Wafer Supply of Belfast 63 



yard has been adopted. This figure has been recommended 

 to water authorities in England by the Local Government 

 Board of Whitehall. The Commissioners have thus taken for 

 Belfast the most efficient rate adopted in existing systems. 



For dealing with that portion of the Belfast supply which 

 comes from the Carrickfergus district, and which amounts to 

 7^ million gallons per day, five filter basins are being con- 

 structed at Oldpark near the present high service reservoir. 

 One bed will be always out for cleansing, so that four will have 

 to do all the work of filtration. The average effective area of 

 each basin will be about 3,800 square yards, and the total of all 

 the beds about 19,000 square yards. The water will be passed 

 on to the filters from the Woodburn Conduit, and, after 

 filtration, it will be delivered into the high-service reservoir. 

 The Forked Bridge station will consist of four filter basins, one 

 of which will always be out for cleansing. The quantity of 

 water to be dealt with here will vary from three to four million 

 gallons per day. Each bed will have an effective area of about 

 2,700 square yards. Thus at the two stations there will be in 

 all some 30,000 square yards of sand area. The mode of con- 

 struction of all the filters is the same. The basins are formed 

 in cutting or filling, as the levels of the ground suit. The 

 bottom and slopes are lined with 9in. thick ot concrete, and a 

 neat cope is formed above the ground line. The concrete was 

 made of about five parts stone and chippings, then two parts 

 sand, and one part cement of best quality. Along the centre 

 of the floor there is a drain or channel for collecting and con- 

 veying the filtered water to the outlet. Now, let me describe 

 the filtering material. This begins at the bottom with a layer 

 of whinstone larger than road metal, gradually reducing in size 

 to chippings, then to gravel. Afterwards comes a 2ft. 6in. 

 layer of Dundrum sand, finishing fine on the top. The total 

 thickness is about 5ft. 6in. ; then there is ift. 6in. water space, 

 and 2ft. of a margin. In total depth the filter basins measure 

 9ft. I now come to the subsidiary works, which require a few 

 words of explanj^tion. The, unfiltered water is conveyed to a 



