Storm & Flood Damage Recovery in Granite City, IL

That is interior drainage, and it is a distinct mechanism from a levee overtopping. When the river runs high, the district cannot let interior runoff flow out by gravity, so it has to be pumped. Rain falling inside the protected area during that period accumulates until the pumps get to it. The levee can be doing its job perfectly while your basement takes water, and the two facts are not in conflict.

It is necessary and it is often not sufficient on its own. On floodplain alluvium with a managed table, water arrives across the whole foundation rather than at one point, so the pump needs a drain system feeding it rather than just a pit in the corner. Capacity matters too, since the pump may run for days rather than hours. And it needs backup power, because the periods of highest demand coincide with storms.

Less than in most places, but not nothing. The regional water table is set by the district and the river, and no lot-level work changes that. What you can control is how quickly water leaves your own foundation once it arrives, and whether the basement is set up so that an event is a nuisance rather than a loss. Raising mechanicals and avoiding finished space at the lowest level are the highest-value decisions here.