The hydraulic model investigations reported herein were concerned with planning and design of a new single-lift, 110- by 670-ft lock (pintle to pintle) at the existing Bankhead Lock and Dam on the Black Warrior River in Alabama. Presently, tows negotiate the 69-ft lift at the Bankhead project through a double-lift lock with chamber dimensions of only 52 by 285 ft. Multiple lockages are required for all but the very small tows. Tests were conducted on two models: a 1:100-scale general model which reproduced the river for approximately 1.5 miles upstream and downstream from the dam and included, in addition to the proposed lock, the existing powerhouse, spillway, and lock; and a 1:25-scale model of the filling and emptying system for the new lock. Two basic plans (sites) for the new lock were considered and preliminary tests demonstrated that acceptable navigation conditions could be provided with the lock at either site. (Author).