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Aquatic Procedia 4 ( 2015 ) 32 – 40

INTERNATIONAL CONFERENCE ON WATER RESOURCES, COASTAL AND OCEAN ENGINEERING (ICWRCOE 2015) Study on Saline Water intrusion into the Shallow Coastal Aquifers of Periyar River Basin, using Hydrochemical and Electrical Resistivity Methods

K.S.Anil Kumara, C.P.Prijub*, N.B.Narasimha Prasadb

aDepartment of Marine Geology and Geophysics, Cochin University of Science and Technology, Lakeside Campus,Cochin 682 016, bGroundwater Division, Centre for Water Resources Development and Management, 673 571, India

Abstract

Seawater intrusion generally occurs when withdrawal of fresh groundwater from coastal aquifers results in declining groundwater levels, facilitating lateral and/or vertical migration of saline water causing deterioration of groundwater quality. Electrical resistivity sounding techniques and hydrochemical studies are widely used to determine the interaction between groundwater and saline water/seawater in coastal aquifers. Vertical electrical soundings were carried out at 15 locations in the midland and coastal plain reaches of Periyar River basin in central Kerala, India (9q 55c-10q 20c N latitude and 76q 05c-76q 25c E longitude) using CRM 500 model aquameter. In-situ water quality parameters of water samples from 63 shallow well were also measured using handheld multi-parameter instrument. The cation and anion content of selected water samples (32 nos.) were also determined. Electrical resistivity profiles were interpreted qualitatively and quantitatively to obtain nature and thickness of different resistivity layers. The depth to fresh-saline water interface was delineated from resistivity model. The study indicates majority of the curves obtained are Q type with 3 layers. The depth to saline-fresh water interface varied from <1 to 5 m at different locations. The high salinity clay horizons are identified at various depths. Hydrochemical data was analysed using hill-piper diagram and statistical plots to understand groundwater-seawater mixing/interaction in the coastal aquifers. The dominant groundwater type is Na-Cl followed by Mg-Cl at few places. Higher pH, EC and TDS is noted in the western part towards seaward side. Turbidity levels are found increasing towards the southern part. The TA, TH, Ca2+,Mg2+,K+ content of the water samples found increasing towards + - 2- southwest parts. The Na , Cl and (SO4) content is found higher in the northwestern parts. © 20152015 The The Authors. Authors. Published Published by by Elsevier Elsevier B.V. B.V. This is an open access article under the CC BY-NC-ND license (Peerhttp://creativecommons.org/licenses/by-nc-nd/4.0/-review under responsibility of organizing committee). of ICWRCOE 2015. Peer-review under responsibility of organizing committee of ICWRCOE 2015 Keywords: Coastal aquifers; Saline water intrusion; Vertical electrical sounding; Hydrochemistry; Kerala

* Corresponding author. Tel.: +91-495-2351858; fax: +91-495-2351808 E-mail address:[email protected]

2214-241X © 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of organizing committee of ICWRCOE 2015 doi: 10.1016/j.aqpro.2015.02.006 K.S. Anil Kumar et al. / Aquatic Procedia 4 ( 2015 ) 32 – 40 33

1. Introduction

About 50% of the world’s population lives in coastal areas, a figure which will probably rise to 75% during this century (Finkl, 1994). The salinization of the environment in coastal plain areas limits the supply of fresh water and damages areas of valuable land use (Vandenbohede et al., 2009). Understanding the distribution and origin of saline waters in an aquifer is a key factor to recognize boundary conditions influencing their movement and response to abstraction (Post, 2005). Geophysical methods, especially electrical resistivity sounding techniques were employed by many for the salinity mapping and delineation of fresh-saline interface (Lee et al., 2002; Bataynch, 2006; Wilson et al., 2006; Morrow et al., 2010; Mario et al., 2011). The problem of salinization of coastal aquifers in Kerala has been mainly reported from Ernakulam, and Alleppey districts (Nageswara and Ramadurai, 1970; Basak and Nazimuddin, 1987; Vinayachandran et al., 2003; CGWBKR, 2007). In Ernakulam district, seawater incursion is severe around at Chellanum and Vypin coasts (Nageswara, 1975; Kunhambu, 2003; Laluraj et al., 2005; Priju et al., 2014). It is also found along Azhikode- and Vatanapally--Punnayurkulam stretch of the coast in (CWRDM, 1984; Vatakkepat and Narasimha Prasad, 1991; Kukillaya et al., 2004). The areal extent of saline intrusion along central Kerala coast and its causes were investigated by some of the researchers (Nageswara and Ramadurai, 1970; Nageswara, 1975; Vatakkepat and Narasimha Prasad, 1991; Vinayachandran et al., 2003; Kukillaya et al., 2004; Priju et al., 2014). However few studies were carried out by applying geophysical techniques for delineating saline intrusion along Thrissur-Ernakulam coast in the Periyar River basin. The present study mainly focus on mapping and delineation of lateral and vertical salinity intrusion in the shallow aquifers of Periyar River basin applying electrical resistivity techniques. The study area is part of the coastal stretch in Ernakulam and Thrissur districts extending from Vypin in the south to Perinjanam () in the north (9q 55c-10q 20c N latitude and 76q 05c-76q 25c E longitude) (Fig. 1). The study area includes major townships viz., Edappally-Ernakulam, Varapuzha, Elur-Kalamassery, Aluva, Paravur in Ernakulam district, Kodungallur and Mala in Thrissur district. Paleo-deltaic deposits of Periyar and Rivers and beach ridges/strandline deposits cover major part of the area. Canolly canal, in the northern part and drainages of Periyar River connects whole area in the north-south direction, carries saline water through the sea inlets (Munambam and Cochin inlets). The shoreline is generally straight, trending - SSE with minor variations and lies as a narrow and low-lying land. Geologically the coastal plain part of the study area consists of fluvial, fluvio-marine and paleo-beach deposits. Laterites, Charnockites and Charnockite gneiss rocks cover in the eastern part of the study area. Groundwater occurs mainly in shallow aquifer condition and it dominantly it is of sandy soil nature with varying silt and clay content.

2. Methodology

Vertical Electrical Sounding (VES) surveys (Schlumberger configuration) were carried out at 15 locations representing different geomorphological setup during pre-monsoon period using Aquameter CRM 500 model (Fig. 1). The apparent resistivity and AB/2 values were plotted on double-log sheet. The layered resistivity model in IPI2Win software (Moscow State University) was used to interpret different resistivity layers. The apparent resistivity (U), thickness (h), depth to layer interface (d) were obtained from the model. In-situ measurements of water quality parameters (pH, Temp., TDS, EC, salinity & turbidity) from 63 shallow open wells were carried out in the pre-monsoon period (Fig. 1). The pH, TDS, electrical conductivity, and salinity of the water samples were measured using pocket type multi-parameter instrument (Eutech PCSTestr35) and turbidity measurements were carried out using Nephlo-Turbidity meter (Eutech EC-TN100IR). Lithological details of well sections also noted. 2+ 2+ + + - 2– The ionic content (Total Alkalinity, Total Hardness, Ca , Mg , Na , K , Cl , SO4 ) of the selected water samples (32 nos.) were determined in the laboratory (APHA, 2005). 34 K.S. Anil Kumar et al. / Aquatic Procedia 4 ( 2015 ) 32 – 40

Fig. 1. Study area showing geology, well sampling and VES locations

3. Results and Discussion K.S. Anil Kumar et al. / Aquatic Procedia 4 ( 2015 ) 32 – 40 35

The results obtained on geomorphology, hydrochemistry and geophysical investigation are discussed below:

3.1. Geomorphology

Geomorphologically the area is characterized by various landform units viz., backwaters, beach ridges, paleo- strandlines, alluvial plains, river alluvium, paleo-channels, paleo-delta, marshy plains and barrier-lagoon complex (Narayana and Priju, 2004). Major part of the area is constituted by paleo-strandlines and deltaic deposits. Paleo- beach deposits and barrier island (Vypin) form hinders at places the flow of the river, thereby trapping sediments and enlarging the alluvial plains. Slope map shows that majority of the areas are nearly level to very gently sloping. Moderately sloping to moderately steeply sloping areas is seen in the eastern parts. Lithologs obtained from well sections show that in most of the places the aquifer is clayey sand to sandy clay. In some places the aquifer is laterite, overlain by weathered crystalline basement. River alluvium, sandy soil, clayey soil and fine sand were also found in some locations.

3.2. In-situ Water Quality Parameters

The pH of the water samples varied from 4.7-8.5 with an average of 4.5. The spatial plot of pH shows that western part of the study area is mainly with alkaline ground water, but acidic nature increases towards eastern and central parts. The temperature of the water samples varied from 27.3-30.5qC. The electrical conductivity (EC) of the water samples varied from 49.8-1926 μS/cm with an average value 369 μS/cm. Higher EC is detected in the water samples collected mainly from the wells nearer to the coast and Periyar River mouth towards south (Fig. 2).

36 K.S. Anil Kumar et al. / Aquatic Procedia 4 ( 2015 ) 32 – 40

Fig. 2. Spatial plots showing variations of pH, EC, TDS and Salinity of water samples

The TDS content in the water samples varies from 1-774 mg/L with an average value 205 mg/L. Higher TDS content was detected in the water samples from the western parts near to the seashore compared to eastern part. The northern part of the study area (Kodungallur coast) shows higher TDS values. The salinity of the water samples ranged from 0.04-1 ppt with an average value of 0.24 ppt. Salinity values are higher in northern and western parts of the study area compared to southern and eastern parts. Munambam-Kodungallur coast is showing highest salinity (1 ppt) in the study area. The turbidity values ranges from 0-12 NTU with an average value of 2 NTU. Higher turbidity values are noted in the water samples collected from southern and western part (Vypin-Ernakulam) of the study area compared to northern part.

3.3. Cations and Anions

The total alkalinity (TA) of water samples range from 21-499 mg CaCO3/L with an average of 319 mg CaCO3/L. Higher alkalinity (TA) is noted in the western part (Vypin, Varapuzha, Kadamakkudi) of the study area. The total hardness (TH) of the well water samples ranged from 20-410 mg CaCO3/L with an average of 135 mg CaCO3/L.

K.S. Anil Kumar et al. / Aquatic Procedia 4 ( 2015 ) 32 – 40 37

Fig. 3. Spatial plots showing variations of Na+, K+, Cl- and SO42– in the groundwater samples

Spatially higher TH is noted in the southern part of the study area in Vypin, Varapuzha and Munambam areas compared northern and eastern parts. Calcium (Ca2+) content in the water samples ranged between 4-108 mg/L with an average value of 32 mg/L. Magnesium (Mg2+) content in the water samples ranged between 4-68.5 mg/L with an average value of 20.7 mg/L. Calcium and Magnesium content is higher in southern and western part of the study area. Sodium (Na+) content in the water samples ranged from 11-518 mg/L with an average of 156 mg/L. High Na+ content were observed in the well water samples from Azheekode, Kodungallur and Pappinivattom in the northern parts and Edavanakkad and Vypin in the southern part. Potassium content in the water samples varied from 1-116 mg/L with an average of 37.6 mg/L. Potassium content is higher in the water samples from Edappalli, Vypin, Munambam and Azheekode compared to other parts. The Cl- values in the water samples ranged from 1-2304 mg/L with an average of 657.7 mg/L. The Cl- content is lower in the region of higher topographic 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 from Vypin, Edavanakkad, 2- Munambam and Azheekode areas compared to the eastern part. The SO4 content in the water samples varied from 2- 2-270 mg/L with an average of 37.4 mg/L. Higher SO4 content is found in the samples from Varapuzha, Vypin, Kadamakkudi, Munambam, Azheekode and Kodungallur areas (Fig. 3).

3.3.1. Hill-Piper plot and Ground water type

The Hill-Piper diagram is used to infer hydro-geochemical facies. A trilinear diagram was created to classify the groundwater from different parts the study area and to reveal any groupings, similarities or trends of the samples. The HCO3-Cl-SO4 anion triangle shows groundwater samples have plotted bicarbonate and chloride type end members, and sulphate is not present in any significant proportion. The Ca and Mg-Na cations triangle shows that the major cations present in the sample are Na and Mg. Eight samples are Mg dominant, twenty four of them are Na dominant. One sample is Na-HCO3 type. These two triangles projected onto the main diamond field account for a number of hydrochemical groupings. It shows that alkaline earths (Ca+Mg) exceed alkalies (Na+K) and weak acids (SO4+Cl) exceed strong acids (HCO3+CO3). The dominant groundwater type is Na-Cl type. It is followed by Mg-Cl type and Na-HCO3. Spatially Na-Cl type is distributed in the western part of the study area adjacent to backwaters and sea. Mg-Cl type distributed in elevated areas in the eastern parts (Fig. 4). 38 K.S. Anil Kumar et al. / Aquatic Procedia 4 ( 2015 ) 32 – 40

Fig. 4. Hill-Piper plot of the groundwater samples

3.4. Geophysical Investigation

Semi-quantitative interpretation of the VES data concludes that majority of sounding curves are Q-type (VES-9, 10, 14, 23, 34, 46, 47 & 48) indicating increasing salinity towards depth. The resistivity curve is KQ-type in VES-30 indicating fresh water horizons in the top layer (Fig.5). VES-25 represents fresh zones with a K-type resistivity curve. The areas representing VES-11, 13, 24, 29 & 31 shows QH type curves representing freshening trend towards bottom layers. The layered resistivity parameters (ρ, h & d values) interpreted for various resistivity layers (1, 2, 3 etc.) is also shown in Fig.5. The depth to saline-fresh water interface can be interpreted from <1 to 5 m at different locations. The high salinity clay horizons also can be identified in different depths in various locations.

VES-10 VES-13

VES-23 VES-24 K.S. Anil Kumar et al. / Aquatic Procedia 4 ( 2015 ) 32 – 40 39

VES-25 VES-29

VES-30 VES-46 Fig. 5. VES plots (AB/2 vs. U) with field curve, master curve and interpreted layered resistivity parameters

4. Conclusion

The study has attempted to illustrate the saline water intrusion in shallow coastal aquifer during pre-monsoon season (2014) in the Periyar River basin of Ernakulam and Thrissur districts of Kerala. It also focused on the drinking water quality status of dug well sources in different parts of the study area in connection with the rapid urbanization in the part of coastal zone. Geomorphologically the area is characterized by various landform units viz., backwaters, beach ridges, paleo-deltaic plain, alluvial plains, river alluvium, marshy plains and barrier islands. In- situ measurements of water quality parameters show that pH of the water samples varied from 4.70-8.50 and the electrical conductivity (EC) of the water samples ranges from 49.8- 1926 μS/cm. The TDS content in the water samples varies from 1.21-774 mg/L and salinity values ranges from 0.037-1 ppt. Hill-Piper plots indicates that the dominant groundwater type is Na-Cl followed by Mg-Cl at few places. Higher pH, EC and TDS is noted in the western part towards seaward side. Turbidity levels are found increasing towards the southern part of the study area. The TA, TH, Ca2+, Mg2+,K+ content of the water samples found increasing towards southwest parts. The Na+, Cl- 2- and (SO4) content is found higher in the north-western parts. Semi-quantitative interpretation of the VES data concludes that majority of sounding curves are Q-type indicating increasing salinity towards depth. The resistivity curve is KQ-type in VES-30 (Varapuzha) indicating fresh water horizons in the top layer. VES-25 (Paravur- vedimara) represents fresh zones with a K-type resistivity curve. The VES locations representing Poyya, Kottappuram, Perumpadanna, Manjali and Kadamakkudi (VES-11,13, 24, 29 & 31) shows QH type curves indicates freshening trend towards bottom layers. The depth to saline-fresh water interface can be interpreted from <1 to 5 m at different locations. The high salinity clay horizons also can be identified in different depths in various locations.

Acknowledgments

Authors thank Executive Director, Centre for Water Resources Development and Management (CWRDM) for the permission and extending support for publishing this work. One of the authors (CPP) thank DST, New Delhi for the Young Scientist project (SR/FTP/ES-43/2007) awarded while in Cochin University of Science and Technology (CUSAT). The VES data used in the paper was collected under the DST young scientist program. KSA thank Dr.N.Chandramohanakumar, Head, Department of Chemical Oceanography, CUSAT for analytical facility for water analysis.

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