ON THE BKADFORU WATERWORKS. 457 



are formed by making an ordinary brick or stone channel a few feet below 

 the level at which the stream is to be received. The channel is in section of 

 the shape of a letter U ; over the top open grating or stonework is placed, in 

 snch a manner as to allow water to flow freely through it. The ground at 

 the sides of the channel is made solid and impervious up to the level of the 

 side walls. Over the channel, and for any convenient breadth on both sides 

 of it, broken stone, gravel, or other filtering media are placed, through which 

 the water has to run before it can find its way into the conduit. In this way 

 any solid matter can be caught and separated from the water, and the water 

 can be obtained in the reservoir fit for immediate use. The water in the 

 reservoir is not liable to be discoloured by any sudden flow of turbid water 

 during heavy rains or thunder-storms, as the excess of water beyond the 

 quantity which can pass through the filter will flow oif down the side and 

 waste channels made for the purpose. 



This mode of admitting water to conduits and reservoirs is entirely self- 

 acting, does not require attention during storms, and the dirt on the filters 

 will be carried away by floods or can be easily removed. 



The works for drawing water out of reservoirs are not without difficulties 

 of their pecuUar Idnd. The mode usually adopted is to make a tunnel or 

 culvert through the embankment at the lowest level at which the water is 

 required to be drawn ; and at the middle of this culvert, but a little within 

 the puddle-core, to erect a strong shaft or well in which to place the valves 

 for di-awing off' the water. The rods and apparatus for opening and shutting 

 these valves are taken up the shaft to the top of the embankment. This mode 

 of construction is attended with many difficulties, and often leads to breakage 

 of the work, and to consequent leakage of water from the reservoir. This 

 breakage arises from unequal settlement ; for if the foundations of the shaft 

 are made rigid and secure, the shaft itself stands, whilst the tunnel or culvert 

 on both sides of it cannot be kept so rigidly in position, and fractures conse- 

 quently take place, generally on both sides of the vertical shaft. The settle- 

 nient under the embankment is also necessarily unequal, the middle and 

 highest part being much heavier than the inner and outer parts. The 

 settlement of the embankment is often both vertical and lateral, on account 

 of the spreading of the foundation work of the embankment, which some- 

 times tears the masonry asunder, and so increases the injury caused by 

 the unequal settlement round the vertical valve-shaft. To avoid these 

 difficulties, the tunnel or culvert is now frequently made in the solid ground 

 at the side of the vaUey, some distance from the middle of the embankment, 

 and where the distui'bance caused by the unequal settlement is not likely 

 to reach. 



When the water is drawn through these valves in the midst of the embank- 

 ment, great vibration is caused by the force of the water passing out. This 

 vibration is liable to increase the settlement of the heavier parts of the em- 

 bankment for some considerable distance round the outlet works, especially 

 when the substrata are of a compressible character, and may cause settlement 

 of the work which would not otherwise occur. 



These difficulties have been pronded against in some of the later Bradford 

 waterworks by placing the outlet valves at the outside of the embankment, 

 and conveying the water tlirough the outer half of the culvert in an iron 

 pipe. The vertical valve-shaft for the rods and apparatus for opening the 

 valves are by this means rendered unnecessary, and the unequal settlement 

 and injury caused by vibration arc altogether avoided. This mode of con- 

 struction has so far been found to work with advantage ; the valve and outlet 



