Flood mitigation (i.e. measures that can be taken to keep water out of the building or measures to make it quicker and cheaper to allow the building to be re-occupied after flooding) is not a matter covered by Building Regulations.
Planning approval may include conditions for mitigation measures.
Advice is given in BS 85500 flood resistant and resilient construction guide to improving the flood performance of buildings. A core standard can be downloaded from www.shop.bsigroup.com