**2. Experimental setup**

The experiments were conducted in the Environmental Hydraulic Laboratory of Nihon University, College of Science and Technology, in order to investigate the hydraulics passing over consecutively assembled boulders. Three different downward slopes (i.e. 1/8.5, 1/12.5, and 1/25) were tested. In the case of 1/8.5 and 1/25 slopes, as shown in **Figure 4**, a half model was installed in a rectangular channel with a width of 0.4 m, length of 17 m, and height of 0.6 m. For the slope of 1/12.5, a symmetric model was installed in a rectangular channel with a width of 0.8 m, length of 15 m,

### **Figure 4.**

*Half model of consecutively assembled boulders. (a) Half model with 1/25 slope. (b) Half model with 1/8.5 slope.*

### **Figure 5.**

*Symmetric model of consecutively assembled boulders (1/12.5 slope). (a) Stepped channel as a base. (b) Consecutively assembled boulders.*

and height of 0.6 m. These models were constructed as 1/10 scale models, and it was assumed that the flow condition might be represented under a Froude similarity. The size of the boulders was set to around 0.6 m in the prototype. The stepped channel model was used as a base of consecutively assembled boulders (**Figure 5**). In order to change the water width in accordance with the discharge, a transverse stepped slope was installed at around 1/10. The assembled boulders were installed on each staircase without hardening the base, and the downstream end of the boulders was stabilized with L-shaped fittings (in the field, use stopper blocks). The experimental conditions are shown in **Tables 1**–**3** for slopes of 1/8.5, 1/12.5, and 1/25, respectively. Here, *B* is the channel width, *h*c is the critical depth, *Q* is the discharge, and *W.L.*d is the downstream water level based on the lowest bottom of the stepped channel at the downstream end of the consecutively assembled boulders. Moreover, the subscript.


### **Table 1.** *Experimental conditions for 1/8.5 downward slope.*

*The Efficacy of Artificially Assembled Boulder Installations in Improving Migration Routes… DOI: http://dx.doi.org/10.5772/intechopen.105198*


### **Table 2.**

*Experimental conditions for 1/12.5 downward slope.*


### **Table 3.**

*Experimental conditions for 1/25 downward slope.*

"p" indicates the prototype. The downstream water level was controlled with a sluice gate located at the channel end. The velocity was measured using a propeller current meter 0.03 m in diameter [15] and the sampling time was set to 20 seconds because of steady supercritical flow. The water and bottom levels were measured using a point gauge with a 0.1 mm reading.
