HYDROGEOLOGY OF THE HIGH FOLDED ZONE
The Hydrogeology of the High Folded Zone, in Iraq is reviewed. This zone is characterized by rugged topography, and presence of deep canyons and narrow valleys with well defined mountainous topography. The oldest exposed rocks are Early Triassic in age, whereas the youngest are of Pliocene – Pleistocene age, which belong to the Bai Hassan Formation, in addition to Quaternary Sediments.
The High Folded Zone can be divided into five major hydrogeological basins, which are: Zakho, NW Barzany, Central Harir, Central Dokan and Sharazoor Basins. And these basins are subdivided into ten sub-basins. Two main groups of carbonate aquifers are described based on geological and hydrogeological characteristics; these are: Bekhme Karst Aquifers (Qamchuqa, Dokan and Kometan formations) and Pila Spi Fractured Karst Aquifers (Sinjar, Khurmala and Avanah formations). In addition to these important carbonate aquifer complexes, some clastic units, such as Quaternary Sediments, Bai Hassan, Mukdadiya, Injana, Fatha, Kolosh and Tanjero formations are sufficiently permeable to form local aquifers.
The source of recharge water within the High Folded Zone is mainly from direct precipitation and snow melt during summer at the highest elevated areas of the zone, and from the Suture and Thrust Zone at the northeast. The Low Folded Zone represents the discharge zone to the area, beside wells and springs. The general trend of the groundwater movement at this area is mainly from north and northeast towards south and southwest, with local different directions due to topographic and structural characteristics of the area. There is a hydraulic continuity between water bearing formations within this zone, depending on the piezometric relations of the water-bearing layers throughout the area.
The depth of the groundwater increases at the high lands and at the flanks of the synclines, and decreases at the central parts of the basins and at the discharge areas. The transmissivity of aquifers often increases at the central parts of the synclines and along river courses, and within the alluvial fans, as more permeable sediments are available.
The salinity of the groundwater is characterized by low values; with the prevailing type of fresh water being Ca (Mg)-HCO3, with increasing magnesium content in dolomites. This salinity and chemical composition of groundwater changes in the presence of gypsum, anhydrite and halite in the Fatha Formation, which is sometimes present in the S and SW parts of the Zone. The hydraulic conditions and chemistry of aquifers within the High Folded Zone are closely linked to the stratigraphic, lithologic, structural and topographic characteristics of the water bearing formations. According to the hydrogeological evaluation of the High Folded Zone, it can be considered as promising zone for groundwater development in Iraq.