The Great Zab River catchment is a major left-bank tributary of the River Tigris and drains a substantial part of the Kurdistan Region, an autonomous region of Northern Iraq. The average annual rainfall in the Great Zab river basin varies from more than 1000 mm/year northeast of the catchment to about 300 mm/year in the southwest. In this study, monthly, seasonally and annually precipitation, temperature and discharge trends of stations in the Great Zab catchment from 1960–2012 were analysed and interpolated. The Mann-Kendall trend test was applied to examine the precipitation, temperature and discharge data. Positive and negative trends at significance levels of 95 and 99% were detected. Water supply was calculated from precipitation stations of catchment using water balance. Water demand for domestic and agricultural sectors were estimated using available secondary data. Within Kurdistan, the water resources of the Great Zab River catchment are under pressure from population increase and are utilized for potable, domestic, agricultural, and industrial supply. As with many parts of the world, effective management of water resources within Kurdistan is hindered by a lack of water quality data and established background concentrations.
This study therefore represents the first regional survey of river water chemistry for the Great Zab River catchment and presents data on the spatial and temporal trends in concentrations of As, Ba, Ca, Cd, Co, Cr, Cu, Fe, Hg, Li, Mn, Mo, Ni, Pb, Sr, Zn, NO3−, SO42−, F−, Cl−, and PO43−, in addition to pH, electrical conductivity, dissolved oxygen and turbidity. As a tool for underpinning the management and monitoring of water quality, background concentrations were defined for the Great Zab catchment using three methods. The influences of geogenic and anthropogenic controls upon spatial and temporal trends in water chemistry are also evaluated. The influence of geogenic loading from underlying bedrock was identifiable within the observed spatial trends, with the most notable differences found between waters sampled from the relatively more volcanic-rich Zagros Zone to the north and those
sampled from the lower catchment underlain by younger clay-, sand- and siltstones. The greatest anthropogenic influence, identifiable through elements such as Cl- and NO3-, is present in the more highly populated lower catchment. The background concentrations identified in the Great Zab catchment would be those expected because of geogenic loading with some anthropogenic influence and represent a more conservative value when compared to those such as the World Health Organization Maximum Admissible Concentration. However, background concentrations represent a powerful tool for identifying potential anthropogenic impacts on water quality and informing management of such occurrences.