ARTESIAN SUPPLY

Evening Post, Volume CXXIII, Issue 55, 6 March 1937, Page 10

ARTESIAN SUPPLY

THE BROKEN STRATUM

HARD TO REPAIR

Although no admission has. been made by the Public Works Department that the operations of the northern dredge at the reclamation work, at the Hutt River mouth were responsible for the big drop in the levels in the artesian wells in the Hutt Valley independent observers are inclined to this opinion. People who are interested in the problem are wondering how the engineers will effect repairs to the broken stratum that protects the water-bearing gravel below.

An opinion was sought from an expert in these matters and he said that in all probability it would be impossible to effect full repairs to the stratum. For a start, it would be very difficult to determine the bounds of the trench. The water did not come up with a rush, but filtered through the silt, and anywhere where the stratum had been weakened the pressure from below would force the underground flow through. It was a mistake to think that the deposits each fresh brought down the river would fill in the trench and confine the underground flow again.' A slight improvement could be expected (this has already been experienced after recent freshes), but what happened was that the heavier material sank to the bottom and remained there and the lighter binding material was forced away by the pressure from below. The upwards pressure was such that the binding silt, could not stay long enough in position to achieve its purpose, and,' without the binding material, the heavier deposit was not fully effective.

The expert said that where an artesian well was no longer needed and the owners wanted it stopped, the task was very difficult, but yet it was simple compared with repairing the broken stratum in.a river bed. Concrete could not be used in running water. The only thing to do when stopping an artesian well was to determine the limits through which the water was leaking upwards and then build a concrete encircling wall just outside these limits. In • this chamber the water would rise to the full static height and then become "dead," and concrete could then be used in repairing the damaged bed and would set in the still water. The upper part of the. wall could then be demolished. All that sounded very complex and costly, and probably was ruled out as impracticable, but it was about the only certain way of stopping a flow from an artesian source.

' A suggestion made at another source was that the necessary plant should be built and the artesian water pumped from the place in the river from where the flow is escaping. -