430 Tra))sacf/07}s. 



well in the Christchurch artesian area, the well at Islington, though sunk 

 deeper, not giving a flow at the surface. 



Series No. -3. — Coastal Belt : Sefton to Estunrij of Avon and Heathcote. 



(Plate XIII.) 



This series gives a selection of w^ells from along the coastal belt reaching 

 from Sefton to the north of the Ashley River, through Kaiapoi and NeAv 

 Brighton to the Port Hills at the estuary of the Avon and Heathcote. In 

 the extreme north of this belt the supply of water is poor, but fairly good 

 flows are obtained in Woodend and at Kaiapoi ; nevertheless, the suppl}' 

 is both deficient in amount and in the height of rise as compared with wells 

 in the immediate neighbourhood of Christchurch. The relative small 

 lieight of rise can be readily seen by comparing the Kaiapoi Borough Council 

 well, sunk to a depth of 450 ft., with deep wells in the middle of Christchurch. 

 The Kaiapoi well gives a rise of only 10 ft. from that depth, whereas the 

 Christchurch wells give a rise approximating to, or even exceeding, 30 ft. 

 This well gave a flow of 50 gallons per minute at a height of I ft. when first 

 sunk, an amount which compares favourably with deep wells further 

 south ; but the comparative smallness of supply is borne out in the case of 

 other wells. Inland from the town the supply falls off considerably, for at 

 Ohoka a well sunk to a depth of 374 ft. gave only a 2 ft. rise. In this case, 

 however, the beds were almost exclusively of shingle, and the conditions of 

 texture were decidedly unfavourable for the production of much artesian 

 water. As a general rule, the beds of Kaiapoi and its immediate vicinity 

 show the presence of a large proportion of shingle, from which it may be 

 inferred that a large river has occupied the present position of the \Vai- 

 makariri for a considerable period of time. Just to the north of Kaiapoi, 

 and also to the south, beds composed of finer detritus become more 

 important, till when the estuary is reached they are almost wholly of fine 

 material, with an entire absence of shingle. 



The two important factors controlling the conditions of texture of the 

 beds are the presence of Banks Peninsula to the south and the delta of the 

 Waimakariri in the north. This river has pushed out its delta beyond the 

 general trend of the coast-line, and the finer material brought down is 

 deposited on either side of the mouth. This accounts for the area of swamp 

 immediately to the north about Woodend, and also the extensive deposits 

 of fine material in the neighbourhood of New Brighton. An important 

 factor in the latter case is the strong littoral current which runs down the 

 coast during northerly winds. At that time the Waimakariri is usually in 

 flood and heavily charged with sediment, so that the conditions are 

 eminently favourable for the transport south of large quantities of detritus. 

 A part' of this is carried landwards, and ultimately forms dunes along the 

 shore ; and another part is deposited in shallow water oft'shore, or in 

 estuaries formed behind the sand-dunes. Such aestuarine deposits are 

 indicated in the sections given by the wells by the frequent marine shells 

 which are brought up from the bores. These show that on the site of the 

 present estuary of the Avon and Heathcote the conditions have been the 

 same for a long period of time. No peat or other land deposits are met with 

 in this part of the district till deposits of angular matter are reached at the 

 base of the series, derived without any doubt from the disintegration of 

 masses of volcanic rocks on the Port Hills. 



The wells along this belt of country close to the shore lise in sympathy 

 with the tide, and the water contains a high percentage of salt. 



