Sloping interfaces of fine over coarse porous material have been considered for use as barriers to infiltration for many years. Previous literature has developed analytical solutions for flow over such interfaces, numerical simulation of such flow, and the effects of anisotropy on the diversion capacity of such a system. In all of these analyses, however, the interface was assumed to consist of a constant slope, facilitating certain calculations. In this note it is shown that both from a performance perspective (as measured by the ability to divert fluid) and a design perspective (ease of computing diversion capacity) the shape of the interface should be curved, typically in a parabolic shape. Use of this shape is predicted to double barrier diversion capacity. Interfaces made up of easy to construct segmented approximations to the parabola are predicted to provide significantly enhanced performance as well.¿ 1997 American Geophysical Union