TY - JOUR ID - 68025 TI - Comparison of Temporal and Spatial Changes of Groundwater Level in Isfahan-Borkhar, Najafabad and Chadegan Plains JO - Physical Geography Research JA - JPHGR LA - en SN - 2008-630X AU - Ghafari, Sedigheh AU - Moradi, Hamidreza AU - Modares, Reza AD - MSc. Student in Watershed Management Engineering, Faculty of Natural Resources and Marine Science, Tarbiat Modares University, Iran AD - Associate Professor of Watershed Management Engineering, Faculty of Natural Resource and Marine Science, Tarbiat Modares University, Iran AD - Assistant Professor of Watershed Management Engineering, Faculty of Natural Resource, Isfahan University of Technology, Iran Y1 - 2018 PY - 2018 VL - 50 IS - 1 SP - 141 EP - 160 KW - Groundwater level KW - aquifer hydrograph KW - zoning KW - Mann-Kendall KW - Sen's slope Estimator DO - 10.22059/jphgr.2018.226430.1006999 N2 - Introduction Isfahan province is one of the driest provinces in central part of the country where two-thirds of its water requirement is supplied by groundwater resources. In recent years, with population growth and the increase of water demand in different sectors of agriculture, industry, drinking, and health, groundwater resources have faced a lot of pressure. Thus, understanding the behavior of the groundwater body and its long term trends are essential for making any management decision in the areas. Mann–Kendall statistical test has been commonly used in many researches to assess the significance of trends in hydro-meteorological time series. Geostatistical analysis has been theoretically defined and applied by many researchers and they have emphasized that geostatistics is a management and decision support system tool for analyzing spatial and temporal variations of groundwater level fluctuations. Geostatistical approaches can provide more helpful, reliable and efficient tools to increase the number of measurement points at un-sampled locations, and variogram analyses for examining structural relationship of data (Rakhmatullaev et al. 2011).   Materials and Methods In this study, the temporal and spatial variations of groundwater level for Isfahan-Borkhar, Najafabad and Chadegan plains, is investigated with a 25 years period (1990-2015). Monthly water level data have been collected from 29, 40 and 8 observation wells in Isfahan-Borkhar, during the study period. Precipitation data from synoptic, climatology and rain gauge stations were used in this research. The trend analyses have been conducted at monthly, seasonal and annual scales using Mann-Kendall Test and Sen's slope estimator nonparametric methods by MATLAB.AB 7.11 software. The Mann-Kendall test is a non-parametric method used for trend analysis of time series data. In this method, the presence of a statistically significant trend evaluated using Z value (equation 1).   (1) A positive value of Z indicates an increasing trend and a negative value indicates decreasing trend. In this research, the null hypothesis (H0) stated that “there is no trend in time series of groundwater levels”. The hypothesis is rejected if the absolute value of Z is greater than ±1.96 and ±2.58 in 5% and 1% level of significance, respectively. If the value of Z is out of this range, the null hypothesis is accepted and there isn’t any trend in time series (Yin et al. 2015). For investigation of the relationship between groundwater level depletion and rainfall for each of plain, the linear regression was done in annual scale. The groundwater level hydrograph was drawn also for each of plain during 25 years (January 1990 to October 2015). Prior to the geostatistical estimation, it requires a model to compute a semivariogram for any possible sampling interval. The experimental semivariograms were fitted with various theoretical models like spherical, exponential, Gaussian, linear and power in GS+ software. The underground water level zoning maps were prepared by Ordinary Kriging method for every year of the study period. Spatial zoning maps were prepared and ultimately, an iso-falling map was created at the beginning and end of the study in ArcGIS 10. Results and Discussion The spatial distribution of trend by the Mann-Kendal test for annual groundwater level data indicated a general trend in all plains where most piezometers groundwater level is negative. The piezometer wells with positive trend were very low and the most positive trend is related to Isfahan plain. In Chadegan plain there wasn’t any positive trend in piezometers level. The investigation of trend line slopes revealed that in average, the groundwater level of Isfahan-Borkhar, has been decreased about 0.468, 1.12, 0.638 m y-1. The general trend of the groundwater level hydrograph shows that the level and storage of water is continuously decreased in the last years.   Gaussian variogram model was the best for spatial structure of these data. Generally, the spatial pattern of zoning groundwater maps indicated that direction of groundwater flow is northwest to southeast on all study plains. As well as, the iso-falling map showed that groundwater level has dropped in most parts of the plains during the study period. This was in agreement with the results of the research by Rahmati et al. 2014, Azareh et al, 2014, and De Brito Neto et al. 2016. The cause of this agreement could be a vulnerability of arid region ecosystems into human interference and other stress factors. Conclusion Due to the lack of rainfall trend in most of the stations in the study area and low correlation between rainfall and groundwater level change, the major cause of reduced groundwater could be related to human factors. Overexploitation, as a result of population growth, and increasing number of wells are the most important factors in decreasing of the groundwater table. Therefore, the decision is required to manage groundwater in the study area. It is necessary to immediately practice water conservation methods and water harvesting systems in the study area to prevent the causes of more damages to the available water resource. UR - https://jphgr.ut.ac.ir/article_68025.html L1 - https://jphgr.ut.ac.ir/article_68025_be9c433eb01db73013c2e023b9e7af62.pdf ER -