Experimental study of the effect of floor roughness on wave characteristics resulting from dam break in indirect pathway

Considering the comparison between the number of dams constructed around the globe and the number of dam failures, the estimated probability of occurrence of failure in each dam is 10-4 dams a year. Although this probability is seemingly low, the experiences of these accidents through the history indicate that it is irrational and unreasonable to overlook the importance of this issue. Despite the extremely high accuracy of calculations and studies conducted for the construction of reservoir dams as well as the comprehensive, complete, and highly accurate research, the probability of dam failure and the need for preparedness for crisis management and floods caused by dam failures cannot be overlooked due to some limitations such as the lack of accurate statistics on the hydrology and flood characteristics on dam construction sites, the complicated geological problems and issues, foundation construction and full waterproofing challenges, flaws in dam construction, and unpredicted problems in the construction or the operation phase. The construction of most reservoir dams in meanders and rocky river beds explains the rational for this research, which was carried out in a flume with a tangent path.

The present study was conducted at the physical and hydraulic models laboratory of Water Sciences and Engineering Faculty of Shahid Chamran University of Ahvaz. The rectangular flume used in this research consisted of three 90-degree bends including an acute angle bend, a normal angle bend, and a mild angle bend. A gate was installed and the flood wave created by the dam failure was simulated in the flume. The gate installed divided the flume into an upstream section (the dam reservoir) and a downstream section (the river path). A pneumatic jack was installed on the gate. The jack suddenly sent a wave to the flume downstream using a pressure compressor, thereby simulating the wave caused by the dam failure. The experiments in this study were conducted in the normal-angle bend in this flume. The wave speed and the wave front height of the wave originating from the dam failure were calculated with high accuracy using a fast-switching camera.

In the dry downstream, there was no opportunity for the formation of the wave body after it flowed beneath the gate due to the considerable depth height difference between the upstream and downstream sections and the enormous energy. Besides, the wave and the wave failed mass formed at the beginning when the wave passed by the gate before it entered the curved path. The wave continued traveling without showing any fungal or dive state. Moreover, the wave height at the bend inlet was at its peak and it continued towards the end of the canal with a considerably decreasing slope. On the water surface with an upstream of 25 cm, the downstream was dry and the bed was smooth. Besides, the wave speed difference from the angle of 0 to the angle of 45 degrees and the angle of 45 to the angle of 90 degrees showed a 30% increase and a 7% decrease as compared to the beginning of the bend, respectively. This trend showed a 29% increase and an 11% decrease with the 10-mm roughness. It also showed a 25% increase and a 5% decrease with the 16-mm roughness and a 13% increase and a 4% decrease with the 20-mm roughness as compared to the beginning of the bend. The aforesaid trend decreased with an increase in the upstream height because the volume of water released from behind the gate increased, the wave did not hit the flume bed, and the wave continued moving. Moreover, the wave height at the bend inlet was at its peak and it continued moving towards the end of the canal with a considerably decreasing slope. On the water surface with an upstream of 45 cm, the downstream was dry and the bed was smooth. Besides, the wave speed difference from the angle of 0 to 45 degrees and the angle of 45 to 90 degrees showed a 23% and a 15% decrease as compared to the beginning of the bend, respectively. This trend showed a 21% and a 23% decrease with the 10-mm roughness. It also showed a 23% and a 13% decrease with the 16-mm roughness, and a 23% and an 8% decrease with the 20-mm roughness as compared to the beginning of the bend.

Since the speed increased at the apex of the bend, the speed was higher at the distances following the apex as compared to a direct path, and the construction of pumping stations or recharge points in the second half of the meander was feasible, it is recommended to take protective measures or cut the meander and turn it into a direct path to control and reduce the loss caused by the failure-induced flood.