Two story CMU building on a slope

I'm working on designing a two story building (same as the attached sketch) & here are the conditions:- The building is 72 ft x 32 ft;- The lower level should be all concrete & waterproof, the top level is CMU with an A-frame roof;- The building is in a flood zone & the first floor will be completely submersed in water when it floods;- This is an industrial structure in a water plant.I have not designed a structure like this before & I have concerns about the lower level; What are the main things to look out for or be concerned about in my design? Do I need drainage? Or a retaining wall (or other methods of stabilizing the soil) so the soil on the bottom of the building wouldn't be washed off over time? Is it a concern for the passive pressure of the soil behind the building causing overturning or sliding down the slope?What would you recommend for the foundation? A slab? Piles?...I'd appreciate your advise and help!

This is definitely not my field but I had to research construction in a floodway once when I was in land development and a resident came in enquiring about building a detached garage in the floodway.  So, I remember reading about some of the requirements.  Why are you building in a flood zone?  What year event will flood the lower floor?  What is the water surface elevation of the 100 Year event?  What flood zone designation are you building in? 

If I remember correctly, the structure needs to be uninhabited which it sounds like this will be.  I also recall that you either need to water proof it, or allow the flooding (with wall openings).  It sounds like you are shooting for waterproofing?  I think waterproofing vs flood openings makes it more challenging because you now need to design to counter the uplift buoyancy forces. 

Check out FEMAs site, they have some really good info.  https://www.fema.gov/media-library/assets/documents/100537  This is a link to the floodproof provisions but surf around their site, I think you'll find lots of info and publications on building in flood zones. 

Also check with the local jurisdiction's Building Department and check their Municipal Code.

In general, I think you will want to build on piers or piles. 

You're welcome.  Don't mention it.