*2.1. Testing Facilities*

The experiments were carried out in the large-sized current flume at Southwest Jiaotong University. As shown in Figure 1, the flume is 60 m long, 2 m wide and 1.8 m high with side walls comprised of steel frames and toughened glass, which provides a clear and wide visual range during the testing. There is a scour section in the large-sized current flume, which is 7.5 m long, 2 m wide, 0.35 m deep. A test rack is installed above the sand pool and used to fix the testing physical models. A flow pump is installed at the inflow point to generate steady current in the flume. An outlet is set in the tail part. The water flows into the outlet through an annular channel under the flume and backs to the pump to realize the flow circulation.

**Figure 1.** The testing facility: Photo and detail of the current flume.

The layout of the scour testing facilities is shown in Figure 2. As shown in Figure 2a, the bridge pier model is inserted 20 cm into the riverbed. The top of the pier model is fixed with the test rack by the bolts to ensure the structural rigidity in the scour testing process. An Acoustic Doppler Velocimeter (ADV) was used to measure the flow velocity, and the maximum allowable flow velocity was 4 m/s. As shown in Figure 2b,c, ADV can be moved up and down to measure the velocity distribution along the water depth in this test. The ADV device in this study can also be used to measure the scour depth and obtain the shape of the scour pit around the foundation. Figure 2d,e shows the setup of ADV for the measurement of the range and depth of scour hole around piers.

**Figure 2.** Layout of the testing facilities: (**a**) installation of test model; (**b**) Acoustic Doppler Velocimeter (ADV) flow velocity measurement; (**c**) velocity measurement probe details; (**d**) scour depth measurement by ADV; (**e**) depth measurement probe details.
