Analytical Assessment of the Proposed Raw Water Intake Pollutant Diversion Structure

The St. Anthony Falls Laboratory was contracted by Short ElBott Hendrickson to perform an assessment of potential sedimentation related issues associated with the installation of a flow diversion structure at the Minneapolis Water Works raw water intake. The Minneapolis Water Works raw water intake withdraws water from the Mississippi river at approximately river mile 858.5, Following treatment, the water becomes the primary water supply for Minneapolis and some suburbs. To continue to operate following a contaminant spill upstream of the intake requires the installation of a diversion structure which can effectively divert non~water soluble contaminants past the intake structure. The project involved the review of key riverine related issues including: • The potential for siltation to occur in the region downstream of the diversion structure between the island and intake. • The potential for erosion of the far bank and the island caused by channel constriction. • The potential for de~pening of the primary channel due to the constriction. • The potential for sediment and contaminants to enter the downstream end of the channel. • The general stability of the island. In addition to these issues, several secondary operational related issues were also reviewed.