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Description:
Source: https://erdc-library.erdc.dren.mil/jspui/ ; Tests were conducted on a 1:25- scale model to develop the most feasible and permanent solution to a vortex problem at the Lower St. Anthony Falls Lock Intake on the Mississippi River at Minneapolis, Minnesota. On 10 March 1974, a lock employee in a small boat was accidentally drawn into the vortex and killed. Since that time a delayed valve-operating schedule has been used, which results in a fill time in excess of 14 min or about twice the design fill time; and although the vortex condition is reduced, the conditions are not considered satisfactory or safe. The lock is 56 ft wide, 400 ft long, and has a lift of 25 ft. The recommended design (type 5) moved the intakes from the top of the upper gate sill and positioned a new intake in the upstream face of the sill, lowered the approach geometry in the approach to the intake ports, lengthened the bull-nose pier 28.75 ft between the existing lock and a possible future auxiliary lock and replaced the 7.5-ft-radius nose of the pier with an elliptical nose, added a vortex suppressor across the 56-ft-wide approach, and modified the culvert tainter control valve schedule from 2.07 min to 4.14 and 6.21 min. These modifications to the intake, geometry of the structure, and approach, together with the slower valve schedules, permited vortex-free operation of the lock. The lock filled in 7.9 min with a 4.14-min valve schedule. The lock can be filled in 8.9 min with a 6.21-min valve schedule. In order to obtain these satisfactory operating conditions and vortex-free operation, the type 5 design as described must be adopted and operated as recommended. Optimum conditions will not be obtained with adoption of only parts of the type 5 design.