پديد آورندگان :
سيف، عبداله نويسنده استاديار دانشكده جغرافيا ، دانشگاه اصفهان , , جعفري اقدم ، مريم نويسنده دانشجوي دكتراي ژيومورفولوژي، دانشگاه اصفهان , , جهانفر ، علي نويسنده دانشجوي دكتراي ژيومورفولوژي ، دانشگاه تربيت معلم سبزوار ,
چكيده لاتين :
Introduction
Protection of karst water resources, due to their high vulnerability and susceptibility to contamination is one of the most important activities in the karst water resources management. Geographical researches on the groundwater pollutions focus on two categories, including distance from pollution and contaminants sources. Accordingly, the European Commission presented the COST Action 620 approach in order to assess vulnerability and taking the map of karst water resources risks. The Golin karstic aquifer due to the presence of limestone formations, past and present climate conditions and tectonic and geomorphologic characteristics of karst, has valuable groundwater resources. The Golin Mirage has average discharge of 545 liters per second and its annual output volume is 17.187 million cubic meters. This mirage is the main source of drinking and agricultural waters for all villages of Deireh rural district of Gilangharb city and the rest water is reserved in the Zagros reservoir dam for drinking and agriculture. Therefore, it seems essential and important to evaluate vulnerability and present management solutions in order to preserve the Golin karstic aquifer from contamination. The purpose of this research is to utilize the COP model using geographical information system as an effective method for evaluation of contamination risk of the karst water resources and finally taking the vulnerability maps of Golin karstic aquifer and recognition of the type of karstic system of the study aquifer.
Methodology
In this study, on the basis of the field studies, at the first, the aquifer realm was determined, then using the geohydrologic parameters, ? coefficient, the death time of spring, dynamic storage volume, type of aquifer karst system were specified. In order to determine the type of karstic system of the aquifer, the quantitative models and monthly discharge data over the course of 12 years were used. The vulnerability as a result of three factors of C, O, and P is evaluated in the COP model. In this method (O) is covering layer, (C) is current density, and (P) is the precipitation regime. The O factor is the description of groundwater protection by upper layers of saturated zone. The C factor is calculated based on the karst geomorphology, vegetation and topographic gradient. The P factor includes the amount of precipitation and its temporal distribution (intensity) and determines the water power for transport of contaminants from surface into aquifers.
Results and discussion
According to geohydrologic parameters, the Golin spring is an artesian system. Golin spring ? coefficient is mild (i.e. 0.002), which shows that the aquifer system is artesian. Dynamic storage volume is high, indicating lesser development of karst in the study region. The displacement (motion) of the water in the aquifer is very slow due to low development of karst channels. The death time of the Golin spring is indicative of low sensitivity of the spring to precipitation fluctuations. In the case of precipitation stopping the spring death occurs after 361 days, which is due to low development of karst channels. Therefore it can be concluded that the karst of the aquifer is less developed, which in turn caused to reducing the penetration amount and diffusion velocity of contaminants and therefore reduced the vulnerability of the Golin karstic aquifers. The results of the COP model also show that the karst geomorphology, topography gradient and vegetation have the greatest impact on the amount of C factor. 65% of the region has high and moderate vulnerability risk and just 8% of the region has very low vulnerability risk, indicating that the region is being vulnerable in terms of the propagation of contamination in karst water resources. In the map of the O factor, the thickness of formations, lithologhy of formations and soils have the most important role, respectively. The area entirely located in a zone with very high and high vulnerability risk due to the expansion of the limestone formations and Quaternary deposits. Likewise, the results of zoning of the P factor range from 0.7 to 0.9 and the widest extent belong to the area with low vulnerability, and the area with moderate vulnerability risk just located in the highest parts of the study region.
After calculating of C, O, and P factors and mapping their vulnerability, the final vulnerability map of the region is plotted. The vulnerability values of the region were between 1 and 6.12, which finally they were classified into three levels, including very low, low and medium.
Conclusions
Geohydrologic indices were shown that the Golin aquifer is artesian type. The low development of karst channels is the characteristic of this system. In the artesian system the penetration amount and diffusion velocity are low, therefore they show lower vulnerability against contamination diffusion in relation to the systems with well developed karst channels. In order to assess and taking the vulnerability map of Golin karstic aquifer the COP model composed of three parameters of C, O, and P were used. After ranking into three factors and converting into raster layers, the amount of the COP index was calculated as 1 to 6.12 and the vulnerability was classified into three levels, including very low, low and medium. In the entire of the study region C, P and O have the greatest impact on the vulnerability of the region, respectively. Study of the obtained vulnerability map shows that the C factor plays the main role in the low vulnerability value in the study region, because of the low extent of the developed karstic zone, the large extent of non-karstic areas, and high topography gradient of the region. On the other hand, the precipitation is relatively low in the region, which in turn reduced the contamination penetration rate, and thereby reduced the vulnerability rate. The O factor map shows the high to very high vulnerability of the region, indicates the expansion of the permeable limestone, sandy-gravely formations in the region. The vulnerability of the O is modified by two other factors and the region has low to moderate vulnerability, totally. Finally, it could be mentioned that the COP model has a good efficiency for vulnerability assessment of the karstic aquifers.
