Mo. Rev. Stat. § 227.270
Whenever the construction or operation of any waterpower and/or hydroelectric project results in the inundation of any portion of a state highway, the state highways and transportation commission is authorized to abandon said portion of said highway, and, in addition to the relocations mentioned in section 227.260, to relocate, construct and maintain, as in its opinion may be best from considerations of good engineering, safety to the general public, economy and directness of route and service to the locality, so much of said highway as in the judgment of said commission is necessary on account of such inundation, and abandon the portion of the highway in lieu of which the relocation is made, provided that any such relocation shall not deviate from any designated point, if any named in any law, unless such designated point shall itself be inundated; provided, that when the seat of county government of any county is inundated by virtue of the construction or operation of any waterpower, and/or hydroelectric project, rendering necessary the reestablishment and relocation of such seat of county government, such seat of county government having prior to such inundation, been a designated point on any state highway, such relocation and reestablished seat of county government shall be considered for all purposes of state road designation and construction, as the original seat of county government of such county.
§ 227.270, RSMo