Reconstruction of beaches from washing away the sand and / or the dunes, raising the beaches to make them ready for the sea level rise require new beach profiles. Because of the huge sand volumes it is necessary to perfectly estimate this.
Because of the slight slopes of the existing situation and the theoretic profiles, this can only be realized with accurate volume-calculations on the 3D-models.
It is important to create a good 3D-model of the zone between high and low water of the existing situation because it is difficult to make a good survey here.
Also, often, other coordinate systems and vertical reference systems are used on land and make everything more complex.