In areas prone to flooding, tanks must be installed at or above what level?

The correct answer is based on the requirement that tanks must be installed at or above the design flood elevation in areas prone to flooding. This level takes into account the anticipated highest flood level during a significant flood event, allowing for sufficient protection against potential flooding.

Installing tanks at or above the design flood elevation helps to prevent water from entering the tanks, which could lead to contamination of contents and structural damage. Moreover, adhering to this level is essential for compliance with local building codes and regulations, ensuring safety and resilience in flood-prone areas.

The other choices do not reflect the specific requirements set out by the relevant guidelines pertaining to flood risk management. For instance, base flood elevation refers to the level at which flooding is expected to occur during a 100-year flood event but does not account for additional safety margins that the design flood elevation considers. Options like standard flood level and safety flood line are not defined terms recognized in the context of flood management practices relevant to tank installations. Thus, the design flood elevation is the most accurate and applicable standard for ensuring tanks are safeguarded against flooding risks.