Energy Loss from Different Bank Protection Structures

A comparison is made of the flow-energy loss associated with channel restoration structures utilizing spurs and submerged vanes. The comparison is limited to subcritical flows and structures that are submerged and angled upstream into the oncoming flow at relatively small angles of attack. The energy loss is calculated from standard, high-Reynolds-number-drag force relations. The drag coefficient for submerged vanes that are located away from banks is obtained from analogy with airfoil theory. The relationships are validated in laboratory tests. The study shows that a system of submerged vanes can be designed to provide the same erosion protection of a given stream bank as can a system of upstream-angled spurs or rock dikes, designed according to NRCS standards, and can accomplish the task at comparable, and sometimes less, energy expenditure. When placed away from the bank submerged vanes are more efficient (in terms of energy expenditure) than spurs in creating vertical mass transfer.