Computational Model for Gradually Varied Flow in Channel Networks with Hydraulic Structures

Abstract

There is a need for regulation and control of irrigation conveyance systems for sustainable agriculture. Design and analysis of hydraulic structures within complex channel systems are essential for conservation and efficient use of irrigation water. An improved computational model based on gradually varied flow assumptions and capable of solving discharges and water levels in complex channel network systems to include lateral weirs is presented. Results include water levels, discharge distribution, and computation of flow over or dimensions of lateral structures. The model uses the simultaneous solution method (SSM) to solve the continuity and energy equations at several channels reaches, in addition to the lateral weir equation. The nonlinear system of equations produced when applying this method is solved with the Newton-Raphson procedure. A series of successive approximations leading to the solution requires the solution of a set of linear equations. The biconjugated gradient stabilizer with preconditioner method (BiCGSTAB) is used to solve the linear system formed by large sparse matrices occurring in channel networks. Comparison of the SSM results with the standard step method (StdSM) as included in Hydrologic Engineering Center-River Analysis System (HEC-RAS) for parallel channel systems, with and without lateral structures, was excellent. The capabilities of the SSM are demonstrated solving a channel network in which three lateral weirs are designed and two more are analyzed during the same program execution. The model is easy to use, converges in a few iterations, and can be applied for design or analysis of lateral structures in irrigation engineering.