A good multi-wan router will allow you to connect multiple access methods to the Internet:

For redundancy, try using 3 separate access methods: Fiber, GPRS, and Satellite e.g. These can be bonded for increased bandwidth, and configured to failover, so that if one or two points go down, the third will still route. There are many other methods to access the Internet, the above lists just a few fairly common ways.

Maintaining electricity is also important, so beyond your wired lines, you want solar/wind and a diesel generator placed above any potential flood line. Because it is precisely during a flood when power goes out, but you need to keep your Internet running. Even a bicycle powered generator with battery backup can kick out 50-100 watts and keep the router and a minimal node running.

Hope for the best, but prepare for the worst.