The Fundamentals of Seacoast Jetties

In American practice the term Jetty is applied to a structure built at the entrance to a harbor or at the mouth of a river to confine and direct the currents so as to maintain a navigable channel and to protect such channel from sand movement which would cause deterioration. The two main classes of jettied entrance channels, involving somewhat different methods of treatment, are those in which river discharge is the principal agent in causing scour and those in which the chief dependence is placed upon tidal flow. These two classes naturally merge, as we rarely find a harbor into which at least one stream of some size does not discharge. However, in nearly every case either river discharge or tidal flow is greatly predominant. In this country tidal flow is the factor of major importance in practically all of our jetty problems and this class will be given the greater attention in the following pages. The mouths of the Mississippi furnish an outstanding example of the other class.