Investigation on the effect of inclined crest step pool on scouring protection in erodible river beds

One of the aquatic structures that are used for protect water channels against bed erosion is serial step-pool. These steps similarity of the vertical drops structure are exposed to danger of scouring downstream of such structures. The objective of this paper was to evaluate the capability of the step-pool method using a ramp at the upper edge to protect channels bed against erosion meanwhile increase required distance between two consecutive step-pool and reduce the downstream scouring depth due to waterfall on the step-pool. For this task, a laboratory flume was used. The experiments conducted on step-pools with ramps having nightmares slope angles of 0 degrees, 20 degrees, 30 degrees and 40 degrees and discharges of 10, 20, 30, 40 and 50 L per second and channel slopes of 1%, 2% and 3% for clear water. The results showed that by installing a ramp segment on the steps with a slope angle of 40 degrees the maximum of downstream scouring depth would be decreased at 41%, 15% and 21% for flume bed slope of 1%, 2% and 3% respectively, comparing ordinary step pools (steps without ramp). These results showed that installing a ramp on the steps should cause location of maximum scouring depth point to move significantly toward downstream, and this should increase the step stability of this protective structures. Based on the results of this research may assert that using a ramp segment on the step increases the pool step efficiency for protecting mountainous river beds especially for subcritical flow regimes on slopes smaller than 2%.

Automated summary

The study evaluated the effectiveness of using a ramp on step-pools to protect water channels against erosion and reduce downstream scouring depth. Results showed that installing a ramp on the steps can significantly decrease the maximum scouring depth downstream, enhancing the stability of protective structures.