THE COVER PICTURE, showing the late F. B. Ross and Dwight Spencer. of the Emporia State biology faculty, at the largest of the springs on the F. B. and Rena G. Ross Natural History Reservation, was taken by the college photographic service. The other photographs were taken by members of the biology faculty. Except as otherwise noted, the sketches were drawn by Dr. Robert Boles, of the biology faculty.
Volume 9, Number 4 - May 1963
The Water Table
by John Breukelman
ABOUT THIS ISSUE
Published by The Kansas State Teachers College of Emporia
Prepared and Issued by The Department of Biology, with the cooperation of the Division of Education
Editor: John Breukelman, Department of Biology
Editorial Committee: Ina M. Borman, Robert F. Clarke, Gilbert A. Leisman, David Parmelee, Carl F. Prophet, Dixon Smith
Online fomat by: Terri Weast
The Kansas School Naturalist is sent upon request, free of charge, to Kansas teachers and others interested in nature education. Back numbers are sent free as long as the supply lasts, except Vol. 5, No. 3, Poisonous Snakes of Kansas. Copies of this issue may be obtained for 25 cents each postpaid. Send orders to The Kansas School Naturalist, Department of Biology, Kansas State Teachers College, Emporia, Kansas.
The Kansas School Naturalist is published in November, January, March, and May of each year by The Kansas State Teachers College, Twelfth Avenue and Commercial Street, Emporia, Kansas. Second-class mail privileges authorized at Emporia, Kansas.
The Water Table
by John Breukelman
"The water table went down so far during the dry 50's that it may never come back up again."
"All that rain in 1962 certainly raised the water table."
"Irrigation by means of wells will certainly ruin the water table."
"Don't worry about the falling water table; the first big rain will bring it back up."
"Draining the wet lands will lower the water table of the surrounding land."
THE WATER CYCLE
What is this water table that seems to go up and down, and may be ruined? To go back to the beginning, let us look briefly at the circulation of water from the sea to the atmosphere, from the atmosphere to the land, and from the land back to the sea. This circulation, known as the water cycle or hydrologic cycle, is an endless one.
It has been estimated that almost 100,000 cubic miles of water evaporate each year from the oceans and continents. Total evaporation equals total precipitation. when considered over a long period of time. About 25.000 cubic miles of water falls annually on the land surface of the earth. Sketch by courtesy of United States Department of Agriculture.
Ground water zones and belts, and the location of the water table relative to these.
Top: Where the water table dips down toward the stream. water moves from the soil into the stream.
Bottom: When flooding or high water occurs. water moves from the stream into the soil.
The pressure in an artesian well depends on the height (H) of the water table in the porous layer which supplies the well. The higher H is above the level of discharge of the well, the greater is the pressure.
A spring marks a place where the water table meets the surface.
Since the sea covers about three fourths of the earth's surface, most of the water vapor in the air comes from the sea. Only a relatively small amount comes from the land and fresh water.
Whenever air, especially warm air, blows over a water surface, some water evaporates into the air, unless the air already contains as much water vapor as possible, that is, unless the relative humidity is already 100 per cent. The relative humidity is the percentage of water vapor in the air, as compared with the amount that could be present at the temperature involved. The water vapor capacity of the air goes up and down with the temperature. For example, at ordinary atmospheric pressure a cubic meter of air at 10 degrees Centigrade can hold 9.33 grams of water; at 15° C, 12.71 grams; at 20° C, 17.12 grams; and at 25° C, 22.80 grams.
When the air warms up and the actual water content stays the same, the relative humidity falls. Thus, a cubic meter of air which contains all the water possible at 10° C (9.33 grams) has a relative humidity of 100 per cent. If this cubic meter of air is warmed to 15° C, its capacity is 12.71 grams, but it still contains only 9.33 grams. The relative humidity is now 9.33/12.71 or 73 per cent.
When the air cools, the relative humidity rises; if it reaches 100 per cent of the water vapor capacity, the air is said to be saturated. The temperature at which the air is saturated is often referred to as the dew point. If the temperature falls below the dew point some of the water vapor condenses as fog, mist, rain, snow, or sleet. Thus a cubic meter of air containing 17.12 grams of water at 20° C is saturated, and the dew point is 20° C. If this air is cooled to 10° C, the water capacity is only 9.33 grams. The difference between 17.12 and 9.33, or 7.79 grams, is condensed as some form of precipitation. The portion of the precipitation that falls on t11e land is of special concern to agriculture, horticulture, forestry, and all other growth activities that depend on the soil.
When rain and other forms of precipitation fall on the land, all or part of the water enters the soil by infiltration; the water that does not infiltrate flows away and is called runoff. Of that water which enters the soil, most goes down by percolation. Some goes down and down until it reaches a level below which the ground is saturated with water. This may be near the surface or several hundred feet down. The upper surface of this zone of saturation is known as the water table. This is the level at which water stands in a well that is not being pumped.
In some cases water percolates down until it reaches a water-tight layer of rock and flows along the surface of this layer, to emerge as a spring or in a "seepy" area. Of the water that remains near the surface of the soil, some returns to the air by evaporation, and some passes through growing plants to be returned to the air by transpiration. Thus water that falls on the soil may leave the soil in four ways; runoff, springs or seepage, evaporation, transpiration. Under ideal conditions, some water should leave in each of the four ways, and not too much or too little in any one way.
Water held within the soil after runoff has stopped can be transpired by plants or lost by evaporation. If the soil surface is free of plants and covered with a layer of litter or mulch, both the rates of transpiration and of evaporation are low. If there are many growing plants, the transpiration rate is high. The rate of evaporation from unprotected bare soil is high.
THE ZONES OF SOIL WATER
Water that infiltrates the soil and is not absorbed by plant roots and transpired may percolate downward to the ground water reservoirs. Such subsurface water occurs in a zone between the surface and the lower limits of porous, water-bearing subsoil formations. This zone is further sub-divided into a zone of aeration and a zone of saturation, as shown in the accompanying figure.
The zone of aeration is divided into three layers, or belts, often called the soil water belt, the intermediate belt, and the capillary fringe. These belts are not sharply defined; each grades into the other.
The soil water belt consists of topsoil and that portion of subsoil from which water is returned to the atmosphere either by direct evaporation or by transpiration of plants. The water in this belt is of particular importance to farmers and gardeners because it furnishes the water supply for nearly all vegetative growth.
The water that passes through the soil water belt enters the intermediate belt and continues its downward percolation toward the zone of saturation. The intermediate belt may vary in thickness from zero, in which case the soil water belt is in immediate contact with the zone of saturation, to several hundred feet. The greater the thickness of the intermediate belt the longer it takes water to pass from the surface to the zone of saturation.
The water table does not coincide exactly with the top of the zone of saturation, because water rises by capillary attraction, as in a lamp wick, and in some cases the rise may be considerable. The rise brings about capillary fringe, which lies between the intermediate belt and the zone of saturation. The thickness of the capillary fringe depends upon the kind of material in which it is located. In a silty or clay soil, it may be two feet or more thick, whereas in gravel, it may be less than an inch.
The zone of saturation forms a huge reservoir of ground water that feeds springs, streams, and wells. As noted before, the upper surface of the zone of saturation is referred to as the water table. All of the spaces or pores in this zone are filled with water. The thickness of this layer also depends upon the type of material in which it is located. The lower limit is the level at which subsoil or rock materials are so dense that water cannot penetrate them.
The zone of saturation is of importance to everyone, because it acts as a great water supply reservoir, receiving water from precipitation and providing the supply from which water is discharged to streams, springs, and wells.
Since water seeks its own level, the surface of the zone of saturation, or the water table, tends to be a level surface. But it may be modified in many ways. As is shown in the accompanying figures, the level of the water surface in the stream may either fall below the water table or rise above it. When the water in the stream is below the water table, water seeps from the soil into the stream, thus maintaining the water table, water moves into the soil from the stream.
Thus the zone of aeration receives and holds water for the use of plants and transmits water downward into the soil reservoir. The zone of saturation receives and stores water, providing a source of supply for wells,
springs and streams.
This artesian well, at the Meade County State Park, is a special favorite of the children.
Collecting aquatic animals from the small stream that flows out of the Stafford County artesian well, near the Big Salt Marsh.
Great Spirit, or Waconda Spring, with the sanitarium in the background.
The Big Springs at Scott County State Park yield about 400 gallons of water per minute.
Harris Marsh, in Barton County.
The marshy area which covers several acres about the Stafford County artesian well has a lush growth of sedges, smartweed, arrowhead, and other semi-aquatic plants.
The water table is not always the upper limit of a single layer of soil-stored water. There may be several storage layers, separated by impervious strata. Such conditions may give rise to artesian wells or to springs which discharge far above the levels of the streams which they supply. Sometimes the term artesion is used only for wells from which water flows at the surface of the ground without any pumping or other artificial aids, Such wells are also called self-flowing wells. In other cases, the term artesian is applied to any wells in which the water rises, under its own pressure, to a level above that at which it was first encountered, even though it may not reach the surface. The discharge from a free-flowing artesian well depends on the amount of precipitation and the arrangement and porosity of the strata through which water flows to the well. A well drilled near Louisville, Kentucky, to a depth of 2000 feet, is said to have delivered water at the rate of 2,300 gallons per minute. This amounts to almost a third of a million gallons per day - enough to supply a fair-sized town. The rate of flow of this well decreased with time and eventually it had to be pumped. Two even more remarkable wells near Edgemont, South Dakota, drilled to a depth of almost 3000 feet not only delivered almost a million gallons per day, but the water came out at a temperature of 100° F, Kansas has only a few free-flowing artesian wells. One illustrated in this issue of The Kansas School Naturalist is located in Stafford County, about midway between Stafford and Ellinwood, near the Big Salt Marsh and the sand dunes. About the well, and especially to the south of it, is a marshy area of several acres covered with a variety of semi-aquatic plants. Another well known artesian well is on the grounds of the Meade County State Park, about 13 miles southwest of Meade. The discharge from this well eventually finds its way into the Meade County State Lake.
Kansas is not especially famous for its springs. Most of them are small, among the largest being Rock Springs, 15 miles southwest of Junction City, which sometimes attains a flow of 1000 gallons per minute. Compared to the half million gallons per minute of Big Spring, in Big Spring State Park near Van Buren, Missouri, this is small indeed. Nevertheless, springs have been of great importance in the development of Kansas. In his paper on the geography of Kansas, Schoewe0 reported that springs have been responsible for the names of at least 45 creeks and rivers in 33 counties in Kansas, as well as the names of many towns. Among the latter are Baxter Springs, Bonner Springs, Conway Springs, Diamond Springs, Geuda Springs, Russell Springs, Sharon Springs, Springdale, Spring Hill, and Springvale. In this paper, Shoewe described all of the better known Kansas springs, including information such as location, size, chemical characteristics of the water, and historical or commercial interest.
The most famous spring in Kansas is Waconda, or Great Spirit Spring, in Mitchell County, near Cawker City. The spring is on top of a mound, formed by deposition of material from highly mineralized water. This water was supposed to have medicinal value, and the area became prominent as a health resort. A sanitarium, started in 1881, was in operation until recently.
In swamps or marshes, the water table is at the surface at least part of the time. The surface soil is either saturated with water or actually covered by shallow water most of the time. Kansas has but few such areas. Best known are the salt marshes in Stafford County, but fairly extensive marshes exist in Barton, Cloud, Jewell, Lincoln, Mitchell, Republic, and other counties of the state. In certain parts of the Stafford County salt marsh, the concentration of salt is high enough so that in times of drought, when the water has evaporated away and the soil is dry, the layer of salt covering the soil makes the whole area a dazzling white "salt desert."
A portion of the salt marsh and sand dune area of Stafford County has been set aside as a wildlife refuge, under the supervision of the United States Fish and Wildlife Service.
THE CHANGING WATER TABLE
The water table falls during dry periods and rises during rainy periods. Whenever water is removed from wells at a faster average rate than that by which the zone of saturation is refilled, the water table falls but removal and refilling must be compared by taking averages over a long period - a year or several years.
As water is pumped from a well, lowering the water level below the water table, water flows from the saturated layer into the well. When the rate of flow into the well equals the rate of pumping the inverted cone-shaped depression in the water table, the cone of depression, remains in a constant position. If the rate of pumping is increased, the cone of depression moves downward; if pumping is stopped, the cone of depression moves upward, and eventually disappears until pumping is resumed.
The nearer the water table is to the ground surface, the higher is the rate at which plants use water from the zone of saturation. For example, cattails, which grow best with their roots almost in water, may use as much as 75 inches of water per year. The desert mesquite, on the other hand, which has been known to send its roots down as far as sixty feet, may use only two or three inches of water a year. i\lost Kansas plants function between these extremes.
Irrigation practices and other water uses may be closely related to the depth of the water table. For example, when California was settled, the ground water supply in the Antelope Valley was sufficient to supply artesian wells that flowed 900 gallons per minute at pressures of 10 pounds per square inch. By 1920, most of the wells had stopped flowing and had to be pumped. By 1950 the annual pumping rate was 110,000 acre-feet and the estimated annual replacement was 65,000 acre-feet, and the water table had been dropping at the rate of three feet per year.
The relationship between water supply and water use is especially important in Kansas. Water is one of the most important resources of our state. The State Geological Survey of Kansas said in a Miscellaneous Report published in January 1961(1) that:
"Without water, farmers could not grow crops on the soil, however fertile; in the absence of a water supply, industrial establishments could not function and transportation would stand still; life as observed on this planet would be nonexistent, and all the reserves of petroleum and other mineral substances might well stay in their natural reservoirs to remain unused deposits. In Kansas, where many rural and urban communities depend upon wells for adequate water supplies for agricultural and industrial use, knowledge of the occurrence and availability of ground water is a must in the maintenance of a dynamic economy. It is therefore no accident that study of ground-water resources has always had a place on the agenda of Geological Survey activities ...."
(1) Muilenburg, Grace. Activities of the State Geological Survey of Kansas, Miscellaneous Report, State Geological Survey, January 1961.
If a well is pumped so that water is removed faster than it comes in from the surrounding porous layer, a cone of depression is formed. The difference between the level of water in the well and the general level of the water table is the drawdown.
The ground water regions of Kansas are scattered and variable, supplying wells that yield from far above 500 gallons per minute to far below 50. Equally variable are the water table levels as shown here for wells in Ford, Harvey, Mitchell, and Shawnee counties. The depth shown in the graphs is the number of feet down to water below the soil surface. This figure and the photograph on page 13 were supplied by the State Geological Survey of Kansas, through the courtesy of Grace Muilenberg, who prepared the Miscellaneous Report for the year ending June 30. 1961, in which this figure appeared.
The automatic recorder on an observation well
The report went on to say that the increased use of ground water for irrigation has required further detailed study of the ground water resources of any areas depending on wells for irrigation. The irrigation pumps brighten the landscape, increase crop yields, and make it possible to grow special crops - but how do they affect the water table? The State Geological Survey has been making a careful study of water table changes by periodic checking of the water levels in more than 800 observation wells. The measurements are so important that eleven of the wells were equipped with devices to record, automatically and continuously throughout the year, the rising and falling levels of waters in the wells.
At the close of 1961 the water levels in 818 wells in 77 counties, about equally divided between the Missouri River and Arkansas River drainage basins, were being observed. The locations of these wells, by counties and by drainage basin, are shown in Table I, which was taken from Bulletin 159 of the State Geological Survey of Kansas.(2)
The objectives of the observation-well program are "to provide an evaluation of available groundwater supplies, to facilitate the prediction of trends in ground-water levels that will indicate the probable status of important groundwater supplies in the future, to aid in the prediction of the base flow of streams, to provide information for use in basic research, and provide long-term continuous records of fluctuations of water levels in representative wells. These selected records serve as a framework to which may be related many shortterm records collected during an intensive investigation."
(2) Broeker, Margaret E., and V. C. Fishel, Ground-Water Levels in Observation Wells in Kansas, 1961, Bulletin 159, State Geological Survey of Kansas, Lawrence, Kansas.
|Table I - Number of observation wells in Kansas at end of 1961 .|
|County||Missouri Basin||Arkansas Basin|
Table II, also from Bulletin 159 of the State Geological Survey, shows data from a graph made a continuously recording instrument on a well in Sedgwick County. All data were for 1961. The highest level ever recorded in this well was 11.73 feet below the land surface, in August 1961; the lowest, 21.76 feet below land surface, in February 1958. Records for this well are available since 1954.
This is the last issue of the 1962-63 volume of The Kansas School Naturalist; the next issue will be that of November 1963, Volume 10, Number l. The mailing list for Volume 10 will not be changed; all those now on it will be kept on, except for anyone who moves from his present address and does not notify us of his new address. The Kansas School Naturalist is sent by second class mail; this is not forwarded, and unclaimed copies are returned to us. Therefore it is important to keep us informed concerning address changes.
The editorial committee of a magazine such as this enjoys hearing from the readers. Communications are always welcome, especially information about ways in which The Kansas School Naturalist has proved useful to teachers and suggestions for future issues.
On the lower part of this page is a coupon which may be cut out and filled out in case an address change is necessary. Anyone who does not wish to cut up his magazine can of course send us the new address on a post card.
Plans for future issues are always tentative, but several are either in process of preparation or have been tentatively scheduled. In the next couple of years we shall probably have an issue on the geology of Kansas, one each on building of equipment for elementary science and on experiments for elementary science, one on lizards in Kansas, one on science projects for the elementary level, and possibly one on birds and one on microclimates. It is possible that the 1963 Workshop in Conservation will produce an issue, comparable to Attracting Wildlife for Observation, March 1963, which was produced by the 1962 Workshop.
Those printed in boldfaced type are still available, free of charge except Poisonous Snakes of Kansas, which is sold for 25¢ per copy postpaid, to pay for the increased printing costs due to the color plates.
The out-of-print issues may be found in many school and public libraries in Kansas.
1963 WORKSHOP IN CONSERVATION
FIRST SECTION, June 3 to 21
Credit: 3 semester hours
Outline of Program
June 3-11: soil and water, grasslands, field trips
June 12-18: wildlife, conservation education
June 19-21: individual projects, completion of reports
SECOND SECTION, June 24 to July 12 Credit: 1, 2, or 3 hours for 1,2, or 3 weeks
This section is open to any student interested in conservation or conservation education.
To be admitted to this section a student must have completed a course in conservation or been a participant in the first section, and have demonstrated ability to write clearly. There will be no formal program, the objectives and procedures being determined by the group. This section will be devoted largely to the production and revision of projects and activities useful in the teaching of conservation.
Anyone interested in further information should write the director, Thomas A. Eddy, Department of Biology, Kansas State Teachers College, Emporia, Kansas.
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