A high accuracy boundary element method is used to compute the propagation of solitary waves from a constant depth region onto a plane slope. Initial wave heights range from H/h = 0.06 to 0.775, slopes between 1:35 and 1:1.73 (30°) have been investigated. The prebreaking shoaling shows very different characteristics on gentle slopes (1:20 and less) and on steeper slopes. A diagram constructed on the basis of a large number of numerical experiments gives a simple limit between which waves break on which slopes and which not. Typical examples of the range of wave behavior are shown. Waves that do not break at run up often break during run down. The velocity fields for the two types of breaking are compared and found to be very different. A simple explanation for this is offered.
