GROUND WATER MODELING OF NELLORE COASTAL ZONE

International Journal of Civil, Structural, Environmental and Infrastructure Engineering Research and Development (IJCSEIERD) ISSN(P): 2249-6866; ISSN(E): 2249-7978 Vol. 4, Issue 1, Feb 2014, 101-110 © TJPRC Pvt. Ltd.

GROUND WATER MODELING OF NELLORE COASTAL ZONE 1

2

M. MOHAN BABU , G. K. VISWANADH & V. VARALAKSHMI

3

1

Department of Civil Engineering, Sri Venkateswara College of Engineering & Technology(Autonomous) (SVCET), Chittoor, Andhra Pradesh, India

2

Professor, Department of Civil Engineering, JNTUH College of Engineering Hyderabad (Autonomous), Hyderabad, Andhra Pradesh, India

3

Associate Professor & HOD, Department of Civil Engineering, Marri Laxman Reddy Institute of Technology & Management, Dundigal Village, Quthbullapur, Hyderabad, Andhra Pradesh, India

ABSTRACT Groundwater model is regarded as the best tool to conceptualise the hydro geological situation in the groundwater basin and to predict the potential environment and socioeconomic impacts of the groundwater abstractions. Rise in sea level due to the climate change accelerates the saltwater intrusion into the aquifer and maintain the same depth to water level consequently reducing the quality of water. This phenomenon is observed in the sea coast of Nellore district which 0

0

0

0

situated between the 14 10’ to 14 50’ of North latitude and 80 00’ to 78 10’ of East longitude covering an area of 1530 km2 from the ground water flow model it is observed that the annual recharge of the study area is 435.04 MCM and river leakage is 7.22 MCM. From the total input, 12% (i.e, 52.20MCM) is gone through evaporation loses from surface and ground water bodies and 50% of water is extracted from ground in the form of pumping (i.e,194.85 MCM) and the remaining 28% (i.e, 131.18 MCM) is due to the river leakage and saltwater intrusion in the study area.

KEYWORDS: Groundwater Model, Visual MODFLOW, Pumping INTRODUCTION Groundwater is one of the earth’s most broadly distributed and most imperative natural resources for municipal, agricultural, industrial development and environmental aspects. In analysing groundwater system, consideration must be given to the effective groundwater withdrawals on fluctuation of water levels in the nearby wells or in a wetland. Groundwater model is regarded as the best tool to conceptualise the hydro geological situation in the groundwater basin and to predict the potential environment and socioeconomic impacts of the groundwater abstractions. Rise in sea level due to the climate change accelerates the saltwater intrusion into the aquifer which reduces the fresh groundwater resources. With the impact of sea level rise and over pumping combined together the problem becomes even more serious and requires fast solutions. It is est imated that the mean sea level will rise in the r ange of 20 to 88 cm during the current century (IPCC 2001). The rise in sea level will shift the saltwater interface further landwards. As a result, the extraction wells that were originally in fresh groundwater may then be located in brackish water or saline water and up coning may occur. Consequently, the abstraction rates of these wells may have to be reduced or the wells abandoned. This is considered one of the most serious effects of sea level rise. The objective of the present work is to find the aquifer parameters by developing a transient groundwater flow model in Visual MODFLOW and to pr edict the groundwater head for future years in the five mandals of Nellore district situated at sea coast. The area chosen for aquifer modeling consist of five mandals of Nellore district lies in the 14

0

10’ to 14 14050’ of

North latitude and 80 0 00’ to 78 010’ of East East longitude covering an area of 1530 km 2 Figure 1. The drainage pattern is

102

M. Mohan Babu, G. K. Viswanadh & V. Varalakshmi Varalakshmi

dentric to sub-dentric and trellis. The terrain is flat to gently undulating except for few. The study area consist the command area. Major part of study area mainly underlain by dharwar super group, peninsular gneissic complex that includes a variety of granite gneisses, schists intruded by basic dykes. The alluvium of fluvial origin comprises sand, silt and clay in various proportions occur along the banks of pennar extending Allur to Muthukur mandals. The thickness of alluvium varies from 50-150m. The ground water occurs in consolidated to unconsolidated formations. In consolidated formation ground water occur in weathered (4-6m) and fractured zones (6-18m) with li mited yields (1-2lps).

Figure 1: Location Map of the Study Area

LITERATURE REVIEW MODFLOW (Modular Three Dimensional Finite-Difference Ground water Flow Model) is the name that has been given to the United State Geological Survey (USGS) Modular Three-Dimensional ground water flow flo w model which assumes that aquifers consist of porous media only [McDonald and Harbaugh, 1988]. Because of its ability to simulate a wide variety of systems, its extensive publicity, available documentation, and its rigorous USGS peer review, MODFLOW has became the worldwide standard ground water flow model. MODFLOW is used to simulate systems for water supply, containment remediation and mine dewatering. When properly applied, MODFLOW is the recognized standard ground water model (Kumar, 1992; Pollock, 1994; Anderman and Hill, 1997; Restrepo et al., 1998; Hill et al., 2000; Konikow, 2001; Merritt and Konikow, 2000; Kumar, 2001 and Jyrkama et al., 2002). Now a days the modflow is also used to estimate the climate change effect on groundwater and sea level rise in aquifers. The impacts of climate change on groundwater has been investigated by many researchers (Loáiciga et al., 2000; Varanou et al., 2002; Brouyère et al., 2004; Allen et al., 2004; Krysanova et al., 2005; Scibek and Allen, 2006; Andersen et al., 2006; Jyrkama and Sykes, 2007 , Venot, 2009; Garg et al., 2011a, P avelic et al., 2012).The sensitivity of an aquifer to changes in recharge and river stage, consistent with projected climate-change scenarios for the Grand Forks aquifer, located in Canada was done by D. M. Allen et al (2004). Scibek and Allen (2005) used Visual MODFLOW to study the impact of climate change on two small aquifers, in western Canada and in the United States. The results of the study indicated only a minor impact from climate change on recharge and groundwater levels at both study areas. F. El Yaouti et al (2008) modelled a three-dimensional finite-difference groundwater flow model to investigate the variety of hydro geological conditions and to simulate the behaviour of the flow system under different stresses in the unconfined aquifer of

Ground Water Modeling of Nellore Coastal Zone

103

Bou-Areg. The modeling package MODFLOW, employed in the Groundwater Modelling System (GMS), was applied for this purpose.

METHODOLOGY Groundwater modelling begins with a conceptual understanding of the physical problem. The next step in modelling is translating the physical system into mathematical terms. In general, the results are the familiar groundwater flow equation and transport equations. The governing flow equation for three-dimensional saturated flow in saturated porous media is:

  h    h    h  h     K K K W S xx yy zz s x  x  y  y  z  z  t Where K xx xx, K yy yy & K zz zz are values of hydraulic conductivity along the x, y & z co-ordinate axes which are assumed to be parallel to the major axes of hydraulic conductivity H

is piezometric head.

W

is a volumetric flux per unit volume and represents sources and/or sinks of water.

Ss

is the specific storage of the porous material.

t

is time.

The governing equation for groundwater systems are usually solved either analytically or numerically. Analytical models contain analytical solution of the field equations, continuously in s pace and time. In num erical models, a discrete solution is obtained in both the space and time domains by using numerical approximations of the governing partial differential equation. Various numerical solution techniques are used in groundwater models. Among the most used approaches in groundwater modelling, three techniques can be distinguished: Finite Difference Method, Finite Element Method, and Analytical Element Method. All techniques have their own advantages and disadvantages with respect to availability, costs, user friendliness, applicability, and required knowledge of the user. In the present study, steady state aquifer ground water flow modeling is achieved under steady state condition using VISUAL MODFLOW software with Finite Difference method. Data Used

Differential levelling was carried out in the study area to find out the ground elevation and elevation of water table of the observation wells with respect to mean sea level. To study the effect of pumping in the area, water level fluctuations in nine observation wells were collected. Pumping test data of rate of five pumping wells and number of pumps exist in the study area was collected from state Ground water Board, Nellore. The model is initially tested with steady state calibration using may 2012 and then converted to transient during the period May 2012 to November 2012. Model Set Up of the Study Area

The basic assumptions made regarding the aquifer modeling are The Penna river is ephemeral river and may become affluent and influent depending on the flows and surrounding groundwater conditions and are thus simulated by River Package. The specified head at the sea coast is zero and there will be continuous leakage to the Fracture zone from

104


the overlying weathered zone. The entire study area was divided into a rectangular grid pattern of 30 columns and 30 rows as shown in Figure 2. The each block in the grid was chosen as a square of 1000 m side. The conceptual model consists of 2 layers covering an area of 1530 km 2.

Figure 2: Model Grid Domain

The stratiographic units are represented by two layers, merging soil cover and weathered zone in first layer depth varying between 6-8m and partially weathered, jointed and fractured in second layer with varying depth 12-16m respectively from the top. Therefore the top spatial domain represents the ground surface while the bottom boundary of the domain is set bottom levels of the jointed and fractured zone shown in figure 3 and 4.

Figure 3: Horizontal Cross-section of Aquifer Layers (Row 12)

Figure 4: Vertical Cross-Section of Aquifer Layers (Column 16) Boundary Conditions

Hydrological features adjacent to and within the model domain must be represented in the model by mathematical boundary conditions. The main inputs of freshwater come across lateral boundaries of th e system and these boundaries are modelled as a general head condition. Specified head of 0m was applied to the sea (Figure 5). Spatial extents of rivers, tanks, canals and drains would accommodated through river package, drain package and head boundary available in MODFLOW (Figure 5).


105

Figure 5: Boundary Distribution in the Study Area

The main source of recharge in the study area is rainfall, streams and rivers. Areal recharge to the flow system is spatially variable due to lakes, streams and drains contribute to the groundwater system based on the gradient between the surface water body and groundwater regime, soil type and geological structures (Venkateswara Rao, 2006). The delay in recharge to aquifer is inappreciable and the hydro geological parameters do not change during the period for which the aquifer is simulated. (Thangarajan, 1981). The heterogeneity is incorporated into the model by varying the recharge values represented in Figure 6. The permeability values are adopted based on geology and soils of the study area and varying from 4 to 4.80 m/day

Figure 6: Recharge Distribution in the Study Area

106


The groundwater draft has been assigned through well package. The Study area is mainly dependant on rainwater, canal water and groundwater for its irrigation. Based on stage of ground water development in Indukurpet mandal is categorized as over exploited (more than 100%), T.P.Gudur mandal is categorized as semi critical (70-90%) and allure, Muthukur, Vidavalur mandals are categorised as safe. (less 70% of available resource), the groundwater utilisation is estimated based on the land cover and residential flat pattern and the data collected from APSGWD (Table 2). The groundwater withdrawal in the study areas was simulated appropriately through well package with groundwater pumping rates varying from 100m3/day to 500m3/day per grid, considering the urbanization, land use etc. (Figure 8) Table 1: Mandal Wise Groundwater Utilization of the Study Area Mandal Name

Ground Water Utilisation in MCM

Allur 9.07 Vidavalur 30.96 Indukurpet 86.29 T.P.Gudur 51.84 Muthukur 18.31 Total 196.47 Source: Report of APSGWD (2004-2005) and CGWB Report, 2007 The groundwater head in the aquifer model was computed by using visual MODFLOW (Guiger and Franz, 1996).WHI Solver package of MODFLOW has been used the solver checked for the maximum change in the solution at every cell after completion of every iteration. If the maximum change in the solution was below a set convergence tolerance then the solution had converged and the solver stops, otherwise new iteration was started (McDonald and Harbaugh, 1988). The flow model was calibrated by adjusting several parameters within a narrow range of values until a best fit was obtained between observed data and simulated results. The accuracy of the computed water le vels was judged j udged by a mean error, mean absolute error and root mean squared error. Figure 7 sho ws the comparison of water level altitudes as measured in the field and those observed in the si mulation of the model. The minimum and maximum deviation between the observed values of water levels in the field and those observed in the si mulated model are -0.45m to+10m (Figure 7).

Figure 7: Calibration Results in Steady State (Postmonsoon2012)

107


Figure 8: Variation of Observed and Calculated Ground Water Levels Values in the Study Area during November 2012

Figure 9: Variation of Observed and Calculated Ground Water Levels Values in the Study Area during November 2012

From mass balance of the ground water flow model, we observed that the annual recharge of the study area is 435.04 MCM and river leakage is 7.22 MCM. From the total input, 12% (i.e, 52.20MCM) is gone through evaporation loses from surface and ground water bodies and 50% of water is extracted from ground in the form of puming (i.e,194.85 MCM) and the remaining 28% (i.e, 131.18 MCM) is the river leakage and saltwater intrusion in the study area ( Figure 10).

Figure 10: Zone Budget

108


CONCLUSIONS Groundwater flow model was developed using Visual MODFLOW and the aquifer parameters for the area were estimated. Groundwater head for the area was obtained from the model run. From mass balance of the ground water flow model, we observed that the annual recharge of the study area is 435.04 MCM and river leakage is 7.22 MCM. From the total input, 12% (i.e, 52.20MCM) is gone through evaporation loses from surface and ground water bodies and 50% of water is extracted from ground in the form of pumping (i.e,194.85 MCM) and the remaining 28% (i.e, 131.18 MCM) is the river leakage and saltwater intrusion in the study area.

REFERENCES 1.

Allen, D. M., Mackie, D. C., and Wei, M.: Groundwater and climate change: a sensitivity analysis for the Grand Forks aquifer, southern British Columbia, Canada, Hydrogeol. J., 12, 270 – 270 – 290, 290, 2004

2.

Anderman, E.R. and Hill, M.C. : Advective-Transport Observation (ADV) Package, a Computer Program for Adding Advective-Transport Observations of Steady State Flow Fields to the Three-Dimensional Ground-Water Flow Parameter-Estimation Parameter-Estimation Model MODFLOW‖ U.S. Geological Survey Open -File Report 97-14, 67 p.,1997.

3.

Andersen, H. E., Kronvang, B., Larsen, S. E., Hoffmann, C. C., Jensen, T. S., and Rasmussen, E. K.: Climate-change impacts on hydrology and nutrients in a Danish lowland river basin, Sci. Total Environ., 365, 223 – 237, 237, 2006.

4.

Brouyère, S., Carabin, G., and Dassargues, A.: Climate change impacts on groundwater resources: modeled deficits in a chalky aquifer, Geer basin, Belgium, Hydrogeol. J., 12, 123 – 123 – 134, 134, 2004.

5.

El Yaouti, F., El Mandour, A., Khattach, D., Kaufmann, O.: Modelling Groundwater flow and Advective contaminant transport in the Bou-Areg Bou- Areg unconfined aquifer (NE Morocco)”, Journal of Hydroenvironment Research, Vol. 2, pp. 192-209, 2008.

6.

Hill, M.C., Banta, E.R., Harbaugh, A.W. and Anderman, E.R. : MODFLOW-2000, the U.S. Geological Survey Modular Ground Water Model, User’s Guide to the Observation, Sensitivity, and Parameter -Estimation Parameter -Estimation Process and Three Post-Processing Programs‖, P rograms‖, U.S. Geological Survey Open -File Report 00-184, 209 p. 2000.

7.

Jyrkama, M.I., Sykes, J.F. and Normani, S.D.: S.D. : Recharge Estimation for Transient Ground Water Modelling‖, Ground water, Vol.40, pp.638 – pp.638 – 648, 648, 2002.

8.

Jyrkama, M. I. and Sykes, J. F.: The impact of climate change on spatially varying groundwater recharge in the grand river watershed (Ontario), J. Hydrol., 338, 237 – 237 – 250, 250, 2007.

9.

Konikow, L.F., Harte, P.T., and Hornberger, G.Z. : Simulating Solute Transport Across Horizontal-Flow Barriers‖, In: Seo, Poeter, Zheng, and Poeter‖ (Eds.), Proceedings MODFLOW 2001 and Other Modeling Odysseys Conference: International Ground Water Modeling Center, Colorado School of Mines, Golden, CO, September, 2001, pp. 510-516, 2001.

10. Krysanova, V., Hattermann, F., and Habeck, A.: Expected changes in water resources availability and water quality with respect to climate change in the Elbe River basin (Germany), Nord. Hydro, 36, 321 – 321 – 333, 333, 2005. 11. Kumar, C. P.: Groundwater Modelling In. Hydrological Developments in India SINCE Independence‖. A Contribution to Hydrological Sciences, National Institute of Hydrology, Roorkee, pp. 235-261, 1992.


109

12. Kumar, C. P. : Common Ground Water Modelling Errors and Remediation‖, Journal of Indian Water Resources Society, Volume 21, Number 4, October 2001, pp. 149-156, 2001. 13. Loáiciga, H. A., Maidment, D. R., and Valdes, J. B.: Climate-change impacts in a regional karst aquifer, Texas, USA, J. Hydrol., 227, 173 – 194, 194, 2000. 14. Mc.Donald, M. G. and Harbaugh, A. W.: A Modular Three Dimensional Finite-Difference Groundwater Flow Model‖, Techniques of 273 water resources investigations of the U.S. Geological Survey book 6, 586p, 1988. 15. Merrit, M. and Konikow, L.: Documentation of a Computer Program to Simulate Lake Interactions Using the MODFLOW Groundwater Flow Model and the MOC3D Solute- Transport Model‖. US Geological Survey Technical Report 00-4167, 146p, 2000 16. Pavelic, P., Patankar, U., Acharya, S., Jella, K., and Gumma, M. K.: Role of groundwater in buffering irrigation production against climate variability at the basin scale in South-West India, Agr. Water Manage, 103, 78 – 78 – 87, 87, 2012. 17. Pollock, D.W. : User's Guide for MODPATH/MODPATH-PLOT, Version 3; A Particle Tracking Post-Processing Package for MODFLOW, the U.S. Geological Survey Finite-Difference Ground- Water Flow‖, U. U. S. Geological survey open-File Report 94- 464, 249p, 1994. 18. Scibek, J. & Allen, D.M.,: Comparing modelled responses of two high-permeability, unconfined aquifers to predicted climate change”, change”, Journal Journal of Hydrology, Vol. 333, pp.165 – pp.165 – 181,2005 181,2005 19. Scibek, J. and Allen, D. M.: Modeled impacts of predicted climate change on recharge and groundwater levels, Water Resour. Res, 42, W11405, doi: 10.1029/2005WR004742, 2006. 20. Venot, J. P.: Rural dynamics and new challenges in the Indian water sector: the trajectory of the Krishna Basin, South India, in: River Basin Trajectories: Societies, Environments and Development, edited by: Molle, F. andWester, P., CAB International 2009, 214 – 214 – 237, 237, 2009. 21. Varanou, E., Gkouvatsou, E., Baltas, E., and Mimikou, M.: Quantity and quality integrated catchment modelling under climate change with use of soil and water assessment tool model, J. Hydrol. Eng., 7, 228 – 228 – 244, 244, 2002.

GROUND WATER MODELING OF NELLORE COASTAL ZONE

Recommend Documents