a9 
Ww 
~I 
1891. | Van Wyk’s Vley. 
read before the Institute of Civil Engineers, I think in 1887, Mr, 
Gamble did me the honour to quote from some report of mine that 
(in our Northern districts) it was necessary to impound the flood 
waters from one hundred acres in order to ensure the irrigation for 
the year of one acre, and, he continues, ‘‘ this is a very remarkable 
statement.” In April 1888, not having Mr. Gamble’s address, I 
wrote to Mr. Merriman asking him to convey to Mr. Gamble my 
impression that my estimate would prove to have been too sanguine. 
Six years’ experience at Van Wyk’s Vley now shews that the drainage 
from four hundred square miles enables us to cultivate one square 
mile under a wheat crop. The-cultivation of garden ground and supply of 
water to stock may perhaps reduce this extravagant proportion to, say, 
300 to 1 as effective power of the dam. 
My first measurements were made on farmers’ dams which allowed 
a large proportion of the flood water to escape over the artificial 
“ by-wash ” and the quantity escaping could be only roughly estimated, 
while Van Wyk’s Vley has never been filled and the data are therefore 
_reliable for that one particular case. 
These figures however only shew after all a peculiarity common to 
the enormous flats of our North-west districts and they are not appli- 
-cable to any districts materially differing from ours in feature or in 
respect to rainfall. 
With us they shew that but few dams catch so much more water 
during the rainy season, than will be lost by evaporation and soakage 
during the whole year, as will enable the owner to irrigate more than 
-a small patch of land below each dam. In the case of Van Wyk’s 
Viley the surplusage was easily measurable and finding this to be so 
very little it became necessary to increase the area draining towards 
the dam ; this it was possible to effect on two sides of the estate as 
I pointed outin my published report for 1886 (G. 30—’87). I was 
not however satisfied as to the necessity of immediate action, the 
waste of water by tenants in 1886 under the crude regulations then 
in force was so great as to preclude any fair calculation as to the 
effective power of the reservoir, and I reported further to the effect 
that action would be premature if undertaken then. 
Mr. Bain paid his first visit to the estate in October, 1887, and inspected 
the better of the two suggested traces for a canal in aid of the dam 
with the results that I was instructed to make surveys and sections 
for, and ultimately to construct, a canal by which to divert a portion 
of the flood waters from the valley to the eastward of the reservoir. 
