CHAPTER ONE
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.
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.
The Roman philosophers, including Seneca Pliny, followed the Greek ideas and contributed little to the subject. An important step forward, however was made by the Roman architect Vitnvius he explained the now accepted infiltration theory that the mountains receive large amounts of rain that percolate through the rock strata and emerge at their base to form streams.
The Greek theories persisted through the Middle Ages with no advances until the end of the Renaissance. The French Poffer and Philosopher Bernard Palissy (1510 – 1589) reiterated the infiltration theory in 1580, but his teachings were generally ignored. The German astronomer Johannes Kepler (1571 – 1630) was a man of strong imagination, who likened the earth to a huge animal that takes in water of the ocean, digests and assimilates it, and discharges the end products of these physiological processes as groundwater and springs. The seawater theory of the Greeks, supplemented by ideas of vapourizaton and condensation processes within the earth, was restated by the French Philosopher Rene’ Descarfes (1596 – 1650).