ABSTRACT

Rawanduz sub-basin located approximately 110 kilometers northeast of Erbil. The area of interest lies between longitudes and latitudes of (44°30’00″E and 45°0’00″E) and (36°20’00″N and 36°50’00″N), respectively. The study is focused on the Rawanduz River in the area, which runs from the northeast to the southwest and has a length of about 65 km from the upstream to downstream in the area. The sub-basin area is about 978 km². Tectonically the studied area is located on three main tectonic zones (High Folded Zone to Imbricate Zone and Zagros Suture Zone). However, the stratigraphic succession in the studied region ranges from the Early-Middle Jurassic to the Upper Cretaceous.

The study area is a part of regions which is influenced by the Mediterranean climatological system. The climatic data are obtained from the Soran Meteorological Station for the period between 2000-2020 for each element of water availability and water losses because this station is the nearest station to the study area. The mean annual precipitation was 750.50 mm/year, relative humidity was 53.20 %, average temperature was 18.50°C, sunshine duration was 8.00 hrs/day, and annual pan evaporation was 1497.80 mm/year. Potential evapotranspiration (PET) was computed using Thornthwaite method with value is 1036.18 mm/year. The annual surface runoff and recharge are 289 mm/year and 255 mm/year, respectively. According to SPI drought indices analysis, it represented  a moderately dry in years (2007, 2011, and 2017), and dry in years (2005, 2008, 2010, and 2020) which are effecting on the groundwater recharging and river discharge in the study area.

Detailed morphotectonic analysis of the study area is applied, which is based on the morphometric analysis and geomorphic indices parameters to determine the morphological analysis and active tectonic intensity in the region by using digital satellite images and valuable data for this study, such as the Advanced Land Observing Satellite DEM (ALOS PALSAR DEM) with 12.5 m resolution, accessed from the Alaska Satellite Facility. The drainage pattern is dominated by sub-dendritic to dendritic, sub-parallel to parallel, sub-rectangular to rectangular, and radial types, which reflect structural controls in addition to variable lithological characters of the basin rocks. All groups of morphometric parameters are used, such as linear, aerial, and relief parameters. The study indicates that the Rawanduz sub-basin has 7^th– stream orders and  the sub-basin has relatively high drainage density and high basin relief values, which involves high run-off and, consequently, a low infiltration rate. The elongation ratio and the circularity ratio of the basin indicate a slightly elongated sub-basin, which reflects strong structural controls on the morphology of the sub-basin and the central sub-basin extended to the southern direction in the area and which reveal the low permeable material, high relief, steep slopes, and drainage pattern controlled by the lineaments and the fracture traces. Also, the geomorphic indices are used such as (HI, S, SL, Vf, Af, and T). The relative active tectonic (IRAT) index is calculated using the overall geomorphic indices. The result of  IRAT rating is 2.33, indicating moderate to high tectonic activity in the region.

The hydrochemical and water quality index (WQI) determines the surface water in the Rawanduz sub-basin. The twenty-three water samples are collected along the Rawanduz River with tributaries for both periods; for each sample, the physical parameters are analyzed such as pH, EC, T ̊C, Turb., TDS, and TH. Also, the chemical parameters are analyzed which are Mg²⁺, Ca²⁺, K⁺, Na⁺, HCO3^–, Cl^–, SO4^2-, and NO3^–. The results obtained from the surface water classification from Piper and Schoeller in both periods indicate (Ca-Mg-SO4-bicarbonate) water type. Moreover, based on Gibbs Diagram, water samples in both seasons fall into the chemical weathering of rock dominance. According to WHO, (2011) guidline for WQI, most samples have a great WQI, except for samples S3, 5, 6, 8, 11, 19, 20, and 22, where the WQI was unsuitable during the wet season because of high water turbidity values caused by surrounding settlements and tourist areas where residents disposed of their waste in the water. Furthermore, depending on Na%, SAR, and carbonate and bicarbonate classifications, the water is suitable for irrigation purposes.

The groundwater potential zone map (GWPZ) model is recognized that it is necessary to identify and delineate the groundwater potential zone (GWP), which can be used to augment the groundwater source for the sub-basin. The effective thematic layers of groundwater conditioning factors (Slope, TWI, TPI, Geology, Rainfall, Elevation, Ds, lineament density, drainage density, and soil) were derived from the spatial database. Subsequently, groundwater potential maps were produced from the map index calculated using AHP in a GIS situation. The result represented the zone obtained that is divided into four classes such as: a highly potential zone was about 15.59% (147.45 km²), a moderate zone was 25.87% (244.70km²), a poor potential zone is about 36.88% (348.86 km²), and a very poor potential zone is about 21.66% (204.83 km²), which are based on the availability of groundwater.