Author

Leonard Erie

Document Type

Thesis - Open Access

Award Date

1954

Degree Name

Master of Science (MS)

Department

Agricultural Engineering

Abstract

Infiltration, as defined by Horton, an internationally recognized authority on hydrology, is the process involved when water soaks into the ground. In other words, infiltration refers to that process whereby winter enters the environment of the soil through the immediate surface. It is not synonymous with percolation. The latter refers to the movement of water into the soil. It is true that percolation is generally involved in the process of infiltration, but this is not necessarily the case. The rate at which water can enter the soil is called the infiltration capacity. In this thesis, infiltration capacity, infiltration rate, and intake rate are used synonymously. Infiltration and intake are used in reference to the quantity of water penetrating for a period of time. In irrigation studies it is important that we recognize both a maximum and minimum infiltration capacity of soils. For any give irrigation, the maximum value obtained would be at the beginning of the irrigation. It decreases rapidly at first, depending upon the soil structure, and then gradually reaches a somewhat stable minimum. The minimum infiltration capacity approaches the percolation rate of the soil profile. The infiltration capacity of a given soil is a very changeable property. It changes with season and management. However, Horton has observed that the maximum and minimum infiltration capacities have fairly definite values for a give season. The most important factors affecting the infiltration capacity are the permeability of the soil profile, the condition of the soil surface, and the soil moisture content. The permeability of the profile controlling barrier and its location in the profile are directly instrumental in determining the point at which the infiltration capacity reaches its minimum. A controlling barrier near the surface would mean the minimum infiltration capacity would be encountered soon after water was applied. A controlling barrier at six feet would rarely effect the infiltration capacity under ordinary irrigation conditions. Infiltration capacity measurements are needed as a guide in the proper design and management of all types of irrigation systems. These measurements are also needed for hydrology and drainage studies. Infiltration capacity measurements are an important criteria for determining correct lengths of run, size of streams of water, and cut back streams. The filtration capacity must be known to properly design a sprinkler irrigation system. Correct infiltration capacity measurements are essential in designing for high efficiency of water use. Infiltration capacities are also needed in drainage studies to determine possibilities of leching. The amount of runoff as determined in hydrological studies are determined by the ability of a soil to absorb rainfall and transmit it through the profile. Heretofore, many irrigation projects, individual irrigation and sprinkler system units, have been designed on the basis of an estimated infiltration capacity for a particular soil textural classification. This was, and perhaps still is, the best information available, as a large percentage of the land placed under irrigation available as a large percentage of the land placed under irrigation has its soil classified. This method is sometimes quite risky due to the infiltration capacity variance possible within any one class, and the fact that many soils contain barriers within the profile. A soil may be classified as a silt, loam, or clay, and the sand content may vary from 0 to 50 per cent within the textural class without changing the classification. The content of sand within a soil can, however, change the infiltration capacity considerably. If a barrier exists near the surface, its ability to transmit water would be the key to proper design and irrigation water management, while a barrier below the root zone would probably not affect the system design. Infiltration may be controlled by the permeability of a lower strata, and hence by the degree of saturation of the soil just below the infiltration interface.

Field infiltration capacity measurements can be determined where irrigation water is available. However, in most new irrigation enterprises neither water nor an irrigation system are available. Since infiltration capacities are necessary for the design of the system, an easy, quick, economical and accurate method is desirable to obtain these infiltration capacities. Light weight equipment requiring a minimum of water should be designed. Correlation of this equipment with field infiltrations should be accomplished. Infiltrometer rings have been used throughout the western irrigation areas. These rings are of various diameters ranging from six to twenty four inches. A varying number of rings and heads of water was utilized in determining infiltration measurements. Inquiries for information produced the following recommended procedures and varying thoughts: (1) In Region I, Bureau of Reclamation, a head of one to two inches was maintained while the Soil Conservation Service, Boise, Idaho, used a one to eight inch head, (2) Region IV, Soil Conservation Service, used a 10 inch ring with a 22 inch buffer, while the Soil Conservation Service at Boise, Idaho and the Bureau of Reclamation, Region I, used no buffer. Rings were driven into the ground at variable depths ranging from one to six inches. These differences between the government agencies on their recommended practices does not mean they are incorrect and not workable, but they point out the need for an analysis of the equipment and procedures being used. If some of the numerous variables can be eliminated, a technician may then take into account his own particular problems. Then with standard equipment and standard procedures of known limitations, he should be able to obtain dependable information.

Library of Congress Subject Headings

Irrigation farming

Description

Includes bibliographical references (pages 69-72)

Format

pdf

Number of Pages

77

Publisher

South Dakota State University

Rights

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

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