456 REPORT — 1873. 



that springs of water are met with, and great difficulties are sometimes 

 experienced in dealing with them. If the springs run in from the sides of 

 the trench at a level above the stratum on which the puddle is to rest, they 

 do not constitiite any permanent difficulty ; the water may be pumped out of 

 the trench whilst the work is in progress, and may be gradually turned back 

 with the puddle, which is put into the trench as the work proceeds. If, 

 however, a spring rises from the bottom of the trench, it cannot be disposed 

 of in that way. It must be built round in some safe manner by concrete or 

 stonework and collected, so that it can be brought up in an iron pipe in the 

 work, or conveyed to one end of the puddle-trench and discharged at the 

 surface of the ground clear of the embankment. Springs in the ground which 

 is to form the bottom of the reservoir do not indicate that the site is not a 

 good one, but generally the contrary; and they sometimes show where the 

 embankment can be placed with the greatest advantage. 



The existence of the springs may show that there is some impervious 

 material lying across the valley somewhere below the line along which they 

 issue ; and on this impervious material, and below the springs, it is probable 

 the embankment may be most easily formed : at any rate, the springs show 

 the line immediately above which it would not be desirable to place the 

 embankment. 



The works for admitting streams into reservoirs are of several kinds. In 

 cases where the whole stream is taken, a pool or lodge is made by a dam 

 placed across the stream at the head of the reservoir. This dam arrests the 

 flow of the stream, and gives time for any solid matter carried on by the 

 water to fall, and to a great extent saves the reservoir from being silted up ; 

 the solid deposit is caught in the lodge, from which it can be easily removed. 

 The size of the lodge can be regulated to suit the character and requirements 

 of each case. 



In cases where turbid or coloured water is not to be taken, side channels 

 for carrying floods past the reservoirs must be made ; and the usual mode of 

 admitting the streams is by what are called leaping-weirs. This contrivance 

 consists of a weir built across the stream, to stop the water and cause the 

 water to flow over the conduit which is intended to receive it and carry it to 

 the reservoir. The conduit intended to receive the water is built across the 

 stream inside the weir, and a long narrow opening is made through the crest 

 of the weir along the top of the conduit. The weir on one side of this 

 opetaing is made a step lower than it is on the other side, and the stream in 

 passing has to fall down this step. When the quantity of the stream is small, 

 it will run close over the edge of the step and fall through the narrow opening 

 into the conduit below ; but when the stream is swoUen and large, it will run 

 with greater velocity, and will leap from the toj) of the step over the opening 

 and pass away down its original course. 



The size of the opening can be adjusted so as to take any given quantity of 

 water required from the stream. It is self-acting, so far as regards the 

 passing of dangerous floods ; but it is not altogether so, so far as the rejection 

 of turbid water is concerned. It does, however, make a selection of water to 

 some extent, as it usuaUj' happens that when the water is most turbid and 

 during sudden storms, the streams would be so much increased that they 

 would overleap the opening through the weir, and so pass ofl' without entering 

 the works. 



Another mode of taking in streams and obtaining only clean water from 

 them, is to construct a filtering-conduit under the bed of the stream to receive 

 the water before it is admitted into the reservoir. These filtering-conduits 



