There are a number of regulatory authorities that have authority over placing structures like docks and piers in waterways. It could require permits from the state, USEPA, US Army corps of engineers, your county, and possibly a homeowners organization. I would beqin the inquiry at the county level. Fines and penalties for doing it without permission can be substantial, so be careful and get it in writing.
Depending on the type of property you have, towers might have a negative impact on your property. Whether it is a nice home site or agricultural property where the towers will limit the possibility of pivot irrigation, there could be impacts. However, if it is a planned line that doesn't exist yet, you could get a cash settlement for agreeing to place the towers on your property.
The county likely will have flood maps that show the likelihood of flooding in any specific area. I'm not sure if they will have documentation of any past floods.