The Excavation of Hidden Waters by al-Karaji

by Meam Wye on January 31, 2010

'Inbat al-miyah al-khafiyya' (The Excavation of Hidden Waters) was written around 1000 AD by Al-Karaji (953 -1029),  a Persian Muslim mathematician and engineer. This book is regarded as the oldest known book on Hydrology. The book contains technical and scientific details of finding the water level, instruments for surveying, techniques for water searching, construction & maintenance of the conduits and their lining, Qanats etc. The book also describes water flow, the classification of soils, origins of under-ground water, surface indication of underground water, the different types and hydraulic characteristics of aquifers, effects of earth quakes on water resources, procedures for determining water quality, treatment of water etc. The information presented in the book is inline with modern theories, most of which was discovered by the west more than 700 years later!

Al-Karaji had discussed the complete hydrological in al-Khafiyya; the description is scattered throughout the book. At one place in his book, he mentions:

“The transformation of water into air in the hot regions and air into water in the cold regions creates a constant cycle which guarantees the prosperity of the lands”.

He concludes that clouds stem from evaporation on the sea; the sun taking only the freshest water from the surface of sea. For this reason, according to karaji, the water remaining on the surface is the most saline, whereas with increasing depth, the sea water becomes progressively fresher, with fresh water being at the bottom of the sea. Karaji also distinguishes between three types of sub water: original (juveline) water, condensed water and common ground water.

Discussing various techniques for searching for water, Karaji mentions one such technique that involved geology, now called Hydrogeology as follows:

“The higher the ratio of the amount of stone to the amount ofsoil in a particular mountain, the less the chance to find a supply of groundwater. Thereis no groundwater in the small and separated mountains especially those which havehard rocks, because no snow can last long on their tops. In case there would be a chainof mountains covering a vast area, it is more likely to find a good supply ofgroundwater, because such mountains enjoy many valleys that can hold ice and snowuntil summer. If a mountain has a flat top with thick vegetation casting shadow on theground and protecting the soil moisture from sun, there would be a better chance tocome across an aquifer……….all the lands linked to the aforementioned mountains contain a good supply ofgroundwater, especially the land which is the lowest as well as the closest to the Earth’score….”

In al-khafiyya, al-karaji provides information on ditch lining that is inline with modern theories:

“If waterway is loose and permeable, the bed should be covered with large bricks and dark lime… or they have to dig the bed about a meter down, and then refill it with clay and compact it by beetle as the bed ditch stands at the same level. Both sides of the ditch should he inclined and built with the same material. Adding some water to clay makes the ditch more efficient. But the water shouldn’t be cut so that its original moisture remains. Lining the ditch with compacted mixture of clay, sand and loam increase its firmness. Our ancestors said, “let the quadrupeds go through ditches to trample”. Lining the ditches with compacted mixture of slaked lime, sand and clay with original moisture became very stiff after a while. Sometimes the bed of canals became so stiff that well sinkers are not able to dig it. Many times those loose lands are covered with rocks and their porous filled with the mixture of clay, lime and sand.”

In the modern science of hydrology, the amount of the bound of well or Qanat is correlated with the type of ground, the amount of seepage and a steady coefficient. Karaji has shown this knowledge in this regard by writing about the role of depth, seepage and ground in designating a bound.

Karaji has also discussed various aspects of earth sciences in his book. He described the earth as spherical ( not flat):

“The Earth with all the mountains and plains on it has a spherical shape. The earth is doomed to spin all the time. Every element on the earth is being drawn toward the center of the earth….”

He also writes in his book:

“whatever higher than the Earth surface such as a building may fall down, and it is attributable to the same attracting force inherent in the Earth and its sphericity.” 

Karaji, thus, succeeded Newton by several centuries in knowing that the earth has a force he named “the tendency to the center” the same that Newton called gravitation! According to Karaji, water is also affected by the force of gravity like every object on the earth.