OCR Text |
Show NO PROGRAM TO UTILIZE AVAILABLE RECORDS FOR DETERMINING GROSS VOLUMES OF WATER SMALL STREAMS AND BRANCHES OF THE MAIN STREAMS ARE GENERALLY WITHOUT RECORDED STREAM FLOW PROJECTS NOW UNDER WAY GENERALLY PROCEEDING IN ADVANCE OF ADEQUATE STUDY OF SUBSURFACE WATER FLOW AND STORAGE AREA OF GREATEST DEFICIENCY IN ACCUMULATED DATA AND RESEARCH IN EVAPOTRANSPIR- ATION Since each precipitation station measurement is for one point only, it can be accepted as representative only of areas of similar rainfall characteristics. An examination of the present distribution of stations will show extensive areas without stations and there is no adequate program of relocation to improve the sampling of the variable amounts of precipitation. ( 2) No program has been formulated to utilize available precipitation records for determining gross volumes of water that could serve as a beginning point for a systematic water resource accounting. The rapidly mounting value of water resources would seem to require the conversion of precipitation measurements, now recorded in inches per year or per storm, to acre- feet or some other common unit of water measurement. ( 3) The volume of surface stream runoff is the only other phase of the hydro- logic cycle for which quantitative data have been systematically collected. Stream measurements have, however, been largely restricted to the larger rivers and streams. Small streams and branches of the main streams are generally without recorded stream flow. Unfortunately, many of the existing records are of such short duration that their dependability is seriously limited. Many of the water resource projects under construction and planned on smaller streams or in areas where data are especially deficient or of short duration. ( 4) Almost completely lacking are measurements or even identification of location and character of subsurface water movements. The conditions of subsurface water flow and storage are infinitely complex and effective management requires extensive studies that generally have not yet been made. When this is done, important modifications and, in some cases, completely different plans of water resource development may be required for sound projects. The present program of ground- water studies of the United States Geological Survey is almost 100 percent tied to projects for which State and local funds are available on a matching basis. This practice leaves little and in many cases no funds for ground- water research in the preplanning stage of the extensive water resource projects being financed by the Federal Government. Projects now under way involve the harnessing, diversion, and control of nearly all of the Nation's great rivers, but these projects are quite generally proceeding in advance of adequate study of subsurface water flow and storage. The complexity of the geological and hydrologic features of subsurface water movement and storage makes the prior gathering of such information essential for sound project planning. When such studies are complete, many opportunities of effective use of subsurface water flow and storage will be evident, either in conjunction with the surface stream flow and storage or in some cases as a complete substitute. ( 5) The area of greatest deficiency in accumulated data and research in the hydrologic cycle is evapotranspiration, or the process of returning water to the atmosphere by transpiration through plants or in evaporation from water and land surfaces. Even in the areas of greatest rainfall the volume of water consumed in evapotranspiration often exceeds the runoff to the ocean. In the extensive closed basins of the arid West there is no outward drainage, so evapotranspiration must return the total precipitation to the atmosphere. For vast areas the surface stream runoff to the ocean is generally only a small part of total precipitation. The fragmentary character or unavailability of data on evapotranspiration leaves many areas without the basic data most needed in effective water resources management. No Federal agency has been assigned the specific responsibility of furnishing quantitative data on this important phase of the hydrologic cycle. Certain important 26 |