تقييم الحقل الاصطناعي منطقة حوض (بلاي ؟بليوستوسين) حالة دراسية: العوجا
Evaluation of Potential Artificial Recharge of the Shallow Plio-Plistiocen Aquifer System / Case Study Al-Auja
كيان صبري رشاد مناصره
kayan sabri rashad manasra
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Al Uja area locates in the Lower Jordan Valley/West Bank, which is a part of shallow lower eastern aquifer located at an elevation of -220 m in the west to -280 m ( b.s.l). The availability of ground water, fertile soil, and warm climate during winter months make it remarkable for its agricultural activities where 600 hectares are under irrigation. There are two sources of water available at Al Uja area ; these are Al Uja Karstic spring that drain water from the Mountain carbonate aquifer system with a discharge rate between 0.5 and 8 MCM/a , and nine groundwater boreholes that tape water from the shallow PlioPlistocene aquifer system, with an annual abstraction of 0.7 MCM/a . The south-north fault system of the Jordan Rift Valley separates the two aquifer system. The shallow aquifer system locates to the east of the fault, where the Mountain aquifer system locates to the west. The Mountain aquifer consists of high fractured and karstified limestone and dolomite of Upper Cretaceous age, and the shallow aquifer system consists of gravel, sand, silt, and clay layers of the Dead Sea group. Groundwater flows from the Mountain aquifer in the west to the Shallow aquifer in the east through the major fault system. 15% of the Al Uja spring discharge infiltrated into the Upper Mountain aquifer system and indirect to the shallow system. The permeability of the Mountain carbonate layers is 2.49*10-1 m/min and decrease to 1.6*10 -2 m/min in the layers of the Shallow aquifer system, this decrease of Kf-value east wards cause a semi-barrier for groundwater flow regime, also water salinity increase from 1500 µS/cm in Mountain aquifer to 3000 few hundred m to the east of the fault and rise to 6000 µS/cm in the eastern part. Lowering of water table and increasing salinity in addition to the presence of water pollution are major obstacles facing the economical development of this region. Due to the iv limitation of natural recharge, and over pumping from shallow aquifer system, water salinity increase and caused a major shift in cropping pattern during the last 30 years, where more salinity tolerance vegetables and trees are becoming dominant crops. The main goal of this study is to investigated and estimated different artificial recharge technique at the area, which are infiltration surface pond, and borehole direct injection. The surface pond consists of soft material of Lisan formation that consists of 22% sand, 23% clay, and 45 % silt. The geo-electrical investigations inside the pond show that the wet front reach a depth of 2.5 m depth after 3 days and the infiltrated water velocity is about 9.6 * 10-4 cm/s. according to this infiltrated water can reach the groundwater table after 50 days of filtration. Different volumes of water were injected in the selected borehole, the static water table raised from 37 m to 34 meter below the ground after five min from the injection. After one and half hour the static water table fall to the original static level after stop the injection. The groundwater salinity of the borehole was decreased from 6000µS/cm to less than 550 µS/cm. The decrease of Ec –value through the well after injection test was cause of the Calcite precipitation. Our investigation recommended Borehole injection method is the best option for direct artificial recharge in Al Uja area within the boundary of the Plio-Plistocene shallow aquifer system and possible to use the available nine boreholes as injection boreholes. And artificial recharge using surface infiltration pond is not recommended.