106 Hugh J. L. Bead n ell — Flou-ing Wells, KJiarga Oasis. 



General Consider atiotis of the Water-supply as a tvhole. 



As I hope shortly to publish the results of experiments carried out 

 to determine the mutual influence of wells, it need only be remarked 

 here that the sensitiveness of any one well to its neighbours is far 

 greater than has, I believe, been generally supposed. For instance, 

 the shutting down of a flowing or the opening of a closed well will 

 produce a most marked eff'ect on a neighbouring well within the short 

 space of sixty minutes, even when the intervening distance is over 

 500 metres. The degree of influence is especially dependent on the 

 amount of difference between the depths, discharges, and surface-levels 

 of the bores. 



When drilling was first commenced in the headquarters district the 

 bores were placed at an average distance apart of 500 metres ; the 

 circumstances of drilling, however, led to there being a great variation 

 in the depths of the bores, with the result that those of comparatively 

 shallow depth and those situated on comparatively high ground were 

 adversely affected by the deeper and more favourably placed ones ; 

 to lessen the effects of this extreme sensitiveness the average distance 

 between the bores has since been considerably increased. 



All bores show a marked decline in discharge for some time after 

 completion, when they settle down to a fairly steady flow, or at least 

 to a flow which decreases at a constantly diminishing rate, except 

 when affected by new" bores subsequently sunk in the vicinity. The 

 same point is brought out by observing the extent and rate to which 

 the pressure and flow can be increased by the temporary closing of 

 a bore. Experiments show that a flow may be augmented bj' as much 

 as 75 per cent, as the result of closing a bore for five days, the increased 

 discharge falling to its normal twelve hours after reopening. 



Data are as yet far too insufficient to warrant an attempt to calculate 

 the supplj" which can safely be drawn from a given area without 

 unduly reducing the pressure and lowering the water-level. In some 

 parts of the oasis there are bores manj^ hundreds of years old still 

 pouring forth their hundreds of gallons a minute ; such wells are 

 probably situated in particularly favourable positions or have been 

 exceptionally fortunate in striking large fissures. There are at the 

 same time hundreds of wells which have ceased running, either through 

 local exhaustion ■ of the sandstones or througli failure to keep the 

 channels open, or through a combination of both circumstances. In 

 many instances new bores sunk in the immediate neighbourhood of old 

 wells, some of which were completelj' extinct while others were 

 yielding feeble flows only, have produced sti'ong discharges of con- 

 siderable volume. 



At the present day there are about 230 native owned flowing wells 

 in the oasis of Kharga, yielding a total discharge of some 295 ' qirats.' 

 The output of wells is for purposes of taxation determined in a very 

 rough and ready manner by measuring the depth of water passing over 

 a weir of definite breadth fixed in the stream. The discharge is 

 reckoned in qirats, a qirat being a water-section of 64 square 

 centimetres. As the velocity of the stream is not taken into account 

 the qirat has a very variable value, low for small and high for large 

 flows, the result being that the smaller wells are being taxed as much 



