WATERWORKS OF EAST LONDON. 333 



cessfully use from y> to 3 grains of sulphate of alumina. 

 However, we find it unnecessary to use any coagulant at all 

 excepting when the water is turbid as a consequence of rains 

 falling in the Amalinda Watershed. In connection with this 

 scheme we laid a couple of thousand feet of j8-inch reinforced 

 concrete pipes. Our experience with these pipes was not alto- 

 gether satisfactory. With a head of less than 28 feet we had 

 20 leaks through the bodies of the pipes and 69 defective joints. 

 This experience would appear to call for great caution before 

 adopting reinforced concrete pipes where they have to be sub- 

 jected to any considerable pressure. 



Settlement in Embankments. 



The earthen embankment of the Amalinda Reservoir was 

 completed in 1884. The total height above the draw-off was 

 27 feet. Presuming it had been made level, I found in 191 7 

 that it had settled in the gorge 2 feet. Had it been raised in 

 the centre at the time of construction, as is required in good 

 practice, then the settlement was greater. 



Rainfalls and Yield of Watersheds. 



The accompanying table (A) shows the mean monthly rain- 

 falls of some nine stations in the watershed of the Buffalo River, 

 for periods varying from 18 to 40 years, and the mean yearly 

 rainfall of all the stations, including Chiselhurst. I think this 

 table may prove of interest to agriculturists, hydraulic engineers 

 and others. 



Mr. T. George Caink, Borough Engineer of Kingwilliams- 

 town, has been good enough to furnish me with the run-off 

 of the Pirie catchment area from September, 1906, to August, 

 1907, and from 191 1 to 1918. It will probably be known that 

 the Buffalo River has its source in this watershed, the extent of 

 which is 143^ square miles. The following table (B) shows 

 a mean annual run-off of 26.95 per cent. I think this table 

 is of great value. 



