*3.3. List of Testing Conditions*

For the conditions given in Table 1, a series of experiments was conducted to investigate the effect of anti-scour collar parameters. Table 2 lists all the working conditions carried out in this study. Based on the scour test of a single cylindrical pier without collar, the optimal design of the collar is carried out to achieve the maximum protection efficiency. Three collar design parameters (collar installation height, external diameter and protection range) are considered to design the experimental scheme. According to the results of threshold velocity and approximate equilibrium scour time, a live-bed scour testing scheme was adopted in this test. Under various tests of cylindrical piers with different water depth and flow velocity, the working conditions of 0.35 m/s flow velocity and 0.5 m water depth were selected.


**Table 2.** Parameters for the test conditions.

As shown in Figure 6, 12 measuring points were evenly arranged around the pier by 30◦ to monitor the scour depth and measure the development of the scour hole for different testing cases. In the experiment, a GoPro camera was used for data acquisition of scour depth around the pier model in water, and an ADV velocimeter is used to judge the evenness of the initial riverbed and to measure the length and width of the scour hole. The measured scour width is the distance between the edges of the scour hole on both sides, while the scour length is the distance between the edges of the scour hole upstream and the highest point of the riverbed behind the pier. In the 60 min, the measuring point reading was recorded every 10 min, and then the data was recorded every 30 min.

**Figure 6.** The layout of measuring points around the cylindrical pier.
