The degree of flood protection required by these regulations is considered reasonable for regulatory purposes and is based on engineering and scientific methods of study. Larger floods may occur on rare occasions or the flood height may be increased by manmade or natural causes, such as bridge openings restricted by debris. These regulations do not imply that areas outside the flood [hazard] district boundaries or land uses permitted within such district will be free from flooding or flood damages. These regulations shall not create liability on the part of the government or any officer or employee thereof for any flood damage that results from reliance on these regulations or any administrative decision lawfully made thereunder.