Geomorphological Factors of Coastal Groundwater Salinity in Central Kerala: Integrated Hydrochemical-Geospatial Approach

8/13/2019 Geomorphological Factors of Coastal Groundwater Salinity in Central Kerala: Integrated Hydrochemical-Geospatial

1/10

Geomorphological Factors of Coastal Groundwater Salinity in Central Kerala 315

Geomorphological Factors of Coastal GroundwaterSalinity in Central Kerala: IntegratedHydrochemical-Geospatial Approach

Priju C P1, Ramisha N, Neerajamol T P,Madhavan K and Narasimha Prasad N B

Centre for Water Resources Development and Management, Kunnamangalam,

Kozhikode673 571, Kerala, India

E-mial; [email protected]

ABSTRACT: Groundwater salinity in the coastal region extending from Ernakulam toAlappuzha of central Kerala was studied in relation to hydrogeology and geomorphology.Geomorphological mapping of the study area was carried out with the help of digital

satellite data (IRS P6 LISS III, bands 1, 2, 3 and 4) acquired in February 2010. The studyrevealed the presence of various geomorphological units viz., barrier islands, spit, lagoon,beach ridges and swale complex, mudflats and intertidal flats, floodplains, marshy areasand mangrove swamps of coastal origin. The landform units of fluvial origin viz., paleo-channels, abandoned channels, point bar, channel Island, swamps/river flood plains etc.were also identified. Well water samples (115 open wells) from various geomorphologicalunits were collected in the pre-monsoon season (2011) and were analysed for waterquality parameters viz. pH, temperature, EC, alkalinity, salinity, turbidity, TDS, chloride(Cl), total hardness, Ca2+, Mg2+, Na+, K+, SO42and Fe2+. The hydro-chemical data obtained

from different morphological/landform units were compared and correlated. Bivariateplots viz., chloride content vs. water level elevation, conductivity vs. chloride and piperdiagram was plotted to understand the geomorphological controls on groundwater salinity.Older and younger coastal plain alluvium consist a major portion of the study area andalso by flood plains, floodplain lowlands, alluvial plain, paleo-channels and abandonedchannels. The water samples from ridges, alluvial and coastal plain areas are generally of

good quality. The water samples from floodplain areas are generally of poor quality, i.e.affected by salinity, turbidity and hardness. However, in the northern part of the study area,i.e, Vypin, Njarakkal, Ernakulam and near Thannermukkam bund, the anthropogenicactivities superseded the geomorphological controls and poor quality groundwater. Thewater level elevation vs. chloride concentration, EC vs. Chloride concentration and piper

plot shows the geomorphological control on groundwater salinity.

Keywords:Coastal Aquifers, Geomorphology, Saline Intrusion, Central Kerala Coast.

INTRODUCTION

Groundwater salinization is extensive and represents a special category of groundwater

pollution in the coastal regions. Most of the freshwater salinization along the coastal areas

International Symposium on

Integrated Water Resources Management (IWRM2014)

February 1921, 2014, CWRDM, Kozhikode, Kerala, India


2/10

316 Integrated Water Resources Management (IWRM2014)

and oceanic islands are due to the encroachment of seawater through surface and subsurface

pathways (Gingerich and Voss 2005; Post 2005; Trabelsi et al., 2007). Seawater intrusion has

received wide attention in the most populated coastal areas since almost 50% of the worlds

total population lives within 60 km of the shoreline (Chen et al., 1997; Izuka and Gingerich,

1998; Salama et al., 1999; Radhakrishna 2001; Lee et al., 2002; Cardona et al., 2004; Bridge

and Allen 2006; Feseker 2007). There are different causes for the salinization of fresh water

zones of aquifers; which mainly depends on local hydrogeological and geomorphic

characteristics. The presence of fissures and cracks and fractures in the aquifer and small-

scale heterogeneities in the hydraulic properties also has great influence on the hydrogeology of

an area and development of the saltwater ingress and groundwater salinization (Bense et al.,

1998; Radhakrishna 2001; Kukillaya et al., 2004; Bridger and Allen 2006). The groundwater

quality problems, especially due to salinization of freshwater aquifers have been mainly

reported from Ernakulam, Thrissur and Alleppey coasts (CGWBKR, 2007). In Ernakulam,

seawater intrusion is severe around Chellanum and Vypin coasts. Many studies have been

carried out on the hydro-geochemistry and water quality of coastal aquifers of Kerala(Keerthiseelan et al., 2001;George and Shrine Clarit 2002; Pareek et al., 2006; Kukillaya et al.,

2004; Laluraj et al., 2005; Manjusree et al., 2009; Harikumar and Kokkal 2009). The

demarcation of areal extent of saline intrusion was also done by some researchers (Basak and

Vasudev 1983; Basak and Nasimudin 1987; Ahmed Ali et al., 1987; Vatakkepat and NarasimhaPrasad 1991;Vinayachandran et al., 2003; Kukillaya et al., 2004). Most of these studies are

on the water quality parameters and did not look into the role of hydro-geomorphological units

Fig. 1:Map of the Study Area Showing Geology and Well Sample Locations


3/10


on groundwater salinity patterns. The present study focuses on mapping different landform

units and to assess the water quality in shallow aquifers representing each hydro-geomorphic

unit. The study area comprises the coastal belt extending from Alappuzha in the south to

Ernakulam in the north and laterally it extends towards midland region in the east (Figure 1).

The area receives an average annual rainfall of about 3000 mm and is drained by six major rivers

viz., southern arm of Periyar, Muvattupuzha, Pamba, Achankovil, Manimala and Meenachil.

Vemband backwater system and associated wetlands constitute a major part of the study area.

MATERIALS AND METHODS

Geomorphological mapping of the study area was carried out with the help of digital satellitedata (IRS P6 LISS III, bands 1, 2, 3 and 4) acquired on February 2010. Geomorphological unitswere identified and the corresponding well sample locations were noted. Water samples from115 shallow wells were collected during pre-monsoon 2011 period (Figure 1). The pH,Temperature, TDS, electrical conductivity, salinity of the samples was measured in-situ using

Eutech multi-parameter instrument. The concentration of major ions (cations and anions) wasanalyzed in the laboratory as per the standard method (APHA 2005). Na

+and K

+in the water

samples was analyzed using Flame photometer (SYSTRONICS Model: 1382). Ca2+

and Mg2+

were estimated by EDTA titrimetric method, and Cl

content was determined by argentometric

titration using standard silver nitrate as reagent. Carbonate concentration of the water sampleswas determined by titration method. Sulphate concentration was determined following turbiditymethod using Nephlo-Turbidity meter.

RESULTS AND DISCUSSION

Hydro-Geomorphology

The area mainly covered by the low land coastal plain and part of lateritic mid land. It is

observed that in most of the places the soil formation is clayey sand to sandy clay. In someplaces the aquifer is laterite overlain on weathered crystalline basement. Riverine alluvium,sandy soil, clayey soil and fine sand were also found in other locations. The coastal landformsare conspicuous in the coastal plain region, consists of sand and alluvium. Other majorgeomorphological features identified from the area are barrier islands, beach ridges, mudflatsand tidal flats, flood plains and mangrove swamps (Figure 2). The ground elevation rangesfrom 0.398 m above MSL. The data shows a smooth gradient in the coastal plain part (08 m)compared to the eastern side adjoining midlands. The maximum ground elevation of 98 mabove MSL is noticed in the eastern part. The lowland area that forms the western partcomprises of backwaters, lagoons and artificial channel networks. The midland areas lyingeast of the low land coastal plain has natural drainages. As a whole the area has a slopedownwards from east to west.

Hydrochemistry

In-situ parameters (Temp., pH, EC, TDS and Salinity)

The water temperature of the samples ranged from 2533.4C. Spatially water temperature in

the wells near to the coast/coastal inlet is comparatively higher than the wells adjacent to the


4/10


Fig. 2:Hydro-Geomorphology Map of the Study Area Showing Different

Landform Units and Ground Elevation from MSL

river mouths. pH of the water samples varied from 5.89 with average of 7.4. Most of the

samples have pH within the drinking quality limit (BIS). The spatial plot of pH shows that

north-western and southern part of the study area is covered by alkaline water. Alkalinity of

water samples is higher in the coastal region compared to midland areas. Acidic nature water

is noted along northeastern and southern part of study area. The electrical conductivity (EC)

of the water samples varied from 4439670 S/cm with average of 1703 S/cm. Higher ECwas detected in the water samples collected around Cochin inlet and in the areas viz.,

Kadamakkudi, Elangunnapuzha, Kumbalam, Maradu and Vaikom. The TDS content in the

water samples varied from 1523630 mg/L with average of 813 mg/L. In most part of the

study area the water is fresh (TDS


5/10


Vallarpadam, Kumbalam and Trippunithura areas. TDS content shows an increasing trend in

the wells around Cochin inlet and the areas adjacent to the Lake The salinity of the water

samples ranged from 022.84 ppt with average of 0.75 ppt. Salinity of water samples follows

the same trend of electrical conductivity and total dissolved solids. Higher salinity (>1.0 ppt)

was observed in Kadamakkudi, Vallarpadam, Kumbalam, Marad, Trippunithura and Vaikom

areas compared to the southern parts (Figure 3).

Laboratory Analysis of Water Samples

Major Ions: The results show that CaHCO3 hydrochemical facies is the dominant water

type. All the wells are tapping groundwater from the shallow aquifers and there is more

heterogeneity in the major ion composition in the water samples. Eight different

hydrochemical facies are identified among the water samples.

Cations (Ca2+

, Mg2+

, Na+ and K

+): Calcium (Ca

2+) content in the water samples ranged

between 31488 mg/L (average 64 mg/L) within the permissible limit in most of the samples(WHO, 1995). Magnesium (Mg

2+) content in the water samples ranged between 0505 mg/L

(average 25 mg/L). Calcium content is higher in Kadamakkudi, Kumbalam areas andmagnesium content is higher in Kadamakkudi, Vypin, Vallarpadam and Fort Cochin areas(Figure 4). Sodium (Na

+) content in the water samples ranged from 51424 mg/L with average

of 124 mg/L. High Na+content were observed in the well water samples from Trippunitura,

Maradu, Kadamakkudi, Kumbalam, Vallarpadam, Kavalam areas (Figure 4). Lower Na+values

are exhibited south western parts of the study area. Potassium (K+) content in the water samples

varied from 1106 mg/L with an average of 12 mg/L. Potassium content is higher in the watersamples from Trippunitura, Marad, Kadamakkudi, Kumbalam, Kumarakam, Vaikom,Nedumudi, Vadakkal areas (Figure 4).

Fig. 4:Spatial Plots Showing Variations in Ca2+

, Mg2+

, Na+and K

+in the Water Samples

Total Alkalinity (TA) and Total Hardness (TH): The total alkalinity of water samples range from9836 mg/L with an average of 164 mg/L. Higher alkalinity (TA) is noted in the southern,western and northern eastern parts of the study area, whereas lower alkalinity is noted alongCherthala, Talayolaparabu areas (Figure 5). The hardness (TH) of the well water samplesranged from 164400 mg CaCO3/L with an average of 272 mg CaCO3/L. The results showthat in most parts of the study area, groundwater is fresh with TH


6/10


Fig. 5:Spatial Plots Showing Variations in TA, TH, Cland SO4

2in the Water Samples

Anions (Cl

and SO42): The Chloride (Cl

) values in the water samples ranged from 84477

mg/L with an average of 282 mg/L. The Cl

content in most of the water samples are within

the desirable limit as per BIS (< 250.0 mg/L). The Cl

content is less in the region of highertopographic elevation than in the surrounding coastal areas indicating groundwater

composition in alluvial aquifers are largely influenced by seawater intrusion, the main source

of chloride. Chloride (Cl

) content is higher in water samples collected from Trippunitura,

Marad, Kumbalam, Vallarpadam, Kumarakam areas (Figure 5). The Sulphate (SO42)content

in the water samples varied from 2640 mg/L, with an average of 48 mg/L. Higher SO42

content

was found in the samples from Varapuzha, Vallarpadam, Kumbalam and Marad, Kumarakam

areas. Generally SO42

content is lesser in the areas with higher elevation (Figure 5).

Iron (Fe2+

): Iron (Fe2+

) was detected in few samples (34 out of 115) and is at low concentration

(max. 1.4 mg/L).Higher Fe2+

content was noted in Mararikulam, Arathungal and Cherthala areas.

The Fe2+

values obtained for the water samples are within the desirable limit (BIS, 1993).

Hill-Piper Plot and Ground Water TypeThe HCO3-Cl-SO4 anion triangle plotted show groundwater samples have bicarbonate andchloride type end members and sulphate is not present in significant proportion. The Ca-Mg-Na

Fig. 6:Pie Diagram Showing Proportions of Different Hydro-Chemical Facies


7/10


cation triangle show that the major cations present in the sample are Ca and Na. Sixty three water

samples are Ca dominant, 43 of them are Na dominant and 9 are Mg dominant (Figure 6). It

shows that alkaline earths (Ca+Mg) exceed alkalies (Na+K) and weak acids (SO4+Cl) exceed

strong acids (HCO3+CO3). Overall eight water types are seen from the study area. The

dominant hydrochemical facies (53 samples out of 115 samples) is Ca-HCO3followed by Na-

Cl and Na-HCO3. Spatially Ca-HCO3 facies is distributed in the western part of the study area

adjoining Vembanad Lake and sea.

Hydro-Geochemical Relationships

Correlation Coefficient:The correlations between various hydro-geochemical parameters are

obtained from the correlation coefficients. The results show a very good correlation (0.700

0.862) between TDS and TH, Ca2+

, Na+, Cl

as well as TH and Ca

2+, Mg

2+(0.8320.86). Na

+

also shows very good correlation (0.7450.825) with K+, Cl

. Good correlation is seen between

TDS and TA, Mg2+

, K+, SO4

2 (0.4800.674). Ca

2+ also shows good correlation (0.5230.745)

with sodium, potassium, chloride and sulphate. TA with TH and calcium (0.4350.604) and

TH with sodium and chloride (0.5300.536) also show good correlation. Good correlation is

also noted between Mg2+

and Cl

(0.542), Na+and SO4

2(0.470) and Cl

and SO4

2(0.497).

Bivariate plots:Scatter plot of the water table elevation vs. chloride concentration shows an

inverse correlation (R = 0.1). i.e., as the water table elevation decreases, the chloride

concentration increases (Figure 11). Very good positive correlation is seen between hardness

(TH) vs.Calcium (R = 0.77), Magnesium (R = 0.81) and Electrical Conductivity (R = 0.81).

Positive correlation is also seen between Conductivity (EC) vs. Chloride (R = 0.72) and

Sodium vs.Chloride (R = 0.56). The ratio of Sodium and Chloride (Na+/Cl

) plotted against

log EC shows an inverse correlation (R = 0.14).

Fig. 7:US Salinity Diagram Showing Salinity and Alkalinity Hazard of the Water Samples


8/10


US Salinity Diagram:The US Salinity diagram (specific conductance vs. sodium-adsorption

ratio) shows that majority of the water samples have medium-high salinity hazard and low-

medium sodium hazard (Figure 7). Low salinity hazard is exhibited by twenty six samples

and very high salinity hazard by two samples collected from Manakkodam and Kadamakudi.

In case of sodium hazard, six samples belong to high category and eight samples belong to

very high category.

CONCLUSION

The study is an attempt to investigate the interrelation of ground water quality with hydro-geomorphology along Ernakulam-Alappuzha area. Geomorphologically, the area is covered

with extensive backwaters/lagoon system and dynamic barrier-island complexes with ridge-

swale topography. This forms an ideal landform setting for the study of coastal aquifer system

with respect to geomorphology and saline intrusion. The surface elevation model shows a

smooth gradient in the majority of the study area, except in the eastern part adjoining the

midlands. An elevation of 98 m above MSL is noted in the eastern part and it ranges from 08

m above MSL in the coastal plain areas.

The temperature of well water samples ranged from 2533.4C. The pH of the samples variedfrom 5.89 (av.7.4). Most of the samples were found within the permissible limit (BIS). The

electrical conductivity of the samples varies between 4439670 S/cm (av.1703 S/cm). The

TDS level in the water samples ranged from 1523630 mg/L (av.813 mg/L). The salinity ofthe water samples ranged from 022.84 ppt (av.0.75 ppt). TDS levels indicate that majority

of the samples are within safe limit (250 mg/L) and rest mainly within 500 mg/L. Different

water types (eight) were obtained from Hill-Piper plots of hydrochemical data. The dominant

hydrochemical facies (53 samples out of 115 samples) is Ca-HCO3followed by Na-Cl and

Na-HCO3. Spatially Ca-HCO3 facies is distributed in the western part of the study area

adjoining the lagoon and sea. All the wells are tapping groundwater from shallow aquifers,

thus there is more heterogeneity in the major ion concentration of water samples. Totalalkalinity (TA) in the water samples ranged from 9836 mg/L is found within permissible

limit (BIS). Total hardness (TH) of the water samples ranged from 164400 mg CaCO3/L

(av.272mg CaCO3/L). Iron content (Fe2+

) is reported only in few of the samples. The chloride

(Cl

) content in majority of the water samples are within 100 mg/L, few samples exceeding

the limit. The hydro-geochemical relationship of the samples was obtained from correlation

coefficients and bivariate plots. The results show a very good correlation (0.7000.862)

between TDS and TH, Ca2+

, Na+, Cl

as well as TH and Ca

2+, Mg

2+ (0.8320.86). Na

+also

shows very good correlation (0.7450.825) with K+, Cl

. Good correlation is seen between

TDS and TA, Mg2+

, K+, SO4

2(0.4800.674). Ca

2+also shows good correlation (0.5230.745)

with sodium, potassium, chloride and sulphate. TA with TH and calcium (0.4350.604) and

TH with sodium and chloride (0.5300.536) also show good correlation. Good correlation is

also seen between Mg

2+

and Cl

(0.542), Na

+

and SO42

(0.470) and Cl

and SO42

(0.497).The US Salinity diagram shows that majority of the water samples have medium-high salinity

hazard and low-medium sodium hazard.

The hydro-chemical data obtained from different morphological/landform units shows good

interrelationship. Older and younger coastal plain alluvium consist a major portion of the

study area and also by flood plains, floodplain lowlands, alluvial plain, paleo-channels and


9/10


abandoned channels. The water samples from ridges, alluvial and coastal plain areas are generally

of good quality. The water samples from floodplain areas are generally of poor quality, i.e.

affected by salinity, turbidity and hardness. However, in the northern part of the study area, i.e,

Vypin, Njarakkal, Ernakulam and near Thannermukkam bund, the anthropogenic activities

superseded the geomorphological controls and poor quality groundwater.

ACKNOWLEDGEMENTS

Authors thank Executive Director, Centre for Water Resources Development and Management

(CWRDM) for the permission and extending support for publishing this work. This paperform part of the Plan N40 project of CWRDM sanctioned under Kerala State Council for

Science, Technology and Environment (KSCSTE) funding. Authors thank Dr. P.S. Harikumar,

Head, Water Quality Division, CWRDM for extending the facility in analyzing the water

samples.

REFERENCES

Basak, P. and Nasimudin, M. (1987). Seawater intrusion in coastal unconfined aquifers of the southwestern

peninsulaa case study. Jal Vigyan Sameeksha, a publication of high level technical committee on

hydrology, 2(1): 7280.

Basak, P. and Vasudev (1983). Saltwater intrusion in typical coastal aquifers of Kerala. Paper presented in

the workshop on the recent advances in the groundwater exploration and management at NGRI,

Hyderabad, pp. 2729.

Bense, V., Hooijboer, A. and Brokx, W. (1998). Morphotectonic and hydrogeomorphic control on the

hydrogeology of the Buffelsrivier catchment. Technical ReportA hydrogeologic case study on the

Great Escarpment in Namaqualand, South Africa, Vrije Universiteit, Amsterdam, 101p.

Bridge, D.W. and Allen, D.M. (2006). An investigation into the effects of diffusion on salinity distribution

beneath the Fraser river delta. Hydrogeology Journal, 14:14231442.

Cardona, A., Carrillo-Rivera, J.J., Huizar-Alvarez, R. and Graniel-Castro, E. (2004). Salinization in coastal aquifers

of arid zones: an example from Santo Domingo, Baja California Sur, Mexico. Environ. Geol., 45: 350366.

CGWBKR (2007). Hydro Geological Conditions of Kerala. http://cgwb.gov.in/KR/

Chen, H., Zhang, Y., Wang, X., Ren, Z. and Li, L. (1997). Salt-water intrusion in the lower reaches of the

Weihe river, Shandong Province, China. Hydrogeology Journal, 5(3): 8288.

Feseker, T. (2007). Numerical studies on saltwater intrusion in a coastal aquifer in northwestern Germany.

Hydrogeology Journal, 15: 267279.

George, A.V. and Shrine Clarit, C.G. (2002). Influence of saline water intrusion in the freshwater bodies of

Vypin Island, Ernakulam district, Kerala. Proc. of National seminar on current environmental problems

and management,Christ College, Irinjalakuda, Kerala, pp 194200.

Gingerich, S.B. and Voss, C.I. (2005). Three-dimensional variable-density flow simulation of a coastal aquifer

in southern Oahu, Hawaii, USA.Hydrogeology Journal,13: 436450.

Harikumar, P.S. and Kokkal, K. (2009). Environmental Monitoring programme on water quality. Kerala State

Council for Science, Technology and Environment, Thiruvanathapuram. 174p.

Izuka, S.K. and Gingerich, S.B. (1998). Estimation of the depth to the fresh-water/salt-water interface fromvertical head gradients in wells in coastal and island aquifers. Hydrogeology Journal, 6: 365373.

Keerthiseelan, K., Kapoor, S.L., Suresha, A. and Prakash, T.R. (2001). Salinity intrusion from tidal recharge

and its impact on groundwater quality in Goa state.Jour. Geol. Soc. India,57: 257262.

Kukillaya, J.P., Padmanabhan, K. and Radhakrishnan, K. (2004). Occurrence of Brackish groundwater in

fractured hard rock aquifers of Puzhakkal-Avanur area in Thrissur, Kerala. Jour. Geol. Soc. India,64

(1): 3242.


10/10


Laluraj, C.M., Gopinath, G. and Dineshkumar, P.K. (2005). Groundwater chemistry of shallow aquifers in

the coastal zones of Cochin, India.Applied Ecology and Environ. Research,3(1): 133139.

Lee, S., Kim, K., Ko, I., Lee, S. and Hwang, H. (2002). Geochemical and geophysical monitoring of saline waterintrusion in Korean paddy fields. Environ. Geochemistry and Health, 24: 277291.

Manjusree, T.M., Sabu Joseph and Jobin, Thomas (2009). Hydrogeochemistry and groundwater quality in the

coastal sandy clay aquifers of Alappuzha district, Kerala.Jour. Geol. Soc. India, 74 (4): 459468.

Pareek, N., Jat, M.K. and Jain, S.K. (2006). The utilization of brackish water, protecting the quality of the

upper fresh water layer in coastal aquifers.Environmentalist,26: 237246.

Post, V.E.A. (2005). Fresh and saline groundwater interaction in coastal aquifers: Is our technology ready for

the problems ahead?Hydrogeology Journal, 13: 120123.

Radhakrishna, I. (2001). Saline fresh water interface structure in Mahanadi delta region, Orissa, India.

Environ. Geol., 40(3): 369380.

Salama, R.B., Otto, C.J. and Fitzpatrick, R.W. (1999). Contributions of groundwater conditions to soil and water

salinization.Hydrogeology Journal, 7: 4664.

Trabelsi, R., Zairi, M. and Dhia, H.B. (2007). Groundwater salinization of the Sfax superficial aquifer,

Tunisia.Hydrogeology Journal (online version),DOI 10.1007/s10040-007-0182-0.Vatakkepat, H. and Narasimha Prasad, N.B. (1991). Salinity of groundwater in the Kole lands of Trichur

district, Kerala. Proc. Sem. Groundwater Development and Management in irrigation and other water

sectors, CWRDM, Kozhikode, pp. 235242.

Vinayachandran, N., Kunhambu, V. and Nayagam, S.P. (2003). A study on seawater ingress in the coastal

aquifers in parts of Alleppey and ernakulam districts, Kerala state, Unpub. Rep., Central Ground Water

Board.

Documents

Geomorphological Factors of Coastal Groundwater Salinity in Central Kerala: Integrated Hydrochemical-Geospatial Approach