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30° THE PROGRESS OF RIVER IM- PROVEMENTS IN THE VI- CINITY OF PITTSBURG. BY J. W. ARRAS. (Continued from Feb. 4.) About June 8 the stage of water for the first time this season be- came favorable for raising the mova- ble dams in the Pittsburg district, and all of the dams previousty man- euvered were put up. Nos. 3 and 4 had just been completed by the con- tractors and a little work still re- mained to be done by the govern- ment, such as clearing away remains of cofferdams, removal of sediment- ary deposits in lock gate recesses, placing of a few horses, props and | witkets; etc. few days and on June 25 No. 3, and on the 30th No. 4, were also up, completing fér the first time in this locality a movable dam slackwater 35 miles in length, extending from Aspinwall on the Allegheny to Merrill, three miles below Beaver, on the Ohio. No blaring of trumpets or ostentation of any kind accompanied these initial operations, which were performed in the usual way, much as if the structures had been in use for years. For a short time the full benefits of all the pools were not at- tained. An extension of the lower guide wall at Davis island dam neces- sitated the depression of pool 2 about } i below its normal, level... until its completion in August. Immedi- ately above dam 4 the Jones & Laugh- 'tin Steel Co. was engaged, under a contract, in constructing a huge water intake pier, and cuiverts con- necting it with a pump station at bank. The gravel cofferdams_ sur- rounding a part of this work, and the immense caisson for pier, located directly above one of the bear-trap gates and the Chanoine wicket weir for regulating pool 4, were considered - so much a menace to the operation of the dam that it was deemed best by those in charge to afford every reas- onable facility to the contractor for speedily prosecuting his work to a stage more favorable for the dam maneuvers. This required about one month, during which time the pool was held down from 1 to 3 ft. below' its full height. ENTIRE WORK ACCOMPLISHED. Happily, this entire been successfully and its obstructiveness we menace' to the dam .- removed. Necessarily also during the progress of construction deposits and various debris accumulated in the vicinity work has accomplished, of the locks, which, being indifferently These required only a_ - THe Marine REVIEW removed by. contractors, occasioned slight obstructions to navigation when diverted from the open river channel to locks. These, as the season pfo- gressed, were removed by the govern- ment dredges, together with a low bar below lock 3 and a small ridge deposited in the recently dredged channel through Lacock's bar below dam 5. Accordingly these pools are now in excellent condition, having remained full during the recent un- precedented drought and the locks and dams in perfect working order, re- quiring under the present water con- ditions very little attention, consider- ing their newness. The number of breakages has been exiremely small, and of no importance wortny of men- tion, In view of the long service of Davis island dam, of which general type are also all the other movable dams in this district, it is singular what strange views should be entertained concerning them. Some persons--and not a few--had been patiently awaiting the construction of ordinary fixed dams. Others apparently understand- ing the dams are movable, never ex- pect to see them lowered. The mov- able feature in their estimation was only intended to facilitate their ini- tial raising or establishment. Even some navigators, although thoroughly familiar with the nature of these dams and their navigation, were quite in- credulous as to the new ones, and are only being reassured by degrees that there is no greater reason for doubting the capacity of one to re- main up and fulfill its mission than another. DESIGN OF MOVABLE DAMS. While it is true the general design and main characteristics of these movable dams. and their Jocks is the principles are involved in all, yet in dimensions and in the character and details of construction they differ wide- ly. The wickets, which comprise the important feature of all the dams, are of the Chanoine type, a French production invented over half a cen- tury ago, and extensively used in Europe. In outline they resemble each other closely, except as to length, but in details of construction they. dif- fer, 'Those in the older. dams, at Herr island, Davis island, and. at Merrill, are paneled wickets having heavy oaken frames. filled in with 2-in. planks. The modern wickets are built of heavy timbers throughout, enabling them to better withstand the abuse to which they are inevita- practically the same and same bly subjected. They are uniformly 3 ft, 9 in: wide, being set 4 ft, be- tween centers, thus leaving 5 1n. spaces for clearance in maneuvering and for the more exact regulation of pools, In length they vary from 9 ft. 9 in, of the shortest weir wickets at Davis island dam to 17 ft. 105 in. of the longest pass wicket at dams 2 and 3. These form the principal movable fea- ture of the dams proper and those parts of the weirs extending from bear-trap gates to abutments. They are raised endwise against the stream and in lowering fall with it, lying parallel with the current. In rising or lowering they act much as would a door or shutter hinged at its upstream end. But to facilitate their raising they are hinged near the middle to a_ steet iramework called the "horse,'\ which at its lower end is in turn hinged to the concrete foundation of the dam, thus forming a double hinge. When up they are supported by huge steel props, one end of which is attached to the horse where it is hinged to wicket, while the upstream or bottom end of wick- ets rests against sill of dam. At both ends of wickets, are handle plates in which engage hooks used for maneuvering them by the operat- ing forces on the boats. The manip- ulation of the raising and lowering hooks requires trained men. These usually become so expert in a few years as to be able to engage the raising hook in the wicket handles without much difficusty regardless of the velocity, or. erratic movements of the current. Having taken hold of the handle the wicket is quickly drawn upward, although retaining a compar- atively horizontal position, by means of a_ specially constructed hoisting engine on the maneuvering boat un- til the foot of prop is heard to drop into a notch in the cast iron hurter also attached to the concrete foun- dation of the dam. Then the hook is released and the current with slight assistance drives the upstream end of wicket down against the sill. ia lowering, the top of downstream end of wicket is drawn upstream by the maneuvering boat engine only a few inches until the foot of the prop drops a second time into a sliding step by which in lowering the prop is diverted around the first notch into the proper channel or track in hurter for again raising it. This mechanism is extremely simple and hence readily adaptable to great strength, which is most essential. NAVIGABLE PASSES OF MOVABLE DAMS. In the Pittsburg district the navi-