[al-] Karaji, Mohammed ibn al-Hasan al-Hasib (early 10th century AD).
The advanced knowledge of the Persians concerning groundwater is demonstrated by a recently discovered book by Mohammed
Karaji titled: The Extraction of Hidden Waters.
This book reveals a profound and exacting technical understanding of
groundwater theory and is the oldest known text on the subject. Karaji's knowledge of groundwater, which surpassed
that of western scholars 7 centuries later, is in general agreement with modern understanding of the subject. For
example, Karaji was familiar with the general concepts of the hydrological cycle. While he never featured the whole
cycle as we know it, he records in different passages of his book each individual phase.
Karaji spent most of his life in Bagdad, working mainly as a mathematician. He wrote several books on algebra
and geometry which were translated into German during the 19th century.
These translations introduced Karaji to western
scholars where he is now counted with the classical Arabic mathematicians. At an advanced age, Karaji returned to the
central highlands of his native Persia. As a means of earning his subsistence, he published
Karaji and other Persian scholars were familiar with the basic hydrologic, geologic, and engineering principles
associated with groundwater. Karaji himself exhibited extensive skills and expertise regarding: (1) the classification
of soils, (2) the search for fresh water, and (3) the different types and hydraulic characteristics of aquifers.
He pioneered work on the use of plant growth as an indicator of groundwater aquifers, and invented ingenious devices
employed in surveying and tunneling. Much of the Karaji's book deals with the techniques of exploring for groundwater,
mainly how to dig wells and qanats. The methods he describes are still used in many parts of the Middle East and Asia.
References: Pazwash, Hormoz and Gus Mavrigian,
1980, "A Historical Jewelpiece-Discovery of the Millennium
Hydrological Works of Karaji," Water Resources Bulletin, December, pp. 1094-1096; Nadji,
Mehdi and Rudolf Voight, 1972,
"'Exploration for Hidden Water' by M. Karaji-Oldest Textbook on Hydrology?"
Groundwater, September-October, pp. 43-46.