Even though there always has been plenty of fresh water on Earth, water has not always been available when and where it is needed, nor is it always of suitable quality for all uses. Water must be considered as a finite resource that has limits and boundaries to its availability and suitability for use. Figure 1. Offstream uses depicted on the left are those in which water is removed from its source, either by pumping or diversion. Instream uses depicted on the right are those in which water remains in place, and typically refers to stream rather than groundwater.
Where water supply is limited, conflicts may result between and among the various uses. The balance between supply and demand for water is a delicate one.
The availability of usable water has and will continue to dictate where and to what extent development will occur. Water must be in sufficient supply for an area to develop, and an area cannot continue to develop if water demand far outstrips available supply. Further, a water supply will be called upon to meet an array of offstream uses in which the water is withdrawn from the source in addition to instream uses in which the water remains in place. Figure 1 represents the demands on water as a tug-of-war among the various offstream and instream uses.
Traditionally, water management in the United States focused on expanding or manipulating the country's supplies of fresh water to meet the needs of users. A number of large dams were built during the early twentieth century to increase the supply of fresh water for any given time and place. This era of building large dams has passed. In the twenty-first century, the finite water supply and established infrastructure require that demand be managed more effectively within the available sustainable supply.
Water-use information can be used to evaluate the impacts of population growth and the effectiveness of alternative water management policies, regulations, and conservation activities.
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Water is constantly in motion by way of the hydrologic cycle. Water evaporates as vapor from oceans, lakes, and rivers; is transpired from plants; condenses in the air and falls as precipitation; and then moves over and through the ground into waterbodies, where the cycle begins again. The water-use cycle is composed of the water cycle with the added influence of human activity. Dams, reservoirs, canals, aqueducts , withdrawal pipes in rivers, and groundwater wells all reveal that humans have a major impact on the water cycle.
In the water-use cycle, water moves from a source to a point of use, and then to a point of disposition. The sources of water are either surface water or groundwater.
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Water is withdrawn and moved from a source to a point of use, such as an industry, restaurant, home, or farm. After water is used, it must be disposed of or sometimes, reused. Used water is either directly returned to the environment or passes through a treatment processing plant before being returned. The U.
Water Resource Management Models
Geological Survey compiles nationwide water-use data every 5 years. The year is the last year for which full datasets are available. The majority of fresh-water withdrawals, about , MGD, or about 77 percent, came from surface-water sources, while about 76, MGD came from groundwater. The source of saline water is surface water. Even though discussions of water use typically focus on fresh-water use, saline water use also is important in the United States. Some categories of water use, such as thermoelectric, industrial, and mining, use saline water, mainly for cooling generators in thermoelectric power plants.
Industries and mines use saline water to cool machinery and to wash and transport products, mainly for cooling of machinery. Geological Survey categorizes water use for analyzing current patterns and predicting future trends. Commercial water use includes fresh water for motels, hotels, restaurants, office buildings, other commercial facilities, and civilian and military institutions. Domestic water use is probably the most important daily use of water for most people. Domestic use includes water that is used in the home every day, including water for normal household purposes, such as drinking, food preparation, bathing, washing clothes and dishes, flushing toilets, and watering lawns and gardens.
Industrial water use is a valuable resource to the nation's industries for such purposes as processing, cleaning, transportation, dilution, and cooling in manufacturing facilities. Major water-using industries include steel, chemical, paper, and petroleum refining. Industries often reuse the same water over and over for more than one purpose. Irrigation water use is water artificially applied to farm, orchard, pasture, and horticultural crops, as well as water used to irrigate pastures, for frost and freeze protection, chemical application, crop cooling, harvesting, and for the leaching of salts from the crop root zone.
Models can predict interactions between ground-water and surface water bodies, as well as flows and their constituents in stream and river channels. These routing models can be based on simple mass balance and advection-dispersion relationships, or they can be based on hydrodynamic computations. They can also include ecological components of aquatic systems. Models can be used to study reservoir operation; to forecast floods and plan flood-control programs; to predict storm surges, embankment erosion, and dam breaks; and to plan for ecosystem restoration.
Federal, state, and local water-resources planning agencies can and do use models for the real-time operation and management of water systems and for assessing water supply availability and reliability, taking into account projections of basin development, administrative and legal requirements, and other constraints related to conveyance and reservoir operations, aquifer pumping, and water demand and distribution.
They use models for determining facility-size requirements for water storage and distribution systems given water diversions for domestic, commercial, industrial, rural, irrigation, municipal, energy, and environmental uses. They undertake watershed hydrology studies for improving river and reservoir administration and operation, the conjunctive use of surface water and groundwaters, water banking, and water exchanges and transfers. Many agencies, consultants, and university researchers are also working to improve water-resource analysis tools to meet their modeling and prediction needs.
Models can predict changes in a river bed form and location, including bank erosion, scouring, shoaling associated with construction or changes in the hydraulic regime, and so on. Models involving the transport of sediment have been used for morphological studies in small- and large-scale rivers of all kinds and in all settings, as well in reservoirs. Simulations can cover a few hours to several decades of high runoff events. These tools are useful for 2- or 3-dimensional spatial calculations, such as delineating watershed boundaries and stream and river paths, defining drainage areas and the areal extent of any other data layer, and for modeling distributed runoff.
In the future, hydrologists will increasingly rely on GIS data and standardized ways of describing them so that they can be used consistently to solve a wide variety of problems at various spatial scales. Water-resources planning and management activities are often participatory, involving groups of individuals with different interests, goals, and needs, thus requiring negotiation and compromise.
The U. To be most useful, shared-vision models must provide the right information, and the right amount of information to meet all stakeholder needs. Meeting these requirements can be a challenge to model developers. Hydroinformatics, a term that originated and was popularized in Europe and was associated at first with computational hydraulic modeling, also recognizes the need to communicate model results in more meaningful ways. Hydroinformatics today emphasizes the use of artificial intelligence techniques e.
These techniques can also be used for mining large collections of observed data or data generated from physically based models for knowledge discovery. The first involves the Potomac Basin and describes how modeling helped solve a highly visible and highly political water-supply problem. The next two examples, involving the Everglades region and part of the Great Lakes Basin, are ongoing studies that require much more detailed modeling methods. Although all three examples are in the United States, many others could have been chosen from other parts of the world.
The Water Supply for the Washington, D. A main reason for these concerns is the rapidly increasing population, particularly in the Washington, D. Traditionally, these agencies have operated independently, concerned only with satisfying the needs of their own constituents. However, with a rapidly increasing population, but relatively stable river hydrology, it became apparent in the s that frequent, severe droughts could lead to serious problems.
To address these concerns, the U. Army Corps of Engineers carried out a number of studies and, in , proposed the construction of 16 new reservoirs in the Potomac Basin. Two were subsequently authorized by Congress, and construction was even begun on one of them in spite of substantial local opposition. A simulation study in the late s and early s by graduate students at Johns Hopkins University showed how the coordinated use of the water stored in existing reservoirs in the Potomac River Basin during droughts would largely eliminate the need for new reservoirs, at least until However, they pointed out, the public would have to accept some risk of water restrictions during droughts, and the three utilities would have to cooperate with each other and coordinate their operations.
This was the first time a regional perspective was suggested.fensterstudio.ru/components/cymadixep/zo-localizar-mi.php
The idea had widespread political, legal, social, and environmental dimensions, and the models played a major role in convincing everyone that a cooperative policy would work. In the end, models were instrumental in bringing about a consensus supporting the nonstructural plan Anon, ; Hagen et al. On July 2, , at a historic ceremony in the District of Columbia Building, contracts were signed ensuring an adequate water supply for WMA until The savings far exceeded the money spent up to that time to support research on water-systems modeling.
The original simulation model, now named PRRISM Potomac Reservoir and River Simulation Model , has undergone several modifications and is currently used to evaluate the response of the system to present and future water demands.