Groundwater sapping is the geomorphic reworking of surface topography induced by water seeping out from an aquifer. In the present thesis, this process is examined using experiments, theory and computations. A laser-scanning apparatus is used to measure the evolving topography of a sand surface subject to the geomorphic action of gullies fed by groundwater. Using a linear complementarity formulation, a theory of the coupling between the subsurface and surface flow is proposed. An original aspect of the theory is that both drainage and recharge of groundwater by the surface runoff are considered. The method of fundamental solutions is used to translate the theory into a computational scheme. The computed solutions are then compared with the experimental measurements and used to guide interpretation of the laboratory observations.