138 



FLOODS AT THE MAKCHESTEE WATERWORKS 



below, with an 80 feet bank, have together an additional 

 collecting ground of about 7,900 acres, making the total 

 drainage to these three reservoirs 15,400 statute acres. The 

 Torside Reservoir is nearly two miles in length, and the 

 Rhodes Wood Reservoir about a mile. 



The following are some particulars of the reservoirs : — 



In the execution of works of this magnitude, placed across 

 a valley down which the ordinary water and impetuous floods 

 of so large a tract of mountain land are hurried with rapidity, 

 it is very important to provide ample means for the safe pas- 

 sage of the water. Observations had accordingly been made 

 with reference to this particular object for some jears pre- 

 vious to the laying out of the works. From these observa- 

 tions it appeared that it was not likely that many floods 

 would exceed 10 feet per second for every 100 acres of 

 collecting ground, and that provision for 15 feet per second 

 would be ample. The ■ Woodhead Reservoir was the first 

 which was laid out for construction, and in designing the side 

 channels or watercourses for carrying away the floods during 

 the early progress of the embankment across the river course, 

 they were formed of such dimensions as would, with the 

 assistance of a large discharge pipe under the embankment, 

 pass off" safely about 1,000 cubic feet of water per second, 

 being at the rate of about 15 feet per second for every 100 

 acres. 



