شبیه‌سازی پیشروی آب‌شور در آبخوان‌های ساحلی (مطالعه موردی: سواحل جنوبی دریای خزر)

نوع مقاله : مقالات پژوهشی

نویسندگان

1 دانشگاه صنعتی نوشیروانی بابل

2 دانشگاه تهران

چکیده

استخراج بیش از حد از آب‌های زیرزمینی می‌تواند منجر به کمبود آب شیرین، نفوذ آب‌شور به آبخوان‌های ساحلی و درنتیجه شوری بیش از حد آن‌ها شود. مدل‌های شبیه‌سازی آب زیرزمینی ابزاری مفید جهت شناخت رفتار سیستم آبخوان‌های ساحلی هستند. سواحل جنوبی دریای خزر یکی از مناطقی است که با معضل پیشروی آب‌شور به آبخوان‌های ساحلی روبرو است. به‌منظور شبیه‌سازی جریان آب زیرزمینی و پیشروی آب ‌شور در آبخوان ساحلی دریای خزر در منطقه ساری- نکا مدل‌های عددی MODFLOW، MT3DMS و SEAWAT در محیط نرم‌افزار GMS10.0 به کار گرفته شدند. پس از شبیه‌سازی برای ارزیابی مدل، واسنجی در مدل کمی برای تراز آب زیرزمینی و در مدل کیفی برای غلظت شوری به مدت 4 سال از مهر 1389 تا شهریور 1393 به‌صورت ماهانه انجام گرفت. مدل واسنجی شده با استفاده از اطلاعات در دسترس برای یک سال آینده از مهر 1393 تا شهریور 1394 برای تراز آب زیرزمینی و غلظت شوری صحت‌سنجی شد. نتایج پهنه‌بندی مکانی مدل حاکی از کیفیت مطلوب آب زیرزمینی در نواحی مرکزی و جنوبی آبخوان ساری-نکا بود. پس از صحت‌سنجی مدل و با فرض ثابت ماندن شرایط هیدروژئولوژیکی آبخوان، نتایج پیش‌بینی مدل برای نواحی با TDS بیشتر از 2000 میلی‌گرم بر لیتر برای 6 سال آینده بیانگر هجوم آب‌شور در مناطق شمالی آبخوان بود.

کلیدواژه‌ها


عنوان مقاله [English]

Aimulation of Seawater Intrusion in Coastal Aquifers (Case Study: the Southern Shores of the Caspian Sea)

نویسندگان [English]

  • M. Nasiri 1
  • M. Hamidi 1
  • H. Kardan Moghaddam 2
1 Babol
2 University of Tehran
چکیده [English]

Introduction: The issue of seawater intrusion has become an environmental problem considering the increasing trend in groundwater extraction from coastal aquifers. Increased groundwater exploitation and lack of coastal aquifers management have caused seawater intrusion into coastal aquifer. The intrusion has led to the salinization of aquifers, causing many problems in the exploitation of water resources. This pumping has continually increased the risk of seawater intrusion and deterioration of freshwater quality in the sari-Neka aquifer. Seawater intrusion limits the usage of groundwater for agriculture, industry, and public water supply.
Materials and Methods: For the present study, Sari-Neka aquifer was selected. The study area is located in the southern shores of the Caspian Sea, in the northern part of Iran. The MODFLOW version 2000 is used to simulate a steady-state and transient groundwater flow system in Sari-Neka aquifer. To simulate solute transport, MT3DMS and SEAWAT are used. In MT3DMS, advection package, dispersion, and source/sink mixing packages are used. The numerical code MT3DMS does not consider the effect the density. Thus, SEAWAT­-­Variable Density Flow package was initialized. The necessary data for modeling of groundwater flow can be categorized into water resources data, meteorological data, hydrodynamic characterization, topography map, and geological information. To build the flow model, flow type (steady-state and transient state), initial conditions (groundwater level in September 2010 for the steady-state) and type of boundary conditions (general head boundary), flow package (LPF package), ‌temporal discretization (48 monthly stress periods from September 2010 to August 2014 in transient condition) and monthly time steps were assigned to the model. To prepare the flow and transport model grid, the study area was discredited horizontally into 3694 active square cells (500×500 m). The MT3DMS model was used to simulate the qualitative changes on the aquifer surface and the SEAWAT model to simulate the depth of the aquifer. Therefore, the conceptual model of solute transport was prepared by making the necessary changes in the conceptual flow model. September 2010 groundwater level data and TDS and Cl data are taken as the initial conditions in the flow and transport model, respectively. The Caspian Sea bordering the study area in the north is represented by a constant TDS concentration of 35000 mg/l and constant CL282.2 meq/l. In this model, we entered the water heads of the observation wells, hydraulic conductivity, storage coefficient, effective porosity, aquifer discharge, and aquifer recharge, porosity, Coefficient of molecular water diffusion, Longitudinal dispersivity, Horizontal transverse dispersivity, vertical transverse dispersivity.
Results and Discussion: The calibration of the flow model was carried out for both steady and transient conditions using the trial and error approach. Monthly groundwater levels of data from 14 observation wells were used for calibration purposes. Steady-state calibration for the flow model was performed by comparing the observed groundwater levels and calculated values of groundwater levels in September 2010. During calibration, hydraulic conductivity values were adjusted, until groundwater level values calculated by MODFLOW were matched the observed values within an acceptable level of accuracy (±1m). After steady-state calibration, the transient model was simulated for the four year period between September 2010 and August 2014 that was divided into 48 stress periods with monthly time steps. At the end of flow model calibration, the resulting hydraulic conductivity ranged from 5.3 to 21. 6 m/day, while the resulting specific yield values were from %3.4 to % 5.9. The validation flow model was simulated for the period between September 2010 and August 2014 (12 stress periods). The values of the correlation coefficient in the steady-state model, transient model and validation model in the flow model were obtained 0.99, 0.98, and 0.97, respectively. The results illustrate a good agreement between the observed and calculated groundwater levels. The transport model was calibrated using TDS and CL concentration data from September 2010 to August 2014 (8 stress periods) by adjusting parameters affecting the dispersion process. To confirm the accuracy of the model, TDS and CL concentration data from August 2014 to September 2015 were used for validation purposes. By considering the TDS and Cl concentration in September 2010 as the initial condition, the transient model was run. Transport model calibration was achieved through a trial-and-error. The values of the correlation coefficient in the transport model for TDS are obtained 0.83 and 0.87 in the transient model and validation model, respectively. The values of the correlation coefficient in the transport model for CL were obtained 0.82 and 0.86 in the transient model and validation model, respectively.
Conclusion: After the validation of transport model and assuming all the hydrogeologic conditions remain, a predictive 6-year simulation run using SEAWAT model indicates that further seawater intrusion into the coastal aquifers can occur in the study area.

کلیدواژه‌ها [English]

  • Coastal aquifer
  • Seawater intrusion
  • Salt concentration
  • , Sari-Neka aquifer
1- Abedi Koupai J., Golabchian M. 2015. Estimation of Hydrodynamic Parameters of Groundwater Resources in Kouhpayeh- Segzi Watershed Using MODFLOW. Journal of Water and Soil Science 19(72): 281-293. (In Persian with English abstract)
2- Anderson M.P., and Cherry J.A. 1979. Using models to simulate the movement of contaminants through groundwater flow systems. Critical Reviews in Environmental Science and Technology 9(2): 97-156.‏
3- Benjakul R. 2010. Simulating dioxane transport in a heterogeneous glacial aquifer system (Washtenaw County, Michigan) using publicly available models and data.‏
4- Cheng Jian M., and Chong Chen X. 2001. Three‐Dimensional Modeling of Density‐ Dependent Salt Water Intrusion in Multilayered Coastal Aquifers in Jahe River Baisn, Shandong Province, China. Groundwater 39(1): 137-143.
5- Chitrakar P., and Sana A. 2015. Groundwater flow and solute transport simulation in Eastern Al Batinah coastal plain, Oman: Case study. Journal of Hydrologic Engineering 21(2): 05015020.
6- Cobaner M., Yurtal R., Dogan A., and Motz L.H. 2012. Three dimensional simulation of seawater intrusion in coastal aquifers: A case study in the Goksu Deltaic Plain. Journal of Hydrology 464: 262-280.
7- Fathi Zaad A., Shahnazari A., Ziatabar Ahmadi M., and Fazloula R. 2017. Investigating of saltwater intrusion in Talar area using the numerical model SHARP‌. 6th National Symposium on Sustainable Agriculture and Natural Resources, Tehran. (In Persian)
8- Guo W., and Langevin C.D. 2002. User's guide to SEAWAT; a computer program for simulation of three-dimensional variable-density ground-water flow (No. 06-A7).
9- GuvanasenV., Wade S.C., and Barcelo M.D. 2000. Simulation of regional ground water flow and salt water intrusion in Hernando County, Florida. Groundwater 38(5): 772-783.
10- Hamidi M., and SabbaghYazdi S.R. 2006. Numerical modeling of seawater intrusion in coastal aquifer using finite volume unstructured mesh method. WSEAS Transactions on Mathematics 5(6): 648.
11- Harbaugh A.W., Banta E.R., Hill M.C., and McDonald M.G. 2000. MODFLOW-2000, the U.S. Geological Survey Modular Ground-Water Model-User Guide to Modularization Concepts and the Ground-Water Flow Process. Open-file Report. U. S. Geological Survey (92): 134.
12- Jabari P., Ghanbarpour M., and Ashbeh A. 2009. Evaluation and determination of groundwater balance in Sari-Neka unconfined Plain. 5th National Conference on Watershed Management Sciences and Engineering of Iran, Karaj. (In Persian)
13- Kardan Moghadam H., and Banihabib M.E. 2017. Investigation of Interference of Salt water in Desert Aquifers (Case study: South Khorasan, Sarayan Aquifer). Journal of Water and Soil 31(3): 673-688. (In Persian with English abstract)
14- Kentel E., Gill H., Aral M.M. 2005. Evaluation of groundwater resources potential of Savannah Georgia region, Multimedia Environmental Simulations Laboratory, Report No. MESL-01-05.
15- Ketabchi H., Mahmoodzadeh D., and Ataie-Ashtiani B. 2014. Effects of climate change on saltwater intrusion in sloping coastal aquifers. 13‌th Iranian Hydraulic Conference, University of Tabriz, Tabriz. (In Persian)
16- Kumar C.P. 2006. Management of groundwater in salt water ingress coastal aquifers. Groundwater Modelling and Management 540-560.
17- Langevin C.D., Shoemaker W.B., and Guo W. 2003. MODFLOW-2000, the US Geological Survey Modular Ground-Water Model-Documentation of the SEAWAT-2000 Version with the Variable-Density Flow Process (VDF) and the Integrated MT3DMS Transport Process (IMT) (No. 2003-426).
18- Ministry of Energy, Regional Water Company of Mazandaran, Report of the water resources Balance of the study area sari-neka (code 1503), Tehran Water and Soil Consulting Engineers, 2014. (In Persian)
19- Narayan K. A., Schleeberger C., and Bristow K. L. 2007. Modelling seawater intrusion in the Burdekin Delta irrigation area, North Queensland, Australia. Agricultural Water Mnagment 89(3): 217-228.
20- Nobi N., and Das Gupta A. 1997. Simulation of regional flow and salinity intrusion in an integrated stream‐aquifer system in coastal region: Southwest region of Bangladesh.
21- Nazari R., and Joodavi A. 1979. Applied flow and contaminant transport modeling in aquifers. (In Persian)
22- Reza pour A., and Saghravani F. 2016. Numerical study of saltwater intrusion in condition of Water table drawdown. The 1st National Conference on Environment, Energy and Biodefense, Tehran. (In Persian)
23- Rouve G., and Stoessinger W. 1980. Simulation of the transient position of the saltwater intrusion in the coastal aquifer near Madras coast. Finite Elements in Water Resources 1.
24- Sherif Mohsen M., Vijay Singh P., and Abdelwahab Amer M. 1988. A two-dimensional finite element model for dispersion (2D-FED) in coastal aquifers. Journal of Hydrology 103.1-2: 11-36.
25- Stein S., Yechieli Y., Shalev E., Kasher R., and Sivan O. 2019. The effect of pumping saline groundwater for desalination on the fresh–saline water interface dynamics. Water Research 156: 46-57.
26- Vafaei F., and Abolghasemi H. 2013. Investigating the change of sea level and groundwater level on seawater intrusion in unconfined aquifers. The 1st National Conference on Environment, Energy and Biodefense, Tehran. (In Persian)
27- Willis R., and Brad Finney A. 1988. Planning model for optimal control of saltwater intrusion. Journal of Water Resources Planning and Management 114.2: 163-178.
28- Zheng C., and Bennett G.D. 2002. Applied contaminant transport modeling (Vol. 2, p. 353). New York: Wiley-Interscience
29- Zheng C., and Wang P.P. 1999. MT3DMS: a modular three-dimensional multispecies transport model for simulation of advection, dispersion, and chemical reactions of contaminants in groundwater systems; documentation and user's guide. Alabama Univ University.