An optimal management of an irrigation network is important to ensure an efficient water supply and to predict critical situations related to natural hazards. Within the context of the MAPPER European project we present a multiscale coupling methodology to simulate numerically an entire irrigation canal over a distributed High Performance Computing (HPC) resource. We decompose the network into several segments that are coupled through junctions. Our coupling strategy, based on the concept of Complex Cellular Automata (CxA), the Lattice Boltzmann (LB) method and the Multiscale Modeling Language (MML) aims at coupling simple 1D model of canal sections with 3D complex ones. Our goal is to build a numerical model that can be run over a distributed grid infrastructure, thus offering a large amount of computing resources. We illustrate our approach by coupling two canal sections in 1D through a gate and a spillway junctions.