Comparison and validation of the ratio of Manning coefficient to flow depth for soil erosion prediction using published data with different external impacts

Purpose Soil erosion leads to non-point pollution and thus water eutrophication; however, the soil erosion rate remains poorly predictable. Hydraulic parameters are essential parts of soil erosion prediction models, and proper parameters can improve the model accuracy. The ratio of Manning roughness coefficient to flow depth ( n/h ) is proposed as an effective parameter for predicting soil erosion, but more evidences are needed to validate the applicability of n/h . Materials and methods The published data from four experiments performed with laboratory artificial rainfall and field simulation scouring were collected. The hydraulic parameters, including Manning roughness coefficient ( n ), Reynolds number ( Re ), Froude number ( Fr ), shear stress ( τ ), stream power ( w ), unit stream power ( P ) and unit flow energy ( E ), and sediment yield rate ( SY ) were calculated to further analyze their relationships and n/h ratio under different external impacts. Results and discussion The n/h ratio representing both the soil and flow character was better than n when the relationships were developed with hydraulic parameters such as Re , Fr , τ , w , P , and E . The sediment yield rate ( SY ) showed better relationships with n/h , w , P , and E than τ , as the expressions of w , P , and E could be described by the n/h , respectively. Conclusions The results indicated that the n/h ratio could explain hydraulics and soil erosion though the external impacts were quite different. The results provided further information for understanding the relationship between hydraulics and soil erosion and verifying the applicability of n/h in soil erosion prediction.