EXPERIMENTAL MEASUREMENTS OF RIVER-BANK EROSION CAUSED BY BOAT-GENERATED WAVES ON THE GORDON RIVER, TASMANIA

Erosion of natural river banks by boat-generated waves is an increasin gly serious problem on the navigable reaches of many rivers, particula rly on the middle and estuarine reaches. An experiment designed to lin k bank erosion rates with easily measured wave characteristics, conduc ted on the scenic lower Gordon River in Tasmania, provides information useful for river management. Within a boat-generated wave train a num ber of characteristics were measured and most showed a high correlatio n with measured rates of bank retreat. Maximum wave height within the train is the simplest measure and is associated with a major threshold in erosive energy on unconsolidated sandy alluvium at wave heights of 30 to 35 cm. At maximum wave heights above 35 cm all but the most res istant bank sediments erode. Reducing maximum wave heights to < 30 cm by limiting boat speeds, and reducing the frequency of boat passages, caused a dramatic decline in bank erosion along the river.