ARTESIAN WELLS

Evening Post, Volume CXXIII, Issue 50, 1 March 1937, Page 10

ARTESIAN WELLS

SOME IMPROVEMENT

BUT NOT NEARLY, NORMAL

EFFECT OF FRESH

It is now a gaw. d many weeks since a sudden and lipiiprccedented fall in the levels and' flfli.vs of artesian wells in the lower parti of the Hutt Valley was noticed and stfc once connected in the minds of mdjs-t people with the dredging; being qarried out at the mouth of the riverj in connection with the big reclamation at Scabey Island. That has never bc^n proved nor disproved, but the vgry fact that there has been some improvement, thougn not nearly back toi> normal, following the recent heavy fishes i.. the river, appears to give sowmd confirmation of that belief. I

Any fall in the ftow from wells in the valley is a serums matter to the three local bodies drawing water from the underground ' supplies, to firms which largely rely uiion such water for the carrying out of!, their industries and to private property owners who use artesian water vj holly or in part for domestic and garden supplies. The Public Wo^ks Department operated two drag-Imp excavators, and following the astonisrfing drop in well ievels—amounting to '• as much as 54 inches in certain of i^he Lower Hutt Borough wells near Gracefield Road— the northerly drag li.o c ceased work and has not since beeq operated. Now this equipment is beftnig shifted to a new position. The ottysr drag line has continued . working, btht ihe cut has been kept shallow, riot going down more than 15 to 20 fcht. It was stated at,the time the trouble was first discovered thiit the more northerly drag line had cut down to probably 60 feet or morq, which would take the trench so deej) as to break through the imperviousl.l, layer of silt into the water-bearing ' gravel from which the artesian supplAss are drawn. The silt which was being cut out during the last few days of operation of this drag line was a grey,!. sea-deposited silt very fine when broken up, but so consolidated in position as. to form a practically impervious -(layer. The silt taken out by the otlnfcsr drag has been of quite a different texture, less consolidated at its lesser'\ depth, and rather black and sloppy ais delivered from the bucket. . ( FRESHES IN RIVVJt. Recently a diver has .'be an working from a punt moored above.the line of the deeper cut, but so lon® a period has elapsed, during which a of freshes have occurred, that) it Js probable that the trench has l£een considerably altered. It would; furthermore be a most difficult matlter to locate the point of trouble iii a deep trench, even if it were not partially or wholly filled with shingle, since the upward flow, though con siderable, would be small at any .point iilong the line in comparison with the volume of river water. Nor would the vtee of an electric torch greatly assist ito water not made clearer by the operation of shingle drag lines higher up. i A fortnight or more ago a light fresh came down the river and a very slight improvement was noted in tl»e well levels, and from this it was aelduced that a certain amount of shingi.e had been carried down and into the ttrench and so was giving a little more, head by the added frictional resistance. The heavier freshes of1 the past week -^'ould have carried down a good dehl of shingle, filling the trench further; and this has' been followed, as had jbeen anticipated,'by a still further improvement in head. y ' If this is so it would appear fthat when the trench is completely filled with shingle the improvement in l(?vel will end and a new normal will| be reached, still below that which heldjbefore last month and still giving those drawing upon artesian supplies caiise for concern. \. There are several possible causes for variation in artesian flow. Tiqal effects, for instance, result in a datyy variation, but the drop in the Hutft wells appears to be constant as regards both high and low tide former levels Whether anything c^n now be donte is for engineers to decide—after they have decided, before .'more weeks or months go by, whether there is in factj a direct relationship between dredging and fail in well levels—but the popula-f tion in the valley is steadily increasing; and the city will also have to draw on: these supplies next summer. From anypoint of view the position is not at all. happy.