Riprap at bridge piers

The influence that protective riprap have on the scour holes that develop n ear bridge piers has been studied in clear water conditions with circular a nd rectangular piers. Non-dimensional graphs, relating the characteristic d imensions of the scour holes with the riprap elevation above bed level and its width, are presented. Also, the necessary minimum width of riprap, dedu ced from tests, is compared to criteria proposed by various authors.