تحليل فضايي مخاطرات طبيعي ناشي از برداشت بي‌رويه آب زيرزميني در آبخوان ساحلي اروميه

Spatial Analysis of Natural Hazards Resulting from the Over- Exploration of Ground Water in the Coastal Aquifer of Urmia Region

آب زيرزميني بخش زيرسطحي و حياتي چرخه هيدرولوژيكي را تشكيل مي دهد كه تحت تأثير فرآيندهاي هيدرولوژيكي، بوم شناسي و بيوژئوشيميايي قرار مي گيرد. مديريت مناسب و كارآمد منابع آب زيرزميني پيش نياز تعيين تغييرات كيفي و كمي آن است. منابع آب زيرزميني اغلب با درگيري هايي همچون مخاطرات طبيعي و فعاليت هاي انساني روبه روست. در چند سال اخير، برداشت بي رويه آب زيرزميني از آبخوان اروميه باعث پايين آمدن كيفيت آب زيرزميني و، همچنين، هجوم آب شور به آبخوان اروميه شده است. به دليل اثرات زيست محيطي جبران ناپذير و وخيم شدن شرايط آبخوان، مطالعه خطرهاي طبيعي و آسيب پذيري آب زيرزميني بسيار ضروري است. در اين پژوهش، با استفاده بررسي هاي هيدروشيميايي، سيستم اطلاعات جغرافيايي و تصميم گيري چند معيار وزن دار، نقشه آسيب پذيري، براي تعيين روند كاهش كيفيت آب زيرزميني به علت نفوذ آب شور و برداشت بي رويه آب زيرزميني، طراحي شده است. شش لايه مؤثر بر ارزيابي مخاطرات طبيعي شامل كل املاح محلول، دبي چاه پمپاژ، ضخامت آبخوان، افت آب زيرزميني، هدايت هيدروليكي آبخوان و فاصله از ساحل يكپارچه شده و وزن و رتبه هاي مختلف براي آن ها معين شد. نتايج پژوهش نشان داد: مخاطرات طبيعي در شرق و شمال شرق آبخوان به علت نفوذ آب شور درياچه اروميه و برداشت بي رويه آب زيرزميني بسيار بالا است.

Coastal aquifers comparing noncoastal aquifers, are faced to natural hazards more rapidly due to incorrect managements (Bear et al. 1999). Aquiferrsquo s vulnerability to various pollutants or intrusion of saline water to coastal aquifers have been studied by several researchers so far (Chachadi et al., 2002 Cardona et al., 2004). Overlay models are produced to overlay physical indicator maps and weight them (NRC, 1993). There is a high potential in applying methods based on spatial analysis, in hydrogeological studies. Assessment of natural hazards due to overextraction of groundwater in Urmia coastal aquifer is the aim of this study which can leadto evaluating of groundwater quality fluctuations in coastal aquifer and also salt water intrusion in coastal aquifer. Study area is Urmia plain coastal aquifer. This plain is bounded from North, East, South and West by Zola chai and Kherkhere chai watersheds, Urmia Lake, Gadar Chai watershed and boundary mountains of Iran and Turkey respectively. Present study focused on, utilization of overlaid natural hazards substantial evaluation groundwater over extraction indices spatial models method, using Geographical Information System (GIS). Flow chart of the Methodology of present study is depicted in figure Fig 1. Methodology flowchart of present study Drawdawn is meaningless?? ldquo Counductivit ldquo is wrong ldquo conductivityrdquo is true. Six parameters that have crucial importance in hazards caused by groundwater overextraction and groundwater quality depletion subsequently, have chosen upon to literature review, various studies and authors expertise (Nobr et al, 2007 Hammouri and ElNaqa 2008). Weights and ranks were indicated base on experimental results or authors judgment and experts knowledge in similar studies and statistical methods. Used indices final weights were determined as below: Total dissolved solid (TDS) (1), discharge of water wells (2), hydraulic conductivity (1), Aquifer thickness (1.5), Water table depletion (3), Distance from lake shore (1.5). Weight of every layer is given to layers ranks. Final map was determined and areas with low, moderate, high and very high vulnerability was ranked eventually considering the vulnerability amounts importance. Fig 2. Final map of Spatial Analysis of Natural Hazards in the aquifer of Urmia region The results of this study revealed that natural hazardrsquo s rates in Urmia Lake coastline due to salt water intrusion and also in aquifer central part is very high, which caused by groundwater overextraction. Final map shows the areas with low vulnerability has covered 191 square kilometer (about 20 percent of the study area). In these areas groundwater extraction is low and the thickness of aquifer is also negligible. Areas with moderate and high vulnerability contain 353 (37 percent) and 119 (13 percent) square kilometer respectively. In the coastal and central parts of the plain, groundwater extraction is so high and of course features the very high vulnerability that covers 30 percent and 280 square kilometer of the study area.