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A power-scheme must of necessity be reliable in its working : this condition will make conduits expensive. Generally in steep country a tunnel in the solid rock will be found the most economical in the end. Races or canals and flumes will be more liable to damage by slips and exceptional rainstorms. A break in a conduit means loss of revenue ; stoppage of industrial work with its attendant losses to employers and workers alike, and frequent or repeated failure would give impetus to the employment of competing types of prime movers, working independently of weather conditions. For lake schemes, a tunnel carrying pure water should last an indefinite time. For river schemes, where silt-laden water would at times have to be taken, tunnel-linings would not last so long, but how long it is "not possible to ascertain, except by trial. A properly constructed tunnel is the ideal conduit, giving a'maximum of safety with a minimum of loss of water and of power. In the lake-to-lake schemes, and in all others where possible, the works could be designed to avoid loss of pressure due to varying Any scheme undertaken should be developed to its full extent, or if only partially developed at first, the works executed should be integral parts of the works required to develop the scheme to its full extent, so that there may be no abandonment or reconstruction of works when the scheme comes to be completed. The temptation to follow other courses will be great, but if given way to will lead to much useless expenditure. Before designs for the complete utilisation of all the power available in any proposed scheme can be prepared, a series of observations extending over a sufficiently long period would be required to determine the quantity of water likely to be available under all or the worst conditions. For lakes, the total annual flow is required for as many years as possible, to ascertain if the lake is of capacity sufficient: (1) To equalise the variations of flow from month to month in each year ; or (2) to equalise the variations in flow from year to year as may be possible in the case of some of the larger lakes, or lakes whose area is large relatively to their drainage-areas, or whose storage-capacity can be effectively increased by the construction of dams. To obtain the requisite data for lakes, it would be necessary to keep a daily record of the level of the outflowing river at various selected points, and to gauge the outflow at intervals when the river was at various levels. It would then be possible to compute the annual outflow to such a sufficient degree of approximation as would enable works to be designed with some degree of confidence. In the case of rivers where no storage is available, the minimum flow will be the governing factor, unless it were possible to find uses, as it may be, for power during the annual periods of high flow. It will be, perhaps, more difficult to get complete data for rivers than for lakes. In both cases there will be cost and trouble in uninhabited localities. In schemes to use the low-water flow of rivers the chances of error, and inadequate design arising therefrom, would be greater than for rivers regulated by lakes. In river schemes where partial storage would be possible, the total annual flow and the variations in flow would be essential factors, in addition to the minimum flow. j , -S. Rainfall-records can only be of partial assistance in dealing with|water- power It is not only the total quantity of water which falls on a catchment basin that requires to be known, but the percentage of that quantity that flows off at the various seasons of the year which has to be determined. The percentage of flow-off varies with the storage-capacity of the rock-fissures and sub-surface strata of the river-basin, vegetation-covering, wind, cloudiness, and other conditions, so that rainfallobservations cannot be substituted for the more laborious and costly methods of continuous records of river-levels, combined with frequent gaugings of flow. In some cases where there is no great difference in altitude in the various parts of a river-basin for which rainfall-records are available, these records might be used to extend back the results of gaugings to previous years after a connection had been obtained by observation between the rainfall and flow-off in any such case. It is evident from the data already obtained that generally the rainfall on New Zealand mountains is very much greater than on the lower ground contiguous to them, where most of the rain-gauge stations are now located. It is not possible to account for the flow from any of the lakes and in many of the rivers except by assuming that the mountain rainfall is much greater than on the lower tracts of country. The fluctuations of rainfall from year to year on the mountains may coincide with those observed for rainfall on the low adjacent country, and they may not. It would be of service to have some records to establish a connection, if there is any. Bach proposed scheme for water-power development would require independent observations to determine, completely, the local conditions governing the flow from the catchment-area proposed to be utilised. From the information available, and on present-day conditions, there seems to be every reason to suppose that the gradual development of water-power would accelerate the general industrial progress of the colony by providing a supply of cheap power, much cheaper than steam or other motive power, and in a form to easily meet many varying conditions of service. The conditions for the successful installation of hydraulic-power schemes will, perhaps, alter materially as time goes on, as regards the industrial uses of electricity and the capabilities of electric machinery and devices for generation of and transmission of energy to long distances ; also as regards the efficiency of steam and other engines for generating motive power ; so that many conclusions that now seem valid may in the future be shaken, or be put on a firmer basis. Rates of interest to be paid for capital may fall, and cost of plant may decrease, rendering possible the development of relatively more costly schemes than herein considered. Judging from the figures given herein, showing the growth of revenue for the " Jonage " and " Chevres " power installations, it takes a considerable period to get sale for all the power capable of being produced by a power-installation—three or four years in their case, and, possibly, it would be quite as long before any scheme installed in New Zealand would find sale for all its energy. The utilisation of all the hydraulic power available in the colony seems to be quite probable in the not very distant future. A considerable amount of power is now used, and there has been a fair rate of increase in the past few years. Also the quantity of power used per head of population may increase, thus accelerating the annual rate of increase. The development of hydraulic power will shift present and create new industrial centres in the colony. __ .