Jackson lock and dam will replace three out-of-date, small, low-lift locks and dams on the Tombigbee River. The lock is to be of the high-lift type with chamber dimensions of 110 by 600 ft, and will be located in the right bank about 600 ft landward of the river's edge. Model tests were conducted on a 1:120-scale model that reproduced approximately 2.3 miles of the river and the lock and dam structure. The model investigation was concerned principally with navigation conditions in the upper and lower lock approaches and over the fixed-crest spillway under various flow conditions, and determination of the best dredging plan, lock wall arrangements, and methods of overcoming any undesirable conditions. Another purpose of the model was to permit navigation interests to observe the structure in operation and satisfy themselves of its acceptability from a navigation standpoint. (Author Modified Abstract).