Let us consider an urban flood prone area, whose surface is A. It is assumed that measurements or estimates are available for the maximum water depths that occurred during a flood event of given occurrence frequency, so that the portion Aij of A which is inundated with water depths falling within the range hi; hj is known. Let X be the total value of properties within A: the property value per unit area x X=A can be evaluated. If the percent damage pij which occurred due to the water depths falling within the range hi; hj is known, then the total flood damage D can be expressed as