Entropy-based approach for rating curve assessment in rough and smooth irrigation ditches

The aim of the present work is to propose an expeditive methodology derived from the one-dimensional (1D) entropy-based model to evaluate the water discharge in rough and smooth irrigation channels based on the knowledge of relative submergence. Recent studies have demonstrated that, for flow in the presence of high and intermediate roughness, corresponding to low flow depth generally, the entropy parameter seems to be dependent on the relative submergence. Whereas, in the case of very low roughness or smooth channels, the mean-to-maximum velocity ratio can be assumed constant at all water stages. Using detailed laboratory data, collected on smooth and rough flumes with different cross section geometries, the paper discusses the relationship existing between the entropy velocity ratio and the relative submergence to give an operative practical rule for water discharge computation and rating curve assessment in irrigation ditches. The comparison between observed and calculated discharges shows very low errors underlying the reliability of the proposed approach.