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Investigation of Coastal Geometry Effects on Freshwater Discharge to Saline Lakes

Asadi, Sara | 2016

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 48632 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Ataie-Ashtiani, Behzad
  7. Abstract:
  8. Groundwater is the most important freshwater resource in the coastal zones. There are some factors contaminate fresh groundwaters. Sea water intrusion (SWI) is one of the most important components of groundwater salinization. Also Submarine groundwater discharge (SGD) occurs when hydraulic gradient is from landside to seaside in coastal aquifers. There are many factors intensify SWI and SGD. In this research at the first part, coastline shape effect on SWI and SGD is investigated. For to this 4 different aquifers with different coastline shapes as stepped coastline, vertical coastline, steep slope coastline, and mild slope coastline are simulated with the same hydraulic parameters and aquifer length and thickness. Ferthermore two different hydraulic conductivity values and two landward boundary conditions as flux landward boundary condition and head landward boundary condition is considered in the simulations. The results show hydraulic conductivity value in landward part of the aquifer has considerable effect on SWI and SGD values. Hydraulic conductivity value in seaward part of the aquifer has not considerable effect on SWI however it has considerable effect on SGD which can not be ignored however it is not as much as hydraulic conductivity value effect in landward part of the aquifer. In addition in the cases with low hydraulic conductivity values, landward boundary condition has considerable effect on SGD and SWI. The results of these cases do not show considerable effect of coastline shape on SWI and SGD value although simplifying vertical coastline as step coastline understimates SWI and SGD values in aquifers with stepped coastline shape. Moreover these cases simulated with high seawater density values. The results show for the case with stepped coastline, seawater density has considerable effect on SGD value. In the second part to consider the effect of adjacent high density sea and seawater drop on SGD and SWI which is occurred in Urmia Lake of Iran, a new unconfined aquifer with adjact seawater with high density (1200 kg/m3) is simulated with graual sea level drop of 0.5 meters every year. The results showed considerable intrusion of seawater in aquifer with adjacent high density sea. In addition sea level drop implemented with coastline movement and without coastline movement in the simulations. The results show in the cases without coastline movement SGD increases as sea level drops gradually, however in the cases with coastline movement, SGD increases as sea level drops 0.5 m but after 0.5 m drop of sea level, as sea level drops gradually, SGD decreases because of the decrease of velocity vectors magnitude. In addition in the case of sea level drop with coastline movement, SGD value is one order of magnitude bigger than SGD value in the cases without coastline movement, because the most part of SGD in the cases with coastline movement discharges from dried aquifer bed which is ignored in the cases without coastline movement. These cases simulated for aquifers with two flux control and head control landward boundary conditions. SGD value variation was more considerable in the head control cases, because in the cases with flux control landward boundary condition, landward head of the aquifer decreases as sea level drops, which recovers the effect of sea level drop on hydraulic gradient
  9. Keywords:
  10. Seawater Intrusion ; SUTRA Numerical Model ; Numerical Modeling ; Hydraulic Conductivity Coefficent ; Sea Level Change ; Submarine Groundwater Dischange (SGD)

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