River Barge Port
The Continental Grain Company owns a barge port on the Minnesota River where they load grain. Recently sedimentation of the port has required the company to dredge to maintain operations. SAFL researchers studied the problem and were able to identify a natural shift in channel alignment that was causing the deposition. That problem, left unchecked, would require even more dredging. SAFL recommended placement of a spur dike to control the channel alignment and reduce sedimentation within the port.

Wilmarth Cooling Water Intake Model Study
A Large migrating bar threatened to bury the intakes in sand of a power plant on the Minnesota River near Wilmarth, Minnesota. Physical and numerical studies at SAFL allowed replication of the bar and its underlying causes. Further study resulted in design of 3 rock spur dikes to deflect flow and restore favorable conditions at the intake. The dikes have been installed and are operating successfully. This study was commissioned by Northern States Power Company.

Mississippi River Bridge at Little Falls
Construction of a new bridge over the Mississippi River near Little Falls, Minnesota, has led to problematic changes in river discharge patterns, sedimentation and water quality. The bridge includes a span over the main channel on the right bank, a long approach embankment through the upper part of a reservoir, and a short span over a minor channel near the left bank. The long approach embankment was suspected to cause increased reservoir sedimentation, decreased depth, and stagnant water, all of which led to degraded water quality as evidenced by odors arising from the deposition zone. SAFL conducted physical and numerical modeling to diagnose the causes of the changed sedimentation patterns by comparing pre- and post-project conditions. Results showed that the long embankment section cut off a third, central channel, which resulted in the large stagnant area and the associated problems. SAFL researchers proposed and tested various mitigative measures including dredging and adding a third span. A third span at the former channel location would have alleviated many of the symptoms but would be too costly. Instead, dredging and increasing the conveyance of the second channel was determined to have similar benefits and was recommended due to its lower cost.

Countermeasures to Protect Bridge Piers from Scour
Scour around bridge piers is the most common cause of bridge failure in the U.S. Performance, applicability, and cost of countermeasures to protect bridge piers from scour was recently studied at SAFL. Two kinds of countermeasures were examined: flow altering, such as sacrificial piles, and armoring countermeasures such as mattresses, riprap and cable tied blocks. None of the flow altering countermeasures were found to be overly effective. Riprap using a geotextile sealed to the pier and a mattress of cable tied blocks underlain by a geotextile tied to the pier were found to be the most effective.

Minnesota River Bridge Model Study
Severe constrictions caused by flooding at the Hwy 69 bridge crossing the Minnesota River just north of LeSueur, Minnesota, were causing scour that endangered piers and caused a large bar to form. A 1:200 distorted scale model study to test below- and above-bankfull corrective measures was built at SAFL. T-spur dikes, permeable dikes, and other maintenance oriented corrections were tested. Recommended changes have been in place for over a decade and are operating successfully. The study was funded by the Minnesota Department of Transportation.