**2. Materials and Methods**

Experiments were carried out at the University of Windsor in Windsor, Canada. The laboratory facility contains a horizontal flume that is 10.5 m in length, 0.84 m in depth, and 1.22 m in width. A schematic of the flume is shown in Figure 2. The flume was fitted with two flow conditioners upstream of the test section. As shown in Figure 2, a PVC ramp led to the test section, which was a sediment recess of 3.68 m in length and 0.23 m in depth, encompassing the width of the flume. The sediment recess was filled with granular material with *d*50 = 0.74 mm, standard deviation of particle size <sup>σ</sup>*g* = *d*84/*d*16 = 1.34, coe fficient of uniformity *Cu* = *d*60/*d*10 = 1.56, and coe fficient of gradation *Cc* = *<sup>d</sup>*230/(*d*10 × *d*60) = 0.96. (Here, *dXX* is the sediment size for which *XX* percent is finer). The material was classified as poorly graded sand according to ASTM standards. The critical velocity for incipient motion of sediment ( *Uc*) for the bed material was evaluated using standard methods which have been described in previous works [13,19].

**Figure 2.** Schematic of the laboratory flume used for experimentation.

A boundary layer trip was located at the beginning of the sediment recess. Flow measurements in the absence of the cylinder indicated that the streamwise velocity was self-similar in the streamwise direction in the test section at the location of the cylinder. Further details are provided in Williams [25]. The depth of flow at the cylinder was adjusted by a gate located at the downstream end of the flume, preceding the outlet tank. The flow was serviced by a 60 HP centrifugal pump. The flow was calibrated with 30◦, 60◦, and 90◦ v-notch weirs, using methods described in the U.S. Department of the Interior Bureau of Reclamation Water Measurement Manual [26]. The Kindsvater–Shen relationship and 8/15 triangular weir equation were used to calculate flow rate and develop the performance curve for the flume pump in the absence of the installed test section [26]. The orientation of the flume and experimental measurements corresponded to *X* in the streamwise direction, *Y* in the vertical direction, and *Z* in the spanwise or transverse direction. The bed level was taken as zero in the vertical direction for all experiments, and the geometric centre of the cylinder was taken as the origin in the *XZ* plane for local scour tests.

In the current investigation, three local scour tests were carried out under varying conditions (see Table 1). In Table 1, *te* is the time to equilibrium. Prior to testing, movable PVC walls were installed in the flume and adjusted to the desired width, *b* (see Figure 3). This was done in order to alter the blockage ratio *D*/*b* while maintaining cylinder diameter *D* thus isolating the e ffects of *D*/*b*. The sediment in the test section was levelled using a trowel, and the necessary pier was installed in the centre of the channel. The flume was then filled with water to the desired depth (for which the resolution of measurement was accurate within ±0.5 mm) [25], and the pump was started and brought up to the required flow rate corresponding to an approximate flow intensity ( *U*/*Uc*) of 0.85, used in order to maintain clear-water conditions for local scour.


**Table 1.** Experimental conditions for tests of the current investigation.

**Figure 3.** Schematic of the experimental setup.

The tests were conducted for a period of 24 h, after which the pump was slowed gradually in order to avoid disturbance of the bed material and then shut o ff. The flume was then drained slowly in order to avoid disturbance of the scour formation and a Leica laser distance meter was used to measure bed profiles in the streamwise direction along the centreline in the *XY* plane ( *Z*/*D* = 0) and around the contour of the bed formation in the *XZ* plane ( *Y*/*D* = 0). The uncertainty of the acquired bed measurements due to the accuracy of the laser distance meter was determined to be ±0.05 mm from the resolution of the measurements.
