HlLGENDORF. — Artesian Wells in the Christchurch Area. 157 



It has been often asserted by myself, along with others, that it is incon- 

 ceivable that the rainfall should supply all the water outflowing at the 

 Christchurch wells, but I have made a calculation that, whatever its faults, 

 makes the case at least not inconceivable. 



Population of Christchurch suburbs within the artesian areas 

 — i.e., from Sockburn to New Brighton and from Papanui 

 to the Port Hills— 86,661 (say) .. .. 90,000 



Gallons of water used per capita per day, including hydraulic 



lifts and cranes, street- and garden-watering- — 

 Auckland (1910) . . . . . . . . 58 



Wellington (maximum) . . . . . . 60 



Dunedin (maximum) . . . . . . 61 \ 



Say, average for Christchurch (where street-watering 



comes from river) . . . . . . . . 60 



Two rams at College lift water an average of 22^ ft., and 

 waste water is seven times that pumped. As this is 

 above average height, we may say proportion of water 

 used to that wasted . . . . . . . . One-tenth. 



Then, total water drawn from artesians in Christchurch 



90.000 x 60 x 11 x 365 x 10 _. _ K1 __. J 

 area per vear = -^rsrrr^ •• 90,251, /o0 tons. 

 1 -.240 . « ; 



Air oil- — 



Population having been taken as from Sockburn to New 

 Brighton — 

 Length of catchment-area . . . . . . 10 miles. 



First-stratum wells outcrop two miles up plain (Speight) : 

 d 3ep wells (450 ft.) outcrop about eight miles away ; 

 .'. width of catchment-area (about) . . . . 6 miles. 



Average rainfall . . . . . . . . . . 25 inches. 



1 in. of rain = in tons per acre . . . . . . 101 



Then rain falling on catchment-area per year 



= 10 x 6 x 640 x 101 x 25 . . . . 96,960,000 tons . 



If there is any approximation to accuracy in this calculation, then 

 each additional well put down to any of the strata at present in use can 

 receive its water only by robbing its neighbours, a condition of affairs that, 

 in the upper strata has long ago been reached. As for the lower strata 

 they have probably not been largely drawn on so far, and there is every 

 reason to suppose that there are still lower strata available but still 

 untouched. 



In favour of the Waimakariri assisting the water-supply are these 

 tacts : (1.) Water does undoubtedly percolate from the beds of some of 

 the rivers, as stated by Speight (loc. cit.), and I am able to add that near 

 Bealey a considerable amount of the Waimakariri flows underground. 

 This water is almost certain to leak into every porous bed, especially where 

 the thin deposit of silt that forms on the river's bed has been removed 

 by scour. (2.) The great degree of constancy of the Christchurch supply, 

 and the smallness of the annual variation in the Museum well during 

 the three periods it has been under observation. I should be inclined to 

 think that water from the river does assist the Christchurch wells in 

 some degree, but the Lincoln well in no degree ; but a longer period of 

 observations would be necessary to establish any opinion on the matter. 



