Hill. — Artesian-water Basins of Heretaunya Plain. 441 



fall is less than 4 ft. to the mile. A similar remark applies in the 

 ease of the Tutaekuri River, but not in the case of the Tukituki. 

 Now, the Ngaruroro and Tutaekuri Rivers bring down large 

 quantities of fine material from the back country, where com- 

 paratively soft rocks abound, and we find that in times of heavy 

 flood many hundreds of acres of temporarily submerged land 

 are considerably raised, and therefore improved. But this 

 improvement is at times a great loss to settlers who may be 

 residing in the lower basin of these rivers. The slope or fall in 

 the case of each river is much greater than it is with larger and 

 more important rivers in Europe and America, for few of them 

 have a fall of more than 24 in. to the mile, but the Ngaruroro 

 and Tutaekuri, even when nearing their entrance to the sea, 

 have a fall of nearly 4 ft., or 48 in., to the mile. 



How, then, comes the trouble from overflow in times of an 

 excessive rainfall ? The answer is to be found in the difference 

 of slope or inclination between the upper and lower course of 

 each river. In the upper course the water rushes down at a 

 great speed, owing to its high inclination, and the carrying- 

 capacity equally with the denuding-capacity is very considerably 

 increased. Thus it comes to pass that what is easily carried 

 bv the River Ngaruroro in that part of it where the inclination 

 amounts to 40 ft. to the mile cannot be carried where the in- 

 clination diminishes to 6 ft. to the mile, and finally to 4 ft. The 

 rate of flow is stayed, and the carrying-capacity is diminished, 

 so that flooding and the deposition of silt must immediatelv fol- 

 low. It is for this reason that there has been so much spreading 

 of material as soon as the flood-waters have reached the present 

 plain-area, and the filling-in of one area has only opened a way 

 for an adjoining area to be similarly dealt with ; and this will 

 explain in a large measure why there is so much general likeness 

 in the beds that go to form what is known as the artesian basin. 

 It would be impossible to suppose that the beds forming the 

 Heretaunga Plain should be identical. The surface material 

 of the plain to-day varies in quality and variety of material for 

 the reason that deposition has taken place at different times. 

 Speaking generally, there is comparatively little alteration in 

 the character of the underlying water-bearing beds between 

 Napier and Pakowhai, but they vary considerably in the direction 

 of Redcliffe and West Clive. In other words, the beds in the 

 general direction of the dip show more points of agreement than 

 do the beds in the direction of their troughing. And just as the 

 wells vary somewhat in their bedding, so also do they varv in 

 depth. But the changes, whether in the depth of the water- 

 bearing beds, or in the varying characters of the material passed 

 through in the process of sinking, are only what might have been 



