Technical Abstract: Efforts are underway to rehabilitate the irrigation districts, such as in the Rio Grande River Basin in Texas. Water distribution network models are needed to help prioritize and analyze various rehabilitation options, as well as to scientifically quantify irrigation water demands, usages, and losses, and to help manage gate automation. However, commercially available software packages were limited in applications due to their high cost and operational difficulty. This study is to develop a modeling tool for modeling the water flow profile in irrigation distribution networks and addresses the issues of GIS (Geographic Information System) integration to aggregate spatial distributed information and GUI (Graphic User Interface) building for user-friendly access to enhance the tool. The goal of developing the modeling tool is to make the modeling process simple, fast, reliable and accurate. On the basis of theoretical study, the procedures and algorithms are developed and verified from a single channel to a branching network with higher complexity. The developed modeling tool will be able to play an important role in water quantification for planning, analysis and development for modernization of irrigation systems.