ON VAN WYK'S VLEY RESERVOIR. 

 By J. E. Macnellan, C.E., 

 [Late Resident Engineer on Van Wyk's Vley Works.T 

 [Read 27th October, 1886]. 



Before proceeding with the main subject of this paper, it may not 

 be out of place to make a few remarks on Boer dams in s'eneral 

 showing that more care should be taken in the selection of their sites 

 and in their mode of construction. 



Many of these sites are far from being good ones, some havings 

 such small catchment areas that they never half fill, and their con- 

 structors have the mortification of seeing a huge bank, with little 

 water, besides being put to much unnecessary expenditure ; others 

 again are constructed on a porous stratum through which the water 

 percolates away rapidly, rendering the dam almost useless for irri- 

 gation purposes and only giving water for stock for a comparatively 

 short time. These faults can be avoided by making a proper survey 

 with levels, and by sinking pits along the proposed line of bank, ta 

 ascertain the nature of the strata forming the foundation. 



A common fault in many of these dams, is that the inside or water 

 slope is made too steep, causing the pitching to get loose and fall 

 out in many places, thus giving free access to the wash of the water 

 and to the ravages of crabs. This if not noticed and repaired at 

 once, may often cause the entire destruction of the bank, and the 

 loss of a whole season's water and crops. 



More care should be taken to incorporate the bank with the ground 

 on which it is to be made. This is done by removing all loose stones 

 sand and bushes, and picking the ground to a depth of eight inches 

 or so, before beginning the first layer of the bank. 



The general method adopted amongst the farmers in the construction, 

 of their dams is to convey the ground to the site of the bank in 

 carts or scrapers, allowing it to assume its natural slope, or angle of 

 repose. This for most kinds of ground is quite insufficient, when 

 exposed to the action of rain or standing water. A farmer once 



