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Show ried out progressively during the next 10 years. This will assure that most of the minimum necessary data will be available for the sound planning, design, construction, and operation of future hydraulic structures and water-supply development projects. Hawaii.-The economy of the Territory of Hawaii de- pends greatly on the availability and location of water supplies for agricultural, domestic, municipal, military, and industrial uses. Certain areas on the leeward side of the islands in the Territory have scarcely any precipita- tion and, consequently, very little water is available. The permeability of the ground is generally high where the surface is composed of volcanic rocks, but alluvial deposits in valleys are relatively impervious. Alluvium composes the caprock providing artesian head in many wells near the coasts. A stream-gaging program for Hawaii was started in 1909 in which the Geological Survey is cooperating with the Territorial government. At present, records of dis- charge are obtained at approximately 120 points on streams and irrigation ditches. The drainage basin of a characteristic stream on these islands is short with steep slopes, extending from the crests of mountains to the sea in narrow, closely-spaced valleys. Flows of the natural surface streams are highly variable with frequent high intensities of runoff. The high permeability and steep gradients of the ground surface make the storage of water in reservoirs uneconomical except on a very small scale. The high value placed on water for irrigation, the im- portance of observing water rights, and the growing im- portance of flood control create a great need for a con- tinued and an expanded stream-gaging program. It is recommended that the present coverage of gaging stations be increased 50 percent during the next 10 years. Of all our island possessions and trust territories, the Hawaiian Islands are best known from the standpoint of ground-water hydrology; however, much still remains to be done there. Ground-water reconnaissance studies ranging from low to high order have covered all the major islands of the Territory of Hawaii, and in a few local areas intensive studies have been made. The geology is complex and recharge to the aquifers is highly variable from place to place and from time to time. It is believed that large additional ground-water supplies can be safely developed in some areas, but other areas ap- parently are either overdeveloped resulting in salt-water intrusion, or are nearing that stage. The draft on the ground-water reservoir in the Honolulu area already ex- ceeds the annual recharge. Detailed investigations of the fluctuations of the salt water fringe and the levels and volumes of recharge will be increasingly necessary in the next decade in order that existing supplies are protected from salt contamination during dry years. Only a relatively small amount of information is avail- able about the chemical quality of surface and ground water in the Hawaiian Islands. Available data indicate, however, that the quality is generally good and satis- factory for practically all purposes except in those areas where the fresh water is contaminated with sea water. Salt-water intrusion in ground water is the principal quality problem in certain areas, especially where ground water is used for irrigation. This has been partially overcome by collecting fresh ground water in tunnels and galleries just above the salt water layer on which the fresh water floats. Additional information is needed con- cerning the extent and thickness of the fresh water lens during different periods of the year in order to make more effective use of the available fresh ground-water supplies. Information on sanitary quality as affected by sewage pollution is generally adequate. Periodical inspections of sources of pollution and analysis of water samples are conducted by the Territory of Hawaii Board of Health. Additional data are required on pineapple cannery and on sugar mill wastes in certain areas, and on the dis- tribution and effects of these wastes in the receiving waters. To guarantee that existing water sources are utilized in the most economical manner, it is imperative that an adequate network of gaging stations and ground water observation wells be established in the near future. Sur- face and ground water sources are heavily used for irri- gation. An expanding population in Honolulu will soon require the diversion of water now used for irrigation to municipal use. Equitable adjustment of this problem will require an expanded program of data collection which must be started immediately if the data are to be avail- able when the various needs for water begin to conflict. Available basic hydrologic and meteorological data in the Hawaiian Islands are probably more complete than for any other area under the jurisdiction of the United States. There are approximately 825 precipitation and 60 tem- perature stations in the 6,420 square miles comprising the islands. Of this total, records from about 300 precipi- tation and 60 temperature stations are published by the Weather Bureau. The greatest density of precipitation stations, 1 for about 2/4 square miles, is found in the Island of Oahu, while the least density, 1 gage for about 20 square miles, is found in the Island of Hawaii. Tem- perature station distribution varies from a density of four per square mile in the Island of Oahu to 1 per 200 square miles in the Island of Hawaii. Although a very dense network of precipitation gages is in operation, the number of recording gages is very small. With the exception of Oahu, which has about 20 recorders, all of the other islands have but 1 or 2 each. Another consideration of the precipitation network in the Islands is an unbalanced distribution of gages. For example, the Island of Hawaii with a total of about 220 gages has about 190 located at elevations below 5,000 feet. The remaining 30 gages are installed at elevations between 5,000 and 9,500 feet, while the maximum elevation of the Island is about 14,000 feet. The area above 5,000 feet elevation represents about one-third of the area of the island. In view of the unusual density of the nonrecording precipitation network, it is recommended that about 20 recording and 10 storage-type gages be added to the network. Most of these gages would be installed on the islands of Hawaii and Maui at the higher elevations. There were four evaporations stations in operation on the Islands until two or three years ago, at which time they were closed. It is recommended that these stations be reopened or that an equivalent number be established at different locations if more desirable sites are available. Soil moisture data are also needed in Hawaii for more precise interpolation of hydrologic data. It is estimated that installations of several hundred stations in the next 10 years will suffice for improving the techniques of 353 |