52 On the Supply of Water 



stances of the Wormbete district, meteorological, hydrogra- 

 phical, and physical ; evaporation, rain-fall, general configura- 

 tion, soil, &c. &c, not only within the bounds of the catch- 

 water district, but the surrounding country generally, as well 

 as other varied circumstances, such as the prevailing winds, 

 and other counter-agents bearing on the results. All must 

 be taken into account and properly considered, with such ac- 

 curate information as I may have been enabled to collect and 

 record, so as ultimately to give me a perfect basis from which 

 to deduce a calculation that can be depended upon in its 

 resultant facts, not forgetting to take into account that the 

 water shed commences at a high level, (something bke twelve 

 to fifteen hundred feet above the sea board,) falling with steep 

 but regular gradients towards the valley, ensuring a rapid 

 conduction of the water falling on its surface to the reser- 

 voir, thereby diminishing the likelihood of extensive evapo- 

 ration and mineral impregnation. 



Touching the vexed question of evaporation in these colo- 

 nies, I may here state that the hitherto theoretical opinions 

 formerly held by several parties in Victoria, have been con- 

 siderably toned down by practical experience. It should not, 

 however, be forgotten, that evaporation is more or less modi- 

 fied by several attendant causes acting on the atmosphere, such 

 as temperature, moisture, force and direction of the wind, all 

 tending to that uncertain condition, which, ever varying the 

 evaporation, precludes the possibility of having any fixed 

 rule, excepting an average founded on actual observation in 

 the locality, and extending over a considerable space of 

 time. 



My opinion, founded on actual colonial observation, on 

 large bodies of deep and almost quiescent water, such as 

 reservoirs in a still state, enables me confidently to pronounce 

 it as considerably under fifty-two inches per annum, and very 

 probably the opinion held by Major (now Colonel) Cotton, from 

 more extended observations in the colony as regards time, 

 are still more in conformity with the fact. His opinion was 

 forty-five inches.* 



* Touching evaporation I have considerable pleasure in adding that, from 

 subsequent information from the resident engineer at Yan Yean, he states 

 that from careful observation during the time that the aqueduct, feeding the 

 reservoir was closed for the completion of the tunnel, the water being then 

 five and a-half feet deep in reservoir, the evaporation from the same -was 

 one-tenth of an inch per day during the summer months of January, Febru- 

 ary, and March, 1856. And again, in October of the same year, during which 

 month the supply had been taken from the river, the evaporation was much 

 the same, being an average for the entire year of but 36 inches. 



