sampled the transducers at 100 Hz on the basis of [PERSON]'s law [43], equivalent to a sampling time interval of 0.01 s. The transducers were calibrated in the air and the hydrostatic pressures were measured prior to the experiments in order to provide a comparison of water level before and after the experimental hydrodynamic pressures were applied. At least 8192 effective samples were taken in every experimental case. The complete set of samples was first analyzed for effective data, then decomposed using an infinite impulse response (IIR) filter in MATLAB (The MathWorks, Inc., Natick, MA, U.S.). Finally, the parameters of the hydrodynamic pressures were calculated using MATLAB.  
The sediment used was from the Yellow River and was classified as fine silt and clay of particle sizes ranging from 0.001 mm to 0.05 mm and a median particle size of 0.008 mm. The concentration of mud was determined by its concentration at the nappe. Viscosity was measured by an NDI-8S (Shanghai Yueping Scientific Instrument Co. Ltd., Shanghai, China) rotational viscometer. After testing each case, the viscosity of the sediment-laden flow was measured at room temperature. Each case was repeated five times and the results were averaged for analysis.  
Experiments were conducted in two sets for a downstream water depth of 0.1 m. The first set of experiments evaluated fresh water at three upstream water heads (1.80 m, 1.85 m, and 1.90 m) to determine its energy dissipation in the plunge pool. The second set of experiments consisted of three concentrations (50 kg/m\({}^{3}\), 150 kg/m\({}^{3}\), and 250 kg/m\({}^{3}\)) of sediment-laden flow to determine its energy dissipation at each of the three evaluated upstream water heads. The densities of the suspensions were 1.02 kg/m\({}^{3}\), 1.05 kg/m\({}^{3}\), and 1.08 kg/m\({}^{3}\) for sediment concentrations of 50 kg/m\({}^{3}\), 150 kg/m\({}^{3}\), and 250 kg/m\({}^{3}\), respectively. The details of all twelve experimental cases are presented in Table 1. The experimental errors were controlled to less than 1%.  
Figure 1: Schematic diagram of the experimental (a) re-circulating flume; and (b) deep outlet.