Harold Holmen

Document Type

Thesis - Open Access

Award Date

1955

Degree Name

Master of Science (MS)

Department / School

Agricultural Engineering

Abstract

One of the principal sources of water for irrigation is the underground water stored beneath the surface of the earth. Various methods have been devised to extract this water so that it may be applied to growing crops in regions of inadequate rainfall. Near the Sioux River in Eastern South Dakota, ample water has been obtained at shallow depths to irrigate average sized fields in certain areas. A sandpoint well system, which consists of four or five sandpoints connected to a centrifugal pumping unit, is being used to remove the water from the ground and force it through a sprinkler irrigation system. Many problems have been encountered in the application of such a system and several of them remain unsolved. One of the more important considerations involves the optimum spacing of the sandpoints to obtain the greatest discharge. Other problems such as a convenient means of priming the pump, methods of installing the sandpoints, and the value of gravel packing the wells also need attention. It is the purpose of this study to determine the effect of the sandpoint spacing on the quantity of water secured from a sandpoint well system by obtaining the discharge for various spacings of from one to five sandpoints connected in series. In order to present the material necessary for the solution of this problem, it is expedient to introduce some concepts involving ground water hydrology. Underground water is found between the aggregates and the rocks which usually occur is well-defined layers varying greatly in thickness. Such information or layer of permable materials capable of yielding appreciable quantities of gravity ground-water when saturated is known as an aquifer. An aquifer may be located just a few feet below the topsoil, or it may occur at great depths and be confined under pressure by another layer of impervious material that prevents the water from escaping. This confining layer is known as an aquiclude and creates an artesian condition. A more familiar condition is the non-artesian or unconfined aquifer which has a free water surface known as the water table. Below the water table is the sone of saturation where the aquifer has the ability to transmit a certain quantity of water under an existing hydraulic gradient. A hydraulic gradient is represented by the elevation to which the water rises at successive locations along a line of flow. The term coefficient of transmissibility introduced by thesis is coming into popular usage in ground-water hydrology. The coefficient of transmissibility is defined as the rate of flow of water in gallons per day through a vertical strip of the aquifer 1 ft wide and extending the full saturated height under a hydraulic gradient of 100 per cent at a temperature of 60 degrees F. The coefficient of transmissibility is related to another term known as the coefficient of permeability. This coefficient multiplied by the thickness of the aquifer equals the coefficient of transmissibility. The water table has several peculiarities. It may be entirely level where there is no underground flow, or it may slope considerably due to a hydraulic gradient when there is lateral movement of water in the ground. Changes in barometric pressure can cause vertical fluctuation of the water table elevation, especially under artesian conditions. If the water table is near the surface of the ground, it will fluctuate during the day because of water that is removed by superficial evaporation and plant transpiration. Over a long period of time the water table will gain or lose some elevation due to regional change. This fluctuation may occur from replenishment by rainfall and melting snow, or it may represent a gradual decline due to transpiration, evaporation, or outflow from the aquifer. When an aquifer is penetrated by a well and water is removed by pumping, the deprivational effect on the water table will be noticed first in the immediate area of the well. As the amount and duration of pumping is increased, the areal extent of influence on the water table becomes greatly widened.

Library of Congress Subject Headings

Wells
Big Sioux Aquifer (S.D.)

Description

Includes bibliographic references

Format

application/pdf

Number of Pages

50

Publisher

South Dakota State University

Rights

No Copyright - Non-Commercial Use Only
http://rightsstatements.org/vocab/NoC-NC/1.0/

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