ECO-CHRONICLE 187

ECO CHRONICLE ISSN: 0973-4155 RNI No. KERENG/2006/19177 Vol. 13, No. 4, December, 2018 PP: 187- 196

EVALUATION OF GROUNDWATER CONDITIONS IN A RIVER BASIN: A CASE STUDY USING GEOGRAPHICAL INFORMATION SYSTEM (GIS)

Sreeja, R1., Arun, P.R2., Mahesh Mohan3, Pradeepkumar, A.P4. and Narasimha Prasad, N.B2.

1. AWH Special College, Kallai, Kozhikode, . 2. Centre for Water Resources Development and Management, Kozhikode, Kerala. 3. School of Environmental Sciences, Mahatma Gandhi University, Kottayam, Kerala. 4. Department of Geology, University of Kerala, Trivandrum 695 581, Kerala. Corresponding author: [email protected]

ABSTRACT

Karamana river basin in Kerala, southern , has been subjected to an integrated groundwater investigation, employing Geographical Information System (GIS). The river basin has been categorised as four zones, namely, Low, Moderate, High and Very High in terms of groundwater potential. It is estimated that about 40% of the basin comes under the very high to high category. The annual groundwater availability and gross annual groundwater draft have been computed. The stage of groundwater development has been calculated as 47.65%. The basin has been categorized as ‘Safe’ for further groundwater development. Key words: Geographical Information Systems, Karamana river, Groundwater potential, Groundwater Assessment

INTRODUCTION

Geographical Information Systems (GIS) are well known distribution is very important to meet the rising demand for the capability to integrate spatial data sets. For as well as to formulate groundwater development groundwater studies it is necessary to integrate data on strategies. In this context, the present study has been various characteristics like topography, lithology, geology, taken up with drainage basin as the unit, in the Karamana lineaments, structures, depth of weathering, extent of river basin, which originates in the and fractures, slope, drainage patterns, etc. The use of drains through District of Kerala remote sensing techniques in combination with GIS aids State in Southern India (Fig. 1). to integrate these data sets in a very convenient manner to facilitate quick decision support. The primary METHODOLOGY requirement for the most advantageous management of ground water resources is the evaluation of the All the available data on geology, hydrogeology, hydrogeological conditions prevailing in the region of geomorphology, landuse/landcover, borehole lithologs, interest. The watersheds or drainage basins should be rainfall and other related and relevant data were collected the unit for better understanding of the hydrologic system from different agencies / publications and were suitably as well as accurate assessment of the available processed through modern statistical and spatial analysis resources (Narasimhaprasad et al, 2013; Arun et al, tools. 50 observation wells were established in the 2014; Sreeja et al., 2015). The drainage basin has been Karamana River Basin for this study (Fig. 2). Seasonal seen as the fundamental hydrologic areal unit through depth to water level was monitored from these dug wells which precise description of data could be collected, for three years (2014 - 2016). The observed seasons organized, and analyzed (Eze Bassey Eze and Joel are Pre-monsoon, Monsoon and Post-monsoon. Details Efiong, 2010). Proper understanding of the groundwater of aquifer parameters have been taken from the already condition in a given area according to availability and published literature of CGWB and Centre for Water 188 ECO-CHRONICLE

Resources Development and Management (CWRDM). Department (GWD), Government of Kerala, were also Well inventory was carried out in three sample areas used for this study. All the above results have been representing different physiographic regions such as low integrated in ArcGIS environment to conclude the land, mid land and high land regions covering the groundwater condition in the Karamana River Basin in Karamana River Basin. Details of existing wells, growth terms of potential, present draft and future developmental and usage pattern of each well type, density of wells prospects. etc., have been determined through this well inventory. SALIENT FEATURES OF THE STUDY AREA Survey of India toposheets, satellite imageries, SRTM Location Digital Elevation Model (DEM) and aerial photographs The Karamana River Basin is located between North have been used to demarcate various geomorphological latitudes 8° 05’ and 8° 45’ and east longitudes 76° 45’ units and distribution of lineaments in the basin. Thematic and 77° 15’ (Fig.1). It has a drainage area of 702 km2. map layers like drainage, geology, contour, watersheds, Among the west flowing rivers of Kerala, Karamana river geomorphology, land use and lineaments were prepared ranks 15th and 17th with regard to river catchment and using SOI toposheets, IRS LISS III Imagery, Landsat stream length, respectively. The river originates from Imagery and SRTM DEM. Derived map layers like slope, Chemmunji mottai, a peak in the Western Ghat mountain drainage density and lineament density were prepared ranges, at an altitude of 1717m amsl (above mean sea using the Spatial analysis tools in GIS environment. level). The Karamana river falls within the small ArcGIS software has been used for data editing and mountainous river category (head water elevation analysis. All the maps were geo-referenced to common between 1000m and 3000m amsl) of Milliman and reference point in the Universal Transverse Mercator Syvitski (1992). The crest of the Western Ghats (UTM) plane co-ordinate system. This was accomplished constitutes the interfluves between the Karamana (west by establishing reference points common to all maps flowing) and the Thambraparni (east flowing) river basins. chosen for the purpose. The entire base maps were The river flows about 68 km before joining the transformed to a common format for further analysis and Lakshadweep Sea near Thiruvallam (PWD, 1974). The identification of groundwater prospect zones (Pratap et river drains wholly through Thiruvananthapuram District, al. 2000, Dinesh Kumar et al, 2007, Narasimhaprasad which hosts the Capital City of Kerala state. et al, 2013). This output map is correlated with the groundwater data collected in the field. Details of aquifer Physiography parameters have been taken from the already published Physiographically Karamana river basin is characterized literature of Central Ground Water Board (CGWB) and by, the coastal belt or lowland in the west (between MSL CWRDM. Datasets collected from the Ground Water and 7.5m AMSL), The midland region, mostly covered by laterites in the Figure 1. Location map of the study area. central portion (7.5 – 75 m AMSL) and the highland (>75m AMSL) in the east, comprising the foot hills and hill ranges of Western Ghats, formed by crystalline hard rocks (Arun, 2006). The most dominant peaks in the study area are Agasthyamalai (1860 m), Chemmunji mottai (1717 m), Panditheri malai (1560 m) and Athirumalai (1594 m).

Rainfall The Karamana river basin receives an average annual rainfall of 2600 mm. While the ECO-CHRONICLE 189 southwestern part of the basin receives less than 1400 land. The monsoon rains normally begin in the District mm of rainfall, the northeastern portion receives rainfall at the end of May or beginning of June every year. Late of about 4200 mm (Arun, 2006). The eastward or early onset of monsoon does not have any relationship enhancement in rainfall is not merely due to the altitudinal with the amount of rainfall that the district may receive effect, but also due to factors like slope of the ground, during the monsoon season. The showers during post synoptic systems affecting rainfall, and configuration of monsoon season are convective in origin and the rainfall is very heavy. October is the rainiest month. Figure 2 Observations wells in Karamana river basin The pre-monsoon rainfall is also convective shower.

Analysis of the last one hundred years of rainfall data reveals that the annual averages vary from 69% to 170% with respect to normal rainfall (Sreeja, 2017). Spells of heavy to very heavy rainfall produce floods. But its magnitude in terms of frequency and areal coverage can increase markedly due to anthropogenic factors like deforestation, inappropriate management of floodplains and unscientific agricultural practices (Eapen et al, 2000).

Drainage: Pattern and Density The drainage patterns have a complex arrangement in the basin with considerable variation in spatial arrangements controlled by topography, slope, rock type and structural deformations. The basin is characterized by dendritic to sub-dendritic type of drainage pattern with variable density. Angular joint/ fracture controlled drainage also observed Figure 3 Drainage network of Karamana river basin (Fig.3). The densest dendritic pattern is developed on the hard crystalline rocks. In some areas the drainage pattern is sub dendritic reflecting structural control. The Karamana river basin is a 7th order stream with a drainage area of 702 km2. The total length of the stream is 68 km and the perimeter of the basin is 172 km. The density analysis carried out under this study has revealed that the drainage density varies between 0.02 to 6.0 km/sq.km depending on the geological and geomorphological setup at different locations within the Karamana river basin (Sreeja, 2017).

TERRAIN CHARACTERISTICS Geology The study area that falls within Kerala State forms an important segment of the South Indian Pre-Cambrian terrain, where the Archaean continental crustal rocks such as granulites, granites, gneisses and greenstones are excellently preserved. Geologically, the State is occupied mainly by 190 ECO-CHRONICLE three major rock units 1) Pre-Cambrian crystallines, 2) formations range in age from Miocene to Recent. Table I Tertiary sedimentaries, and 3) Quaternary deposits. shows the general geological sequence of Kerala About 85% of the Kerala State is covered by crystalline (Sreeja, 2017). rocks and the remaining by Tertiary and Quaternary sedimentaries. A major portion of the crystallines and Geologically, the Karamana river basin is composed of Tertiaries are capped by laterites. Along the coast, diverse rock types from Archaean crystallines to recent sedimentary formations (Tertiaries and Quaternaries) alluvium. Nearly 90% of the study area is composed of overlie the crystalline basement. The sedimentary garnetiferous-biotite-sillimanite gneiss with or without graphite (khondalite). The remaining area is Fig. 4 Major lineaments of Karamana river basin composed of garnet-biotite gneiss with associated migmatites, quartzo-feldspathic- hypersthene granulite and garnetiferous granite gneiss. These rocks are intruded at many places by acidic (pegmatites and quartz vein) and, basic (gabbro and dolerite) rocks. A few patches of quartzofeldspathic and calc granulites are also reported from the area. In addition to these, a few patches of Quaternary sediments represented by pebble beds, sand and clay deposits are also reported from places like Kottakkakom, Aryanad, , Mundela and (Sreeja, 2017). Arun, (2006) reported the age of peat as 3300 ± 90 years before present (ybp), at a depth of 2.5m below ground level at Changa (Near Aryanad). This is a clear evidence of the occurrence of Late Quaternary (Holocene) sediments in the study area.

Geomorphology Geomorphologically, the Karamana river basin exhibits undulating topography with

Table I. General geology of Karamana River Basin (GSI, 1995; Sreeja, 2017) Era Period Group Lithology Holocene Marine Sand Fluvio-marine Clay and silt Quaternary Fluvial Sand, silt, clay Pleistocene Palaeo-marine Sand Pebble bed Mio-Pliocene Laterite Mesozoic Acid Intrusive Quartz vein Tertiary (61-144 Ma) Basic intrusive Pegmatite Dolerite Proterozoic Migmatite Complex Hornblende gneiss Hornblende-biotite gneiss Granite gneiss

Archaean Charnockite Group Charnockite/charnockite gneiss Pyroxene granulite

Peninsular Gneissic Complex Hornblende-biotite gneiss PRECAMBRIAN Wayanad Group Magnetite quartzite Quartz-mica schist Fuchsite quartzite Base not recognized Amphibolite Metapyroxenite Talc-tremolite-actinolite schist ECO-CHRONICLE 191 steep slopes in the eastern reaches. The basin has been hydrogeomorphological features within the basin have classified as lowland, representing the coastal belt, been identified. Based on the relationship among the midland, comprising mostly of laterites and, highland topography, lithology and drainage, the study area has region, covered by hard rocks. However there are small been classified into different hydrogeomorphological intermittent hillocks of 100 to 500 m amsl in the midland units such as lateritic uplands, buried pediments, Alluvial region. These small hillocks of midland region are plains, flood plains, beach and coastal plains (Sreeja, covered by laterites. Through remote sensing, various 2017). Structural hills are normally considered as poor

Fig. 5 Slope map of Karamana river basin source of groundwater (Narasimha Prasad et al, 2013). However, in the study area the structural hills are characterized by a number of lineament intersections and therefore, in such places extraction of groundwater can be done through deep bore wells. Residual mounds are formed by the prolonged erosion and weathering of pre-existing surface features of the plateaux, plains and even original complex tectonic mountains and are considered as poor in groundwater prospecting. Pediments are formed where a thin veneer of soil overlies a hard rock terrain. The groundwater condition in pediments is expected to vary depending upon the type of underlying folded structures, fracture systems and degree of weathering. Groundwater prospecting in pediments can vary from normal to poor (Narasimha Prasad et al, 2013), but presence of any lineaments or fractures can provide some scope for movement of groundwater and hence good for groundwater exploration. Valley fills and water bodies are seen as isolated or inter Fig. 6 Land use of Karamana river basin connected patches in the entire study area. Valley fills result when streams dump their sediments suddenly due to obstruction and a reduction in flow velocity. Since they have high moisture content, they are thickly vegetated and can easily be identified in the imagery by their tone and texture. Valley fills are considered as good potential zones for groundwater exploration (Sarkar et al, 2001).

Lineaments Lineaments provide the pathways for groundwater movement and are hydro geologically very important (Seker, 1966). A lineament is defined as large-scale linear feature, which expresses itself in terms of topography of the underlying structural features. Lineaments, being surface manifestations of structurally controlled linear or curvilinear features, are identified from the satellite imageries by their relatively straight tonal alignments. Lineaments can be joints, fractures, dyke systems, straight course of streams and vegetation patterns. In hard rock 192 ECO-CHRONICLE terrains, lineaments represent areas and zones of It is observed in some places that the lineaments faulting and fracturing resulting in increased secondary intersect each other and such areas are expected porosity and permeability. Hence they are good to be more favourable for groundwater development indicators of the accumulation and movement of (Seker, 1966; Narasimha Prasad et al, 2013, Sreeja groundwater. In Karamana river basin the lineaments et al, 2015). A lineament density map is a measure are dominant in the midland region, followed by of quantitative length of linear features expressed highlands and coastal region (Fig. 4). Major lineament in a grid. Lineament density map of an area can direction is NW-SE. Most of these lineaments are found indirectly reveal the groundwater potential, since the to follow linearly arranged valleys and hence are presence of lineaments usually denotes a permeable potential for groundwater development. The lineaments zone. Areas with high lineament density are are cross checked in the field at a few places and found favourable for groundwater development the water levels in the nearby existing wells at very (Narasimha Prasad et al, 2013; Arun et al, 2014; shallow depth and all are perennial. Sreeja, 2017).

Fig.7 Spatial distribution of groundwater fluctuation Slope The Karamana river basin exhibit a spectrum of slope classes from level - nearly level (A) to very steeply sloping (G) features. The slope characteristics of the study area are depicted in Fig.5. Gently sloping (3 - 5%) to moderately steeply sloping (10 - 15%) classes cover a greater part (52.21%; 367 km2) of the study area. Nearly level (<1%) to moderately sloping (1-3%) classes constitute 6.83% (48 km2) and occupy in the lower part of the study area. Steeply sloping to very steeply sloping areas (287 km2; 40.95%) are confined to high altitude zones.

Landuse Landuse describes how a parcel of land is used for agriculture, settlements or industry, whereas landcover refers to the material such as vegetation, rocks or water bodies, which are present on the surface (Anderson et al. 1976). Based on ground truth verification, the landuse of the study area has been classified. Landuse plays a significant role in the

Table II. Criteria for demarcating groundwater potential zones

Category Criterion

Alluvial formation, valley region, low drainage density, High lineament density, Flat to gentle slope (<5%), Depth to water table (DTW) at 1 to 3 m below VERY HIGH ground level (bgl), and availability of water throughout the year (Perennial).

Low land or valley portions in the Lateritic midlands areas covered by lateritic soil, low drainage density, High lineament density, Having flat to gentle slope HIGH (<5%), and availability of water throughout the year (Perennial).

ZONES Lateritic formations in midland region, low to moderate drainage density, moderate lineament density, slope between 5% to 20%, and availability of MODERATE water throughout the year (Perennial).

Laterites or hard rocks in the highland region with more than 20% slope, high GROUND WATERGROUND POTENTIAL LOW drainage density, low lineament density, seasonal water availability. ECO-CHRONICLE 193 development of groundwater resources. In this study, the sedimentary formations comprise the (1) Recent alluvium landuse map is taken as one of the thematic layers for that occur along the coastal plain and in the valleys and preparing groundwater potential zones. Agricultural lands are mainly composed of sand and clay (2) Tertiary cover a major part of the Karamana river basin (Fig.6). formation such as Warkali, Quilon and Vaikom beds and Of the various land use classes identified in the study (3) laterites which occur as a capping over crystallines area, forests and forest plantations in the uplands (CGWB, 2013; Sreeja, 2017). The river basin is covered constitute about 16.4%. The watershed area of by phreatic, semi-confined and confined aquifers. In the reservoir is used extensively for agricultural coastal/river alluvium, laterite, weathered and fractured activities and settlements whereas the catchment of rock, groundwater occurs under phreatic condition. In Peppara reservoir is mainly forest and forest plantations. deep seated fractured crystalline rocks, groundwater Paddy cultivation is limited. Agricultural plantations cover occurs under phreatic or semi-confined or confined a greater part (451.88 km2; 64.37%) in the middle and conditions. lower regions. , rubber, plantain and tapioca are extensively raised in the area. Depth to Water Level Observation wells were established in such a way that HYDROGEOLOGICAL CONDITIONS different physiographic region is represented and wells Groundwater Occurrence and Movement are equally distributed. Based on these criteria, 50 wells were established in the Karamana basin. Seasonal The Karamana river basin is characterised by crystalline monitoring of depth to water level was carried out for rocks of Archaean age in the eastern part and is overlain almost three consecutive years. The lowest depth to by sedimentary formations ranging in the age from water level (bgl) is found to be 0.18 m at Miocene to Recent along the western coast. Based on during the post-monsoon and the deepest water level is the water bearing properties, the entire basin can be found to be 36.20 m during pre-monsoon. broadly classified into crystalline formation (Deep The spatial distribution of groundwater level fluctuation aquifers) and sedimentary/laterite formations (Shallow during the study is presented in Fig.7. The analysis of aquifers). The crystallines which include khondalites, the long-term water level reveals that the area does not charnockites, migmatites and intrusives occur from face any severe groundwater availability problems. From shallow or deep levels, with or without fractures. Whereas the figure, it is clear that deeper water level of more than Fig. 8. Groundwater potential zones of Karamana river basin 20 m bgl is encountered in areas like Peringamala and Mukkola. The deeper water levels in these areas can be highly correlated with the physiographic set up of the area. These are the areas of occurrence of thick laterites and sandstones belonging to the Tertiary formations. Seasonal fluctuation indicates that in the major portion of the district, there is rise in water level in the range of 0– 5 m except in a few isolated patches (CGWB, 2013).

An analysis of the data shows that the depth to water level during pre- monsoon and post-monsoon is minimum in alluvium and maximum in laterites. This may be due to the fact that since alluvium occurs in the discharge zone, water level is shallow and fluctuation less. The high fluctuation shown by wells tapping laterite can be attributed to the cavernous and porous nature of laterite, by which it gets easily recharged by a heavy showers and 194 ECO-CHRONICLE due to the same porous nature water easily drains off coastal lowland, lateritic midland and crystalline high land from the aquifer as subsurface run off (Sreeja, 2017). of Karamana river basin. This study was carried out to The long term trend analysis (2002–2011) shows that arrive at estimates of density, usage, growth pattern etc. the water level during pre- and post-monsoon indicates of different types of wells. The three sample areas a rising as well as falling situation. The post-monsoon investigated in Karamana river basin are located in period falling trend ranges from 0.0016 to 0.4975 m/year Pachallur (lowland); Mundela (midland) and Kottur and rising trend ranges from 0.0079 to 0.2352 as (highland) areas. Groundwater in Karamana river basin observed by CGWB (2013). is extracted through large diameter dugwells tapping shallow phreatic aquifers in alluvium, laterite and Saturated Thickness weathered formations. Borewells are being used to tap The data on pre-monsoon and post-monsoon depth to the deep fractured aquifers in crystalline rocks. Filter point water level and the depth to bedrock in the Karamana wells are also being used to tap the groundwater from basin has been used to obtain the respective seasonal the coastal alluvial aquifers (Sreeja, 2017). saturated thickness. The lowland region has a saturated thickness of about 2–10 m during pre-monsoon and 6– The density of dug wells in Karamana river basin is 13 m during post-monsoon. In midlands this varies considerably high due small land holdings (less than 1 between 0 (Dry) to 16 m and 0.8 to 17 m during pre- hectare) and each family has its own well. In the river monsoon and post-monsoon respectively. In highlands basin, the analysis of well inventory data shows that on pre-monsoon saturated thickness is 0 to 6 m and 0.3 to an average in 1 sq.km area there will be typically 281 8 m during post-monsoon. dug wells in lowland, 224 dug wells in midland and 92 dugwells in highland region. The analysis also indicates GROUND WATER POTENTIAL ZONES that in 1 sq.km area, about 85% of the wells is exclusively used for domestic purposes. Less than 10% are found Integrating all the gathered information such as geology, to be exclusively used for irrigation purposes. The density geomorphology, drainage, slope, lineaments, aquifer of dug wells, even if it is extrapolated to the other areas, parameters, ground water level fluctuation and saturated remains more or less constant for the entire basin thickness, the Karamana river basin has been classified (Sreeja, 2017). into different groundwater potential zones viz VERY HIGH, HIGH, MODERATE and LOW using overlay Details of wells for different uses have helped in analysis tools in Geographical Information System (Fig. estimating the draft from different types of wells in 1 sq.km 8). The criteria for classification is presented in Table II. in the study area. These results have been suitably averaged and extrapolated to get the draft within the Valley fills, pediments and moderately dissected plateaus Karamana river basin. In Karamana river basin about of the basin are found to be favourable geomorphic units 80% of the dug wells and 100% of the bore wells are for groundwater exploration and development, whereas fitted with energized pumps. More than 90% of these structural hills, residual hills, residual mounds, and lin- wells are fitted with pumps of less than 2 HP and these ear ridges are poor groundwater potential zones. wells are mostly pumped for 20–30 minutes in a day. Hydrogeomorphology, lineament and slope play vital Most of the energized wells are used for domestic roles in the occurrence and movement of groundwater purposes. Only very few wells are used for irrigation or in the study area. This integrated hydrogeological study irrigation-cum-domestic purposes. Irrigation through revealed that the downstream portion of the Karamana pumping of wells, in the basin, is for coconut, arecanut, river basin is categorised as very good to good ground- banana and other plants grown within the house water potential zone whereas the eastern portion of the compound (Sreeja, 2017). basin is categorized as of poor to moderate groundwa- ter potential. It is estimated that about 30% of the basin Based on the results of the well inventory, the comes under the very high to high category in terms of groundwater draft from different types of wells has groundwater potential, while the remaining area comes been estimated for Karamana river basin. Considering under the moderate to low category. an average of 5 person per well using 100 litres of water each per day throughout the year, the total CURRENT STATUS OF GROUND WATER groundwater draft per well will be about 180 m 3 per DEVELOPMENT year. Considering about 1500 litres of water extracted per day from each well for irrigating garden and As part of the present study, well inventory was carried plantation crops within the house compound during out in selected sample areas of about 1 sq.km each non-rainy days, total groundwater draft per well will representing different physiographic regions such as be 270 m3 per year. ECO-CHRONICLE 195

In areas having less than 20% slope, the average density CONCLUSIONS of wells is 250/sq.km in the Karamana river basin. In areas having greater than 20% slope, the average Valley fills, pediments and moderately dissected plateaus density of wells is 92/sq.km. 80% of the wells are of the basin are found favourable geomorphic units for exclusively for domestic purpose and 5% of the wells groundwater exploration and development. It is estimated are exclusively for irrigation purpose. Considering the that about 40% of the basin comes under the very high above assumptions the draft from the wells for domestic to high category in terms of groundwater potential. purpose is 25.54 Million cubic meters (MCM)/year and Groundwater assessment has shown that the stage of for irrigation is 2.37 MCM/year in the Karamana river development in the Karamana Basin as 47.65% and that basin. Thus the total groundwater draft in the river basin there is no significant decline of water table in the pre- is 27.91 MCM/year. monsoon and post-monsoon intervals. Hence the basin can be categorized as “SAFE” for future groundwater GROUND WATER EVALUATION FOR FUTURE development. In the coastal low land regions, no serious DEVELOPMENT saline water intrusion problem is reported within the basin. However, since there is a possibility of saline water Groundwater evaluation for the Karamana Basin intrusion especially during peak summer, future involving annual ground water availability, computation groundwater development in the coastal region should of stage of ground water development and categorization be taken-up with caution. Consequently, a well-planned for future development as per the Ground water programme of groundwater development to meet both estimation Methodology of Central Ground Water Board drinking and irrigation water requirements (with the (CGWB, 2004) is presented in this section. The former being given greater priority) can be safely initiated groundwater assessment unit for the basin comprises of in the Karamana river basin to optimally utilize the the total river basin area. Portions having slope less than groundwater potential and at the same time, ensure that or equal to 20% have been demarcated and groundwater the groundwater development is both sustainable and assessment made only for such portions. has no adverse environment impacts.

The area in which ground slopes are less than or equal to ACKNOWLEDGEMENTS 20% within the Karamana river basin is 531 sq.km. The first author acknowledges the financial support Groundwater assessment is made only for this area. provided by the Woman Scientists Cell of Kerala State Substituting 2600 mm for the normal (long term average) Council for Science, Technology and Environment rainfall and 7% for the rainfall–recharge factor for laterites, Committee (KSCSTE) through the Woman Scientist the rainfall recharge in an year is estimated as 96.64 MCM Program and motivation by the Director and staff, School by the rainfall–infiltration factor method. Substituting 2.37 of Environmental Sciences, Mahatma Gandhi University MCM for the groundwater draft for groundwater-based in pursuing her Ph.D. irrigation and 25% of the applied water contributing to recharge by return flow, the recharge due to return flow REFERENCES from ground water based irrigation is computed as 0.59 MCM. Substituting 96.64 MCM for rainfall recharge, Arun P.R., M.S. Anish, V. Geethu Krishna, N.B. 0.59 MCM for return flow from groundwater irrigation, 38.66 Narasimha Prasad., 2014. Identification of Groundwater MCM for base flow, the net annual groundwater availability Potential Zones through Spatial Information Systems: A th is estimated as 58.57 MCM. Case Study, Proceedings of the 4 International conference on “Hydrology and Watershed Management- Present annual groundwater draft for drinking and ICHWAM 2014, 29 Oct-1 Nov 2014”, Vol. 1, pp. 164- domestic water supply and groundwater irrigation are 173, Allied publishers, New Delhi. 25.54 MCM and 2.37 MCM respectively. Hence annual gross groundwater draft for all uses is 27.91 MCM. Arun, P.R., 2006 Sedimentology and Hydrogeochemistry of Aruvikkara and Peppara Reservoir Basins, Kerala, The net annual groundwater availability is 58.57 MCM India. Unpublished Ph.D. Thesis. Cochin University of and the gross annual groundwater draft is 27.91 MCM, Science and Technology. the stage of groundwater development is computed as 47.65%. Both pre-monsoon and post-monsoon water CGWB., 2004. “Groundwater Estimation Methodology”, levels do not show any significant declining trend. Ministry of Water Resources, Government of India. Consequently the Karamana river basin can be categorized for future groundwater development as CGWB., 2013. Ground water Information Booklet of ‘Safe’. Thiruvananthapuram District. 36p. 196 ECO-CHRONICLE

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