عنوان مقاله [English]
Introduction: Groundwater aquifers are unignorable and important freshwater resources. In addition, they are very sensitive to contamination caused by the rapid infiltration of contaminated surface waters. Morover, Groundwater modeling has been proposed in the recent years as a powerful tool in management, optimization of consumption and forecasting of groundwater resources. In drought condition, groundwater resources play the most important role to compensate different water resources needs. Therefore, it is vital to study and pay attention to the issue of drought to prevent the intensification of damage and its negative conditions.
Material and Methods: The purpose of this study was to simulate groundwater level changes and investigate the effect of drought on groundwater quantity using MODFLOW code and SPI drought index in Bijar-Divandere plain located in Kurdistan province. To simulate the groundwater flow of the plain aquifer, the MODFLOW code from the codes in the GMS software was used. To investigate the observational and simulated level of groundwater in the study area, different data of 26 observation wells during statistical period of 6 years (October 2010 to June 2016) were used. Nevertheless, for drought investigation by standard rainfall index, meteorological data used were from year 1987 – 2015.
Results: The results showed that the north of the aquifer had hydraulic conductivity with values between 9 to 13 m/day. The lowest value belonged to the eastern part of the aquifer, which varies from 6 to 7.5 m/day. The central area of the aquifer also had values ranging from 7.5 to 9 m/day. In the simulation of groundwater for the steady state conditions according to the results obtained for RMSE = 0.8 m, MAE = 0.73 m and R2 = 0.999, the model was able to simulate the groundwater level values with suitable accuracy. For unstable state condition, based on the results of RMSE = 0.88 m, MAE = 0.85 m and R2 = 0.99, the model was able to perform simulation operations with appropriate accuracy as well. In general, the results indicated that the model was able to show, well groundwater level changes behavior in aquifer. Therefore, it can be used to implement management scenarios. The results showed that in the study area and during the period of investigation, severe drought did not occur and often the phenomenon of drought with intensity and extent was very low and close to normal. From the results of drought and the decrease of groundwater level in the same period, it can be concluded that in the aquifer under study, the decrease of groundwater level was not effective due to drought.
Conclusions: According to the findings of this study, it can be concluded that: there was no severe drought and most of the drought phenomenon was very low in intensity and limits and close to normal; in Bijar-Divandarreh plain of Kurdistan province, the decrease of groundwater level was not effective due to drought, but also the other factors such as harvesting increase, climate change and the area under cultivation increase could play a role; during of the annual simulation period, a decrease of 0.5 m in the aquifer was occurred; The volume of Bijar-Divandere plain aquifer was reduced by about 1.1 mm3 annually; Different management solutions, such as installing volumetric meters on existing and active wells, blocking unauthorized wells, and other management strategies such as artificially feeding in suitable areas and change of cultivation pattern are necessary to be able for preventing of groundwater draw down.