پايش مكاني شوري آب هاي زيرزميني در سال شاخص خشكسالي و ترسالي مورد: دشت تبريز

Spatial Monitoring of Groundwater Salinity in Drought and Wet Periods Case Study: Tabriz Plain

اين مطالعه براي مديريت بهينه ي منابع آب در دشت تبريز، به پايش مكاني شوري آب هاي زيرزميني در سال هاي شاخص خشكسالي و ترسالي مي پردازد تا تغييرات كيفيت شيميايي آب هاي زيرزميني را در مواقع حداكثرهاي اقليمي (خشكسالي ها و ترسالي ها) پيگيري نمايد. براي اين منظور از متغيّرهاي اقليمي شامل بارش هاي ماهانه (86-1351) و نتايج تجزيه شيميايي آب هاي زيرزميني بويژه شاخص EC ، SARو TDS مهرماه سال شاخص خشكسالي و ترسالي استفاده شد. براي مقايسه و پايش تغييرات شاخص هاي كيفي آب هاي زيرزميني در سال هاي شاخص خشكسالي و ترسالي نقشه هاي هم ارزش EC و SAR با استفاد از سامانه ي اطلاعات جغرافيايي (GIS) و نرم افزارهايArc/View و Arc/GIS ترسيم شدند. نتايج اين مطالعه نشان مي دهد كه ميزان آب هاي زيرزميني شور و خيلي شور در دشت تبريز در سال شاخص خشكسالي 2/28 درصد و آب هاي زيرزميني با قلياييت زياد 35/25 درصد بوده در حالي كه در سال شاخص ترسالي آب هاي زيرزميني شور و خيلي شور 15/18 درصد و با قلياييت زياد 92/4 درصد آب هاي زيرزميني را تشكيل مي دهند.

Groundwater, which forms part of hydrologic cycle is a reliable source for supplying the water required by human being. The occurrence of droughts and heavy precipitations are the most important climatic extremes having both short and long-term impacts on the ground- water availability. The results of climatic extremes propagate through the hydrological system, including surface water and groundwater (unsaturated zone and saturated groundwater). These impacts include changes in groundwater recharge resulting from the erratic behavior of the annual and seasonal distribution of precipitation and temperature; changes in evapotranspiration resulting from changes in vegetation. Drought is a recurring, natural phenomenon, which affects every part of the hydrological cycle. Droughts are mostly caused by periods of lower than average precipitation and propagate through the hydrological system. Fall of water table and decrease of groundwater chemical quality cause secondary soil salinity, surface water salinity and reduction of soil fertility in arid and semi-arid regions. These phenomena, which salted soil and water resources, are effective factors of desertification in the world. Thus, spatial monitoring of groundwater chemical quality at the time of climatic extremes is necessary for stable management and planning water and soil resources in the area of exposed to salinity hazard. Continued and intense droughts occurred in Iran and Tabriz plain in past years (1998-2008). The impacts of droughts make dry surface water resources and bring down water table strongly. In Tabriz plain, Farmers used surface waters of Aji-chai, Komor-chai and snikh-chai rivers. Also, they used groundwater of plain. In drought periods, that precipitation declines and groundwater level falls, high exploitation of groundwater resources change chemical quality waters. Low quality waters aren’t suitable for agriculture. Also, salt waters cause secondary soil salinity in plain. Therefore, the aims of this research are determination of drought and wet periods in Tabriz plain by SPI index and spatial monitoring of chemical quality groundwater in the study years in Tabriz plain. Tabriz plain is located at the east of Urmia lake. Its west limit is salty swamps of Urmia lake margins. Moro Mountain is located in the north of Tabriz plain and Sahand Mountain is the south limit of Tabriz plain. The Onebne-ali elevations are forming the east limit of Tabriz plain. Aji-chai River is flowing in Tabriz plain toward Urmia Lake. Other rivers such as Saeedabad-chai, Mehranrud-chai and Gomanab-chai are joining to Aji-chai River. There are two types of aquifers in Tabriz plain (Confined aquifer and unconfined aquifer). Unconfined aquifer located in east, northeast and southeast of the study plain. There are confined aquifer and unconfined aquifer in parts of west. Unconfined aquifer into plio-pleistocene tuffs has high quality waters and located in North Slope of Sahand Mountain. The plio-pleistocene tuff is composed of red and green andesitic tuff admixed with large quantities of blocks, gravel and sand of volcanic and alluvial origin. Also, unconfined aquifer into alluvial tuff is the most important aquifer in the area has been known for many years as a good aquifer.