Niagara Falls 100.000-Hp. Development

26 ] Niagara Falls 100,000 Hp. Development Enlarging Channels and Erecting the Station Special Drill Boat Used for Excavating Channel Due to High Current Velocities. Details of Cofferdam Construction. By O. D. Dales Construction engineer Niagara Falls Power Company, Niagara Falls, N. Y. THE excavation of the 20-ft. channel from the head of the canal out into the Niagara River was through limestone for the first 1,000 ft. out from the shore, the balance being in hardpan. The drilling was done by four drill boats with steam drills, the holes being placed on 4-ft. centers each way. Drilling was carried down to 3 ft. below the finished grade. The dredging was done by three dipper dredges with 64-yd. buckets. The excavated material was placed in dump scows and towed out into the river just above the upper rapids, this class of excavation being similar to most dredging opera- tions in large rivers. Disposing of the excavated mate- rial was rather difficult on account of the location of the dumping ground. Extreme caution was exercised by the contractor, but in spite of this one dump scow broke its two tow lines and floated down the Canadian channel to below the upper cascade rapids where it went aground on some rocks about 800 ft. from the Canadian shore. The two men on board were removed by the Fort Niagara life-saving crew by means of shooting a line out to the scow and bringing them ashore in the breeches buoy. Most of the piers for supporting the two inner lines of booms were built in previous years and consist of concrete piers upon rock-filled timber cribs. These offered considerable resistance to the water so another type of pier has been developed which consists of Lackawanna steel sheet piling driven through the hard- pan to the rock, which is from 6 to 15 ft. below the bottom of the river. These piers were built as 6 ft. diameter cylinders filled with concrete from the hardpan to the top. Details are shown on an accompanying drawing. This type of pier was used in the outer line of booms and were placed 50 ft. apart except in the deep dredged channel where they were 150 ft. apart. As there was no hardpan in the dredged channel the bottom of the 6-ft. cylinders were encased in 19-ft. 6-in. square concrete bases 12 ft. high. The past winter was very severe and a large amount of ice passed through the Niagara River thoroughly testing these piers and booms. It has been the intention for a number of years to deepen the canal to 20 ft. below mean water level with a cross-section approaching as nearly as possible the typical section shown on the drawing herewith. Exca- vation had been carried on in the canal for a great number of years and up to 1912 had been excavated on the right-hand half, looking downstream, down to 20 ft. for nearly the entire length of the canal. The left-hand side of the canal was left at 14 ft. deep, while under the bridges it was approximately 14 ft. deep on both sides. In order to have sufficient water available for the operation of the new plant along with the old plants it was necessary to excavate and clean up the canal to a depth of 20 ft. for the entire width approaching the typical section shown on the drawing. The excava- Stoindard 5O-€t. Boom FIG. 35—ICE PROTECTION AT CANAL INTAKE ON NIAGARA RIVER