Rock excavation. Abstract of bids received at Louisville, Kentucky, September 24, 1870, in response to advertisement dated Louisville, Kentucky, July 24, 1870, calling for proposals for improving the Tennessee River, below Chattanooga, Tennessee. No. 1.-Bidder: O. J. Jennings, Syracuse, Onondaga County, New York. Guarantors: C. J. De Graw and D. E. Fay, Fulton, Oswego County, New York. Certified by James D. Lusher, assistant assessor 3d division of 22d district, New York. Abstract of bids received at Louisville, Kentucky, September 24, 1870, &c.-Continued. No. 2.-Bidder: J. H. Dennis, Louisville, Kentucky. Guarantors: Isham Henderson and E. Graves, Louisville, Kentucky. Certified by I. L. Divine. Ross's Tow-head: Widow's Bar: Quantity in cubic yards. Amount Belfont Shoals: Quantity in cubic yards. Abstract of bids received at Louisville, Kentucky, September 24, 1870, &c.—Continued. No. 3.-Bidder: J. J. Hinds, Decatur, Morgan County, Alabama. Guarantors: D. C. Whitney and J. M. Hinds, Decatur, Morgan County, Alabama. Certified by George E. Spencer. Amount 25.00 Gunter's Reef: Number. Abstract of contracts between Major G. Weitzel, Corps of Engineers, on behalf of the United States, and J. H. Dennis, for the improvement of the Tennessee River at certain points. Name of contractor. Respectfully submitted. 1 J. H. Dennis. Louisville, Ky. Isham Henderson $50, 000 | Oct.20, 1870 Ross Tow-head $4.00 $225 375 2.25 375 2.25 * Supplementary contract. G. WEITZEL, Major of Engineers. M 1. UNITED STATES ENGINEER OFFICE, Chattanooga, Tennessee, August 9, 1871. MAJOR: In compliance with verbal instructions, and in reply to Department letter of the 14th ultimo, approving of the application of $35,000 for the improvement of the Tennessee River above Chattanooga, and suggesting that a report of the project in detail be submitted, I have the honor to submit the following: GENERAL CHARACTER OF OBSTRUCTIONS. The obstructions to navigation above Chattanooga, like the majority of those below, are "low-water obstructions," and consist of bars, either rock or gravel, extending across the river, with a length varying from 60 feet to two miles; the depth of water over these bars varying from 10 inches to 30 inches, at extreme low water; and the current varying from three to six miles per hour. Between these bars the stream is deep and the current less swift, and the river is thus divided into pools and chutes. The general nature of the rock-bed is limestone, at some points largely interpersed with flints. Across these bars the water has, in many instances, cut for itself, at low water, a channel-way, always crooked, generally narrow, and with isolated rocks or loose boulders obstructing them, thus rendering the navigation of these passages both difficult and dangerous. FORMER IMPROVEMENTS. Attempts to improve the navigation have already been made at some of the obstructions. The first, in 1832, by Colonel Long; the second, in 1856, by Colonel J. McClellan. The method employed in both instances was the construction of "wing-dams," for the purpose of con- . tracting the water-way at low water, with a view of deepening the water on the shoals. Time and experience have shown that the work done at those periods was inadequate, if not, to a certain extent, incorrect. The following are the defects as now seen: 1. Cross-section of the dam too small. 2. Fragments of stone used in their construction so small and light as to be carried away by the force of the current and the action of drift, 3. The timber employed in their construction being exposed to the influence of wet and dry rot, has been dislodged or carried away, to the great destruction of the dam. 4. In many cases the axis of the dam makes too great an angle with the axis of the current, thus tending to pile the water up suddenly along the entire face of the dam; instead of deflecting the water, and causing it to accumulate on or above the obstruction, to expose the crest of the dam to greater abrasion and prevent the deposition of sediment; all of which ill effects would be, to a great extent, avoided by dams making small angles with the axis of the current. 5. The junction of the dams with the shore insecurely established, thus enabling the water to seek a passage between the end of the dam and shore, and thereby destroying, in a measure, the efficacy of the dam. As a result of the above defects, but little benefit is now obtained at the points where work has been done. PROPOSED GENERAL PLAN OF IMPROVEMENT. In view of the above facts, and of the small amount to be expended in comparison with the obstructions, the following general plan of improvement is proposed : Removal of a small amount of solid rock from the natural channel. Removal of isolated rocks and boulders from the natural channel. Removal of gravel, sand, and snags from certain bars. Construction of riprap dams to contract the water-way, all at such points as shall best improve the navigation, and give at extreme low water a channel-way over these obstructions at least 3 feet deep and 140 feet wide. POINTS FOR IMPROVEMENT, WITH DETAILS OF PLAN. 1. Sandy Creek Shoals, the first important obstruction above Chattanooga, situated about thirty-five miles above Chattanooga. The obstruction consists of a rock-bar, a gravel-bar, and a rock-reef, the passage through which is much obstructed, at low water, by detached rocks. Over the rock-bar there is at low water but 20 inches of water; over the gravel-bar, but 15 inches; the detached rocks in the passage are exposed to view at extreme low water. Former improvements consisted of a dam extending from the head of Tow-head to left bank, angle being about 70°, for the purpose of accumulating all the water, at low water, on the right chute or channel (the river being divided by the Tow-head and island below) of a dam connecting the Tow-head and island, and of a long dam at the foot of the island to confine the water and carry over the rock-ledge below. The dam at the head of the Tow-head has been so abraded as to be of little or no use; the connection between this dam and the left bank has been destroyed, so that there is now a channel for steamboats between the head of the Tow-head dam and bank, the same between the end of the Tow-head dam and the island, while the dam at the foot of the island is also much broken, owing to decay of timbers. It is proposed to construct a new dam at the head of the Towhead, diminishing the angle to 45°, and extending two-thirds of the way across the river, to remove a portion of the old dam near left bank, to repair |