Ground Water, Continued
RecoveryPrenciples of Recovery
The discharge from a well is produced by a pump or some other lifting device or by artesian head (for a more detailed discussion of the principles of recovery, see Meinzer, 1923a, pp. 60-68). When water is being discharged from a well there is a resulting drawdown or lowering of the water level, or, in a flowing artesian well, an equivalent reduction in artesian head. The water table is lowered in an area around the well to form a depression resembling an inverted cone. This depression of the water table is known as the cone of depression, and the distance that the water level is lowered at the well is called the drawdown. In any well, the greater the rate of pumping, the greater will be the drawdown.
When water is withdrawn from a well, the water level declines rapidly at first and then more slowly until it finally becomes nearly stationary. Conversely, when the withdrawal ceases, the water level rises rapidly at first and then more slowly until it eventually resumes its original position (Fig. 8).
Figure 8--Graph showing the recovery of water level in well 53. (Measurements by Woodrow W. Wilson.)
Construction of Wells
All but one of the wells listed in Table 10 are drilled wells. Well 22 consists of a battery of two dug wells used to supply water for irrigation. One driven well was observed during the course of the investigation but it could not be measured.
Drilled wells are excavated by means of a percussion or rotary drill. They generally are 4 to 6 inches in diameter although the railroad, industrial, and municipal wells may be much larger. The domestic and stock wells generally are cased with galvanized-iron casing but a few are cased with wrought-iron casing. Most of the large-diameter wells are cased with wrought iron.
Almost all wells in Seward County obtain water from unconsolidated deposits, principally the Rexroad (?) and Meade formations. Wells in these deposits generally are cased to the bottom of the hole to prevent caving. In most of the domestic and stock wells the water enters only through the open end of the casing but in the larger wells the casing generally is perforated below the water table to provide greater intake facilities. The size of the perforations is an important factor in the construction of a well and the capacity or even the life of the well may be determined by it. If the perforations are too large fine material may filter through and fill in the well; if the perforations are too small they may become clogged so that water is prevented from entering the well freely.
Some wells in unconsolidated sediments are equipped with well screens or strainers. It is common practice to select a slot size that will pass 30 to 60 percent of the water-bearing material, depending upon the texture and degree of assortment. Retention of the coarser particles around the screen forms a natural gravel packing that greatly increases the effective diameter of the well, thereby increasing its capacity.
Gravel-wall wells generally are effective for obtaining large supplies of water from relatively fine-grained unconsolidated deposits and are widely used for irrigation in the upland areas of western Kansas. In constructing a well of this type, a hole of large diameter, 30 to 60 inches, is drilled and is temporarily cased with unperforated pipe. A well screen or perforated casing of smaller diameter than the hole is then lowered into place and centered in the larger pipe opposite the water-bearing beds. Unperforated casing extends from the screen to the surface. The annular space between the inner and outer casings is then filled with sorted gravel. The outer casing is then withdrawn part way to uncover the screen and allow the gravel packing to come in contact with the water-bearing material.
According to McCall and Davison (1939, p. 29), drawdown can be kept to a minimum in several ways:
First, the well should be put down through all valuable water-bearing material. Secondly, the casing should be properly perforated so as to admit water to the well as rapidly as the surrounding gravel will yield the water, Third, the well should be completely developed so that the water will flow freely into the well ... Increasing the depth of a well will have a greater effect on reducing the draw-down than will increasing the diameter, so long as additional water-bearing formations are encountered.A report (Davison, 1939) containing descriptions of different types of pumping plants, the conditions for which each is best suited, construction methods, and a discussion of cost of construction is available from the Division of Water Resources, Kansas State Board of Agriculture, Topeka, Kansas, and the reader is referred to this publication for a more detailed discussion of construction of wells.
Several wells in Seward County, such as no. 77, are reported to be blowing wells--that is, air blows into or out of the well at irregular intervals causing a whistling or sighing noise. The phenomenon is not an uncommon one and its explanation by Lugn and Wenzel (1938, p. 64) is satisfactory. They indicate that the phenomenon is related to changes in atmospheric pressure and occurs in those wells in which there is an unsaturated layer of relatively permeable material above the water table but beneath some relatively impermeable bed. During an interval of high atmospheric pressure the air above the water table is compressed causing the air to escape through the well casing. The air is sucked into the well when the atmospheric pressure declines rapidly.
Methods of Lift and Types of Pumps
The stock- and domestic-supply wells in Seward County almost without exception employ lift or force pumps to raise the water to the surface. Both types of pumps have cylinders or working barrels attached to the lower end of the drop pipe and placed in the well about at the level of the water table. A wooden or metal jet rod connects the plunger of the working barrel with the source of power, usually a windmill but sometimes a hand jack. Unlike a force pump, a lift pump cannot raise the water above the pump head.
The drop pipe, which generally is about 2 inches in diameter, is commonly supported by wooden or metal clamps of various designs that are supported in turn by the top of the casing or by some specially constructed device such as blocks of wood, brick, or concrete. Most of the wells in the county are equipped with sheet-metal covers placed between the clamp and the top of the casing to prevent small objects from falling into the well.
The wells supplying water to the railroad, to municipalities, to industries, or for irrigation are generally equipped with turbine or centrifugal pumps. These may be operated by electric motors, by steam engines, or by internal-combustion engines utilizing oil, natural gas, or gasoline for fuel. Turbine pumps are installed when the depth to water level, including drawdown, exceeds the effective suction limit of the centrifugal pump. The report by Davison (1939, pp. 23-44) contains descriptions of different types of pumping plants, the conditions for which each is best suited, construction methods, and a discussion of cost of construction.
Kansas Geological Survey, Seward County Geohydrology|
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Web version Sept. 2001. Original publication date March. 1948.