Groundwater potential and quality modelling of Batman Plain using geographic information system (GIS)

The need of surface and groundwater use has reached significant level in recent years due to population and industrial and commercial activities. Reasons such as the lowness of the amount of fresh water resources for the purpose of drinking and utilization, deterioration of water quality in undesired direction with the losing of its original state over the earth has been required the beneficial use and the protection of water resources and also its quality to be a desirable level at our age. The drinking and utilization water needs supply from surface and groundwater resources in all residential areas. Water needs in areas where surface waters are absent and inadequate make it compulsory that supplying from drilled wells with the convenience provided by technology from groundwaters in recent years. Although groundwaters are obtained more expensive they are more qualified than surface waters because they are clean and it is difficult to pollute them. Batman Province supplies all drinking water needs and most of the irrigation water needs from the groundwater resources by means of wells drilled at various dates. Therefore in this study model maps were created with thematic maps using Geographic Information System (GIS), Inverse Distance Weighted (IDW) and DRASTIC methods for the assessment of the groundwater potential and water quality at residential areas and plains located within Batman Province borders. The data related the study throughout Batman Province were collected from the government agencies and private drilling companies operating at the study area. In the first phase of the study groundwater potential was modelled by means of static water level, dynamic water level and well yield maps. According to this, static water levels vary between 20–160 m and dynamic water level 80–160 m at the large part of Batman Province. Static and dynamic water levels range vary in different areas. Respectively the City Centre, Hasankeyf, Gercüş, Kozluk, Beşiri and Sason Districts align in terms of well yield. It is seen inefficient at a large area approximately 85 % of Batman Province (between 0–5 l/s) where Gercüş, Kozluk, Beşiri and Sason Districts place. The remaining 13 % area (5 –25 l/s) low efficient and 2 % area (25–55 l/s) efficient which were determined at the City Centre, Gercüş and Hasankeyf Districts. Batman Plain (the City Centre) and Beşiri Plain (Beşiri) the two big plains of the Batman Province are area where agricultural activities are frequently made. It is also seen from the well yield map that these areas are not efficient. It is not appropriate to drill wells for irrigation in these two plains. In the second phase of the study vulnerability maps related to Batman Province groundwater aquifer's vulnerability to contamination were created using the raster map data of the seven hydrogeological layers and overlaying in the environment of GIS based DRASTIC method for the assessment of the areas which are vulnerable to contamination and have risk to contamination. DRASTIC Index values were obtained between the lowest 54 and the highest 180. The City Centre, Gercüş, Beşiri, Hasankeyf and Sason Districts which 81.69 % area of the Batman Province have low vulnerability that bear no risk of pollution. A part of the City Centre, Kozluk and Beşiri Districts have medium vulnerability with 11.71 % area, Kozluk District has high vulnerability to pollution hazard with area 0.37 % at local level. Overall of Sason District has low vulnerability so it is not under the influence of pollution. Therefore it can be said that overall of Batman Province demonstrates low vulnerability and is not under the influence of pollution hazard according to the aquifer vulnerability map. In the third phase of the study groundwater water quality parameters' model maps were created using the data of the water quality parameters belonging to the wells in the Batman Province and its districts and were compared wiht the predicted values according to the quality criteria of the relevant standards. Accordingly among the parameters studied for water quality that nitrate and nitrite pollution values were found high. It was found that the nitrate values were 0-167.19 mg / l and the nitrite values were 0-1.65 mg / l range in groundwater at Batman Province and its districts. The nitrate values (0-25 mg / l) were low in the southern and northern parts of the province and were high in the central part of it (25-50 mg / l and 50-165 mg / l) according to the model classification map. A part of the City Centre, the majority of Beşiri and Kozluk Districts carry the risk of pollution above the limit values recommended in the standards. Therefore nitrate pollution was found to be high as a result of the increase in the utilization of fertilizers originating from agriculture at Batman and Beşiri Plains. Exceeding the criteria of water quality values related to nitrogen compounds verify this. Nitrite values (1-1.65 mg / l) were found above the limit values in the northern of the Batman Province where in a small area of Sason District and also the values were found (0.1-1 mg / l) at a part of the same district and a part of the Gercüş District in the southern of the study area. Except of these areas, the nitrite values overall of Batman Province are between 0-0.1 mg / l and below the limits recommended in the standards so there is no risk of pollution. It was determined that a very few area in the Sason District has acidic character with pH <7, and except this all province have basic character with pH> 7 in groundwater. The values of the other water quality parameters EC, BrO3, F, As, Cu, B, Hg, Cd, Cr, Fe, Al, Se, Ni, Pb and CN which were analized of overall Batman Province belonging to wells were imported to GIS environment and so it was estimated about groundwater quality of the province. These water quality parameter values were far below the limit values recommended in national and international quality criteria standards. As a result of that there is no pollution in the groundwater related to these parameters. Attaching importance to necessary vulnerability to groundwater and also not polluting which have a significant place in fresh water resources throughout Batman Province is very important. In general, the utilization of fertilizers originating from agriculture should be controlled and surface water sources should be used instead of groundwater resources. It is suggested to make the using of irrigation water widespread in waters at dam reservouirs for irrigation to be constructed surface and groundwater irrigation facilities by using within the bounds of possibility of Southeastern Anatolia Project (SAP).