154 



C. W. DARLEY. 



corrugated galvanized iron, resting upon hardwood supports. 

 Central section of roofing a segmental arch without principals ; 

 segmental portion at sides covered with a lean-to roof resting 

 against the parapet wall. Gutter channel formed at junction of 

 lean-to and foot of arch. 



Of this type four Reservoirs have been constructed, the sizes, 

 capacity, and cost are as follows : — 



Avail, cap. in gals. Cost per 1,000 gals. 



No. 



Dimensions. 



60' diam. 12' deep 

 60' „ 15' „ 

 60' „ 15' „ 

 30' „ 12' „ 



198,200 



246,600 



246,600 



49,500 



£9 16 S . lid. 



£7 1 3s. Od. 



£8 10s. 7d. 



£17 16s. 4d. 



All the foregoing types of Reservoirs have concrete floors vary- 

 ing from six to twelve inches in thickness, according to the nature 

 of the bottom, the concrete being thickened for a square of about 

 three feet under each pier or roof support. The concrete is 

 rendered over with a coat of cement mortar three-quarters of an 

 inch thick, over which are laid two courses of bricks laid on their 

 flat, flushed and grouted full in cement mortar, the upper course 

 of brickwork being finally rendered over with a coat of cement 

 mortar three-quarters of an inch thick. This has in all cases been 

 found sufficient to make a thoroughly sound and water-tight 

 bottom, in not one single instance has any leakage been observed. 



The brick abutments are in all cases backed with from nine to 

 twelve inches of cement concrete carefully laid in layers as the 

 brickwork rises — this ensures a perfectly sound filling between 

 brickwork and the face of the excavation, which should in all 

 cases be taken out as carefully as possible to prevent any slips or 

 disturbances in the surrounding formation. 



In my opinion the use of puddle clay under the floor or behind 

 the walls of a Reservoir should be studiously avoided, although 

 this form of construction is frequently illustrated and recommended 

 in text books. Upon examining a Reservoir that was in course 

 of construction in this way not many years ago, I observed con- 



