The Role of Geomorphologic Factors in Formation and Nourishing Of Underground Water Table (Case Study: Zahab Plain)

In this research، the relationship between geomorphologic factors with underground water resources in Zahab plain (in west of Kermanshah) has been analyzed using by analyzing-deducing and weighting methods. First، by using of pizometeric and exploratory well data، variation of water table in Zahab plain has been comparative analysis with geomorphic unites and then، the Zahab watershed was zoned in hydro-geomorphic units by overlapping of seven environmental variables such as: slope، geology، geomorphology، land use، hypsometry، rain fall and drainage density in GIS environment. Results of both of methods have shown significantly relation between geomorphic features and underground water resources in Zahab plain. In fact this study showed that although the syncline plain with young sediments prepared a suitable bed to form aquifer in Zahab plain، but alluvial fans in easterner part of Zahab plain and floodplain of Jegiran River have the main role to feed it. These features not only penetrate 5/112 m-m³ agriculture return water and 4/147 m-m³ water from rain (of course together with plain sediments)، also cause penetrate 7/570 m-m³ water from run off was penetrated in to the Zahab plain aquifer. Dividing of Zahab watershed in to hydro-geomorphologic units indicates that deposited plain with alluvial sediments and alluvial fan has the most important role to penetrate the water in to the underground. Erosive plains covered with slope material، are second importance in this regard. Irregular and uneven slopes also have influence on water penetration when they are covered with scree and badlands have indirect role in water penetration. The runoff of these areas penetrates in to the Zahab aquifer through alluvial fans when they are drained in to the eastern part of Zahab plain through Jegiran River.