Deriving and evaluating hydraulics and detachment models of rill erosion for some calcareous soils

Rill erosion plays an important role in the amount of soil detachment and the transport sediment load on hillslope. Quantification of the soil erosion requires a more precise understanding of the processes and development of rill erosion models. The objective of this study was to derive and evaluate hydraulics and detachment models of rill erosion in calcareous soils of northwestern Iran. Rill erosion experiments were carried out at 55 locations with three replications under field conditions. At each point, the rill plots were created with a 0.2 m width and 4 m length on agricultural soils. The inflow rates were 4, 12, 20 and 30 l min−1 with varying slope from 4 to 25.5%. The results indicated that all conditions of flow regimes including sub- and super-critical (laminar and turbulent) were observed in created rills by overland flow. The mean flow velocity and rill depth have been described well by flow rate and slope gradient, while rill width and flow depth have been explained well by flow rate. The prediction detachment rate by rill flow based on stream power model by non-linear regression yielded the best results (R2 = 0.545 and RMSE = 0.00213 kg m−2 s−1) for all combinations of slope classes. However, there are no significant differences between prediction accuracy of linear and non-linear models, when individual slope classes were considered.