The problem is with the ground saturated, rain pretty much goes directly into creeks and streams, to larger waterways etc. Also, levees, which are made of earth and not covered in waterproof material for the most part also become saturated and therefore weaker and less resistant to breakage. The ground under concrete structures can become saturated, again weakening things. As bad as this can be where I am, pretty close to the headwaters of the major drainage systems, it obviously gets worse the further downstream you go in terms of volume of water in the rivers. Fortunately where I am we are about as insulated from any hurricane related effects as you can get in the USA.
