DDT 70- Isocotes of PPRI n°20080025 CC du Val de Semouse

The isocotes of the PPRI are the altimeter values (Z in the NGF 69 marker) of the flood heights calculated for the reference flood. Subject to the rules for constructions and the recommendations to be observed, laid down in the regulation of the PPRI, isocotes make it possible to calculate the altimetry of the highest waters which should be observed for the installation of an authorised construction. This height is calculated as follows: Z = (a * z2 + b * Z1)/(a+b) with Z1 = nearest isocot of highest value, Z2 = closest isocot of the lowest value, a = distance between the Z point and the Z1 isocot measured perpendicular to the isocot route, B = distance between the Z-point and Z2 isocot, measured perpendicular to the isocot route. A schematic generally makes this formula explicit in the appendix to the PPRI presentation note.