Tex. Loc. Gov't Code § 263.203

If a county owns and controls land, or an interest in land, that is used or proposed to be used as a part of the site of a flood control, river and harbor improvement, water conservation, or other civil works project constructed or to be constructed by the United States, the county judge of the county, on order of the commissioners court or on a request of the United States that is supported by an order of the commissioners court, may convey an easement, or other interest in land, necessary for the construction, operation, and maintenance of the project to the United States or to a political subdivision, agency, or instrumentality of this state that is cooperating with the United States in the project.