For our Water Supply, 



239 



How is it then that he is enabled to find a very abundant 

 supply for 191,500? 



The following table gives Mr. Hodgkinson's calculations 

 reduced to feet^ in the reservoir of 1,450 acres. 



Supply, 



5 inches available rainfall over 62|- square miles, equal 

 to 40,000 acres 



7'inches ditto over drainage area of reservoir, equal 

 to 3,000 acres 



Rainfall on reservoir of 1,400 acres 32 inches. Dew 

 10 inches ,.. 



Total 



Demand. 



Amount lost in the swamps ... 2 5^' 



Left to maintain the How in the river, 500 gallons 



per minute ... * . . . . , , ... ... g 



Evaporation 6G.6 inches over 1,400 acres 5 4*33 



Loss of flood water, and loss from absorption, equal 



to 6 inches over 1,400 acres ... 5.79 



Balance equivalent to supply 191,500, at 40 gallons 7 0-52 



Total 15 11-64 



1. Trom the above table it will be observed that Mn 

 Hodgkinson assumes 5 inches over 62^ square miles, instead 

 of 4J inches over 60 square miles, and in this way gains 

 1 foot 7 inches. 



2. He only leaves 500 gallons per minute, or 8 inches in 

 the reservoir, for the use of the district, instead of 900 

 gallons, or 14 inches, and thus gains 6 inches, 



3. He assumes that the whole of the available rainfall, 

 less 500 gallons per minute, will be available for the reser- 

 voir ; whereas, I tliought it unsafe to rely on any estimate 

 deduced from English tables, and preferred an estimate 

 based on the measurements, which leaves a balance of 1 foot 

 5J inches in his favour, and which I considered unsafe to 

 rely on. 



4. He assumes that 10 inches of dew will be condensed on 

 the surface of the reservoir, whereas I only allowed 2 inches, 

 and in this manner he gains 8 inches. 



5. He assumes the evaporation in this colony at 5 feet 

 6-6 inches, rejecting Dr. Davey's estimate of 9 feet, and thus 

 gains 3 feet 4 inches. 



These amounts will stand thus:— 



Feet. In, 

 11 6-16 

 1 2-48 

 3 4-55 

 16 1*19 



