514
Deficiency
of data for
precise calculation
of flow-off.
Preliminary expenditure to be sanc-
tioned, $20,000.
Programme of operations.
11. I regret that I am unable to form a more precise estimate of the probable yields of the increased gathering-ground. I have been carefully through the data which have been collected, during the past 12 years, and I shall give, in an Appendix,. an abstract of the results which I have obtained, with regard to the percentage of the rainfall which is available under various conditions of rainfall. The value of the data, which has been collected, is however greatly diminished by the fact that it is not practicable to estimate, with even approximate accuracy, the quantity of water which escapes through the waste-weir, during heavy rain. The only plan is to con- fine one's self to the investigation of periods, during which there was no overflow, thus materially reducing the number of available observations. Again, the methods. of measurement, now available, are not sufficiently accurate to give precise results. I shall offer later on some suggestions as to improvement in this matter.
12. I shall not attempt to give any estimate of the probable cost of the works which I have recommended. The data before me, in the form of plans, are not sufficient to permit of the preparation of even a rough estimate. The submission of estimates, based on insufficient data, is a most objectionable practice and one apt to mislead. I therefore recommend that the sum of $20,000 be sanctioned for preliminary work, such as surveys, gaugings of streams and the like.
13. The first thing to be done, is to commence a survey of the Taitam Valley, extending from sea-level to about 300 feet above it. This survey should be made with the utmost accuracy, so that it may be available as a portion of the new survey of the Island, a work, so much needed, as I have frequently pointed out. Whilst surveying, it would also be well to include the whole gathering ground of Taitam, including areas utilised, by means of catch-water drains. I would here observe that sections 21 and 22, of Ordinance 16 of 1890, Demarcation and Reservation of gathering-grounds, do not appear to have been complied with. The Taitam gathering-ground should therefore be carefully survey- ed and delineated with permanent Boundary Stones. Whenever convenient, for example those at the summits of hills, should serve as trigonometrical points, and their positions should be referred by means of rectangular co-ordinates, to some one fixed point, such as the Kowloon Observatory. I cannot too strongly insist upon the necessity for recording, permanently, leading survey-points; so that they may be available for future work. It is greatly to be regretted that this was not done, in the case of the Collinson Survey of 1845. I, and many others, have invariably failed to find on the ground, the trigonometrical points, on which this survey was based. Therefore, all the valuable information, which is contained in the field-books and computation sheets, which exist or did exist, in the R. E. Office, are practically valueless. Had the trigonometrical points been permanently marked, by means of substantial pillars or otherwise, much of the work of 1845 would still be available,. for purposes, such as the present.
•
As an example of the importance of permanently marking survey-points, not only on the ground, but by records also in the office, I may site the Survey of Malta, with which I was formerly connected. The trigonometrical points were well marked on the ground, and the co-ordinates of each recorded in the office. Government surveys, for any purpose, whatsoever, were all connected to two or more points. The result was that, in the course of not very many years, a nearly complete cadastral plan has been produced, at trifling expense. Whereas here, surveys have been made of the City, of the Peak district, of Taitam and other places, but there is nothing to link them together.
Levelling-operations need not in the first instance be carried higher than is required, for the immediate necessities of the case.
Two gauge-weirs should be erected, on the main Taitam-tuk stream, at sites which have been selected. One of these, which should be at least 40 feet in width, is intended to measure moderate floods, up to 4 inches per day. The other, a V