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USGS1974

Summary appraisals of the Nation's ground-water resources; Texas Gulf region

Ground water in the Texas-Gulf Region is a large and important resource that can provide a more significant percentage of the total water supply of the region. Total water requirements within the region are projected to rise sharply from 14 million acre-feet (17 cubic kilometres) in 1970 to nearly 26 million acre-feet (32.cubic kilometres) in 2020. About half of the water used in 1970 was ground water. An estimated total of 1.04 billion acre-feet (1,280 cubic kilometres) of recoverable water containing less than 3,000 milligrams per litre dissolved solids is stored above a depth of 400 feet (122 metres) in the aquifers of the region. In addition, part of an estimated 3.28 billion acre-feet (4,040 cubic kilometres) of water in storage below 400 feet (122 metres) is recoverable. Although not all of the ground water in storage is recoverable, a significant amount is available for development, and an enormous quantity is accessible should occasions prompt its use on a time-limited basis. The total steady-state yield (amount of water that approximates the maximum perennial replenishment from precipitation) of the region's aquifers is about 4.6 million acre-feet (5.7 cubic kilometres) annually, or about 2.3 times the ground-water usage in 1970 if the large mining draft on the High Plains is not considered as part of the total steady-state yield. Because of the large quantity of recoverable ground water in storage, the steady-state yield can be augmented for a very long time on a 'deferred' basis, whereby the economic use of the water that is withdrawn from storage in excess of the steady-state yield may result in a strengthened economy. An important goal in programs for meeting future water needs should be to identify the full potential of the available ground-water resources. The subsurface reservoirs may be utilized not only as sources of fresh and treatable water, but as storage facilities for other fresh-water-supplies and as possible sources of geothermal energy. Some saline-water reservoirs may be suitable for liquid-waste storage or disposal. Large-scale and unregulated ground-water pumping may result in hydrologic problems such as declining water levels, streamflow depletion, and land-surface subsidence; but studies on proper development of the groundwater reservoirs could provide solutions to many of the problems. Water rights and other legal concepts should be based on sound hydrologic principles to assist development of water resources in an orderly and efficient manner. Because significant amounts of ground water are available, the opportunities for expanded and conjunctive use of ground water and surface water should be considered in regional plans for water development and conservation. The complexities of water management and the difficulties of achieving an integrated system of total water management will require additional technical information.

Louisiana, New Mexico, Texas↗
USGS1977

Summary appraisals of the Nation's ground-water resources; Souris-Red-Rainy region

A broad-perspective analysis of the ground-water resources and present and possible future water development and management in the Souris-Red-Rainy Region is presented. The region includes the basins of the Souris River within Montana and North Dakota; the Red River of the North in South Dakota, North Dakota, and Minnesota; and the Rainy River within Minnesota. The region includes 59,645 square miles, mostly in North Dakota and Minnesota. The terrain is relatively flat, but ranges in altitude from 2,541 to 750 feet. Annual average precipitation ranges from 14 inches in the west to 28 inches in the east and about 75 percent of it is rain. The mean annual snow fall ranges from 32 inches in the west to 64 inches in the east. Temperatures range from -55° to 118°F (-48.3° to 47.8°C). Irrigation is needed at least part of the time to assure crop production, particularly in the western part of the region. Sand and gravel deposits in the drift form the most important fresh-water aquifers. Other aquifers are found in at least parts of the region in the Precambrian, Paleozoic, Cretaceous, and Tertiary rocks. The potentiometric surface in the bedrock generally decreases in altitude toward the Red River of the North, indicating that the general direction of ground-water movement is toward the river. Ground-water with less than 3,000 milligrams per liter dissolved solids is available throughout the region. Ground water with less than 1,000 milligrams per liter occurs in most of the region east of the Red River of the North and in most of the shallow aquifers west of the river. The total volume of water available from storage having less than 3,000 milligrams per liter dissolved solids is estimated to be 5 x 10 8 acre-feet. In addition to the fresh and slightly saline water, the region has abundant highly mineralized water that can be considered as a resource. Yields of wells in individual bedrock aquifers are generally less than 100 gallons per minute but locally yields may be as much as 500 gallons per minute and more. Yields in drift aquifers are frequently less than 100 gallons per minute but range from 5 to 1,000 gallons per minute. In a few places outwash yields more than 1,000 gallons per minute. Ground water is the sole or a primary source of water supply in much of the region, including supplies for irrigation, domestic and livestock, municipal, and industrial needs. Reportedly, the potential irrigation development is 1,550,000 acres, as compared with 50,200 acres in 1975. Both ground- and surface-water supplies would be required to meet these demands. Rural domestic and livestock water supplies are derived almost entirely from ground-water sources. Smaller communities and towns generally rely on ground water, and the cities and industries use ground water, surface water, or both. The municipalities using surface water generally depend upon reservoir storage. Water quality rather than quantity is the greater water-supply problem for many communities in the region. Increased demands on both ground-water and surface-water supplies likely will be made in the future. Storage of surface water in the ground-water reservoirs during times of surplus for withdrawal during times of scarcity would aid in meeting these demands. The surplus (flood) water is of better chemical quality than underlying ground water in parts of the western half of the region. Fresh water could be stored in saline- or fresh-water aquifers, and pumped out later, as needed. Thus, the ground-water reservoirs have a definite present and potential role in water management. To understand the hydrologic system for management purposes there is a need to determine more adequately the geologic and hydrologic characteristics of existing aquifers and the location of new aquifers. Also, as pumping and other stresses on any part of the hydrologic system affect other parts of the system, monitoring programs ideally should be started and maintained to detect changes and determine effects of the stresses. Many alternatives are available for managing water in the region. Some of these are operational and others are undergoing research. Adequate hydrologic information is needed to aid in solving problems of water supply, use and pollution.

Minnesota, Montana, North Dakota, South Dakota↗
USGS1975

Summary appraisals of the nation's ground-water resources – Upper Mississippi region

The Upper Mississippi Region in general is rich in water-surface water is plentiful, and ground water is a large, important, and manageable resource. Total potable water in storage in the outwash and alluvial aquifers of the Mississippi River valley and the subbasins is about 45,000 billion gallons. This is about 10 percent of the water in storage in Lake Ontario. Water in storage in other aquifers of the region is probably at least several times that in the outwash and alluvial aquifers. Estimated ground-water recharge in the subbasins is 23,000 million gallons per day. A comparison of ground-water withdrawals with estimated ground-water recharge suggests that the large ground-water resource of the region is not being fully utilized. Ground-water use by domestic, commercial, and rural interests is only 4 percent of recharge. Ground-water use (1965) by industry is only 3 percent of recharge. Water in the outwash and alluvial aquifers of much of the valley of the Mississippi River in and south of St. Paul, Minn. of the Illinois River, the Lower Minnesota River, the Wisconsin River, the Lower Black River, the Wapsipinicon River, the Lower Rock River, and the Upper Des Moines River can be considered a regional resource. In these areas the ground-water resources are of sufficient magnitude to satisfy more than just local needs. For example, under certain specified conditions, ground water in the above areas can supply approximately 20 million additional people. Factors other than water supply, of course, will be constraints on development in the region. Advances in techniques in ground-water hydrology during recent years have provided methods that the hydrologist and planner can use for planning and design of ground-water developments. Therefore, the planner can now resolve some of the development and management questions that historically have bred uncertainty when this part of the water resource was considered for development.

Illinois, Indiana, Iowa, Missouri, Minnesota, Sout↗
USGS1974

Summary appraisals of the nation's ground-water resources – Upper Colorado region

The Upper Colorado Region covers about 113,500 square miles (293,965 km 2 ) in parts of Arizona, Colorado, New Mexico, Utah, and Wyoming. Drainage from about 97 percent of the region is to the Colorado River. About 60 percent of the land is owned or administered by the Federal Government, and another 15 percent is in Indian trust. The predominantly arid to semiarid region is sparsely populated (averaging about three persons per square mile, or about two and one-half persons per km 2 ) and is used chiefly for grazing, recreation, and mineral development. The water supply for the region comes from precipitation within the region, which averages about 95 million acre-feet (117,182.5 hm 3 ) per year. Development of the region's water supply has been limited almost entirely to surface water. Only about 2 percent of the total estimated volume of water withdrawn (about 5.7 million acre-ft, or 7,030.9 hm 3 ) and consumed (about 3.6 million acre-ft, or 4,440.6 hm 3 ) in the region in 1970 came directly from ground-water sources. By the year 2020 consumptive use of water within the region and water exports to adjacent regions are expected to total more than 6.5 million acre-feet (8,017.8 hm 3 ) per year. Use of the ground-water resources of the Upper Colorado Region in water-resources management can help to meet these water needs. A tremendous amount of water is stored in the rocks (ground-water reservoirs) of the Upper Colorado Region. Recoverable water in just the upper 100 feet (30.5 m) of saturated rocks is estimated to be as much as 115 million acre-feet (141,852.5 hm 3 ). That amount is nearly four times the total active storage capacity of all surface-water reservoirs in the region. The average annual replenishable supply of the ground-water reservoir is about 4 million acre-feet (4,934 hm 3 ). This amount of water could irrigate about 1.3 million acres (526,1,10 ha) of crops having an annual water requirement of 3 feet per acre (0.9 m/ha), or it could provide about 3,600 million gallons (13,627,440 m 3 ) per day for industrial use. Most of the ground water is in consolidated rocks, which generally yield water to wells slowly. Much of the ground water is saline and, in some places, occurs at great depths. Nevertheless, the ground water is more uniformly distributed than is surface water, both areally and with time; therefore, it can be used advantageously in overall waterresources management. Recent advancements in the field of demineralization and in evaluation and development of ground water make this possible. Options available for use of ground water in water-resources management·in the·region include conjunctive use with surface water or development of ground water as an independent supply. The latter option could be for & perennial supply or for a time-limited supply (mining ground water), depending on the need and the existing ground-water conditions. All options can be carried out so as to meet the requirements of the Colorado River Compact. The options could be implemented to optimally develop the Upper Colorado River Basin's allocation of Colorado River water while meeting the Compact commitments to the Lower Basin.

Arizona, Colorado, New Mexico, Utah, Wyoming↗
USGS1976

Summary appraisals of the nation's ground-water resources – California region

Most people in the California Region live in a semiarid or arid climate, with precipitation less than the potential evapotranspiration- environments of perennial water deficiency. The deficiency becomes most onerous during the characteristically rainless summers and during recurrent droughts that may continue for 10--20 years. However, water from winter rain and snow can be stored for use during the dry summer months, and water stored during a wet climatic period can be used in a succeeding dry period; moreover, perennial deficiency can be overcome by bringing water from areas of perennial surplus. Ground-water reservoirs have especial significance in arid and semiarid regions as repositories where water is stored or can be stored with minimum loss by evaporation. Nearly all the ground-water reservoirs of the California Region are in alluvial sediments of valleys and plains that flank the mountain ranges. The largest, underlying the vast Central Valley, occupies 10 percent of the area of the region, has an estimated usable capacity exceeding 100 million acre-feet (125 cubic kilometres), and has an annual pumpage from wells of about 13 million acre-feet (16 cubic kilometres). Another 10 percent of the region is occupied by 55 developed ground-water reservoirs that are widely distributed; aggregate annual pumpage from them is about 3 1/2 million acre-feet (4 cubic kilometres). In the southeastern desert about 60 ground-water reservoirs occupy still another 10 percent of the region; these have been explored only enough to show that most have some usable water, but current use is negligible. In northeastern California and adjacent Oregon and Nevada, ground-water reservoirs are identified only in valleys and lowlands where wells are feasible, but basaltic rocks of the Cascade Range and Modoc Plateau are excellent aquifers distributed over an area constituting about 15 percent of the region. In sum, slightly less than half the California Region is underlain by ground-water reservoirs, either in valley fill or in volcanic rocks, which can yield significant quantities of water to wells. The rest of the California Region includes the mountains, canyons, slopes, and foothills of the Sierra Nevada, Coast Ranges, and Basin Ranges, whose consolidated rocks and products of their weathering may be permeable locally but are not generally so. Here, the prevailing method of ground-water development is still mostly trial and error, and while in many places a well can yield enough water for a family, some families might have to do without amenities such as flush toilets and automatic washers. For more than half a century the California Region has led all others in North America in pumping of ground water as well as in the area, variety, yield, and export of crops irrigated by water from wells. It has led in the development and use of deep-well turbine pumps for large yield and in the drilling of water wells to great depths. At the same time, such developments have resulted in the elimination of artesian pressures that produced thousands of flowing wells in the 19th century and led to the wide distribution of "falling water tables." Also, California was first to induce encroachment of seawater into wells (in 1906); first to recognize subsidence of land caused by pumping from wells (in 1933), generating news about land sinking in San Jose, Long Beach, and along the Delta-Mendota and Friant-Kern Canals; and first to experience pollution of ground-water reservoirs by brines, chemicals, industrial wastes, and petroleum byproducts including gasoline. The region has led in research in several fields leading to solution of many of these problems. Ground-water problems developed rapidly after World War II with booming population, agriculture, industry, and water demand during several years of regionwide drought. Water levels in wells trended downward almost everywhere as a natural effect of the drought and at accelerated rates in areas of pumping for new enterprises or to supplement subnormal surface-water supplies. The declines in many pumping areas exceeded 100 feet (30 metres), and in some confined aquifers the potentiometric surface was drawn down more than 330 feet (100 metres). The depletion of ground-water storage has had "permanent" side effects, including subsidence of the land exceeding 10 feet (3 metres) in extensive areas, and seawater intrusion that ended the useful lives of many wells along the coast and as much as 6 miles (10 kilometres) inland. Some problems have been solved, but these solutions have at times created other problems. Many ground-water reservoirs have gone through one or more stages - exploration for productive aquifers, exploitation and development for use of the water, restriction to the perennial supply or "safe" yield, importation of surface water, artificial recharge of ground water, conjunctive use of surface and ground water, protection of water quality, and integrated management of use and disposal of water. This evolutionary sequence is unique for each reservoir, and so generalizations become difficult in a regional appraisal; also, the changes with time are significant and varied, and knowledge of prior events is a prerequisite in an appraisal of the resource in a specific year. As of 1970, water levels in many wells had risen significantly from the minimum levels of record reached during the 1960's or earlier; only in areas of new development and in desert areas of long-continued "mining" of nonreplenished water was ground-water storage still being depleted. Land subsidence has continued at diminishing rates and practically has come to a halt in some areas; invading seawater has been stopped or nudged back in most places where problems were significant. The current, favorable situation has been helped by climatic variations, from drought in 1945-52 and exceedingly dry years in 1959 and 1961 to above-normal precipitation in 1969 and 1970; but most of the serious problems have been solved by human efforts, including especially the implementation of the California Water Plan, transporting water from areas of perennial surplus to areas where it is used in lieu of ground water or for ground-water replenishment. All major urban areas now import water to supplement or replace the water pumped from wells. Extensive agricultural areas that formerly were irrigated solely by ground water now obtain some of their water from surface reservoirs and canals, especially in the Central Valley. With surface water available as an alternative supply, well owners can view their ground water with complacency. But complacency can lead to neglect and carelessness and consequent deterioration of the ground-water resource by pollution. Claiming heritage from the English Common Law, the existing California law grants to the landowner (riparian) and private enterprise (appropriator) rights to the water stored in ground-water reservoirs or discharged from them, including the base flow of streams. Ground-water development has been by private and local enterprise, and the California legislature has protected and encouraged local responsibility, control, and management of ground water. As to surface water, a constitutional amendment in 1928 limited riparian rights to the quantities of water that were "reasonably required for the beneficial use to be served." The surpluses have become public waters which are collected, stored, transported, and delivered under various contracts by Federal, State, and other agencies. The agencies have not stored water underground because of uncertainty as to their rights, but some local agencies have been encouraged with favorable pricing schedules to undertake the artificial recharge and management of ground-water reservoirs. Thus, conjunctive use of surface and ground water has become a matter of interagency negotiation. Of all the constraints on effective use of ground-water reservoirs, the most formidable may be the attitudes of people. Assurance of water supply is vital in areas of water deficiency, and Government has assumed increasing responsibility for the welfare of people in these areas. Unfortunately, when Government provides this assurance, most beneficiaries demand continued subsidy to the exclusion of perhaps cheaper private development. Indeed, as the water resources are presently segregated-with private rights predominant in ground water and public interest dominant in surface water-ground-water development has suffered for lack of public concern. The region has the scientific and technologic capability for effective use of groundwater reservoirs, as shown by the achievements and programs of several districts, but many districts are not organized or staffed for such comprehensive management and will need assistance and scientific expertise available from State and Federal agencies. Those agencies, in turn, may not have the scientific data that are essential to prevent haphazard activities and to enable programs to be organized for the most effective and attractive utilization of the water resources. In these days of increasing concern over pollution, existing data are generally inadequate to assess the natural deterioration of ground waters as a basis for defining pollution.

California↗
USGS1976

Summary appraisals of the nation's ground-water resources–Texas-Gulf region

Ground water in the Texas-Gulf Region is a large and important resource that can provide a more significant percentage of the total water supply of the region. Total water requirements within the region are projected to rise sharply from 14 million acre-feet (17 cubic kilometres) in 1970 to nearly 26 million acre-feet (32 cubic kilometres) in 2020. About half of the water used in 1970 was ground water. An estimated total of 1.04 billion acre-feet (1,280 cubic kilometres) of recoverable water containing less than 3,000 milligrams per litre dissolved solids is stored above a depth of 400 feet (122 metres) in the aquifers of the region. In addition, part of an estimated 3.28 billion acre-feet (4,040 cubic kilometres) of water in storage below 400 feet (122 metres) is recoverable. Although not all of the ground water in storage is recoverable, a significant amount is available for development; and an enormous quantity is accessible should occasions prompt its use on a time-limited basis. The total steady-state yield (amount of water that approximates the maximum perennial replenishment from precipitation) of the region's aquifers is about 4.6 million acre-feet (5.7 cubic kilometres) annually, or about 2.3 times the ground-water usage in 1970 if the large mining draft on the High Plains is not considered as part of the total steady-state yield. Because of the large quantity of recoverable groundwater in storage, the steady-state yield can be augmented for a very long time on a "deferred" basis, whereby the economic use of the water that is withdrawn from storage in excess of the steady-state yield may result in a strengthened economy. An important goal in programs for meeting future water needs should be to identify the full potential of the available ground-water resources. The subsurface reservoirs may be utilized not only as sources of fresh and treatable water, but as storage facilities for other freshwater supplies and as possible sources of geothermal energy. Some saline-water reservoirs may be suitable for liquid-waste storage or disposal. Large-scale and unregulated ground-water pumping may result in hydrologic problems such as declining water levels, streamflow depletion, and land-surface subsidence; but studies on proper development of the ground-water reservoirs could provide solutions to many of the problems. Water rights and other legal concepts should be based on sound hydrologic principles to assist development of water resources in an orderly and efficient manner. Because significant amounts of ground water are available, the opportunities for expanded and conjunctive use of ground water and surface water should be considered in regional plans for water development and conservation. The complexities of water management and the difficulties of achieving an integrated system of total-water management will require additional technical information.

Louisiana, New Mexico, Texas↗
USGS1976

Summary appraisals of the nation's ground-water resources – Arkansas-White-Red region

The Arkansas-White-Red Region, an area of265,000 square miles (6.86x10 11 square metres), is characterized by diversity in geography, climate, and geology and, in turn, by diversity in water resources and water problems. The western semiarid part of the region is water deficient, that is, potential evapotranspiration exceeds precipitation. The eastern, humid part has a surplus. Water use in the region in 1970 averaged 10 billion gallons per day (438 cubic metres per second), of which more than 65 percent was ground water. The largest use of ground water was for irrigation of crops, mostly in the water-deficient areas of Texas, Oklahoma, Kansas, and Colorado. Because of its ready availability and widespread occurrence, ground water is used throughout the region to supply municipal and rural water needs. The most productive aquifers, capable of yielding more than 50 gallons per minute (0.0032 cubic metres per second) to individual wells, are alluvium, carbonate. rocks, gypsum, and sandstone. Fresh water in storage in aquifers in the region is estimated to be 2 billion acre-feet (2.5x10 12 cubic metres). In addition, a large, unmeasured volume of saline water (containing more than 1,000 milligrams per litre of dissolved solids) underlies the fresh water at depths generally less than 500 feet (150 metres). The flow of water in each aquifer depends upon the physical and hydrologic characteristics of the aquifer, the climate, and the relation to, and the character of, adjacent rocks and streams. These factors also determine the effect of water-supply development or other man-induced stresses on the flow and the quality of water in the aquifers. Analog and digital models of aquifers can be used to evaluate stresses on aquifers and thereby provide water managers and planners with efficient tools for planning the development and continued use of aquifers.

Arkansas, Colorado, Kansas, Louisiana, Missouri, N↗
USGS1978

Summary appraisals of the nation's ground-water resources – Mid-Atlantic region

The Mid-Atlantic Region covers a total area of about 108,000 square miles. It includes parts of Vermont, Massachusetts, New York, Pennsylvania, Maryland, West Virginia, and Virginia, the entire States of New Jersey and Delaware, and the District of Columbia. It encompasses the entire drainage basins (within the United States) of the Hudson, Delaware, Susquehanna, Potomac, and the James River and includes Long Island and the coastal drainage of New Jersey, Delaware, Maryland, and Virginia. Ground water in the region occurs in three broad types of geologic terrane: (1) unconsolidated deposits in the Coastal Plain seaward of the Fall Line; (2) hard, consolidated sedimentary rocks and crystalline igneous and metamorphic rocks in the remainder of the region; and (3) unconsolidated sand, gravel, and other deposits of glacial origin that overlie the older rocks extensively in the glaciated northern part of the region. Ground water is derived primarily from precipitation; it can be intercepted for use by pumping from wells before it reaches the streams or before it drains into coastal wetlands or the ocean. The natural discharge from the aquifers in the region is estimated to be at about 38.6 billion gallons per day; in addition, at least 140-350 trillion gallons is stored in the rocks. About 949 billion gallons of fresh ground water was withdrawn in 1970. This quantity represents about 9 percent of the total freshwater use of 10,220 billion gallons. Available ground-water reserves indicate that a considerable part of the additional supplies needed for the anticipated increase in economic activity in the region could be developed from ground water.

Delaware, Maryland, Massachusetts, New Jersey, New↗
USGS1978

Summary appraisals of the nation's ground-water resources – Great Lakes region

The Great Lakes Regions, as a whole, has abundant supplies of water. Nearly 805,000 billion cubic feet of water is contained in the Great Lakes. An additional 35,000 billion cubic feet of potable ground water is available from storage in the region. Estimated ground-water discharge to the streams and lakes of the region is 26 billion gallons per day. Despite this abundance of water, the United States part of the Great Lakes basin is faced with many water-related problems, most of which involve water quality and water supply. Other problems concern periods of low flow in streams, preservation of wetlands, detrimental effects of erosion, and flooding. The significance of ground water in these problems is often overlooked. Ground water can be an alternative to surface water as a source of supply, or it can be used conjunctively with surface water to provide flexibility in water-supply management. Ground water supplied approximately 1,800 million gallons per day of the 39,900 million gallons. per day used in the Great Lakes Region in 1970. The ground-water contribution was only 4.5 percent of the water used. Thus, ground water represents a potential source of supply for much of the region. It also can be used, where conditions permit, to maintain lake levels and flow in streams, to dilute poor quality surface water, and to maintain or create wetlands and ponds. In managing water resources, ground water and surface water should be considered parts of a single system. Management includes not only planning and controlling the development but also monitoring the effects of this development. Recent advances in ground-water hydrology have provided methods to resolve some of the development and management questions that formerly slowed the development of ground water. All of the States in the Great Lakes Region have some regulations to control the development or protect the quality of the ground water. These regulations, however, are not as comprehensive as those governing surface water. Future legislation could be designed to encourage the development of ground water and, at the same time, to protect the resource. Efficient development and management of ground-water resources requires a through knowledge of the system. Reports on ground water are available for about 80 percent of tbe Great Lakes Region. Most of these reports, however, are not sufficiently detailed to be useful in comprehensive planning. As ground-water development continues, quantitative groundwater studies, utilizing models as predictive tools, will enable this development to proceed in an efficient manner.

Illinois, Indiana, Michigan, Minnesota, New York, ↗
USGS1978

Summary appraisals of the nation's ground-water resources – Souris-Red-Rainy region

A broad-perspective analysis of the ground-water resources and present and possible future water development and management in the Souris-Red-Rainy Region is presented. The region includes the basins of the Souris River within Montana and North Dakota; the Red River of the North in South Dakota, North Dakota, and Minnesota; and the Rainy River within Minnesota. The region includes 59,645 square miles, mostly in North Dakota and Minnesota. The terrain is relatively flat, but ranges in altitude from 2,541 to 750 feet. Annual average precipitation ranges from 14 inches in the west to 28 inches in the east and about 75 percent of it is rain. The mean annual snowfall ranges from 32 inches in the west to 64 inches in the east. Temperatures range from -55° to 118° F (-48.3° to 47.8° C). Irrigation is needed at least part of the time to assure crop production, particularly in the western part of the region. Sand and gravel deposits in the drift form the most important freshwater aquifers. Other aquifers are found in at least parts of the region in the Precambrian, Paleozoic, Cretaceous, and Tertiary rocks. The potentiometric surface in the bedrock aquifers generally decreases in altitude toward the Red River of the North, indicating that the general direction of ground-water movement is toward the river. Ground water with less than 3,000 milligrams per liter dissolved solids is available throughout the region. Ground water with less than 1,000 milligrams per liter occurs in most of the region east of the Red River of the North and in most of the shallow aquifers west of the river. The total volume of water available from storage having less than 3,000 milligrams per liter dissolved solids is estimated to be 5x10 8 acre-feet. In addition to the fresh and slightly saline water, the region has abundant highly mineralized water that can be considered as a resource. Yields of wells in individual bedrock aquifers are generally less than 100 gallons per minute but locally yields may be as much as 500 gallons per minute and more. Yields in drift aquifers are frequently less than 100 gallons per minute but range from 5 to 1,000 gallons per minute. In a few places outwash yields more than 1,000 gallons per minute. Ground water is the sole or a primary source of water supply in much of the region, including supplies for irrigation, domestic and livestock, municipal, and industrial needs. Reportedly, the potential irrigation development is 1,550,000 acres, as compared with 50,200 acres in 1975. Both ground- and surface-water supplies would be required to meet these demands. Rural domestic and livestock water supplies are derived almost entirely from ground-water sources. Smaller communities and towns generally rely on ground water, and the cities and industries use ground water, surface water, or both. The municipalities using surface water generally depend upon reservoir storage. Water quality rather than quantity is the greater water-supply problem for many communities in the region. Increased demands on both ground-water and surface-water supplies likely will be made in the future. Storage of surface water in the ground-water reservoirs during times of surplus for withdrawal during times of scarcity would aid in meeting these demands. The surplus (flood) water is of better chemical quality than underlying ground water in parts of the western half of the region. Freshwater could be stored in saline- or freshwater aquifers, and pumped out later, as needed. Thus, the ground-water reservoirs have a definite present and potential role in water management. To understand the hydrologic system for management purposes there is a need to determine more adequately the geologic and hydrologic characteristics of existing aquifers and the location of new aquifers. Also, as pumping and other stresses on any part of the hydrologic system affect other parts of the system, monitoring programs ideally should be started and maintained to detect changes and determine effects of the stresses. Many alternatives are available for managing water in the region. Some of these are operational and others are undergoing research. Adequate hydrologic information is needed to aid in solving problems of water supply, use, and pollution.

Minnesota, Montana, North Dakota, South Dakota↗