Water Resources WATER USE AND CONSUMPTION

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1 Water Resources Our planet has a vast supply of water beneath its surface, on its surface, and above its surface in the atmosphere. The Earth holds about 320 million cubic miles of water with more than 97 percent of it contained in its oceans. Because of its high salt content, ocean water cannot be used by humans for drinking or farming. Salt can be removed from the water, but the treatment involved is expensive. Only about 3 percent of the world s water is fresh or unsalted. In addition, only about 25 percent of this amount is readily available. The rest is locked in glaciers and icecaps. The distribution or freshwater throughout the world is not uniform. The ratio of groundwater to surface water also varies from location to location. Minnesota is typical of the rest of the United States in that most of its water (approximately 85 percent) is contained in aquifers or underground formations (such as rock, sand, and gravel) that contain water in its pores or crevices. The remainder can be found in surface sources such as lakes, streams, wetlands, and reservoirs. WATER USE AND CONSUMPTION Vast amounts of water are used for many purposes in Minnesota. The national average for water consumption is approximately 100 gallons per day per person. This figure includes all water used and can vary greatly, especially as a result of variations in industrial usage. More than trillion gallons of water were withdrawn from available Minnesota supplies in The water supply found in Minnesota is used for domestic consumption, municipal needs, industrial production, food processing, irrigation, livestock, navigation, recreation, fish and wildlife habitat, power generation, waste assimilation, and other miscellaneous categories. This water comes from both groundwater and surface sources and is supplied both from public utilities and through privately owned wells. Water Resources 1

2 The importance of water is reflected in its use for consumption. Public water supplies account for approximately 38 percent of the consumptive water use in Minnesota. Domestic use, livestock watering, irrigation, and industrial processing account for the remaining consumptive use, with power generation using water mostly on a pass-through basis. HYDROLOGIC CYCLE The water cycle is a continuous process of water evaporating from the earth, moving to the clouds, and then returning to the ground as precipitation. The water cycle consists of several components: Evaporation/Transpiration The first stage of the process involves evaporation, water changing from a liquid state to a vapor or gas phase. Approximately one-third of the water in the atmosphere comes from the surface of the ocean. Evaporation from inland streams and lakes accounts for the remaining two-thirds of the water vapor entering the atmosphere. When water evaporates, impurities are left behind in the source. This means that saltwater, which is unfit for human consumption, is converted into freshwater through evaporation as the salt is left behind in the sea. Another source of water in the atmosphere is water from vegetation. The process of a plant releasing water vapor directly into the air is called transpiration. Water Resources 2

3 Condensation After the water has entered the atmosphere, it rises until it begins to cool, condenses to water droplets or ice, and forms clouds. Precipitation After the clouds have taken on as much moisture as they can hold, the process of releasing this moisture starts. This takes place in the form of precipitation: rain, sleet, snow, etc. (Virtually all of the world s freshwater supply has been delivered in this manner.) Infiltration Some of the precipitation infiltrates into the soil through percolation to become groundwater while the rest remains on the surface as surface water. Most of the groundwater remains near the surface to be used by plant life, after which it returns to the atmosphere through transpiration. A small percentage of the groundwater evaporates from the soil directly to the atmosphere without being used by the plants. The remaining groundwater continues to percolate through the soil until it reaches the groundwater aquifer. At this point the water may be extracted through wells for human consumption. GROUNDWATER SOURCES Groundwater is the most common source of water for small-to-medium sized communities in the United States. Approximately 75 percent of the nation s water supplies use groundwater for their source, but they supply only 25 percent of the water used in the country. In Minnesota, all but 24 water supplies use groundwater as their source. Groundwater is water that has percolated through the ground into the soil or rock below. Groundwater is water stored in aquifers: consolidated or nonconsolidated geologic materials saturated with water. Groundwater reaches the aquifers through recharge areas, where the aquifer is directly exposed to precipitation, through infiltration from overlying sediment or rock, or where lakes, swamps, wetlands, and other sources of standing water connect to the aquifer. This connection can be through a sand layer or some other porous layer of soil. An aquifer is an underground layer of gravel, sand, sandstone, shattered rock, limestone, or other formation that holds water. An aquifer will not only hold water, but will allow the water to move to an area of lower pressure within the aquifer. A water table aquifer consists of soil or rock, usually near the land surface, containing water that is held above a confining soil layer. An example of this would be beach sand surrounding a lake where the water surface in the sand is generally the same elevation as the lake. Water Resources 3

4 An artesian aquifer is a geologic formation between two confining layers, such as sand between two clay layers. The top of the water in the aquifer is under pressure, causing the water to rise above the aquifer when a well is constructed into the aquifer. The distance that the water will rise in the well is determined by the geology, the hydrologic characteristics of the aquifer, and the elevation of the aquifer recharge area. A flowing well is one constructed into the artesian aquifer where the water reaches the surface by its own pressure. Another type of flowing condition is a spring in a hillside in which groundwater reaches the surface and becomes a brook or stream. Groundwater will flow to an area of lower head or pressure. You could think of the movement of groundwater as an underground river or stream. This area of lower pressure may be a pumping well, spring, lake, or stream. Hydrologic Conditions Found in Aquifers The major groundwater aquifers in Minnesota occur in either unconsolidated glacial drift or consolidated rocks. Water Resources 4

5 Unconsolidated glacial drift aquifers Glacial drift is a general term for clay, sand or gravel deposited by a glacier. Glacial drift can be more than 800 feet thick in Minnesota. It was deposited during the Ice Age. When composed of sand and gravel, glacial drift can be a source of large supplies of water. High clay content, however, makes these deposits less useful for water production. Unconsolidated glacial drift is used for wells in most areas of the state except the southeast, a strip along the Minnesota River, and parts of northeastern Minnesota. Consolidated rock aquifers These are aquifers composed of sandstone, limestone, and dolomite. They underlie varying thicknesses of glacial deposits. These aquifers are used mainly in southeastern Minnesota. Water Resources 5

6 Sequence of Bedrock Aquifer Systems and Confining Beds for Southeastern Minnesota Water Resources 6

7 SURFACE WATER SOURCES Surface waters supply about 75 percent of the water consumed by people in the United States. Even though a larger number of water systems in the United States use a groundwater source, on the average, they are smaller and serve fewer people. Surface water is more likely to supply large cities, such as Los Angeles, New York, and Chicago. These cities can withdraw billions of gallons of surface water each day, and Minneapolis taps directly into the Mississippi River, while St. Paul uses water from the Mississippi after passing it through a chain of lakes. With so many people relying on surface sources for their supply of safe, palatable drinking water, it is important that operators understand the factors that influence the flow of surface water. Surface water comes from precipitation and groundwater that enters the surface supplies through springs or aquifers that connect with a lake or stream. Precipitation Precipitation can end up either as ground or surface water. The intensity of a rainfall can be a factor in determining its destination. A slow, steady rain will soften the ground, allowing the precipitation to percolate into the soils and enter the groundwater flow. This will result in less flow to surface waters. On the other hand, a heavy rain will increase the surface water flow as the ground is packed and hardened by the rain, causing it to run off, instead of penetrating, the soil. The type of soil also makes a difference in determining how much water will percolate into the ground and enter the groundwater flow. A soil heavy in clay may absorb water from a rainfall for a short period of time before it begins to swell and block water percolation. The Red River Valley in northwestern Minnesota, an area that was once the bottom of a prehistoric lake, has very tight clayish soil. Soils of gravel or sand allow water to percolate very readily, thus reducing the chances of localized flooding. The area around the Mississippi River in central Minnesota, from St. Cloud to Becker and Elk River, is an example of this type of soil. The activities of human beings can greatly affect the ability of the soil to absorb water. Paving large areas of land for highways, parking lots, and driveways or draining wetlands, for agricultural use or community expansion results in far less water entering the ground and more of it running off to surface waterways. On the other hand, when rain falls on areas with mainly vegetative cover, more than 75 percent of it eventually finds its way to underground aquifers. Water that doesn t penetrate the ground will reenter the cycle as surface water runoff. Once the soil becomes saturated by the precipitation, additional precipitation will cause runoff, forming creeks, streams, rivers, and lakes. This water will contain large amounts of suspended material (such as silts and organic material) that may contaminate the water, making it unfit for human consumption unless treated. Water Resources 7

8 Regional water resources depend on climate, topography, and the nature of the soils. Minnesota s location in the northern part of the United States produces a cool climate, and when combined with the moderate rainfall the area receives, has contributed to the large number of lakes in the state. Topography The state s topography, which is greatly affected by the glaciers that passed over the land thousands of years ago, also played a role in the development of the lakes. These huge bodies of moving ice produced glacial sand, gravel, and clay deposits and carved depressions in the earth that later served as basins for lakes. Minnesota has more than 15,000 lake basins, mostly in the northeastern and central sections of the state. Numerous lakes have placed the state at the head of three major drainage basins: The Great Lakes, the Mississippi River, and the Red River of the North. Minnesota s 25,000 miles of streams also exhibit considerable diversity. North Shore streams plunge toward Lake Superior, forming rapids and falls. Streams to the west and south of the Arrowhead region become unpredictable, changing quickly from placid flows to heavy rapids. In northwestern and southwestern parts of the state, lakes are scarcer and are typically shallow. In the southeast portion of Minnesota, spring-fed streams tumble through wooded bluffs. Water Resources 8