Geological Survey Water-Supply Paper Volume 1608

Geological Survey Water-Supply Paper Volume 1608

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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. Excerpt: the free surface. It should not be supposed, however, that when the water table reaches a point ru zx at which the unit storage coefficient has exhibited a value M, the specific yield will also exhibit a value M at that point. The specific yield of equation 2 describes the release of water from storage by the process of drainage or unwatering; in this process the free surface moves downward through the aquifer material, so that parts of the aquifer which were fully saturated initially are left containing only that water which is held by capillary retention. The unit storage coefficient of equation 1 describes the release of water from storage within a segment of the aquifer in which the free surface is not present. The physical processes involved are very different from those involved in "dewatering," and depend upon such factors as the compressibility of the water and of the aquifer. Prior to the time at which the free surface reaches a given point in the aquifer, the release of water from storage in the vicinity of the point is described by the unit storage coefficient; when the free surface reaches the point, the release of water from storage is described by the specific yield. A further boundary condition which may be applied to most problems of flow into wells may be expressed as where Q is the discharge of the well at a given instant; I =--j represents the radial head gradient along the well face at the given instant, expressed as a function of z; Z is the elevation of the bottom of the well screen; z is the elevation of the top of the well screen; and r is the radius of the well. Equation 4 assumes that there is no vertical flow entering at the bottom of the well, and that the permeability of the material immediately surrounding the...
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Product details

  • Paperback | 104 pages
  • 189 x 246 x 6mm | 200g
  • Miami Fl, United States
  • English
  • black & white illustrations
  • 1236548302
  • 9781236548306