When doing a site selection for DC build there are literally 100's of things that need to be considered. I have a saying that "I can build a data center anywhere". And this is true. But you have to consider the costs involved in mitigating any man made, and natural risks. I'm curious as to where you're planning to build this, and why it has to be built on the beach?
Flooding is a serious risk to mitigate, but it can be done. Buried power cables are fine. One thing about power cables is, they are waterproof. The cable isn't so much the issue, it's where and how it connects, and what it connects to. Switch gear doesn't tend to be water proof, or even water tolerant.
My key point before is, if you know you haven frequent flooding, then your better off building a multi-story structure, and a 1 story structure. If you are US based, 1 floor structures seem to be the norm. In Asia, mostly multi-story structures are utilized.
Keep in mind that things like hurricane and tsunami as well as other flooding should be examined on a 100 year basis (not just a, "it hasn't happened here in my lifetime" basis).
HVAC (CRAC/CRAH) will have some humidity control if you buy the right units, but not all come that way by default. So you need to consider this carefully.
Also, what Tier objective (Availability) are you planning for? How big will the DC be?
"Everything should be made as simple as possible, and no simpler."