Failure of the Van Yean Reservoir, 



139 



propoi'tion of rain that reaches the rivers is much less than 

 one-eighth. 



Thus, Mr. Hodgklnson, Dr. Davy, and myself, seem to 

 have all arrived, by different and independent modes of inves- 

 tigation, at very nearly the same result. For all practical 

 purposes, our different estimates will produce the same result. 



I attach very little importance to the determination, on 

 theoretical principles, of the watershed of the Plenty. 



The only certain way, as stated above, of finding the 

 amount, is to measure the streams at least one 3 a month, in 

 order to get the mean dischai'ge for the year. But, if the 

 aqueduct could be finished within the next two months, we 

 should then have the very best means of practically testing 

 how much water can be obtained from the winter rains. 



I have availed myself of all the measurements already 

 made, and without deducting tlxe immense loss from evapox'- 

 ation in the swamps, have allowed an increase of two-thirds 

 for the greater watershed of the winter months. 



The members of the Committee have disregarded all these 

 measurements, because they were taken in the summer 

 months, and have calculated the amount of watershed, in 

 accordance with the evaporation tables of Mr. Dempsey, 

 which profess to show the evaporation due to the mean tem- 

 perature of the different months in England, and I should 

 have thought that it required no great amount of scientific 

 knowledge to see that if these tables give a correct result for 

 the mean temperature of England, they are totally inappli- 

 cable to the mean temperature of this colony, and would give 

 a very incorrect result. 



The Committee, in their report, admit that the evaporation 

 from the surface of water is nine feet, which is nearly double 

 the evaporation in England. It seems, therefore, a singular 

 oversight on their part, not to see that the force of evaporation 

 from the surface of the ground here must bear at least the 

 same increased proportion, and, in point of fact, the evapora- 

 tion is far greater than double. 



That portion of the drainage area of the Plenty which is of 

 the clay slate formation, and which may be estimated at fifteen 

 square miles, or one -fourth of the whole, is so much more 

 destitute of vegetation than the cultivated soil in England, 

 that the surface of the ground becomes intensely heated 

 under the influence of the solar rays and evaporation is 

 exceedingly rapid. 



Thus, the reasoning upon which the Committee rely, to 



