The MacArthur Lock is the first lock in the four parallel lock complex. The south canal services the MacArthur and Poe Locks and has a maintained depth of 27.5 feet below low water datum.
The MacArthur Lock was completed in 1943 and has a length of 800 feet between the sills, a width of 80 feet, and a depth of 31 feet of water over the sills at low water datum. The reinforced concrete floor and monolithic concrete walls are constructed on a sandstone bedrock foundation. The monolithic walls each contain a service gallery and a filling/emptying culvert.
The thickness of the lock walls varies from 28 feet to 40 feet. The upper and lower pools are connected by culverts 11 feet wide and 14 feet high, which are located in the lower portion of both lock walls. Two filling and two emptying tainter-type valves control flow through the north and south culverts. The water enters the lock chamber through 11 ports in each of the 24 bottom laterals, which traverse the lock from each culvert. The emptying and filling valves are electric motor driven.
The lock is equipped with five gates plus an additional sill (Gate 1), for which a gate has never been installed, located at the upstream end of the lock. Intermediate gates (Gates 3 and 4), and operating gates (Gates 2 and 5) are located at each end of the lock. The intermediate gates are seldom used. At the downstream end of the lock is the downstream dewatering gate (Gate 6), also referred to as the guard gate. At the upstream and downstream end is a dewatering bulkhead which uses steel framed stoplogs.