DRASTIC model adjusted with lineament density to map groundwater vulnerability: a case study in Rania basin, Kurdistan, Iraq

Abstract

Groundwater has never been heavily relied on as a water source in Northern Iraq as it has been in the last two decades due to the rapid and often unplanned urbanization, industrial and agricultural projects. This paper attempts to present a concise groundwater vulnerability assessment of Rania basin to the local and regional planning authorities to ensure a more sustainable development in the area. The focus of the study is the Rania basin, which is a part of Dokan subbasin in northeast Iraq. The initial groundwater vulnerability assessment is mapped with standard DRASTIC model. It is then modified by adding "lineament density index" to the original seven DRASTIC parameters due to the previously established close relationship between flow and yield of groundwater with lineament. The area is categorized into five vulnerability index zones of very low (26%), low (32%), medium (31%), high (11%), and very high (0.012%). The modified model offers a slightly different vulnerability classification of very low (16.61%), low (35.45%), medium (30.32), high (17.57), and very high (0.05%). Measured nitrate concentration is used to validate the assessment results. A progressive increase in nitrate level somehow reflects the different vulnerability zones identified by both DRASTIC models. Average nitrate values of samples taken in wet season show 14.99 mg/l, 17.94 mg/l, and 18.63 for very low vulnerability, low vulnerability, and medium vulnerability zones in the standard DRASTIC model. However, when the area is mapped by the modified DRASTIC model, the vulnerability classes of very low and medium show slightly higher nitrate values of 15.96 mg/l and 20.1 mg/l and a lower value of 17.68 mg/l for the low vulnerability class. This is despite a noticeable increase in nitrate level between wet and dry seasons due to the rise in water table in the wet season.

Keywords: DRASTIC model; Groundwater; Kurdistan; Lineament; Validation; Vulnerability.