RAINFALL

Hokitika Guardian, 13 September 1930, Page 8

RAINFALL

IMPORTANCE OF RECORDS

LONG OBSERVATIONS NEEDED

CHRISTCHURCH, September 11. “The value to the community of the work done by scientific observers in collecting data 'Oil such subjects as rainfall cannot be too highly estimated,” said Professor J. E. L. Cull, Professor of Civil Engineering at Canterbury College yesterday. “People are inclined to place a low value on it because they see no immediate return for the work, but to engineens and scientists generally, the information so gained is of extreme importance. “The value of such data from the engineer’s point of view can readily be illustrated at present by the situation at Lake Colerdige, by the power shortage at the Otago station, Waipori, earlier in the year, and the similar position at Mangahao in recent years. Before the construction of any such works is undertaken, a careful enquiry is made into such matters as rainfall and water supply. Often, however, all the necessary facts are not available either because they have riot been recorded, before the scheme was .contemplated, or because they are inaccessible. “With a full knowledge the engihee roan go ahead safely, and, provide for extremes. Without it he can. only partially judge, and extreme conditions may arise to upset his calculations. For his purposes the records need to be complete and accurate over a long period of years. LONG PERIOD OBSERVATIONS. “Fifty years’ good records of the rainfall in the catchment area are set out as being a sound basis for calculations of the design of such undertakings as Jhydro-electric works, though some authorities suggest longer periods. It has been stated by these that within fifty years there might not occur all . the extremes necessary to give an indication of what to propare for. and they have spoken of a period of ninety years. There are so many different types of climate that a period which was sufficient in one area would not necessarily suit for another. While engineers try to form rules, they cannot bring the rainfall to conform with a law, and every country and every catchment area is a law to itself.” ... , T Professor Cull showed how by corelating data gathered over a period of forty years from 153 stations, an English authority had demonstrated •the erroneous impression that might be drawn from data applying one to a short period. The grab compiled showed that on a short period of observation the extreme variation above *nd below .the mean average rainfall was far greater than on the full period. 'The longer the period recorded the more nearly the mean of the whole period gave a time impression of tne rainfall. In South African figures the extremes were as much as 75 per cent, above and below the mean over a qne year period 25 . per cent, on a five year period, and less than five per cent, on the forty year period.

NEED for records. Three question at present loomed large in Christchurch affairs, stated the Professor—hydro-electric power, harbour facilities, and river control—and all three were dependent on sufficient and accurate data, which took very many years to accumulate. The Department of Scientific and Industrial Research through its meteorological branch, had been doing extremely valuable work in the matter of collecting rainfall data for many years, and Dr E. Kidson had recently published a report on the subject. There was no organised attempt at getting records of ocean streams about the New Zealand . coasts, and dependence had to be placed on the evidence of masters of vessels ana fishermen. It was interesting to note how often af,ter a wreck it was suggested that unusual currents had existed. On the matter of river flow data the Waimakariri Trust Board had had to do some extensive work, while drainage work was also concerned, especially in Christchurch with the existence of such data. “I feel that much valuable information has been lost or mislaid in the past because there has been no central place where it might be deposited, concluded Professor Cull. “A man may have many valuable data, but they are uselessi unless they are put on permanent record so that they may be readily available when needed.”