Hildendorf. — Fluctuations in Water-level of Artesian Wells. 491 



Art. XLIL- — Fluctuations in (he Water-level oj some Artesian Wells in the 



Christchurch Area. 



By F. W. Hilgendorf, D.Sc. 



[Read before the Canterbury Philosophical Institute, 6lh September, 1916 ; received by 

 Editors, 30th December, 1916 ; issued separately, 10th December, 1917.] 



In 1896 Hutton recorded the fluctuations of two artesian wells at the 

 Christchurch Museum.* Speight continued the observations on one of 

 the wells in 1910,| and since then has taken occasional readings, copies 

 of which he has kindly given me for the purposes of this paper. In 1911 

 I took a series of readings on a 340 ft. well at Lincoln College, fourteen 

 miles south-west of Christchurch, J and have taken monthly readings ever 

 since. From 1912 till the present time Mr. A. D. Dobson, Christchurch 

 City Surveyor, has taken observations on a 217 ft. well at Merivale, a 

 mile and a quarter north-west of the Cathedral, and has given me his 

 readings. In 1914 Mr. Symes and I, aided by a grant from the Hutton 

 Fund, erected a continuous-record machine on a well of uncertain depth 

 on Papanui Road, about three miles north-west of the Cathedral (see 

 this volume, p. 493), and the readings of this well have been used here. 

 The graph shows the fluctuations in the static level of the water in 

 these four wells. The comparatively small variation in the three Christ- 

 church wells as contrasted with the large variation of the Lincoln well 

 affords conclusive proof that the wells in the neighbourhood of Christ- 

 church have a relatively constant source of supply, while the well at Lincoln 

 has a relatively intermittent one. The most reasonable explanation of this 

 feature of the graph is that the main supply of the Christchurch artesian 

 wells comes from the Waimakariri River, while the Lincoln well is supplied 

 chiefly by the rainfall direct, or by percolation from the Selwyn River, which 

 in its middle course flows only during or after heavy rains. 



There are two facts that might be used to controvert this explanation 

 were the evidence of the present graph not so overwhelming. 



(1.) The Christchurch wells do, as was pointed out by Hutton and 

 Speight, respond very rapidly to a day's rain, but that the rainfall is their 

 chief source of supply is rendered improbable by their relative steadiness 

 during the dry years 1914-16. There can be no influence of- either the 

 rainfall or the Selwyn River that would not be more distinctly felt at Lincoln 

 than at Christchurch, as will be shown by a glance at the map in Trans. 

 N.Z. Inst., vol. 44, 1912, p. 146. If either of these influences, then, kept 

 the Christchurch wells steady, they should have kept the Lincoln well steady 

 too, and therefore we are driven to conclude that percolation from the 

 Waimakariri is the chief source of the Christchurch supply. 



(2.) The second observation that does not support this supposition is 

 that floods in the Waimakariri do not influence the level or the flow of the 



* F. W. Hutton, On the Behaviour of Two Artesian Wells at the Canterbury 

 Museum, Trans. N.Z. Inst., vol. 28, 1896, p. 654. 



t R. Speight, A Preliminary Account of the Geological Features of the Christ- 

 church Artesian Area, Trans. N.Z. Inst., vol. 43, 1911, p. 420. 



i F. W. Hilgendorf, Fluctuations in the Level of the Water in some Artesian 

 Wells in the Christchurch Area, Trans. N.Z. Inst., vol. 44, 1912, p. 142. 



