*2.1. Riverine Input*

Most world beaches owe their origin and survival to the sedimentary contribution from rivers (more than 90% according to Pethick [30] and 75% according to Best and Griggs [31] for the Santa Monica littoral cell). It is precisely due to the variations in river input that many of the shoreline oscillations that occurred in historical times are still in progress today. There are numerous natural and anthropogenic factors which, more or less directly, influence river input; some are easily identifiable, and quantification of their effects is rather simple, others are difficult to study and of uncertain effect.
