Okla. Stat. tit. 82 § 571.1
When the board of directors of a conservancy district determines that a lesser estate is needed for flood control purposes than fee simple absolute, the board shall have the right to condemn for easement purposes an easement as may be required.
In such cases, the measure of damages payable to a landowner shall be the difference in the fair market value of the entire tract with the easement and the fair market value of the entire tract without the easement. Commissioners or jurors shall take into consideration in assessing damages for permanent inundation or for flowage easements for intermittent inundation of land, the estimated or anticipated frequency of inundation, the value of the remnant of the estate for landowner's agricultural or other economic use, and such other relevant factors as may be ascertained or anticipated by reasonable evaluation.
Okla. Stat. tit. 82, § 571.1