Scour Due to Riprap and Improper Filters

Scour is usually associated with high velocities, elevated levels of turbulence, and negative piezometric gradients. Riprap and filters have been used to eliminate scour from these sources. Attention is drawn to piezometric gradients stemming from different levels of, water about hydraulic structures and to the scour which might result from these gradients. A flow scheme is presented which demonstrates how piezometric gradients might be magnified in the vicinity of riprap; the magnified gradients could increase the amount of scour. Also, the flow scheme results in elevated pressures which tend to dislodge the riprap. In addition to controlling leaching, it is pointed out in this paper how proper filters eliminate both the magnified gradients and elevated pressures. Scour in a channel due to such natural occurrences as ponding, rainfall, and irrigation in the vicinity of a channel is examined.