English abstract
Sharqiyah region is the third highest populated region in Oman (MNE, 2003), faced water shortage, as a result of over abstraction, continuing increases in water demands and drought periods. Groundwater is the main source of water supply in the region. Two major aquifers have been identified in the Ash Sharqiyah Sands also known as (Wahybah Sands); aeolianite (layer 1) and gravely alluvium (layer 2), with 100 m and 160 m saturated thickness, respectively. The regional groundwater flow is from northwest to the south-east towards the Arabian Sea. The average simulated groundwater velocities range between 1.07E-5 to 7.17E-6 (m/s). The groundwater quality in terms of it's electrical conductivity (EC) and total dissolved solids (TDS) deteriorates in the south direction.
Two wellfields were constructed in the Ash Sharqiyah Sands (Al Kamil/Al Wafi and Ja'alan) to supply the main towns in the region (Al Kamil, Al waif, Ja'alan Bani Bu Ali and Ja'alan Bani Bu Hassan), which have been incepted on March 2004. Regional groundwater flow model using (VISUAL MODFLOW) is applied in this study to understand the groundwater flow system, evaluate the environmental impact of the existing wellfields and advice on the future plans and management of the groundwater system in the Wadi al Batha Basin. The model area was divided into two layers; aeolianite (layer 1) and alluvium (layer 2). The calibrated steady state flow simulation shows good agreement between the calculated and observed heads in the model area. The unsteady state flow simulations were carried out for the ten years historical data flow simulation and future prediction. Two different scenarios were used to simulate the historical and future prediction. The first scenario the models were runs under assumption of no recharge, while the second scenario the mode were runs under assumption of recharge as subsurface inflow (0.32 Mm®/day). Different time intervals are assumed to calculate drawdown. These are 365, 1460, 2555, 3650, 5840, 9490 and 13140 days.
The maximum expected drawdown of the aeolianite aquifer will reach 9 m after 36 years near Ja'alan Bani Bu Ali, while the maximum expected drawdown of the alluvium aquifer will reach 20 m after the same period, under assumption of no recharge. The maximum expected drawdown of the aeolianite aquifer will reach 9 m after 36 years, while the expected drawdown of the alluvium aquifer will reach 15 m after 36 years, under assumption of recharge as subsurface inflow (0.32 Mm®/day). The negative values (-5 m) indicates water table rise may be due to upward groundwater movements from underlying layers near Fault 1 (discharge zone).
The area is showing water table fluctuation and decline with time even before the construction of the two wellfields, due to the expansion of demands and low groundwater recharge due to drought periods. The groundwater resources in the system indicates substantial storage and volumes for long period of time without undesirable environmental impacts or significant interference with the existing entitlements under assumption of recharge as subsurface inflow (0.32 Mmo/day).
