Development of a Hydrodynamic Model of the Irrigation Canal Network using HEC-RAS. A Case Study of Layyah Canal Division, Pakistan

Abstract

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 performance of a canal is determined by its water conveyance efficiency, among other factors. L-Sections (Longitudinal sections) of the canals provide significant details on hydraulic parameters such as canal bed width, flow velocity, Manning's roughness coefficient, and F.S.L (Full Supply Level). However, in most systems, canals are not operated on design discharges because either the canal capacity is insufficient or operated under their designed flow rates. A hydraulic model for a canal is helpful in reproducing practical considerations and operations. The current study represents the development and comparison of a 1D hydrodynamic model of the Munda Branch with a design discharge of 39.5 m3 /s and length of 34.13 km with its 9 distributaries using the Hydrologic Engineering Center River Analysis System (HEC-RAS) and BASEMENT software. Three scenarios were modeled to evaluate the water surface profiles at various cross sections of the Munda: 1. behavior of the canal without lateral and inline structures, 2. the influence of the lateral distributaries, and 3. the impact of inline structures along the canal. Field data and design discharges were used to calibrate and validate the model. The results demonstrated consistent water levels between HEC-RAS and BASEMENT with minor discrepancies. Most of the cross sections of the canal remained submerged under design discharge conditions, underscoring the limiting conveyance efficiency of the Munda Branch. The study highlights the applicability of both modeling tools in design and performance assessment in irrigation systems.