,1886.] Va7i Wyh's Vlei Reservoir. 227 



wiJl be seen that the holding properties of the dam have much 

 improved. In 1884 with a mean maximum temperature of 78°'8, the 

 loss of water for the whole year was 89'6 inches, whilst in 1885 v/ith 

 a mean temperature of 80°' 1, or a daily increase of 1°*3 the loss of 

 water was 76*1 inches, or less by 13^ inches than that of the previous 

 year. This is satisfactory, as it shows that, so far, percolation has 

 decreased. 



There is a rain gauge fixed a few hundred yards from the embank- 

 ment, but it is necessary for estimating the amount of water that 

 might be expected from a certain fall, to have stations fixed at several 

 points of the drainage area of the dam. Such other stations have been 

 established recently. The rains being very partial, a storm may occur 

 only a few miles away and bring a considerable quantity of water to 

 the dam, while the gauge at the bank registers nothing. Judging 

 from the observations that have already been taken here, one half -inch 

 of rain practically gives no increase to the dam, unless it immediately 

 follows a previous fall. (See annexed report on the rainfall, 18th May 

 1885.) 



In conclusion may be given a short description of the distributing 

 channel or furrow. Mr. Alston's tender being accepted, operations for 

 this part of the work were commenced on the 1st of January 18 B5, 

 and finished within the specified time of five months. 



The dimensions of this channel are 3-feet wide at the bottom, 

 11-feet wide at the maximum water level and 2-feet deep, giving a 

 sectional water area of M-square feet. 



Banks were made on either side 2-feet wide on the top with a 

 mininimum height of 3-feet above the bottom of the furrow. 



The slopes were 2 to 1 below, and 1|^ to 1 above the highest water 

 level. Wooden forms were constructed to the finished section of the 

 channel as a guide to the workmen. 



The gradients of the channel are at the rate of 3-feet per mile 

 for the first half mile, 2-feet per mile for the next two miles, the 

 remaining length being at the rate of 1- foot 9 inches per mile. 



The bottom and sides for the first quarter of a mile are pitched 



\with stones, but the remaining part has no such protection, and up to 



:the present time has stood well, the water flowing regularly, without 



scour. Openings, protected by pitching, have been left in the banks 



.at suitable places, to carry off flood water ; these will probably require 



some repairs after storms. 



The branch main road to Kenhardt, via Van Wyk's Vley, is carried 



