An easement gives certain people or agencies a right to use a portion of property for a specific purpose. Common easements are for access, utilities, or drainage, but the easement is only for that stated purpose.
A drainage easement gives an agency (like the Town), the right to use a part of your property for drainage system elements or structures.
The agency granted an easement does not own the property, nor does it have any responsibility to maintain the vegetation on the property. The property owner is responsible for maintaining vegetation.
An easement owner has the right to enter your property to inspect their system and perform maintenance of their system elements. If you have encroached on the easement with structures (commonly a fence), it will have to be removed at your cost. The easement owner does not have to replace anything you have constructed on the easement.