Ground Water, continued
Principles of Recovery
Water is discharged from a well by a pump or some other lifting device or by natural artesian flow (for a more detailed discussion of principles of recovery see Meinzer, 1923a, pp. 60-68). When water is standing in a well, there is equilibrium between the head of the water inside the well and the head of the water outside the well. Whenever the head inside a well is reduced, a resultant differential head is established and water moves into the well. The head of the water inside a well may be reduced in two ways: (1) by lowering the water level by a pump or other lifting device, and (2) by reducing the head at the mouth of a well that discharges by artesian pressure. Whenever water is removed 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.
When water is discharged from a well the water table is lowered in an area around the well to form a depression somewhat resembling an inverted cone, which is known as the cone of depression, and the distance that the water level is lowered is the drawdown. The drawdown in a well increases as the rate of pumping is increased.
The capacity of a well is the rate at which it will yield water after the water stored in the well has been removed; it depends upon the quantity of water available, the thickness and permeability of the water-bearing bed, and the construction and condition of the well. The capacity of a well generally is expressed in gallons a minute. The known or tested capacity of a strong well generally is less than its total capacity, but some weak wells are pumped at their total capacity.
The specific capacity of a well is its rate of yield per unit of drawdown, and is determined by dividing the tested capacity in gallons a minute by the drawdown in feet. Well 247 in northern Stevens County yields 1,326 gallons a minute and has an average drawdown of 14.3 feet; hence its specific capacity is 92.7.
When water is withdrawn from a well the water level drops rapidly at first and then more slowly until it finally becomes nearly stationary.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 or approximately its original position (Fig. 9).
Dug wells are excavated with picks, shovels, spades, or by power machinery and generally are between 2 and 10 feet in diameter. Most of the wells constructed in Grant, Haskell, and Stevens Counties prior to 1900 were dug wells, many of which were quite deep. Nettleton (1892) lists five dug wells in Haskell County in the vicinities of Lockport (sec. 13, T. 27 S., R. 33 W.), Santa Fe (sec. 36, T. 28 S., R. 33W.), and Loco City (sec. 36, T. 30 S., R. 33 W.). The wells were 3 feet in diameter and ranged in depth from 107 feet to 240 feet. The Pugh well in western Haskell County, which served the residents of western Haskell and eastern Grant County prior to 1900, was 236 feet deep. Almost all the dug wells have been replaced by drilled wells, but there are still a few shallow dug wells in the Cimarron and North Fork Cimarron Valleys, most of which are curbed with stone or timber. Most of them are poorly sealed and may be contaminated by the entrance of surface waters. Because of the difficulties of digging by hand below the water table, dug wells generally are excavated only a few feet below the water table and, therefore, are more likely to fail during a drought than are drilled wells, which generally extend many feet below the water table.
Most of the domestic, stock, irrigation, and public-supply wells in Grant, Haskell, and Stevens Counties are drilled wells that have been excavated by means of percussion (cable-tool) or rotary drills. Most of the drilled wells were constructed by means of portable cable-tool drilling rigs and are cased with galvanized-iron or wrought-iron casing. The drilled domestic and stock wells generally are 4 to 6 inches in diameter and those used for irrigation and public-supply purposes generally are 15 to 25 inches in diameter.
Drilled wells in consolidated deposits--Few if any water wells in Grant, Haskell, and Stevens Counties penetrate the consolidated sediments of Cretaceous age, although most of the irrigation wells in the area of shallow water northwest of Ulysses have been drilled nearly to the top of the Dakota formation. Many wells penetrate consolidated sand and gravel ("mortar beds") in the Tertiary and Quaternary deposits, but these generally are well-cemented and probably yield very little water to wells. Inasmuch as the consolidated beds in the Tertiary and Quaternary deposits are thin, most wells are cased through both the unconsolidated and consolidated materials.
Drilled wells in unconsolidated deposits--Almost all the wells in Grant, Haskell, and Stevens Counties obtain all or part of their water from unconsolidated materials of Tertiary or Quaternary age or both. The principal unconsolidated water-bearing deposits are the Rexroad (?), Meade, and Laverne formations, but water is also obtained from unconsolidated alluvium in the larger stream valleys. Wells in unconsolidated deposits generally are cased nearly to the bottom of the hole with galvanized-iron or wrought-iron casing. In some wells the water may enter only through the open end of the casing, but in many wells - particularly those used for irrigation - the casing is perforated below the water table to increase the facilities for intake. The size of the perforations is an important factor in the construction of such a well, and the capacity or even the life of the well may be determined by it. If the perforations are too large, the fine material may filter through and fill the well; if the perforations are too small, they may become clogged so that water will not enter the well freely.
Wells in unconsolidated sediments may be 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, and hence increases its capacity.
Gravel-wall wells generally are effective for obtaining large supplies of water from relatively fine-grained unconsolidated deposits, and they are used widely for irrigation. In constructing a well of this type, a hole 30 to 60 inches in diameter is first drilled by the rotary method or by means of an orange-peel bucket and is cased temporarily with iron or steel 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, preferably of a grain size just a little larger than the openings in the screen or perforated casing, and also slightly larger than that of the water-bearing material. In most wells of this type a medium or coarse-grained gravel is used, but in very fine-grained deposits a fine-grained gravel or coarse-grained sand should be used. 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. Some wells in the Grant-Haskell-Stevens area have been gravel-packed with gravel that is less satisfactory than the water-bearing material it replaced. During the field investigation it was noted that several irrigation wells were gravel-packed with poorly sorted gravel containing pebbles ranging in diameter from less than 1 inch to more than 3 inches. It was stated by several drillers that smaller pebbles could not be used because the perforations in the casing were too large.
In deciding whether or not to use gravel-wall construction it is important to know the character of the water-bearing material, if the material is a coarse gravel, as it is in parts of Grant, Haskell, and Stevens Counties, it generally is unnecessary to use gravel packing. Some wells have been walled with a gravel packing that is finer and less permeable than the water-bearing material it replaced, thus reducing the yield.
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 drawdown than will increasing the diameter, so long as additional water-bearing formations are encountered."
A report (Davison, 1939) containing descriptions 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 additional details of well construction.
Methods of Lift and Types of Pumps
Most wells in Grant, Haskell, and Stevens Counties, particularly those used for domestic and stock supplies, are equipped with lift or force pumps. The cylinders or working-barrels in lift pumps and force pumps are similar and are placed at a level below that of the water table. A lift pump generally discharges water only at the pump head, whereas a force pump can force water above this point-for example, to an elevated tank. Most of the pumps are operated by windmills, but a few are operated by hand. Two wells in the vicinity of Ulysses flow at the surface (p. 45) and therefore do not have to be pumped.
The discharge pipe in drilled domestic and stock wells (1.5 inches to 3 inches in diameter) generally is clamped between two 4- by 4-inch wooden blocks that rest on the top of the casing. A circular piece of galvanized iron or steel is placed between the clamp and the casing on some wells to prevent small objects from falling into the well. If a well is cased with galvanized-iron casing, the clamp may be supported by railroad ties in order to avoid crushing the casing. The irrigation wells in this area are equipped with deep-well turbine pumps, which consist of a series of connected turbines, called bowls or stages, that are placed near or just below the water level and are connected by a vertical shaft to a pulley at the top. Turbines equipped with pulleys generally are belt-driven by gasoline or natural-gas engines, but some turbine pumps have gear heads which are directly connected to the source of power. One irrigation well (46) in Lakin Draw formerly was equipped with a centrifugal pump installed in a pit so that the pumping water level would not exceed the working suction limit, but this well is no longer in use.
Kansas Geological Survey, Geohydrology
Web version May 2002. Original publication date July 1946.
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