Bedform Spacing and Flow Resistance

Experimental work, using rigid bedforms modeled on ripple and dune bedforms developed in sand, shows that the natural spacing of bedforms is that which, for their shape, causes maximum resistance to flow. This result supports a more general hypothesis, developed earlier from existing bedform, armored bed and meander data, that the equilibrium nonplanar shape of a deformable boundary is that which offers maximum resistance to flow past it. This principle, which may reflect some general principle of energy dissipation, should eventually allow bedform spacing to be predicted from bedform shape. In order to predict resistance to flow, however, bedform size relative to flow depth must be known. The maximum resistance principle cannot define bedform size, which must therefore result from the action of some further process that halts bedform growth.