The establishment of highly mechanized, capital-intensive system of agriculture allied to the Cerrado biome climate has led to the development of earth-filled dams to provide irrigation in the MATOPIBA Region in Brazil. In most cases, these dams as-built often differ from as-designed and generally possess a high hazard potential because of their large reservoir capacity. In this study, the usefulness of the use of ground penetrating radar in establishing the as-built condition of the River Balsas dam is investigated. The results showed that is possible to acquire a detailed knowledge of the height above ground, the structural height, the position of the phreatic surface, the thickness of each foundation material and the position of bedrock. The GPR survey was also very useful to delineate the extension of a breach that was affecting the dam’s performance and also showed the importance of paleochannels in providing key information about dam leakage.