Scour around submerged spur dikes with flexible mattress protection

Flume experiments examining the effects of a flexible mattress on bed scour around spur dikes were conducted. Results showed that scour induced subsidence damage to the flexible mattress. If the width of flexible mattress, B, was insufficient, then failure of the spur dike may occur. Results also revealed that (1) scour depth decreased as the area of the protective domain around the spur dike increased (e.g., it reduced 30%, from 20 to 14 cm, as the width B increased from 0 to 0.35 m), and (2) higher approaching velocities resulted in deeper scour holes. On the basis of the experimental data and dimensional regression analysis, empirical formulas were proposed for calculating scour depth and the extent of the scour hole. The formulas were then used to obtain the optimum flexible mattress width