Tampico water managers started the process of developing an Integrated Water Resource Plan in 2004. Although the plan was designed to a full extent on its goals and aims, it cannot be implemented so far. The complex water system and the certainty of short term water availability make of this plan a non-attended issue. The local management based on common-sense still predominant over scientific supported decisions. This thesis develops a tool in order to study the complexity of the River Tamesi Lagoon System. A one dimensional model is created to route the flow along River Tamesi towards Chairel Lagoon, the Tampico and Madero water supply source. The Chairel Lagoon is managed by the River Tamesi Lagoon System average water level. Application of one dimensional modelling allows the individual analysis for Chairel water availability by using reliable and historical data. This research considers a maximum and a minimum flow case to study Chairel water availability. A climate change case is also considered. The work has identified that Chairel Lagoon it will be influenced by Northern Lagoons in the lagoon system once population growth forces water managers to operate these lagoons for water supply. It is concluded that in a minimum flow case availability is ensured due to compensation of the system from lagoons upstream. A maximum flow scenario alleviates flooding upstream, which help to reduce the inflow value at Chairel. Finally, a comparison between a climate change and current scenarios shows for Chairel inlet a variation in discharge values: for winter 0.030 m3 / sec, for spring 0.095 m3 / sec, and no variation for summer and fall. The results of this work are a first step in the study for River Tamesi Lagoon System and can be complemented with other decision support systems in order to facilitate the implementation of an Integrated Water Resources Plan for Tampico.