A drainage easement is a part of your property where the City has limited rights of access and/or use. Generally, you cannot make any improvements in a drainage easement. That means no fences, sheds, walls, trails or buildings. You should avoid planting trees or much landscaping as well.
A drainage easement has two possible purposes. It may be needed for the flow of storm water. For example, drainage ditches and creeks are typically within a drainage easement. In this case, anything that prevents the flow of water; that might catch debris; that might be washed away; or that might cause a dam-like effect is problematic.
Alternatively, the easement may be needed to access drainage infrastructure. In this case, anything that might make it difficult to drive a truck through or dig up an underground pipe is problematic.
Depending on how much rain there’s been, Austin’s creeks may be bone dry, gently flowing with water or a raging torrent. The floodplain is the area of land that is likely to be under water when the creek rushes over its banks. In a sense, the floodplain is the full extension of the creek.
The 100-year floodplain is the land that is predicted to flood during a 100-year storm, which has a 1% chance of occurring in any given year. You may also hear the 100-year floodplain called the 1% annual chance floodplain or base flood. Areas within the 100-year floodplain may flood in much smaller storms as well. The 100-year floodplain is used by FEMA to administer the federal flood insurance program and the City of Austin to regulate development.