supply involved it would not be necessary to restrict the size of lock adopted to conserve water. At the same time it does not appear that the extra cost involved to provide lengths of 600 or 800 feet would be justified. The Board, therefore, is of the opinion that locks with clear inside dimensions of 75 by 450 feet would best satisfy these conditions and at the same time meet the expected requirements of navigation interests. The 75- by 450-foot lock could accommodate 5 barges and a towboat having unit widths up to 35 feet and unit lengths up to 145 feet, and would also accommodate a combination of 30- and 40-foot barges as well as a combination of 25- and 48-foot-wide barges. In selecting the 75- by 450-foot lock as the size best suited to the proposed waterway, it is contemplated that ultimately the economical tow for the waterway will consist of five 35- by 145-foot barges and a towboat of similar dimensions, and it is for this size tow that the waterway is designed.

117. Structural features of locks.-All locks, with the exception of the canal locks, would consist of concrete gravity upper and lower gate bay walls and concrete gravity intermediate walls. The intermediate walls of the 15-foot lift canal locks would be constructed of steel sheet piling tied to parallel sheet pile anchors by means of steel rods. The sheet piling wall would be capped with concrete and the backfill behind it would be paved. All 15-foot lift locks would be provided with 8- by 8-foot loop culverts located in the gate bay walls, while locks of higher lifts would have 9- by 9-foot continuous culverts with filling and emptying ports the full length of the lock chamber. Either type of culvert would be provided with tainter valves. Each lock would be provided with miter lock gates, and the gates as well as the culvert valves would be operated by hydraulic machinery. The pressure for the cylinders of the hydraulic machinery would be maintained by pumps powered by electric motors. Power would be supplied from commercial sources and a stand-by internal-combustion generating unit would be provided in the operating building for emergencies. Both the upper and lower gate sills at all locks would be 12 feet below the minimum pool elevation. All locks would be provided with an upstream guard wall and a downstream guide wall of sufficient length to accommodate the number of units which could be handled in one lockage. These walls would be concrete for all locks except the 15-foot lift canal locks, which would have wood pile and timber guide walls. In the canal, pile clusters to which tows could be moored while waiting for entry into the lock would be provided at each end of the locks. All locks supported on materials other than solid rock would be provided with a reinforced concrete floor with weep holes to relieve uplift pressure. Several of the locks in the canal section which would rest on earth of insufficient bearing strength would be supported by wood piles. The pintle to pintle length of all locks would be about 500 feet.

118. Size of channels and canal sections.-In general, the waterway would have a project depth of 9 feet with 1 foot overdepth and a bottom width of 170 feet, providing for two lanes of navigation for the standard tow 70 feet wide and 435 feet long. In the divide cut and in the Rattlesnake Bend cut-off where the cost of two-lane navigation

would be excessive, one-lane navigation with passing places at least every 4,000 feet would be provided. The project depth in the divide cut and in the Rattlesnake Bend cut-off would be 12 feet with 1 foot overdepth and the bottom widths would be 115 feet and 135 feet, respectively. The passing places would each be 1,000 feet long and 170 feet wide with 500 feet of transition section at each end. These passing places would all be located so that they could be utilized as part of a two-lane channel if it was desired to widen the cut at some future date. Side slopes in earth cut would be 1 vertical on 2 horizontal. In rock cuts the slopes would be 4 vertical on 1 horizontal. Levee sections along the canal would have slopes of 1 vertical on 3 horizontal. All sections of one-lane navigation would be on tangents or on curves with radii greater than 5,000 feet. On bends with radii less than 5,000 feet, the channel would be widened to provide for twolane navigation with a clear distance of 30 feet between each tow and the bank and 30 feet between passing tows, but the maximum widening would be held to 300 feet. The channel for double-lane navigation is designed to permit a towing speed for the standard tow of 5 miles per hour, and the single-lane channels are designed for a towing speed of 3.5 miles per hour with towboats of moderate horsepower. Assuming a draft of 8 feet, the required channel cross-sectional area for two-lane navigation would be 4.5 times the maximum cross-sectional area of the tow. For single-lane navigation the channel area would be three times the maximum tow section. (For detailed channel specifications and studies to determine proper channel cross sections, see appendix II, pt. 2.)1

119. Channel rectification required.-Through the river section dredging would be necessary to obtain the desired channel width and depth. In the lower reaches only occasional widening at curves or deepening immediately below dam sites would be necessary, while in the upper reaches, and especially above Barton Ferry Lock and Dam, channel rectification would be necessary for nearly the entire length. Several cut-off channels are proposed in order to eliminate certain very winding river sections. In the upper reaches these cut-offs would be numerous; however, most of them would be short, not exceeding 2,000 to 3,000 feet each. The longest as well as deepest cut-off would be between Demopolis and Epes Lock and Dam from mile 237.1 to 238.2 designated as the Rattlesnake Bend cut-off. This cutoff would eliminate approximately 10 miles of winding river channel. In all, there would be 17 cut-offs varying in length from 1,000 feet to 6,000 feet each. Of the 180 miles of river channel to be utilized for the proposed waterway between Demopolis and the junction of the canal, approximately 99 miles would need some rectification work. The proposed cut-offs and rectification work would shorten the present length of the river section approximately 31 miles.

120. Water requirements. The summit pool at the head of the proposed waterway would intercept a natural drainage area of about 66 square miles. This area has an estimated average run-off of about 1.32 cubic feet per second per square mile or a total of 87 cubic feet per second. It is estimated that, on the average, this local run-off 1 Not printed.

would supply the natural losses from the summit or Narrows pool plus enough water to make about one lockage per day at the Narrows lock. During dry periods the local inflow would be negligible. One of the chief advantages of the proposed route via the Yellow Creek divide cut is that it permits the diversion of water from the Tennessee River to supply the necessary water for lockages and various losses in the waterway.

121. The main water requirements are for lockage, evaporation, seepage, and lock leakage. The normal lift of the Narrows lock is 43 feet and, since this is the highest lift on the proposed waterway, the lockage requirements for this lock would be the greatest. Average lockage requirements have been estimated at three-fourths of a lock chamber per lockage, which is based on the assumption that lockages are made alternately two each way. For the proposed lock 75 feet wide and 450 feet clear length, a pintle to pintle length of 500 feet is required. The average water requirement for this lock with a 43-foot lift would be 27.8 acre-feet per lockage. Since the maximum evaporation from the summit pool may occur when the local run-off is practically zero, it would be necessary to divert water from the Tennessee River to supply this loss. The maximum evaporation in this region is estimated at about 6 inches per month, which from the 7,200-acre summit pool, plus divide canal, would amount to about 120 acre-feet per day. Seepage from the reservoir basin and through or under the proposed Narrows Dam is estimated to be negligible, but an allowance of 10 acre-feet per day has been made. Leakage through the lock gates and valves has been estimated not to exceed 0.5 acre-feet per day per foot of lift or 22 acre-feet per day at the Narrows lock. The total losses from the Narrows pool would then be 120+10+22=152 acre-feet per day, which, together with the requirements at the Narrows lock for lockages, would be the total water requirement provided additional water would not be necessary at lower sections of the waterway.

122. Except for the Bay Springs lock, the locks in the canal section have lifts of only 15 feet and, therefore, require, on the average, only 9.7 acre-feet of water per lockage. It is estimated that, with the 1 foot of storage provided in each of the lateral canal pools, the evaporation from these pools would be offset by local run-off from the 158 square miles of drainage area intercepted by the lateral canal. However, the loss from possible seepage from the lateral canal cannot be depended upon to be supplied by local run-off. The ground-water elevations during the fall of 1938 were determined, and tests were made as to the permeability of the material through which the lateral canal would have to be constructed. Those investigations showed that certain sections of the lateral canal would require lining in order to prevent possible excessive leakage. The results of the tests of the canal material, as made by the United States Waterways Experiment Station, are included in appendix II, part 2.1 The estimated maxi

1 Not printed.

86805-46- -6

mum seepage from the lateral canal section, as it is proposed to be constructed, is given in the following table:

་

1 Canal lined with material in the optimum state of compaction, having a coefficient of permeability equal to 10-6 cm. per second and a thickness of 1 foot.

123. It will be noted that the total seepage from the lateral canal section is estimated at 122 cubic feet per second, or 244 acre-feet per day. With no lockages, an additional water supply would be required to offset the seepage from the lateral canal and maintain the desired pool elevations. Since the Narrows lock requires about 18.1 acrefeet more water per lockage than the 15-foot lift locks in the lateral canal section, there would be this difference available in the canal section to offset seepage losses. However, it would require at least 13 lockages per day in order that this difference in the water requirement for the 15-foot and 43-foot lift locks would be sufficient to offset the estimated seepage from the lateral canal. With less than 13 lockages per day, it would therefore be necessary to by-pass water, in addition to the water required for lockages, at the Narrows to offset seepage in the lateral canal. It is estimated that the water passed on from the summit and lateral canal sections, together with the increased drainage, would be more than ample to supply the losses and requirements for lockages in the river section.

124. The following table shows the estimated amount of water that would be diverted from the Tennessee River for lockages varying from 0 to 24 per day:

TABLE 26.-Water requirements and tonnage capacities for various numbers of

lockages

1 Based on a 50-percent loading of barges and excluding lockages for pleasure craft.

2 Assuming no run-off from the additional drainage area above the Narrows lock and dam.

125. General foundation conditions. In general there are four geologic formations to be considered in relation to the proposed plan of improvement, namely: Selma Chalk, Eutaw formation, Tuscaloosa formation, and Mississippian rocks, the former two of which are of marine origin. In addition to these four formations, there is also considerable alluvium along the stream valleys. The characteristics of the reworked materials constituting the flood plain, in most cases making up the overburden, are of importance in studying the foundation conditions. Although the alluvial materials would not provide support for structures in very many cases, these materials would form the primary water barriers at most of the structures. Tests of Selma Chalk, the details of which are included in appendix II, part 2,1 revealed that the material is practically uncompressible under loads as great as 20 tons per square foot, and that it is highly impervious. As explained in subsequent paragraphs on foundations, the Eutaw formation was not found to be cemented at all sites. Where it was found to be coherent, however, undisturbed samples were obtained and tested to determine the change in void ratio that would occur upon the application of loads. The results of these tests, as well as of other tests, are indicated on diagrams included in appendix II, part 2.1 In cases of the unconsolidated Tuscaloosa formation, alluvium, and the unconsolidated Eutaw formation, mechanical-analysis diagrams were plotted which furnish a concise mathematical description of the materials encountered at the various sites. The results of the laboratory tests of foundation samples from each site indicated whether or not bearing piles would be required. The determination of coefficients of permeability of undisturbed foundation samples, samples from the canal section and of remolded borrow pit samples furnish bases for calculating seepage. The results of shear tests were plotted on diagrams which are also contained in appendix II, part 2.1 No tests were performed on cores of sandstone and limestone as it was apparent from visual inspection that these rocks would be unyielding under the loads proposed and also otherwise satisfactory.

126. Epes Lock and Dam-Structures (see pl. 53). The Epes Lock and Dam would be the first on the Tombigbee River above Demopolis and would be located at approximately mile 269.8 above Mobile. It would have a list of 31 feet, raising the waterway from elevation 64 to elevation 95. The structure would include a lock, spillway section, and overflow abutment section. The spillway would consist of a concrete gravity overflow section with four 12- by 80-foot drum gates. These gates would be operated hydraulically by pressure from the upper pool and controlled by valves located on the lock wall. When fully depressed the gates would fit into a recess in the top of the overflow section. A high-capacity low-pressure pump would be provided for supplying auxiliary water pressure for operating the gates under emergency conditions and for flushing out the gate recesses. The spillway capacity would be 44,000 cubic feet per second with upper pool at elevation 100, the elevation of the top of the abutment section. With this quantity of water passing over the spillway, the difference between the upper and lower pools would be approximately 1.3 feet. The abutment would be designed to be overtopped at this stage. The net length of spillway would be 320 feet. The maximum spillway section

1 Not printed.