Elected and appointed officialdom turned out in their finest for a groundbreaking celebration on September 8, 1920, for the Thirty-Ninth Street conduit extension. They are posing on a pile driving rig owned by Great Lakes Dredge and Dock Company. Central casting included the two laborers for the sake of diversity. (MWRD photo 7814)

A diversion ditch was created to the south of the East Arm so construction of a sewer could proceed in the bed of the East Arm. Flow is entering the diversion ditch on May 17, 1923, in this view from the Halsted Street headwall looking southwest. The double row of pilings and sheeting formed a barrier to force water into the diversion ditch. (MWRD photo 9716)

Where a wide, open channel diversion ditch was constrained by adjoining buildings and a bridge, a timber flume was constructed, as shown here on July 12, 1923, looking west of Halsted Street toward the Morgan Street bridge. The buildings at left house Union Stock Yards and Transit Company power and water utilities. (MWRD photo 9865)

The western end of the diversion ditch is at left after passing under the railroad in the right foreground. The railroad bridge at right crosses the East Arm. Taken from an elevated walkway on August 14, 1922, this view is looking northwest. The South Fork is in the center background. (MWRD photo 9399)

The cofferdam was built in the East Arm immediately west of the Halsted Street headwall. Looking north on September 26, 1922, a control chamber and transition structure will be built inside the cofferdam to connect the Thirty-Ninth Street conduit to the new sewer extension and diversion ditch. (MWRD photo 9499)

Looking west from the Halsted Street headwall on September 24, 1924, the eastern half of the East Arm has been dewatered. An additional barrier was placed across the arm east of Morgan Street. Construction of the new sewer could begin east of Morgan, while additional work was needed west of Morgan before dewatering could begin. (MWRD photo 11111)

The Thirty-Ninth Street conduit extension, constructed by the open cut method, eliminated the East Arm. The first part of the new sewer is the reinforced concrete invert, shown here completed on September 24, 1924, looking eastward from a point east of Racine Avenue toward the Morgan Street bridge. The walls of the new sewer were cast where the reinforcing rods protrude on each side of the invert. (MWRD photo 11210)

September 24, 1924. Looking in the opposite direction from where Photograph 2.34 was taken, the reinforced concrete side walls and crown of the new Thirty-Ninth Street conduit extension are completed, together with the interior and exterior formwork yet to be removed. The Racine Avenue railroad bridge is in the background. (MWRD photograph 11209)

September 24, 1924. A different view of construction of the Thirty-Ninth Street conduit extension near the same location as Photos 2.10 and 2.11, looking east from Racine Avenue, shows the exterior of the completed conduit at left and, in the center, formwork is being installed for sidewalls for the next segment. (MWRD photo 11208)

On June 12, 1926, looking northeast from a point several hundred feet west of Halsted Street, formwork is being installed for the closing portion of the Thirty-Ninth Street conduit extension. When the sewer is complete, the trench backfilled, and a road built for Thirty-Ninth Street, east and west neighborhoods will be connected. (MWRD photo 11801)

October 16, 1924. The new outfall for the Thirty-Ninth Street conduit extension, located west of Racine Avenue, is still under construction. The railroad bridge at Racine Avenue is in the background. In addition to the outfall, a connection at right was constructed and fitted with a bulkhead for future flow to be diverted to the planned Racine Avenue Pumping Station. The station was not in service until 1939. (MWRD photo 11247)

Although the Thirty-Ninth Street conduit extension barrel was complete, numerous industrial connections had to be completed before the new sewer could be placed in service. The example shown is from June 26, 1925. Due to the cooperation of each industry, all connections were completed expeditiously. (MWRD photo 11865)

The South Fork of the South Branch on June 13, 1977, looking north from the roof of the Racine Avenue Pumping Station. The channel in the foreground receives combined sewage and stormwater pumped during excessive rainfall events. The fill behind the dock wall at right closed off the former East Arm. The Thirty-Fifth Street bridge is in the background. (MWRD photo dated June 13, 1977, unnumbered vault scan)

A District engineer inspects the federal inner breakwater on April 30, 1936, prior to the award of contracts to construct the Chicago River Controlling Works. Looking north on a foggy day from a point east of Randolph Street, the US Coast Guard Station is faintly visible. A wall is mounted on the east side of the breakwater to diminish the force of wind-driven waves. This breakwater will be included in the project to separate the waters of Lake Michigan and the Chicago River. (MWRD photo 21102)

June 4, 1936. Workers on two construction barges are driving timber test piles into the bed of Chicago Harbor where the navigation lock will be built. The test piles will determine the loading capacity of timber piles used for the foundation of lock structures. Looking east beyond the workers, the Chicago Harbor lighthouse on the outer breakwater is in the background. (MWRD photo 21344)

September 3, 1936. A huge cofferdam will be constructed to isolate the area where lock structures will be built in the dry. A laborer is guiding the driving of an interlocking steel sheet pile for one cell that will be part of numerous interconnected cells to form a cofferdam. In the background at left, Municipal Pier, presently known as Navy Pier, is visible. (MWRD photo 22026)

September 30, 1936. The cofferdam consists of numerous interconnected cells enclosing a rectangular area. A bulk cargo vessel is filling each cell with crushed rock and sand to provide stability for the cofferdam to resist the force of water when the space enclosed by the cofferdam is dewatered. Looking west, the US Coast Guard Station and Chicago skyline are in the background. (MWRD photo 22168)

October 27, 1936. If the interlock between individual steel sheet piles fails upon dewatering, the cell wall will deform or split open as it has here. The split can be repaired or minimized allowing construction of the lock structure in the area enclosed by the cofferdam to proceed. (MWRD photo 22306)

A failed cell wall viewed from inside the cell, June 10, 1937. The split has been laced together with steel cables and additional cables have been installed from the opposite side of the cell to restrain further movement. Splits in the cell wall adjacent to the lake do not occur due to the force of the water against the cell wall. (MWRD photo 23245)

The same split is viewed from the dewatered interior of the cofferdam, June 10, 1937. Additional cables have been installed to restrain the split from further movement. This split occurred after timber piles were driven into the lakebed. The gap between the split sheeting will be bridged with timbers and the spilled material put back into the cell so construction can proceed inside the cofferdam. (MWRD photo 23246)

Timber foundation piles are being driven within the west cofferdam, March 19, 1937. The piles are driven into the underlying stiff clay or hardpan clay beneath the lakebed sand. Each pile is driven to refusal. Piles are being driven in two cofferdams for the east and west lock gate structures. (MWRD photo 22858)

By June 1, 1937, all timber foundation piles have been driven in the east cofferdam and construction of concrete formwork is beginning. The top of each pile has been cut to a specified level to accommodate the overlying concrete floor of the lock structure. Looking south, the lock structures in each cofferdam, called gate blocks, are nearly identical. (MWRD photo 23166)

March 19, 1937, the mixing plan for the west cofferdam. A concrete mixing plant has been installed in each cofferdam. The crane is used to load aggregate, sand, and Portland cement into the hoppers on top of the mixing plant and to distribute each batch of concrete from the mixing machine at the bottom for placement in the lock gate structure. (MWRD photo 22859)

Formwork and steel reinforcing rods are being installed in the west cofferdam on April 19, 1937, for the floor of the northwest lock gate structure and the north half of the floor of the lock chamber beneath the closed lock gate. The south half of the floor is in the lower right foreground. (MWRD photo 22986)

April 19, 1937, looking west. Notice how close the formwork and reinforcing steel is to the cofferdam cell sheeting in the west cofferdam. When the lock structure is complete, the cofferdam will be removed. The curving reinforcing steel in the center begins to outline the recess for the northwest lock gate. (MWRD photo 22987)

By May 5, 1937, the northwest lock gate block is beginning to take shape as viewed from the southwest lock gate block looking north. The block will rise another 15 feet when complete. The northwest lock gate will fit into the recess in the block. The top of Navy Pier is in the background. (MWRD photo 23040)

June 1, 1937, looking west from the southeast lock gate. The side walls of the lock connecting the east and west gate blocks are constructed with rock-filled cells. The cells will be topped with a concrete cap enclosing the utility ducts. The 80-foot wide lock chamber will be constructed with concrete sidewalls and floor in the space between the two rows of cells at right. (MWRD photo 23172)