Abstract
A detailed investigation was carried out to evaluate long-term groundwater level fluctuation in regular monitoring wells constructed by the Ministry of Water Resources in Barka, Sultanate of Oman. For this study, groundwater level data for 71 wells and rainfall data from six stations were collected from 1984 to 2003 and analysed. Based on long-term water level fluctuation, groundwater wells are classified into three groups. In group 1, water level shows a long-term cyclic trend without yearly fluctuation whereas in group 2 the water level declined continuously until 1995 followed by a constant water level. In group 3, water level decreases continuously throughout the study periods with rapid annual cyclic variation. Group 1 wells show high water-level fluctuations (5 to 10 m) and seem to be regulated by discharge (lateral flow) from this aquifer and recharge from the adjacent Jabal Akhdar mountainous region. Constant trend in water level after 1995 in group 2 wells illustrates the advancement of saline-fresh water interface to the inland due to heavy pumping which is justified by higher electrical conductivity and CI/HCO3 ratio. In group 3 wells, the water level dropped continuously due to overabstraction by agricultural farms and human settlements. In addition, wells existing near the recharge dams express the influences of recharge dams and rainfall, and exhibit high water-level fluctuations during heavy rainfall periods. The long-term regional variation indicates that water level drops continuously in the coastal and central parts of the study region. Linear regression analysis revealed that the decline in water level is 0.3-0.4 In year(-1) near the coastal and central parts of the study area and is almost constant in the remaining area. We conclude that the contribution of man-made activities on groundwater level is well compared with natural factors. Copyright (c) 2007 John Wiley & Sons, Ltd.