Scour of rock is a complex process and can be very problematic for dams when excessive scour threatens dam stability.  Removal of individual rock blocks is one of the principal mechanisms by which scour can occur, particularly in unlined spillways and on dam abutments.  Block removability is largely influenced by the 3D orientation of discontinuities within the rock mass, which current scour methods tend to ignore or simplify into 2D or cuboidal block geometries.  To better represent the 3D structure of the rock mass, block theory (Goodman & Shi 1985) has been applied to identify removable blocks, determine potential failure modes, and assess block stability due to hydraulic loads.