Development of a hydrodynamic model of the irrigation canal network by using HEC-RAS: a case study of Layyah Canal Division, Pakistan

Water is a crucial and fundamental element in irrigation and agriculture. Understanding water dynamics in natural and engineered channels allows irrigation experts to distribute water efficiently. The irrigation canal network of the Layyah Division is critical to supporting agriculture activities of Punjab but faces significant constraints in the operation and management of canals. The main problem in the canal operation is water shortage occurring in the lower Indus Branch supplying water to the Munda Branch. The condition becomes severe when the lateral distributaries have to operate under flows less than their designed discharges, creating a situation of uncertainty for the tail-end users. A hydrodynamic model for the Layyah Canal network has been developed in HEC-RAS to evaluate the hydraulic performance of the Munda Branch Canal. The model has been optimized, calibrated, and validated with field observations. To evaluate the model's performance, a comparison has been made between the computed water levels at the head and simulated discharges at the tail of the branch canal. The results of the simulation showed that the model can calculate the discharge flowing through the lateral offtakes and outlets with reasonable accuracy, achieving R2 values of 0.9451 for the water levels and 0.9978 for the discharges. The performance of the model is further validated by R2 values of 0.9111 and 0.9888 for the water levels and discharges respectively. Moreover, the manual operation of the sluice gates for the lateral distributaries has been monitored, and it is observed that the distribution of excess water to the lateral offtakes at the head creates a situation of serendipity for the tail-end farmers. The model provides the basis for the effective operation and management of the Munda Branch and is critical for the optimal water distribution of the canals working under low heads of water.