2016 AWRA Annual Conference 13 17 November 2016, Orlando Florida Mitigation of Seawater Intrusion using Subsurface Intakes of Desalination Plants Mohsen Sherif 1, Akbar Javadi 2, Ampar Shetty 1 1, UAE University, Al Ain, United Arab Emirates 2 Department of Engineering, UAE University, University of Exeter, UK
Introduction Coastal aquifers and water resources in arid regions Seawater intrusion: A natural or manmade process? Natural Parameters Type of the aquifer Geometry of the aquifer Rainfall and natural recharge Soil characteristics and natural parameters Geological and boundary conditions Manmade Parameters Pumping and artificial recharge Land use and agriculture practices Hydraulic and physical barriers Modeling of seawater intrusion problems Sharp interface versus dispersion zone approaches Steady versus transient flow and solute transport
Desalination of Seawater - intakes, water treatment, and disposal of concentrates Intakes of Desalination Plants Surface/Direct Intakes: Long- large diameter concrete pipes extending above the seafloor Extensive pre-treatment of the water due to the presence of marine life and other substances Unlimited capacity, identified by the size of intake pipes and pumps Subsurface/Indirect Intakes Collect brackish/saline water from aquifer systems underneath the seafloor or beach wells Semi-horizontal pipes below the seafloor or series of large diameter wells Limited capacity depending on the geological formation
SUTRA Argus-One Idealized study domain Width = 2 km Hydraulic parameters Boundary conditions Seawater density= 1025 kg/m 3 11815 quad element 12044 nodes 4 days of simulation Equipotential lines adjust in a short period of time 2 months of simulation Steady State conditions
Hypothetical Case: Unsteady SUTRA Simulations Equi-concentration lines at different simulations periods 4 days of simulation Rapid change at the early simulation time 1 year of simulation Consistency between potential and concentration lines 10 years of simulation Consistency between different models Steady state
Lowering the Piezometric head at the land side to 5 m 5 m Major changes in the equipotential lines Quick adjustment in the equipotential lines Additional intrusion of 320 m
Effect of Pumping of Fresh Water Pumping of 30,000 m 3 /d (0.347 m 3 /s) Additional intrusion of 450 m Steady no further intrusion 1km 1km 160 m 40 m Pumping of 40,000 m 3 /d (0.462 m 3 /s) Local drawdown near pumping field Steady state equipotential After 10 years of simulation After 20 years of simulation Steady state conditions
Continue to pump 40,000 m 3 /d of fresh water in addition to Pumping of 15000 m 3 /d of saline water Steady state simulation Two separate flow fields Retardation of seawater Effect of Subsurface Intakes of Desalination Plants 150 m 50 m 500m 500m
Conclusions - SUTRA provided very good results for the variable density groundwater flow and solute transport - Indirect intakes via vertical beach wells represent a viable solution to reduce the cost of desalination and mitigate the seawater intrusion problem - The geological and hydrogeological conditions play a vital role in the determination of the proper location of the intakes.