802 



REPORT— 1888. 



The supply is 25 inches on 4,350 square miles. An inch of rain is 14,500,000 

 gallons to the square mile. The amount is 1,576,876,000,000 gallons. 



Deduct from this evaporation and absorption 20 per cent., 5 inches of rainfall ; 

 waste by floods 20 per cent., 5 inches rainfall. This amounts to 10 inches, 

 630,750,000,000 galloiis. Add to this 36,500,000,000 gallons (the present daily 

 demand), and the total is 667,250,000,000 gallons. Deduct this from the present 

 supply of 1,576,875,000,000 gallons, and the surplus over the present demand is 

 about 909,625,000,000 gallons. 



4. The Relation between the Rainfall and the Height op the 



River. 



1. What rainfall in what parts of the watershed is required to produce a flood P 

 Broadly, the rainfall on the east bank in Staffordshire and Worcestershire 



never causes floods, for — 



(1) The tributaries are too small to bring down the }iecessary volume of 



water. 



(2) The porous nature of the rocks. 



(3) The low rainfall. 



To produce a flood the Montgomeryshire rainfall is required in addition. 



2. Local storms, however violent, produce but small efliect on the river. 



(a) August 4, 1886, rainfall at Lincombe, 2'43 inches. The height of the river at 

 Diglis and Tewkesbury on the next days was : — 



August 5 



„ 6 



„ 7 



Besides the Lincombe rainfall on August 4 there had been in IMontgomeryshire 

 falls of r41 inch at Dolanog, and 1-88 inch at Pennant, and on the 5th 2'00 

 inches at Llansainttiraid. The water took two days to reach Diglis. The local 

 fall at most raised the river there 3 inches. 



On September 19, 1886, there was a fall of 1*68 inch on the Banw, but the 

 Severn at Diglis remained unaffected for the next week at 10 feet 5 inches. Indeed, 

 the height gradually fell. To raise the Severn at Diglis there must be at least 

 •20 inch of rain over most of Montgomeryshire. 



The following figures show the Montgomeryshire rainfall and the height of the 

 Severn at Diglis for 1887, and also the mean rainfall for the counties of Salop and 

 StaflTord :— 



The summer rainfall, being mostly storm, produces little effect ; the winter, not 

 being merely local, at once makes itself felt. The average height at Diglis is 



