Riprap, or the piling of
boulders or
concrete rubble along a
shoreline, is designed to protect
manmade structures (such as
railroad trestles,
levees,
dams,
roads) and
property from
flooding and/or
erosion. Natural
riverine systems and shorefronts have their own ways of preventing erosion-- including
vegetation and the occasional flood.
Used along river banks, riprap creates abnormal stream dynamics, increasing stream velocity and so increase erosion downstream on opposite banks (conveniently creating the need for more riprap). Along the oceanfront, it may have unforeseen consequences on the regular distribution of sand. Riprap is often quarried from someplace other than where it is placed- so it doesn't blend in or match the natural geology of the landscape.