GROUNDWATER DEVELOPMENT FOR PORTABLE WATER SUPPLY
ABSTRACT
Groundwater development for portable water supply hydrology may be defined as the science of the occurrence distribution, and movement of water below the surface of the earth. Geochydrology has an identical connotation, and hydrogeology differs only by its greater emphasis on geology. Utilization of groundwater dates from ancient times, although an understanding of the occurrence and movement of subsurface water as part of the hydrologic cycle has come only relatively recently.
SCOPE: Groundwater referred to without specification is commonly understood to mean water occupying all the voids within geologic stratum. This saturated zone should be distinguished from an unsaturated, or earation zone where voids are filled with water and air. Water contained in saturated zone is important for engineering work, geologic studies and water supply development consequently, the occurrence of water in this zones will be emphasized here. Unsaturated zone a re usually found above saturated zones and extend uquad to the ground surface. Because this water includes soil masture within the root zone, it is a major concern for agriculture, binary, and soil science. No rigid demarcation of water between the two zones is possible, for they possess an interdependent boundary and water can move from owe zone to the other in either direction. The interrelationships are described more in some higher hydrogeology texts.
HISTORICAL BACK GROUND AND GROUND WATER THEORIES
Groundwater development dates from ancient times the Old Testament contains numerous references to groundwater, springs, and wells, other that dug wells, groundwater in ancient times we supplied from horizontal wells known as QAUNATS. These persist to the present day and can be found in a band across the regions of the South Western Asia and North Africa extending from Aghanistan to Morocco. A cross section a long a qanat ie shown in fig 1.1 typically, a gently sloping tunnel dug through alluvial material leads water by gravity flow beneath the water table at its upper end to a ground.
FIG 1.1
A vertical cross section along a qanat surface outlet and irrigation canal at its lower end. Vertical shafts dug at closely s paced intervals provide access to the tunnel. Qanats are laboriously hand constructed by skilld workers employing techniques that date back 3000 years.
Iran possesses the greatest concentration of qanats; here some 22,000 qanats supply 75 percent of all water used in the country. Lengths of qanats extend up to 30km, but most are less than 5km. The depth of the qanat mother well (see fig 1.1) ie normally less than 50m, but instances of depth exceeding 250m have been reported. Discharge of Qantas varies. Seasonally with water table fluctuations and seldom exceed 100m3/hr.
GROUNDWATER THEORIES
Utilization of groundwater greatly preceded understanding of its origin, occurrence, and movement. The writing of Greek philosophers to explain origins of springs and groundwater contain theories ranging from fantasy to nearly correct accounts. As late as the seventeenth century it was generally assumed that water emerging from springs could not be derived from rainfall, for it was believed that the quantity was in adequate and the earth too impervious to permit penetration of rain water for below the surface. Thus, early Greek philosophers such as Homer, Thates and Plato hypothesized that springs were formed by seawater. Conducted through subterranean channels below the mountains, then Aristotle suggested that air enters cold dark caverns under the mountains where it condenses into water and contributes to springs.
