Basically Geldof's discussion and criticism involves the fundamental question of the relationship and the comparability between fluid mechanics and transport capacities of rivers and runoff, hence the remark: 'Looking at the method from a fluid mechanical point of view it seems not consistent to combine a formula for the depth of flow (equation ( )) with the Kalinske bed load predictor for turbulent flow (equation (3)). This reply may help to elucidate this important problem as far as our relatively poor knowledge of runoff hydraulics permits a discussion.
First it has to be mentioned that colluviation on loamy cultivated fields occurs mainly in sheetflow with a fairly low unit discharge 4, of the order of 0-15 cm2/s. This means Re values varying between 0-1500 if one introduces for kinematic viscosity v a value fixed at 001 cm2/s (clear water). These flows are laminar to dominantly transitional, for most authors believe a full turbulent state occurs only when Re exceeds, 1000 or even 2400 (Emmett, 1970;. Moreover, for heavily loaded runoff with high c values, Re and the degree of turbulence are overestimated if one does not take into account the increase of v proportional to the load concentration