The degree of flood protection required by this ordinance is considered reasonable for regulatory purposes and is based upon engineering and scientific methods of study. Larger floods may occur on rare occasions. Flood heights may be increased by human-made or natural causes, such as ice jams and bridge openings restricted by debris. Approval of the use of land under this ordinance shall not be considered a guarantee or warranty of safety from flood damage. This ordinance does not imply that areas outside the flood hazard area will be free from flood damage. This ordinance does not create liability on the part of the city or any officer or employees thereof for any flood damages that result from reliance on this ordinance or any administrative decision lawfully made thereunder.