People living in the lower valley of the St. John River, New Brunswick, Canada, frequently experience flooding when the river overflows its banks during spring ice melt and rain. Media reports reveal devastating effects of the latest floods that hit New Brunswick, Canada during the summer of 2008 (CTV, 2008). The rising water levels forced the closure of the New Brunswick Legislature, and also resulted in the temporary closures of the international bridge that links the Province to the United States of America. It also closed the operation of the Gagetown ferry. Fredericton experienced its worst floods in 1973, when the St John River reached the 8.6 m mark (ENB-MAL, 1979). The 2008 flood was recorded as one of the major floods experienced in Fredericton after the 1973 flood (see Figures 1 and 2). On April 24th 2008, due to rapid melting of snow set by an unusually severe winter and combined with intense rainfall, the water level of St. John River reached 7.2 m (TC, 2008). The water levels in Fredericton raised by a meter overnight to 8.33 m on May 1st. Raising St. John River levels peaked at 8.36 m on May 2nd, almost reaching the previous record of 8.61 m set in 1973 (CIWD, 1974). The closure of roads, government buildings followed by the evacuation of people and their possessions during floods is necessary to avoid the loss of life and property. Raising river water levels could affect electrical, water and telecommunication facilities. It could also affect the sewage system. In such a situation, the public buildings washrooms cannot be used. The question that the government officials are facing is: “When can an office be declared risky to occupy?” The decisions to close public utilities require strong reasons. Such decisions have social, economic and political impacts on the community. City Managers will require reliable support for the decision to close down government infrastructure. To facilitate this process, we propose the use of 3D flood modelling,