Water erosion is a phenomenon causes piers to be destructed. Effect of water erosion on structural stability of piers in Khouzestan Sate, Iran is the main purpose of this research. Happening flood and existence of flood plain in this area causes to study the case study subject. The mathematical methods to study about stability changes rather than water erosion are valuable to be considered by applied and useful result obtained to be applicable to prevent destructing rate critically. The Izard-Bravley and Chitale methods have the least errors rather than reality. We reach to the conclusion that, the best methods of determining the depth of scour khouzestan state bridges was Izard-Bravley and Chitale. The end off, reconciling the methods show in this research %8.8 and %2.41 the better than original methods.