A manual of practical hygiene for students, physicians, and health officers . av be situated much more deeply, owing to abrupt changesof level of the imj)ei-meable stratum. Irregularity of the surface of the water table is due largely also tothe rainfall, wliicli, coining at frequent intervals, falls upon surfaces ofdiffering permeability, so that while one part is still draining its waterdownward, another has completed the process and is ready for drought occurs, however, the level becomes more and more uni-form until it may become quite horizontal. With return of rainfall,the level
A manual of practical hygiene for students, physicians, and health officers . av be situated much more deeply, owing to abrupt changesof level of the imj)ei-meable stratum. Irregularity of the surface of the water table is due largely also tothe rainfall, wliicli, coining at frequent intervals, falls upon surfaces ofdiffering permeability, so that while one part is still draining its waterdownward, another has completed the process and is ready for drought occurs, however, the level becomes more and more uni-form until it may become quite horizontal. With return of rainfall,the level rises, and irregularity of the surface of the water table isagain produced. The level at any point is influenced also by theamount of water withdrawn from the soil by the demands made uponwells. When the amount of percolation is exceeded by the amount ofwithdrawal, the level falls ; when the conditions are reversed, the levelrises. The water table in its irregular course touches the surface of theground here and there, and gives rise to springs which may flow the Fig. Outcropping of water table. year round regardless of drought, or may dry up completely with fallof the level. Similarly, all permanent ponds are outcroppings of thewater table, ,and the beds of rivers as well, but the level of the tablein the near vicinity is almost invariably higher than the surface ofthese bodies. Sometimes, however, the water level is so near the sur-face that, without emerging in the form of springs, it extends in a broadsheet just at or below it and pauses marshy conditions. In Fig. 26the manner in which the water table crops out in springs and feedslakes and other bodies of water is shown. By some, the water table is spoken of as an underground river, aterm which is very misleading, in that it suggests a body of waterrather than a condition of saturation of the soil. There are, to be sure,in some localities, especially in limestone districts, bodies of water flow-ing between impermeabl
Size: 2441px × 1023px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, bookpublishe, booksubjecthygiene
