Cause Of Discolouration In Water Supply

Chronicle (Levin), 17 February 1948, Page 4

Cause Of Discolouration In Water Supply

An iiivestigation into the recent discolouration qf the water supply in Levin wak recently made by members of the Levin-Waiopehu Tramping Club,. at the request of; the Mayor, Mr. H. B. Burdekim A. report on their findihgs ,-was received at last night's • meeting of the Levin' Borough Council from the club's president, Mr,. N. M. Thomson, ' - ' ' [ "The trouble has been located in the upper reaches of the nofthern; branch of the Ohau, where an exceptionally violent rainstorm betwe'en Christinas and. New. Year has brough't down large quantitie^ of silt and drift wood," said the report. "In the joint report submitted to your council in 1938 by Cr„ G. C. France and1 the writer, attention was drawn to the' fact that the north; branch of the Ohau had, been more h'eavily hit by the 1936 cyclone than any othcr part of the watershed. Consolidation and rejuvenation .took place some•what more quickly than had been anticipated, and for a nurpber ofyears our water supply has been seldom affected by rises in the level pf the Ohau. However, it * would appear that the recent ' downpour has' succeed'ed in getting behind a' lot of. the old devastation. of ' 1936, and has started on the move again ih a considerabl'e body of earth. It, is not possible to say howTong this wil'l g*o on, but having regard to the .very greater damage that was done in 1936, I am not inclined to think that the present position will' be of very long duration, unless further exceptionally severe conditions. are

experienced on the badly affected country at the head of the north ' branch. "From the short term point of view, however, the position is likely to be -fairly - serious, as large quantities of mud and silt are evident the whole way down the Ohau. This deposit is from a few inches to a few feet above the present level of the river, and a rise caused by any local flooding, or the norma! rise whieh may be expected with the onset of the. winter rains, will certamly .cause quantities of the deposit to go into solution with the obvious effeet on the colour of our water. For how long this will go on will depend on the amoqnt of scouring that takeS place. It would be quite possible for the whole thing. to 'clear itself within a few months, although this naturally depends on how much further soil is removed and caused to slip in the head watqrs of the northern branch. "It will ,bo appreeiated that, although the original cause of the trouble 'is in the northern Ohau," concluded the report, "the immediate problem extends much further down the main river in the form of the depoisit of silt clearly. visible, and no clearance in the water cah be .looked for untif this has been removed in subsequent freshes and floods." The position was a, serious one, commented Mr. Burdekin, and the only way of ameliorating it was for an "old man flood"" to come down the river. Ultimately, the ohly method of saving back country, and the water supply, would be to plant millions of trees On the hills. It was decided to give the matter full consideration at the April meeting of the works committee.