6.3　Vertical Layout

6.3.1　The flood control system of the surface facilities shall have capacity to remove water from a flood of a no less than 50-year frequency.

6.3.2　If the cavern storage is close to a river or lake etc.，its site's minimum design elevation shall be 0.5m higher than the calculated flood level；if it is located in an island，a coastal area，or a river mouth area with significant tidal actions，the minimum design elevation of its surface facilities shall be 1m higher than the calculated water table；in an unsheltered coastal area，the maximum height of waves above the static water surface shall be considered.The calculated water table shall be the tidal level whose high-tide accumulative frequency is 10%.