S.D. Codified Laws § 46A-15-4
The county commissioners of any county bordering the Missouri River may, upon an affirmative vote of the qualified voters of the county, expend money for the purpose of improving navigation on the river where the river borders the county. The funds shall be expended in conjunction with appropriations made by the United States government in proportionate amounts as may be agreed upon by the county board of commissioners and the chief of engineers of the United States Army for the purpose of aiding in the securing of a permanent navigable channel in the river. The funds shall be expended in accordance with plans conforming to the character and approved methods of improvement of the river as determined by the chief of engineers of the United States Army.
The county commissioners may appropriate moneys out of the general funds of the county available for county purposes to meet the expense of any such improvements.
SDCL 46A-15-4