protection should be provided unless the structures are embedded enough to withstand scour equal to at
least one design wave height.
Filtering
In the example of the concrete slab revetment (Figure 17), inadequate filtering also contributed to
failure. Although one of the most important design details, filtering is probably the most neglected and
hence leads to more failures than any other cause. In Figure 19, large rocks have been placed on an
eroding slope without an adequate filter. As waves break on the slope, much of the water seeps into the
soil and flows back to the water level. As it exits the slope behind the rocks, the water carries minute soil
particles with it. Since the spaces between the rocks are so much larger than the coarsest soil particles,
they pass practically unhindered through the revetment. To make matters worse, high velocity jets of
water from waves also penetrate spaces and stir up the underlying sediments. The bank then erodes from
behind the rocks as they settle into the slope.
41
Previous Page
