# Near-Nature Ecological Technique for Pier Scour Countermeasure in a Submerged Overfall
## 3 Experimentation and Methodology
### Experimental Procedure
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Cases** & **0** & **1** & **2** & **3** & **4** & **5** & **6** & **7** \\ \hline Shape of strip 1  & N/A & C & C & C & R & C & C \\ Diameter of strips & & & & & & & \\ \(D_{a}\) (mm) & N/A & 0.1 & 1 & 2 & \(b_{a}\) = 25 & 1 & 1 & 1 \\ Density of strips & & & & & & & \\ (g/cm\({}^{3}\)) & & & & & & & \\ Flexibility index & N/A & 248 & 46 & 110 & 69 & 46 & 46 & 46 \\ \(F_{i}\) & & & & & & & \\ Length of strips \(L\) & N/A & 25 & 25 & 25 & 25 & 37.5 & 50 & 75 \\ \(L/\sqrt{A}\) & N/A & 2821 & 282 & 141 & 100 & 423 & 564 & 846 \\ Flexibility parameter & & & & & & & \\ \(F_{p}\) & & & & & & & \\ \({}^{2}\)\(L/L_{d}\) & N/A & 1/3 & 1/3 & 1/3 & 1/3 & 1/2 & 2/3 & 1 \\ Composition and application of the material & & & Cotton & Cotton & Silk \& satin & Cotton & Cotton & Cotton \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Composition of CKAW and study cases. Figure 7: Evolution of scour depth at 0\({}^{\circ}\) of pier without CKAW (Case 0). The topography was measured after the pier scour reached an equilibrium state, and the protective effect of CKAW is discussed based on the experimental data. After the pier scour reached an equilibrium state, the water in the channel was leaked out from the experiment flume slowly without disturbing the sand bed. With help of three digital single-lens reflex cameras installed and fixed above the experiment flume, the topography of the sand bed can be obtained using post-processing software from the synchronized photographs. The measured topography of Case 0 in the equilibrium condition is depicted in Figure 8. The local scour was triggered around the pier, and the spatial distribution of scour depth was symmetrical. The maximum scour depth in Case 0 was found in front of the pier, and the measured value (\(d_{sn}\)) was 11 cm. This study measured the topography of all experimental cases after the pier scour reached an equilibrium state, and then the maximum scour depth at pier (\(d_{s}\)) can be obtained. Therefore, the protective effect due to CKAW can be estimated by  
\[P_{s}\ =\ \left(\frac{d_{sn}\ -\ d_{s}}{d_{s}}\right)\ \times\ 100\%, \tag{6}\]  
where \(P_{s}\) is the protective effect of CKAW. The water surface above the region of CKAW was also measured after the pier scour reached an equilibrium state, and the effect on water surface due to CKAW is discussed. Above the experiment flume, several movable probes were set up to detect the water surface. After the pier scour reached an equilibrium state, the water surface can be measured by these water level gauges. The measured water surface of Case 0 is plotted in Figure 9. The zero of coordinate X was given between the hunched platform and sand bed. The half length of surface wave (\(\pi_{In}\)) and the magnitude of surface wave (\(\pi_{nm}\)) can be obtained as 10.5 and 3.4 cm, respectively. In the same way, this research can record the water surface of all experimental cases, and then the half length of the surface wave (\(\pi_{l}\)) and the magnitude of surface wave (\(\pi_{m}\)) can be found. The protective effect of CKAW on the water surface can be evaluated using the following formulas:  
\[P_{l}\ =\ \left(\frac{\pi_{In}\ -\ \pi_{l}}{\pi_{l}}\right)\ \times\ 100\%, \tag{7}\]  
\[P_{m}\ =\ \left(\frac{\pi_{nm}\ -\ \pi_{m}}{\pi_{m}}\right)\ \times\ 100\%, \tag{8}\]  
where \(P_{l}\) is the protective effect on the half length of surface wave due to CKAW, and \(P_{m}\) is the protective effect on the magnitude of surface wave due to CKAW. Figure 8: Topography of Case 0 (without CKAW) after the pier scour reached an equilibrium state (the erosion and deposition contour is 1 cm).