Saturday, April 27, 2019

Mississippi Lock and Dam #4 at Wings over Alma, WI

(John A. Weeks IIISatellite)

The dam consists of a concrete structure 1,357 feet long with six roller gates and 22 Tainter gates. The movable
dam has six roller gates (20 feet high by 60 feet long), 18 non-submersible Tainter gates (15 feet high by 35 feet
long), and four submersible Tainter gates (15 feet high by 35 feet long). Completing the dam system is an earthen
embankment approximately 5,500 feet long, located between the movable dam and high ground on the Minnesota
side of the river. The dam foundation consists of piles in sand and gravel.

The lock was put in operation in May 1935. At the time it was built, the dam's combination of roller and Tainter
gates was believed to have been the first of its type to be constructed. Cold weather created several problems
during construction of the complex. Approximately 120 timber pilings split and had to be pulled and replaced;
engineers speculated that sap freezing in the green pilings may have caused the splitting. Ten major injuries, 296
minor injuries, and three deaths were reported during the construction of the dam.

The pool created by Lock and Dam 4 is the longest in river miles (44.1 miles) with the largest water area of all the
Mississippi River pools in the St. Paul District. It encompasses Lake Pepin, which was formed in geologic time by
sediment deposited in the Mississippi River at the mouth of Wisconsin’s Chippewa River. The lake is 22 miles long
and up to 2.5 miles wide. It is the only natural lake in the Mississippi River’s main channel.

Faith Camp shared
Sam Schropp The picture above isn't a current [Spring, 2019] picture. The dams are wide open from Lock 2 to Mel Price at Alton.
I copied a satellite image to show the width of the historic channel cut by the melting ice-age glacier runoff.
I assume the four Tainter gates next to the roller gates are the submersible gates because I presume they are the first ones they would open and they would want to keep the normal flow in the middle of the river to reduce erosion. Note that it appears two of them are open in this image.

John Weeks III

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