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    Earth Dams, A Study
    Earth Dams, A Study
    Earth Dams, A Study
    Ebook98 pages58 minutes

    Earth Dams, A Study

    By Burr Bassell

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    The earth dam is probably the oldest type of dam in existence, The litera- antedating the Christian Era many hundreds of years. ture upon this subject is voluminous, but much of it is inaccessible and far from satisfactory. No attempt will here be made to collate this literature or to give a history of the construction of earth dams, however interesting such an account might be. The object will rather be to present such a study as will make clear the application of the principles underlying the proper design and erection of this class of structures. In no way, therefore, will it assume the character or dignity of a technical treatise. Dams forming storage reservoirs, which are intended to impound large volumes of water, must necessarily be built of considerable height, except in a very few instances where favorable sites may exist. Recent discussions would indicate that a new interest has been awakened in the construction of high earth dams. As related to the general subject of it storage, is with the high structure rather than the low that this study has to do. To the extent that the greater includes the less, the principles here presented are ap- plicable to works of minor importance. Many persons who should know better place little importance upon the skill required for the construction of earthwork embankments, considering the work to involve no scientific problems.
    LanguageEnglish
    PublisherRead Books Ltd.
    Release dateMay 31, 2013
    ISBN9781473381001
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      Book preview

      Earth Dams, A Study - Burr Bassell

      EARTH DAMS

      CHAPTER I.

      Introductory.

      The earth dam is probably the oldest type of dam in existence, antedating the Christian Era many hundreds of years. The literature upon this subject is voluminous, but much of it is inaccessible and far from satisfactory. No attempt will here be made to collate this literature or to give a history of the construction of earth dams, however interesting such an account might be. The object will rather be to present such a study as will make clear the application of the principles underlying the proper design and erection of this class of structures. In no way, therefore, will it assume the character or dignity of a technical treatise.

      Dams forming storage reservoirs, which are intended to impound large volumes of water, must necessarily be built of considerable height, except in a very few instances where favorable sites may exist. Recent discussions would indicate that a new interest has been awakened in the construction of high earth dams. As related to the general subject of storage, it is with the high structure rather than the low that this study has to do. To the extent that the greater includes the less, the principles here presented are applicable to works of minor importance.

      Many persons who should know better place little importance upon the skill required for the construction of earthwork embankments, considering the work to involve no scientific problems. It is far too common belief that any ordinary laborer, who may be able to use skillfully a scraper on a country road, is fitted to superintend the construction of an earth dam. It has been said that the art of constructing earth dams is purely empirical, that exact science furnishes no approved method of determining their internal stresses, and that in regard to their design experience is much more valuable than theory. When the question of stability is fully taken into consideration, it certainly requires a large amount of skill successfully to carry out works of this character.

      Extreme care in the selection of the site, sound judgment in the choice of materials and assiduity in superintending the work while in progress, are all vitally essential.

      Classification of Dams.

      Dams may be classified according to their purpose as diverting dams or weirs and as storage dams. The former may be located upon any portion of a stream where the conditions are favorable, and the water used for manifold purposes, being conveyed by means of canals, flumes, tunnels and pipe lines to places of intended use. These dams are generally low and may be either of a temporary of permanent character, depending upon the uses to which the water is put. Temporary dams are made of brush, logs, sand bags, gravel and loose rock. The more permanent structures are built of stone and concrete masonry.

      Storage dams may be classified according to the kind of material entering into their structure, as follows: (1) Earth; (2) Earth and Timber; (3) Earth and Rock-fill; (4) Rock-fill; (5) Masonry; (6) Composite Structures.

      Low dams forming service reservoirs for domestic water supplies and for irrigation comprise by far the most numerous class. They are not designed to impound a large volume of water and therefore may be built across a small ravine or depression, or even upon the summit of a hill, by excavating the reservoir-basin and using the material excavated to form the embankment. These reservoirs may be used in connection with surface or gravity systems, artesian wells, or underground supplies obtained by pumping. The dams forming these reservoirs being of moderate size and height may vary greatly in shape and dimensions. The form may be made to suit the configuration of the dam site. When the earthwork requires it, they may be lined with various materials to secure watertightness. Often such dams are made composite in character, partly of earth and partly of masonry or some other material. They are also frequently accompanied by numerous accessories, such as settling-basins, aerating devices and covers, which present a diversity in form and appearance. A presentation of the different types of dams thus employed, with a discussion of the questions pertaining to utility in design and economy in construction, would be exceedingly valuable and of general interest. Service-reservoirs will receive only a passing notice, with the hope expressed that some competent authority will discuss them in the future.

      CHAPTER II.

      Preliminary Studies and Investigations.

      The preliminary studies and investigations which should be made prior to the construction of any dam for the storage of water have to do with (1) the Catchment Area. (2) the Reservoir basin, and (3) the Dam site.

      Catchment Area.

      It is thought desirable to define a number of terms as we proceed, for the purpose of correcting erroneous usage and for a clearer understanding of the subject. The catchment area of a reservoir is that portion of the country naturally draining into it. The watershed is the boundary of the catchment area and may be correctly defined as the divide between adjacent drainage systems. In regard to the catchment area it is necessary to determine:

      1. Its extent and area in square miles.

      2. Its topography or the character of its surface.

      3. Its hydrography or precipitation and run-off.

      4. Its geology, or the character of its soils and subsoils, and the nature and dip of its rock strata.

      5. Its flora, or the extent to which it is clothed with forest trees or other vegetation.

      All of these elements affect the volumes of maximum run-off, which is the one important factor in the construction of earth dams that must not be underestimated.

      If the proposed dam or reservoir is to be located upon a main drainage line; that is, upon a river or stream, it is necessary to know both the flood and low-water discharge of the stream. Frequently no reliable data on this subject are available, and the engineer must then make such a study of the whole situation as will enable him to estimate the minimum and maximum flow with considerable accuracy.

      There are numerous factors entering into the solution of this first problem, such as

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