Groundwater Qualitative Vulnerability Assessment Using Fuzzy Logic, Case Study: Zayanderood River Basin Aquifers
Nowadays, regarding to growth of technology, human communities development and extension of industrial activities and the great ration of these affairs in environmental pollution, the attention to the environmental problems of water resources have increased and these concerns and attentions have become multiple by decreasing of healthy water resources in recent years. Among present water resources, due to less pollution susceptibility and also higher storage capacity in comparison with surface water, groundwater is considered as an important water resource to supply human water requirements. But realizing and control of pollution and also removal of pollution from this resource are very difficult and expensive. So the vulnerable zones must be detected and then must be prevented from being contaminated.
One of the commonest methods in order to evaluate the groundwater contamination is DRASTIC method. This method that is applied in this thesis is based on seven parameters that describe hydrogeological settings. In this method each parameter is assigned a rating and then these ratings are multiplied by the weights assigned to each parameter based on its importance and after combining with each other, the vulnerability index is obtained. But in DRASTIC method, the Boolean Logic is used to > This thesis is implemented on Zayanderood river basin aquifers and at last the vulnerability map was provided. This map generally showed that the areas located in the west of the basin in all the cases are of maximum pollution potential and after that, the areas located in the east of the basin are of considerable pollution potential as well. Meanwhile the central areas of the basin in all the cases are of too low pollution potential. The results of single parameter sensitivity analysis showed that the effective weight of net recharge decreases from west to east, and generally the effective weight of maximum net recharge is more adjustable with its theoretical weight. This point emphasizes on the application of this case in order to calculate the f-DRASTIC (DRASTIC modified by Fuzzy logic) vulnerability index. Also, the results of map removal sensitivity analysis showed that with removal of minimum net recharge layer, the most extent of the basin has a little variation in the vulnerability index, as seen in the mean net recharge case. But in the maximum net recharge case, opposite to two previous cases, the west of the basin has a large variation and the east of the basin is of moderate variation and the center of the basin lacks any variation. Then the SI method applied in order to assess specific vulnerability was used and compared with f-DRASTIC model. The results showed that in SI model, vulnerability is of less intensity but in terms of vulnerability mapping, these models are almost adjustable.
Key Words: Groundwater, Vulnerability, Sensitivity Analysis, DRASTIC Method, Fuzzy Logic