Banner Associates presents draft environmental assessment for Big Sioux Division Channel Dike

Banner Associates project managers Kelli Buscher and Kent Johnson presented the draft Environmental Assessment for the Big Sioux Division Channel Dike at the Brookings County Drainage Board’s special session on June 8, 2026. Buscher described a historical dike and a later cut that redirected a portion of the Big Sioux River into a diversion channel and said the diversion has taken more flow since the dike failed prior to 2011. "She said the cost would be roughly $7.8 million to $12.45 million. She said the county would need to replace the bridge on 216th Street; replace roughly forty (40) culverts on 217th Street; and replace the bridge on 469th Avenue (County Road 19)."

The consultants outlined two alternatives: No-Action, which would allow the current flow pattern and growing diversion-channel volumes to continue, and reconstructing a diversion structure at the confluence to restore most flow to the main channel while preserving a small diversion for downstream livestock. Project Engineer Kent Johnson discussed wetland modeling and the indirect impacts of reconstruction and said a construction timeline would be feasible within a seasonal window — "about five months or even next year during the construction season." Commissioners asked whether reconstructing the dike could create issues elsewhere and were told the hydrologic interactions are complex and not easily predicted without further study. The board did not take a formal action on reconstruction and directed further engagement with Banner Associates and budget review in upcoming hearings.