COMPARATIVE ANALYSIS OF SEDIMENT TRANSPORT CAPACITY METHODS FOR PREDICTING CHANNEL BED DEFORMATION IN WEAKLY COHESIVE CANALS

Abstract

Reliable prediction of channel bed deformation is essential for the hydraulic design, rehabilitation, and operation of irrigation canals with weakly cohesive beds. However, the presence of both suspended sediment and a small proportion of cohesive material complicates the application of conventional sediment transport equations. This study evaluates the applicability of four sediment transport capacity methods—Ackers–White, Engelund–Hansen, Yang, and Laursen–Copeland—for predicting bed deformation under weakly cohesive canal conditions using the HEC-RAS hydraulic model. The Amu–Bukhara Machine Canal was selected as the case study, where field measurements of hydraulic and sediment characteristics collected during 2023 were used for model implementation and validation. Model predictions were compared with observed channel deformation and operational sedimentation records. The results show that the evaluated methods produce significantly different estimates of bed deformation. Ackers–White, Yang, and Engelund–Hansen generally overestimated deformation, whereas the Laursen–Copeland method provided predictions that agreed most closely with field observations. For the modeled 2.4 km canal reach, the recalculated Laursen–Copeland results yielded a total deformation volume of 39,091 m³, corresponding to approximately 16,288 m³/km, which was closest to the measured average sediment deposition rate of 11,277 m³/km. The study demonstrates that the combined use of field observations and HEC-RAS modeling provides a reliable framework for selecting appropriate sediment transport equations and improving the prediction of bed deformation in weakly cohesive irrigation canals.