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Show determining the effect of watershed management prac- tices on runoff and water yields and in refining the fore- casting of stream flow and water yield from snow storage and rainfall. Island Possessions and Trust Territories.-Surface water investigations have been very limited, and even non- existent in some cases. A relatively small amount of data is available in Puerto Rico as a result of work done by its Water Resources Authority and other government agencies. The Virgin Islands have practically no streams, and consequently no surface water data. Except for the slight amount of information that may have been obtained for military purposes during World War II, no information is readily available concerning surface-water supplies on the Trust Territories of Guam, Wake, and American Samoa. In all probability, very little data have been collected due to the occurrence of most of the water in the ground rather than on the surface. In the Panama Canal Zone rather intensive surface-water studies have been made over a period of years, particularly in con- nection with maintaining the water level of the canal. Some ground-water studies have been made in these possessions. Reconnaissance studies have been made on Puerto Rico and one of the Virgin Islands group in con- nection with municipal supplies and irrigation. The en- tire Island of Guam has been covered by a medium-order reconnaissance survey and several low-order reconnais- sances. No detailed or intensive studies have been made and only generalized knowledge of the ground water exists. A low-order reconnaissance study has been made covering the Islands of Tutilla, Annuu, Ofu, Olosega, Tau, and Rose of American Samoa. A small amount of information about the chemical quality of surface and ground water in Puerto Rico and the Virgin Islands has been obtained in connection with reports on ground-water supplies. Pratically no records about the quality of water are available for Guam, Wake, American Samoa, and the Panama Canal Zone. Additional data should be obtained on the water re- sources of the island possessions of Puerto Rico and the Virgin Islands in order to determine the availability and evaluate the suitability of all water supplies for industrial and domestic uses. Some information should be ob- tained with reference to public supply, domestic use, and military needs in the Trust Territories. In all of these areas one concern is salt-water intrusion by overdevelop- ment of ground-water supplies. Reconnaissance surveys should be made for over-all water resource needs, followed by detailed studies for those areas where problems exist or are likely to arise. There are at present 92 precipitation, 38 temperature, and 2 evaporation stations on the Island of Puerto Rico. Within an area of 3,435 square miles, this represents a station density comparing favorably with that in con- tinental United States. Only two of the precipitation stations, however, are equipped with recording gages. An addition of about 30 recording rain gages, uniformly distributed, would provide much more adequate infor- mation on rainfall intensity and, moreover, would increase the network density, which is considered reasonable in the absence of specific need for greater density. Within the 133 square miles of the Virgin Islands, there are 19 precipitation stations and 4 temperature stations. This would appear to be adequate coverage with the exception that one evaporation station should be established. Soil moisture data should also be collected in the other insular possessions. Several hundred stations will be needed in these possessions for the fuller interpretation of hydrologic data now being collected or which will be collected in the future. B. Topography Topographic mapping is the science of measuring and depicting on maps the physical and cultural features of a place or region. In general the maps portray (1) relief, the physical features of the earth's surface; (2) drainage, by which is meant streams, marshes, lakes, oceans; and (3) culture, or man-made features, such as roads, rail- roads, buildings, boundaries, place names, and other simi- lar items. Such maps are considered the base maps, or master maps, of the land area. Most of the other types of maps needed by Government and industry are compiled from, or are based upon, the topographic maps. Accurate topographic maps are regarded as a pre- requisite for developments and programs involving land and water utilization. They are important in the planning of all navigation, flood control, and reclamation projects, in land classification, and in conservation pro- grams. Topographic maps provide essential base maps for plotting and analyzing geologic, soil, hydrologic, and other types of basic data. For military use, topographic maps are of paramount importance for conception and execution of operational plans, combat training, troop movements, and coordination of land, sea, and air activities. In the early stages of this country's development most of the mapping done by Federal agencies was for the particular needs of the individual agencies. In the case of the Geological Survey, for example, topographic map- ping was originally undertaken primarily to obtain base maps for geologic and mineral investigations. For many years, no real effort was made to develop coordination of Federal mapping activities into a program of system- atically providing for national map requirements. In 1940, the Bureau of the Budget, recognizing the im- portance of basic surveys of our physical resources and of related mapping and charting, began its work in pro- gramming such activities and in coordinating the opera- tions of Federal surveying agencies toward the effectuation of planned programs. The Geological Survey of the Department of the In- terior is the principal producers of topographic maps, its activities representing approximately 80 percent of the topographic mapping currently being accomplished in this country. Before it and the other Federal agencies concerned begin actual mapping, however, a basis or framework of controlling positions, of latitude and longitude and of elevation above mean sea level, is estab- lished by the Coast and Geodetic Survey of the Depart- ment of Commerce. The Army Map Service of the Corps of Engineers of the Army produces a small volume of domestic maps, although its efforts are mostly devoted to mapping of overseas areas. Likewise, the Coast and Geodetic Survey, requiring topographic information of coastal areas for the nautical 354 |