The groundwater system of the Western Desert of Egypt is divided into
three units, which are interconnected:
• To the north there is the North-Western Basin with the Qattara Depression
and Siwa Oasis. This basin is of subordinate relevance as regards human
use, since its water is mostly salty.
• To the south, separated by the El-Bahariya-Cairo Arch of the basement,
there is Ed-Dakhla Basin, the most important groundwater system in Egypt.
Its northern part is dominated by mostly continental Cretaceous permeable
sediments which cover the less permeable sediment layers of the Palaeo-
zoic era. Over the layers of the Lower Cretaceous, which have a good
water-storing capacity, lie the clayey and denser sediments of the Upper
Cretaceous and the Tertiary. To the south are the continental Cretaceous