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[en] Realizing the importance of climatic and pedologic conditions on the quality and isotope composition of water in the unsaturated zone, the International Atomic Energy Agency set up a cooperative programme to study the changes in and relationship between precipitation and soil water, as reflected in the composition of lysimeter percolates. Lysimeter stations were selected to represent a broad spectrum of climates and soil conditions. This paper presents and discusses results from lysimeter stations for which data accumulated for at least two years. Results of other stations will be published when more data becomes available. Although two years may not be enough for conclusive studies of this nature, the data accumulated so far have interesting implications which may stimulate similar studies elsewhere.
[en] Ten years ago Schoellander measured the age of the icebergs coming from glaciers,using the 14C dating method and found surprisingly low ages; one was 3000 years old and ten others had ages of less than 1000 years. Recently we repeated the measurements using improved sample collection and extraction techniques. When the snow is accumulated in a glacier, some atmospheric air is trapped in the very fine bubbles which makes the ice appear white. Since the ice is practically impermeable, the measurement of the 14C content of the air trapped in the ice is a good measure of the period when the air was trapped. To obtain 50 milligrams of carbon for analysis about 4 tons of ice are required.
[en] The general layout of the project, a study of the groundwater resources in the high plateau and the southern desert of Jordan, is shown. The Dead Sea occupies a structural downdrop block, and is bordered on the east by a major fault. East of this fault line a very steep escarpment rises from about 400 m to more than 1000 m above sea level. In the high plateau, where the precipitation varies between 200 - 600 mm, the rainfall belt is very narrow and follows a north-south direction. The rest of the country receives less than 50 mm precipitation. The major input to groundwater, therefore, is along the escarpment where the precipitation is relatively high; it originates from moist air masses coming from the west. Initially no environmental isotope data were being collected at precipitation stations in the project area. The first task, then, was to sample the precipitation at four stations in the rainfall belt (Irbid Amman, Rabba and Shobak). The precipitation increases in the north-south direction: however, there is also a marked decrease of altitude in that direction. It was expected, therefore, that the altitude effect would be counterbalanced by the amount effect. This has now been confirmed by the stable isotope data.
[en] Karst formations are the most important aquifers in many regions of the world. Three special hydrologic features characterizing them are: the absence of a well-developed surface drainage network; a high infiltration capacity and a concentrated subsurface flow pattern. Several aspects of a karst aquifer system resemble a surface water system. For example, flow in the subsurface karst system is concentrated along major faults, solution channels and fractures, as flow in surface water is concentrated in surface streams. The high infiltration capacity of karst formations is evidenced by scarcity of surface drainage, the disappearance of large rivers into sinks, and large losses of water from lakes through sinks into the subsurface. The discharge of water from springs in large flows at the terminal ends of karst aquifer systems parallels the discharge of water by surface streams in a normal surface water system.
[en] The following papers, oral contributions and discussions, were assembled informally by the Scientific Secretariat of the Panel Meeting on Interpretation of Environmental Isotope Data in Hydrology (Vienna, Austria, 24-28 June 1968). They have not been edited formally, so that minor changes have not been cleared with the original authors. They are reproduced for informal distribution as they may be helpful to hydrologists and others interested in the application of environmental isotopes in hydrologic studies.
[en] Research in application of environmental isotope techniques to hydrologic problems has been active and fertile over the past decade. The development of techniques for use of tritium, carbon-14 and more recently silicon-32 in groundwater dating and the broad spectrum of applications of deuterium and oxygen-18 in water problems has nearly all taken place during this period. However, the practical use of these techniques has generally not kept pace with the research and development. This is due, no doubt, in part to lack of communication between research scientists and people concerned with practical field problems, but also to the fact that water problems in the highly developed nations where the research is carried out, generally are greatly different in type and scope from water problems in the developing nations. For example, the main problems facing hydrologists in Northwestern Europe, a humid, industrialized area, are entirely different from the arid and semi-arid belts of Asia, Africa and South America. Even the most sophisticated techniques for investigating underground raters give results that are crude in comparison with the simple technique of gauging flow in a surface stream with a current meter. Likewise, quantitative estimates of interrelations of surface and underground waters are subject to similar uncertainties because underground flow of some form plays an important role in nearly all flow systems. By the same token, underground flow does not lend itself to application of simple models because of the great complexity of the flow paths. For these reasons the subsurface environment deserves the special attention of isotope workers. The task is complex and difficult but the need is great for better tools.
[en] When using environmental isotope methods, hydrologists should first formulate a hypothesis or hypotheses concerning a given hydrologic problem. The second step is to figure out isotopic patterns that fit the different hypotheses. A few measurements of environmental isotope content of water in the system may then be sufficient to support one hypothesis and reject others. Before drilling a borehole, for example, geologists lave some idea of the formations and the aquifers which can be tapped during the drilling based on surface geology, previous reports, or other sources of information. The isotope worker also should have the same type of knowledge he should have at least a hypothesis before the sampling programme for environmental isotopes is undertaken. In fact, the extent and frequency of the sampling depends on the type of problem and the hypotheses that can logically be developed to study the problem. In general, in areas where little is known about the hydrology, environmental isotope studies are of greatest value. In areas where hydrologic information is abundant, environmental isotope data is useful mainly to give additional confirmation to conditions already largely known.
[en] The paper reviews the urgent need for development of water resources and the role of national and international organizations in that development. After dealing with the problems of water-resources investigations and development, planning and management of environmental isotopes in hydrology is explained. It is pointed out that chemical methods are still of major importance in studying the genesis of waters. These methods now should be supplemented by environmental isotope techniques.
[en] During the hydrologic cycle, the stable isotopic components of the water are exposed to several fractionation effects. One of these effects occurs because the vapour pressure of the light isotopic component, H2 16O, is higher than the heavier components HDO and H2 18O. Another important effect is the molecular exchange between water in the liquid and gas phases which is a complicated process. For several years IAEA has carried out, in cooperation with MO, a collection of the precipitation samples in a world-wide network of about 110 meteorological stations. These samples have been measured for tritium, deuterium and oxygen-18 content, and the following discussion is based on these data.
[en] There are three phases in the water resources development engineering which can be defined as: (a) Exploratory stage: In regions where no or little physical data (climate, geology, hydrology, etc.) are available, it is usual to start with a reconnaissance study to obtain some qualitative information concerning the availability of the water resources and on the possibility of their development for various uses, which are in general, water use for domestic purposes and for irrigation. (b) The Development stage: This is the second stage where detailed investigations are made in order to make quantitative evaluation of the water resources in the region. This stage also involves the construction of the first facilities such as dams, and canals, for storage and distribution of water and exploratory boreholes and wells for groundwater. (c) The Operation and the Management stage: This stage is concerned with the optimal operation of the water resources in use. In this stage much more sophisticated quantitative methods are needed. In all three stages environmental isotopes can be used profitably. The three basic components of a hydrologic system are the inflow, the outflow, and the system itself. The system has 2 kinds of properties (l) ''medium'' and (2) ''state'' (or operational level) parameters. The first are storativity, permeability, transmissivity and the porosity of the system, which do not change with time but may have, and, indeed often do, have large variations from one point to another. The second type includes the instantaneous levels of a reservoir, and volume of storage, at a given time; they are not related to the medium.