would be provided with miter lock gates and the gates as well as the valves would be operated by electric machinery. Power would be supplied normally from commercial sources but a stand-by internalcombustion generating unit would be provided in the operating building for emergencies. 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 each lock. The pintle-to-pintle length of all locks would be about 675 feet. 108. Dams, structural features.-All dams except the Narrows would consist of earth fill with steel sheet-pile cut-offs and concrete gravity spillways. The earth fill sections would be faced with riprap. The Narrows Dam would be an earth and rock fill structure with a low concrete cut-off wall where rock is exposed by the inspection trench. The top widths of the dams would vary from 24 to 26 feet and the side slopes would be 1 on 3, except in two instances where they would be 1 on 4% on the downstream face. Roadways would be constructed across the tops of three of the dams. Spillways, alongside of locks resting on wood piles, would also be placed on wood piles. Heavy stones and timber cribs filled with rock would give protection at the downstream toes of the overflow spillways. The Narrows Dam spillway would discharge through a tunnel. Five spillways, including the Narrows, would have crest gates and three would have fixed crests. 109. Channels and canals. In general, the waterway would have a project depth of 9 feet with 1 foot overdepth and a bottom width of at least 170 feet. In the divide cut where the cost of such width would be excessive, a width of 150 feet with passing places 200 feet wide at least every 4 miles 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 width would be 150 feet. The passing places would each be 1,000 feet long and 200 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 broader channel if it were desired to widen the cut at some future date. Side slopes in each cut would be generally 1 vertical on 2 horizontal. In rock cuts the slopes would be 4 vertical and 1 horizontal. Levee sections along the canal would have slopes of 1 vertical on 3 horizontal. All sections of the narrow channel 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. 110. Channel rectification.-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, some rectification would be necessary for nearly the entire channel length. Several cut-off channels are included in order to eliminate certain 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 Gainesville lock and dam from mile 227.7 to 228.8 designated as the Rattlesnake Bend cut-off. This cut-off would eliminate approximately 10 miles of winding river channel. In all, there would be 21 cut-offs varying in length from 1,000 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 33 miles. 111. Water requirements.-The summit pool at the head of the 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 would supply the natural losses from the summit or narrows pool plus enough water to make about one-half lockage per day at the narrows lock. During dry periods, the local in-flow would be negligible. One of the chief advantages of the 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 water losses in the waterway. 112. The main water requirements are for lockage, evaporation, seepage and lock leakage. Because the normal lift of the narrows lock is 43 feet, the highest lift on the proposed waterway, the lockage requirements for this lock would be the greatest. Average lockage requirements have been estimated to be 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 110 feet wide and 600 feet clear length, a pintle-to-pintle length of about 675 is required. The average water requirement for this lock, with a 43-foot lift, would be 55 acre-feet per lockage. Since the maximum evaporation from the summit pool may occur when the 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-foot per day per foot of lift or about 22 acre-feet per day at the Narrows lock. The total loss 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. 113. Except for the Bay Springs lock, the locks in the canal section have lifts of only 15 feet, and require an average of only 19.2 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, local run-off cannot be depended upon to supply the loss due to possible seepage from the lateral canal. 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 be constructed. Those investigations showed that certain sections of the lateral canal would require lining in order to prevent possible excessive leakage. The estimated maximum 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. 114. 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. Because the narrows lock requires about 35.8 acre-feet more water per lockage than the 15-foot 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 seven 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 seven lockages per day, it would be necessary to bypass water at the narrows lock, in addition to the water required for lockages, to offset seepage in the lateral canal. It is estimated that the water passed on from the summit and lateral canal section, together with the increased drainage, would be more than ample to supply the losses and requirements for lockages in the river section. 115. The data in table 35 show the estimated amount of water that would be diverted from the Tennessee River for lockages varying from 0 to 24 per day. As stated in exhibit A, the diversion of 400 cubic feet per second would reduce somewhat the power potentialities of the Tennessee River, but not to a serious extent. 116. 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 those four formations, there is also considerable alluvium along the stream valleys. 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, revealed that the material is practically uncompressible under loads as great as 20 tons per square foot, and that it is highly impervious. 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. 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 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. 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. 117. Bridges and clearances.-The minimum clearances adopted for bridges over the waterway under investigation are: Horizontal 200 feet; vertical, 52 feet above the normal pool, or 40 feet above that high water which is exceeded only 1 percent of the time, whichever is the greater. The proposed plan of improvement involves the construction or alteration of 13 highway and 7 railroad bridges in order to provide these clearances. Only 3 of the existing bridges on the waterway would be satisfactory. These bridges (1 railroad doubletrack lift bridge and 2 highway fixed high level) do not have the required horizontal clearance; however, as they are practically new bridges and the clearances are only slightly less than required, they are considered adequate. The old Mississippi Highway No. 41 bridge has been abandoned and would be removed. The Mississippi Highway No. 6 bridge would be removed because of the proposed relocation of the highway in the plan of improvement. It is proposed to provide a double-leaf bascule bridge over the Narrows lock, thereby eliminating the present structure over Mackeys Creek at Bay Springs, Miss. The locations, owner and route, and main features of the bridges involved in the plan of improvement are shown in table 36. 1 250-foot truss; 2 95-foot trusses; 2 piers 1 222-foot lift truss; 2 100-foot trusses; 1 210-foot lift truss; 1 120-foot truss; 1 210-foot lift truss; 2 60-foot trusses; 1 210-foot truss; 2 100-foot trusses; 4 1 210-foot lift truss; 1 80-foot truss; 1 210-foot truss; 2 piers; 625-foot con- 1 210-foot lift truss; 2 80-foot trusses; Nothing; traffic to be routed over State 1 210-foot lift truss; 2 80-foot trusses; 4 1 210-foot truss; 2 100-foot trusses; 4 1 210-foot truss; 2 100-foot trusses; 4 1 160-foot, double leaf bascule, integral Nothing; traffic to be routed over See footnotes at end of table, p. 168. |