Jour. Geol. Soc.

India (2023) 99:1417-1426

https://doi.org/10.1007/s12594-023-2488-5

ORIGINAL ARTICLE

Proposed Sequential Process to Identify Smaller Vulnerable Area

from a Larger Area for Groundwater Modelling Studies using
Groundwater Potential Zone and Stage of Groundwater
Development Category Maps – A Study for Cheyyar
River Basin, Tamil Nadu, India
Vishnuvardan Narayanamurthi* and Annadurai Ramasamy
Department of Civil Engineering, SRM Institute of Science and Technology, Kattangulathur - 603 203, India
*E-mail: vishnuvardance@gmail.com

Received: 15 October 2022/ Revised form Accepted: 20 March 2023

© 2023 Geological Society of India, Bengaluru, India

ABSTRACT and Pfister, 2022). As the population increases, the demand for food,
Groundwater modelling requires data from electrical resistivity water supply and economic growth increases the demand for these
surveying and pumping test, which consumes more time and cost water resources. Nearly 80% of water utilisation is for agriculture and
for its collection for a larger area. In this study, using remote sensing the remaining for domestic and industries. The groundwater contributes
data and GIS tools, a sequential process is proposed for finding 95% of the demand in the non-perineal river basins. Thus, groundwater
the suitable vulnerable smaller area for groundwater modelling plays an important role in water management and impacts the country’s
from a relatively larger area. The chosen larger area, Cheyyar sustainability and socio-economic development. Therefore, assessing
river basin, Tamil Nadu, India spreading 4358 km 2 , has and managing this resource becomes important and highly prioritised
groundwater decline due to aquifer groundwater exploitation. (Duttagupta et al., 2020; Han and Currell, 2022). The major problem
Groundwater potential zone with river basin as boundary and stage regarding groundwater is the rapidly declining groundwater level
of groundwater development with firrka boundary are used for due to climate change and groundwater pumping for agriculture in
this study. For comparison, 56 firrkas covering the entire river India and the quality deterioration due to the mixing of pollutants
basin were reduced to 26 firrkas, with at least 95% preserved area from surface water to groundwater through infiltration and percolation
after reducing along the river basin boundary. Groundwater (Patle et al., 2015; Qiu et al., 2018; Das et al., 2020). These issues
potential zones were converted to a firrka-wise representative need to be addressed as soon as possible by evaluating the efficiency
potential zone by considering mode as a central tendency. As all of groundwater monitoring systems; surface water models need to be
the firrkas come under the moderate category, it was further modified with the incorporation of human interventions, and the
reclassified into good-skewed-moderate, moderate and poor- fluctuation of groundwater should be studied with changing climate
skewed-moderate. The combinational class was developed by (Kulkarni et al., 2015; Mukherji, 2022). Furthermore, quality
combining the two category maps for each firrka. The over- monitoring should be improvised on in situ measurement, which will
exploited and critical categories under good-skewed-moderate and be useful for analysing the transport instantaneously—control and
over-exploited under the moderate category were considered prevention measures to be taken on human intervention to pollution
vulnerable combinations. A total of eight firrkas come under the generation (Mukherjee et al., 2015; Prasad et al., 2019; Adimalla
vulnerable category. Based on data availability and data collection et al., 2020).
feasibility in the vulnerable firrkas, Kelur’s moderate Groundwater modelling evolved as a physical model (sandbox
overexploitation category is considered a smaller vulnerable area and analogue) in the initial stages. Later, with the introduction of
for groundwater modelling study. computing machines, mathematical models became analytical models
(Hantush and Mariño, 1996; Hu, 2017). Analytical models are
INTRODUCTION equations having an exact solution. It has limitations that it works
Consumable water, an essential resource for life, is available in well for homogenous and isotropic systems. However, for a complex
about 32% of the global freshwater reserve. About 96% of these system, the solution is approximated, and numerical models come into
consumable waters are stored as groundwater and the remaining as play (Basu et al., 2012; Erol and François, 2018). Modelling done for
surface water (Gorelick and Zheng, 2015; Rodell et al., 2018). In India, the relatively larger area comes under regional groundwater modelling.
the annual average rainfall is 1215 mm generating 4000 km3 of fresh But some local-scale effects on the groundwater might affect the local
water. Of these, 1870 km3 of water is generated as surface runoff, and groundwater environment, which comes under local groundwater
431 km3 is stored as groundwater. Nearly 690 km3 of surface water is modelling (Barthel and Banzhaf, 2015; de Graaf et al., 2017;
only channelised and utilised properly (Leng and Hall, 2021; Kulionis Amanambu et al., 2020). Various numerical models include finite

0016-7622/2023-99-10-1417/$ 1.00 © GEOL. SOC. INDIA

difference, finite element and finite volume for solving the flow Apart from the potential mapping, various agencies in India assess
equations. For nearly three decades, numerical models have been used the ground truth. For example, Central Groundwater Board publishes
successfully for different groundwater simulation and prediction a series of reports on Assessments on dynamic groundwater resources,
models whose accuracy depends on the accuracy of the input data and which provide the stage of groundwater development for each block/
appropriate solving techniques (Zhou and Li, 2011; Wu and Zeng, firrka of India (CGWB, 2006, 2011, 2014, 2017, 2019, 2021; GEC,
2013; Kahe et al., 2021). The data required are classified under 2009 & 2017).
topographical, subsurface geometrical and hydraulic properties, and For groundwater modelling, the data collection is a tedious and
finally, boundary and initial conditions of the modelling volume time-consuming process for a large area. Thus, there is a search for a
(Rojanschi et al., 2006; Pavlovskiy and Selle, 2015). Topographical framework for choosing a vulnerable, smaller area suitable for further
features such as surface elevation, drainage and water body features, groundwater modelling. Unfortunately, there is no standard framework
well location, and land use pattern are prepared using remote sensing or procedure for identifying the vulnerable smaller area. Therefore,
and Geographical Information system tools. But subsurface features this study proposes a novel framework for identifying the vulnerable
such as lithological units, aquifer types, and aquifer geometry properties smaller area for further detailed groundwater modelling studies using
are prepared after subsurface investigation, such as borehole logging Remote sensing and GIS tools for the Cheyyar river basin, Tamil Nadu,
and electrical resistivity methods. Finally, the aquifer’s hydrogeologic India.
properties are determined using a pumping test in the field (Tziatzios
et al., 2021; Baalousha and Lowry, 2022). STUDY AREA
Topographical data is easy to collect and compute for any Cheyyar River Basin (Fig. 1) is a sub-basin of the Palar basin in
resolution. But groundwater is difficult to visualise the movement and South India. Cheyyar river basin is limited within the boundary of
availability unless drilling is done. Thus, making the subsurface 12°55'2.6" N and 12°14'7.3" N latitude and between 78°39'52.4" E
investigation more difficult for large numbers in closer proximity and 79°51'55.5" E longitude with an area of 4358 km2. The Middle
consume a lot of time and cost (Turner, 2006; Forman, 2020). Also, Palar sub-basin bounds the river basin in the northeast and east, the
the feasibility problem for the data collection is reduced by decreasing Killiyar basin in the southeast, the upper Palar basin in the northwest
the area of study for the problem (Beniston et al., 2012; Chang et al., and the Thenpennai river in the south and west. The region is a semi-
2016). Remote sensing data and GIS tools come in handy in selecting arid tropical climatical zone with an annual average normal rainfall of
a suitable reduced area. For the past two decades, groundwater potential 1046 mm. The maximum of 87% in the monsoon (45% in South East
zone maps have been developed for various outputs such as and 42% in North West). In 2020, the region’s rainfall was about
groundwater availability, groundwater recharge, recharging site 1200 mm, 82% from the monsoon season. Figure 2 shows the Cheyyar
selection and check dam site selection (Panahi et al., 2020). It is helpful river is the main river flowing in this study area, with a length of 160
for various decisions and policymakers for sustainable groundwater km along the longest path of the basin. It originates from Jawadhu
management. These potentials are generated by integrating various hills in the eastern part of the basin, flows along the east – the northeast
input layers (Ravi and Sudalaimuthu, 2022; Ravichandran et al., 2022). direction, and drains into the Palar River near Kanchipuram. All the

Fig. 1. Index map of the study area.

1418 JOUR.GEOL.SOC.INDIA, VOL.99, OCT. 2023

 Fig. 2. Drainage map of the study area. Fig. 3. Geomorphologic map of the study area

tributaries from the Jawadhu hills draining into the Cheyyar river are 75%, forest covers in the western Jawadhu hills at about 16%, and
in different locations. Kamandalanaganadhi is one of the major water bodies at about 4%, less than 1% covered as habitation and the
tributaries that travels through Arni town and becomes the water source remaining exist as barren/fallow and wastelands. Fifteen lakhs of
in and around the town. Apart from drainage, there are 549 tanks and habitats reside in the study area, whose major occupation is agriculture,
reservoirs, of which the Kupanatham reservoir of Cheyyar river and and a few small-scale industries based on agriculture are the next
the Senbagathope reservoir of Kamandalanagnadhi have significant occupation. Sugarcane, rice and groundnut are the major crops
water-bearing capacity. Figure 3 shows the region’s geomorphologic grown.
map, consisting of pediment pediplain complex throughout the region
except with dissected hills and valleys in the western Javadhu hills DATA UTILISED
and flood plains around the banks of the drainages. Tiruvannamalai
Groundwater Potential Zone Map
district covers 74.1% of the basin. Vellore and Ranipet districts in the
north, Titupathur district in the west and Kanchipuram district in the Many researchers found a suitable map for groundwater
east, covering 6.1%, 10.6%, 4.9% and 4.2% of the basin area management decisions with spatial variation is the Groundwater
respectively. From district boundaries total of 58 firrkas are available, Potential Zone (GWPZ) map. It qualitatively represents groundwater
out of which three come under the Thirupathur district, six under the prospects by integrating various influencing weighted thematic layers.
Ranipet district, five under the Vellore district and the remaining In this study, the potential zoning for Cheyyar River Basin, South
44 firrkas under the Tiruvannamalai district. Arani, Chengam, Polur, India, using eleven thematic layers from a previously published
Arcot, and Cheyyar are major towns in the basin. Table 1 shows the research article. Weights were assigned to each layer using the most
groundwater resources availability, extraction and stage of widely used Analytical Hierarchy Process integrated with bivariate
ground=water development for each block of Tiruvannamalai analysis. Finally, using GIS tools, the layers were weighted overlayed,
district. Land use pattern covers most agricultural land at about and the final output of GWPZ with four classes Very Good (VG),

Table 1 Tiruvannamalai district block wise groundwater resources availability, utilisation and stage of groundwater development for 2020
Block A B C = A-B D E E = C+B F = E/C Category
(Mcm) (Mcm) (Mcm) (Mcm) (Mcm) (Mcm) (%)
Anakavur 61.4103 6.1412 55.2691 46.092 1.28484 47.37684 85.72 Semi Critical
Arani 53.3625 3.6052 49.7573 36.6872 2.96642 39.65362 79.69 Semi Critical
Chengam 39.0134 3.9013 35.1121 53.3435 1.38022 54.72372 155.85 Over Exploited
Chetpat 68.1351 6.8134 61.3217 52.3962 1.37922 53.77542 87.69 Semi Critical
Cheyyar 58.7379 5.8739 52.864 42.057 3.06015 45.11715 85.35 Semi Critical
Jawadhu hills 18.7935 0.9427 17.8508 22.3 0.9491 23.2491 130.24 Over Exploited
Kalasapakkam 65.413 4.1681 61.2449 61.6019 2.00991 63.61181 103.86 Over Exploited
Keelpennathur 84.0791 8.408 75.6711 79.4484 1.94199 81.39039 107.56 Over Exploited
Pernamallur 89.2918 7.8663 81.4255 85.0172 1.62851 86.64571 106.41 Over Exploited
Polur 78.1155 7.8116 70.3039 76.0352 2.4113 78.4465 111.58 Over Exploited
Pudupalayam 67.7441 6.7744 60.9697 79.985 1.53858 81.52358 133.71 Over Exploited
Thandrampat 82.4183 5.0184 77.3999 68.4736 2.35476 70.82836 91.51 Critical
Thellar 52.1218 2.6106 49.5112 46.8232 1.00329 47.82649 96.6 Critical
Thurinjapuram 66.4193 5.5795 60.8398 60.6317 1.33736 61.96906 101.86 Over Exploited
Tiruvannamalai 50.4013 4.1958 46.2055 37.148 2.31587 39.46387 85.41 Semi Critical
Vandavasi 88.1656 8.8166 79.349 82.4187 2.89551 85.31421 107.52 Over Exploited
Vembakkam 76.2244 5.7258 70.4986 52.2642 2.09701 54.36121 77.11 Semi Critical
West Arani 65.9184 6.5919 59.3265 57.1304 2.93209 60.06249 101.24 Over Exploited
A - Annual Replenishable Groundwater Resources (Total), B - Natural Discharge During Non-Monsoon Season, C - Net Groundwater
Availability, D - Irrigation Draft, E - Domestic and Industry Draft, F - Stage of Groundwater Development
Source: Central Groundwater Board

JOUR.GEOL.SOC.INDIA, VOL.99, OCT. 2023 1419

 (CGWB, 2021). The assessed firrka are categorised into over-exploited
(OE) having greater than 100% of SGWD, critical (C) with 100 – 90
% SGWD, semi-critical (SC) with 90 – 70% SGWD and safe (S) with
less than 70% (GEC, 2017).

METHODOLOGY
Comparing basin boundary with administrative boundary.
GWPZ map can be prepared with an administrative boundary or
watershed boundary. At the same time, the SGWD map is prepared
with administrative boundary (firrka/block). If both maps share the
same border, then no comparison problem arises. But comparing
watershed boundaries with administrative boundaries becomes
difficult. In this study similar type of situation occurred. Thus, the
firrkas (administrative boundary), which covers the entire watershed
Fig. 4. Groundwater potential zone map (source: Narayanamurthi and boundary of the GWPZ map, were chosen. Comparing maps shows
Ramasamy, 2022). that the SGWD map boundary exceeds the GWPZ watershed boundary.
Thus, the SGWD map was clipped with the watershed boundary, and
the firrkas lying on the border of the watershed boundary have reduced
Good (G), Moderate (M) and Poor(P) (Fig. 4) in raster format is area. As groundwater potential is within the basin boundary and SGWD
obtained. The very good and good zones have a higher prospect of indicated a single category for the whole firrka, it becomes unfair for
groundwater existence, and moderate and poor zones are with the trimmed firrkas. Therefore, the firrkas with the reduced area should
descending prospect of groundwater, respectively, than the previous be eliminated from comparing for a perfect comparison. But in this
zones. (Narayanamurthi and Ramasamy, 2022). study, firrkas with 95% of the original administrative area and above
were compared with the GWPZ map, as a 5% error is assumed to be
Stage of Groundwater Development Map fine for initial work. The firrkas covering 95% and above area are
Another quantitative factor for assessing groundwater resources shown in table 2.
is the stage of groundwater development (SGWD) map. The Stage of
groundwater development is the ratio of annual groundwater draft to Normalising the Potential to Single Representative Value for
net groundwater availability in percentage. The yearly groundwater each Firrka
draft includes various groundwater extraction and evapotranspiration. The GWPZ map is a raster image with the river basin as the
The Groundwater Estimation Committee (GEC) (2015) report boundary is converted to a vector map representing one zone for each
estimates net groundwater availability. The SGWD is assessed on firrka border to compare and combine with the SGWD map. The area
block/firrka level administrative boundaries by the central groundwater of each zone in each firrka was computed. The maximum area (mode)
board for the years 2004 (CGWB, 2006), 2009 (CGWB, 2011), 2011 of the zones was considered a single representative zone. But all firrkas
(CGWB, 2014), 2013 (CGWB, 2017), 2017 (CGWB, 2019) and 2020 have moderate representative category (mode). So, the moderate zone
Table 2 Area before and after clipping for 95% and above area preserved firrkas
Name Block Firrka Original Preserved Preserved
Area km2 Area km2 Area %
Tiruvannamalai Arani Agrapalayam 85.76425 85.76425 100
Tiruvannamalai Arani Arni 41.56141 41.56141 100
Tiruvannamalai West Arani Mullipattu 51.45673 51.45673 100
Tiruvannamalai Cheyyar Cheyyar 78.5518 78.5518 100
Tiruvannamalai Kalasapakkam Kadaladi 63.35085 63.35085 100
Tiruvannamalai Kalasapakkam Kalasapakkam Rf 87.47222 87.47222 100
Tiruvannamalai West Arani Kannamangalam 72.91828 72.91828 100
Tiruvannamalai Chetpet Thachambadi 74.15637 71.38608 96.26425
Tiruvannamalai Chetpet Mandakolathur 85.56523 85.56523 100
Ranipet Timiri Kalavai 89.4935 88.96278 99.40698
Tiruvannamalai Polur Polur 81.72054 81.72054 100
Tiruvannamalai Jawathu Hills Pudupalayam 11.73588 11.73588 100
Tiruvannamalai Peranamallur Kolappalur 89.66784 89.66784 100
Tiruvannamalai Arani Sathyavijayanagaram 90.70204 90.70204 100
Tiruvannamalai Pudupalayam Thandrampat 102.7622 102.7622 100
Tiruvannamalai Cheyyar Vadathandalam 95.90156 95.90156 100
Tiruvannamalai Cheyyar Vakkadai 79.48574 79.48574 100
Tiruvannamalai West Arani Vinnamangalam 72.98092 72.98092 100
Tiruvannamalai Vembakkam Dusi 76.47262 76.09061 99.50046
Tiruvannamalai Kalasapakkam Kalasapakkam 85.28864 82.61382 96.8638
Tiruvannamalai Chengam Chengam 101.2878 101.2878 100
Tiruvannamalai Polur Kelur 129.7849 125.3618 96.59196
Tiruvannamalai Thurinjapuram Nayadumangalam 90.92996 87.49098 96.21799
Ranipet Timiri Mambakkam 119.0868 119.0868 100
Tiruvannamalai Polur Sandavasal 126.6971 126.6971 100
Vellore Kaniyambadi Kaniyambadi 105.4929 104.6541 99.20486

1420 JOUR.GEOL.SOC.INDIA, VOL.99, OCT. 2023

is further classified into Good skewed Moderate, Moderate and Poor availability and data collection feasibility was checked. The firrka
skewed moderate based on conditions as follows: having some data available and difficult data collection feasibility was
(i) The firrka, greater than 75% of the moderate area, is considered rejected. Then, Firrka, which has both data availability and data
pure moderate. collection feasibility alone, was selected. These firrka can be used as
(ii) The firrka having less than 75% of the moderate area and greater a study area for groundwater modelling. But in some cases, village-
than 200% of good/poor zone area ratio are categorised as Good level regions are to be chosen based on village maps or micro watershed
skewed moderate. maps overlayed on the chosen firrka. Such a village or micro watershed
(iii) The firrka having less than 75% of the moderate area and greater can be selected for the modelling studies. The final firrka and overlying
than 200% of poor/good zone area ratio are categorised as Poor micro watershed were chosen as a smaller study area for further
skewed moderate. investigation of groundwater modelling. The methodology flowchart
(iv) The firrka, less than 75% of the moderate area and not satisfying for determining vulnerable smaller regions is shown in figure 5.
(ii) and (iii) are considered pure moderate.
The representative GWPZ and modified representative GWPZ RESULTS AND DISCUSSION
are shown in table 3
Comparing Basin Boundary with Administrative Boundary
Choosing a Vulnerable Combination of Two Maps Figure 6 shows the 58 firrkas covering the entire river basin and
Now the attributes of both maps are combined to get the 26 trimmed firrkas covering above 95% of the area within the basin
combinational classes as shown, and the combined area is analysed boundary. As the SGWD is the ratio of net groundwater draft to net
carefully. For a poor potential zone, naturally, the area will be over- groundwater available for extraction for each firrka, the trimmed firrka
exploited in nominal utilisation of groundwater. For a good potential by basin boundary has reduced groundwater potential zones. It makes
zone, the area will be safe for moderate utilisation of groundwater and the representative groundwater potential to be irrelevant for trimmed
semi-critical under-stressed utilisation. But there are some odd firrkas. Therefore, only firrka having 100% area after trimming should
combinations, such as being over-exploited in good potential zones be considered. But as per statistics, a 5% error can be allowed; thus,
and safe in the poor zone. Such abnormality was observed; hence, firrkas with 95%area covered after trimming were considered. Out of
combinations such as G-OE, G-C, GM-OE, GM-C, and M-OE were 56 firrkas, which are present within the basin boundary were reduced
considered vulnerable and require deeper studies in those areas for to 26 firrkas. The firrkas are above 95% of the area preserved after
groundwater over-exploitation. The possible reason may be increased clipping. From 58 firrkas enclosing the basin, boundaries 7, 5, 6, 3,
utilisation despite the availability or decline of groundwater levels and 37 come under Kanchipuram, Ranipet, Vellore, Thirupathur, and
with usual extraction due to below normal rainfall and unsuitable land Thiruvanamalai districts, respectively. After clipping with the basin
use pattern. Thus, these possibilities are to be found only after some boundary, the firrkas were reduced to nil for Kanchipuram and
deeper modelling studies. As in this case study, the vulnerable Thirupathur districts. Only two firrkas from Ranipet and one firrka
combination, such as GM-OE, GM-C, and M-OE, is in 26 firrkas. from Vellore have more than 95% of the preserved area.
Thiruvanamalai district has 23 firrkas after clipping. So, a total of 26
Final Selection of Study Area firrkas were held from 58 firrkas. This elimination can be avoided if
After finalising the vulnerable combinational firrka, data the administrative boundary’s groundwater potential zone map is

Table 3. Representative GWPZ for each firrka before and after the reclassification
Firrka Poor Moderate Good Very Good Mode Poor/ Good/ Modified
Area(%)* Area(%)* Area(%)* Area(%)* Good% Poor% Mode
Agrapalayam 10.21 70.25 19.54 0.00 M 52.26 191.34 M
Arni 1.87 70.84 27.30 0.00 M 6.84 1461.95 GM
Chengam 10.98 84.39 4.64 0.00 M 236.69 42.25 M
Cheyyar 2.13 78.90 18.97 0.00 M 11.22 891.60 M
Dusi 0.17 83.42 16.41 0.00 M 1.03 9694.41 M
Kadaladi 9.62 89.66 0.72 0.00 M 1344.29 7.44 M
Kalasapakkam 15.58 81.28 3.15 0.00 M 495.12 20.20 M
Kalasapakkam RF 15.40 81.82 2.78 0.00 M 554.85 18.02 M
Kalavai 0.01 54.86 45.13 0.00 M 0.01 743583.33 GM
Kaniyambadi 28.30 68.37 3.33 0.00 M 849.04 11.78 PM
Kannamangalam 10.13 85.27 4.60 0.00 M 220.17 45.42 M
Kelur 2.43 82.68 14.90 0.00 M 16.29 613.81 M
Kolappalur 0.36 82.74 16.90 0.00 M 2.16 4633.63 M
Mambakkam 0.18 72.34 27.48 0.00 M 0.66 15152.08 GM
Mandakolathur 17.58 80.18 2.24 0.00 M 785.67 12.73 M
Mullipattu 0.78 65.79 33.43 0.00 M 2.33 4295.51 GM
Nayadumangalam 7.13 90.90 1.97 0.00 M 362.36 27.60 M
Polur 14.93 82.94 2.13 0.00 M 701.81 14.25 M
Pudupalayam 29.25 65.59 5.16 0.00 M 566.49 17.65 PM
Sandavasal 13.18 70.07 16.74 0.00 M 78.75 126.98 M
Sathyavijayanagaram 0.56 50.17 49.26 0.00 M 1.14 8756.44 GM
Thachambadi 0.00 67.80 32.19 0.01 M 0.00 Infinite GM
Thandrampat 5.24 89.98 4.78 0.00 M 109.58 91.26 M
Vadathandalam 2.42 81.82 15.76 0.00 M 15.37 650.60 M
Vakkadai 0.27 57.93 41.80 0.00 M 0.64 15644.07 GM
Vinnamangalam 0.43 71.33 28.24 0.00 M 1.51 6637.68 GM
GM - Good skewed moderate, M - Moderate, PM -Poor skewed moderate, * Source: (Narayanamurthi and Ramasamy, 2022).

JOUR.GEOL.SOC.INDIA, VOL.99, OCT. 2023 1421

 Fig. 5. Flow chart of the sequential process to identify the smaller vulnerable area

generated. This step is only for comparison if GWPZ is generated for and Kolappalur in the east of Cheyyar river are in the place where the
the basin boundary. drainage is lesser and also the higher practice of agriculture. The other
firrkas, such as Chengam, Kadaladi, and Pudupalayam, are along the
Stage of Groundwater Development Category Map Cheyyar river, but the subsurface aquifer may have a lower holding
Figure 7 represents the 2020 Stage of Groundwater Development capacity or recharge capacity of groundwater. Therefore, Kalavai,
map for the 26 firrkas under the Cheyyar river basin. The firrkas under Kaniyambadi and Vadathandalm, located in the basin’s northern region,
critical and over-exploited should be focused on where the extraction might have a lower recharge rate. The safer firrka Kalasapakkam
is nearly equal and higher than the recharged groundwater. The firrkas Reserved Forest has nearly negligible extraction despite the placement
Kalavai, Kaniyambadi and Vadathandalam come under the critical in the hills. But Vinnmangalam firrka has a good amount of population,
category, and eight firrkas such as Chengam, Kadaladi, Kelur, and agricultural activity and is categorised as safe due to the merging
Kolappalur, Mullipatu, Pudupalayam, Sandavasal and Thachambadi of Kamandalanaganadhi major tributary with Cheyyar river and
come under over-exploited category. The over-exploited firrkas such increasing the chances of recharge rate. The rest of the 13 other firrkas
as Kelur, Mullipatu, and Sandavasal in the west and Thachambadi are semi-critical, between critical and safe.

Fig. 6. Firrka above 95% of the area covering the basin boundary Fig. 7. Category map of Stage of Groundwater Development.

1422 JOUR.GEOL.SOC.INDIA, VOL.99, OCT. 2023

Representative Groundwater Potential Zone Map drainage network and near the foothills of Jawadhu hills. Then, four
Figure 8 shows the representative groundwater potential zone map firrkas are good skewed moderate and semi-critical in the middle
for each preserved firrka. The mode of the category area in all the region where the tributary joins the main river and have weathered
firrkas is considered a central representative value because all the gneiss as lithologic units. Finally, two firrkas, Mullipatu and
firrkas comes under the moderate category as a central value. In this Thachambadi, come under good skewed moderate and over-exploited.
study, the moderate category is further reclassified into three categories Mullipattu has a good drainage network and storage unit but also has
Good skewed moderate, Moderate and Poor skewed moderate, based a higher pumping rate, and Thachambadi has a moderate pumping
on certain conditions. After reclassification, 18 firrkas stayed in the rate and lower storage and recharging capacity. The other firrkas are
pure moderate class, six firrkas under Good skewed Moderate and categorised into the remaining six categories each.
two under Poor skewed moderate. Good skewed moderate firrkas in Figure 10 shows the vulnerable firrkas. The firrkas under critically
the middle region have gneisses, and the rest of the firrkas with vulnerable combinations are Chengam (M-OE), Kadaladi (M-OE),
moderate and poor skewed moderate have Charnockite as lithologic Kalavai (GM-C), Kelur (M-OE), Kolappallur (M-OE), Mullipattu
units. Poorly skewed moderate firrkas are Kanniyambadi and (GM-OE), Sandavasal(M-OE) and Thachambadi (GM-OE). Chengam
Pudupalayam, which are closer to the hilly regions and have low and Kadaladi are situated upstream of the Cheyyar river at the foothills
infiltration rate and storage. Other moderate-classed firrkas are in the of Jawadhu hills. Chengam constitutes a valley through which the
flat areas where there is an opportunity to moderately infiltrate and Cheyyar river originates and has a Kuppanathanm reservoir.
store the groundwater. Charnockite lithologic unit with moderate weathering causes the
groundwater availability lowered. Kadaladi, on the left bank of the
Cheyyar river, has the same lithologic units as Chengam and
groundwater conditions. Sandavasal, Kelur and Mullipattu are grouped
in the middle region of the Jawadhu foothills and between Cheyyar
and Kamandalanaganadhi rivers. Charnockite is the major lithologic
unit with moderate weathering, as aquifer systems with lakes and ponds
are the source of groundwater recharge. Kolappallur and Thachambadi
lie in the south-central region, and Kalavai in the north-central part.
Both have hornblende gneiss as lithologic units, which has better than
charnockite groundwater potential. However, the lack of recharging
units such as ponds, and lakes, check dam drainage networks, and
increasing extraction leads to over-exploitation of groundwater. Final
firrkas considered as vulnerable to groundwater resource management
are shown in table 4

Final Area
Fig. 8. Firrka wise Representative Groundwater Potential Zone After finalising the vulnerable area based on the data availability
and feasibility for further modelling studies, based on the data
availability and data collection feasibility, Kelur firrka is finalised for
Combinational Map and Vulnerable Firrkas further research. The data available is insufficient for all the vulnerable
Combining the GWPZ and SGWD categories of each firrka firrkas. Chengam and Kadaldi firrka were studied for groundwater
provides valuable insight for choosing critically vulnerable firrka. management in detail by the Central groundwater board in 2015.
Figure 9 shows the combination map of both GWPZ and SGWD Kalavai firrka is closer to Palar mainstream in the Vellore district and
categories. With three GWPZ and four SGWD categories, 12 is also studied on groundwater management in the Vellore district by
combinations are possible. Poor skewed moderate with safe and many researchers. Thus, these firrkas are eliminated from consideration.
semi-critical are the missed combinations. Maximum 9 firrkas come Thachambadi and Kollapalur, which lies in the southern central portion,
under moderate and semi-critical, which lie in the path of the drainage have many difficulties in data collection and availability due to a lack
network and Charnockite as Lithology. Next, five firrkas have moderate of groundwater importance. So, they have not been considered. The
over-exploited, placed next to the previous category away from the balance firrkas Kelur, Sandhavasal, and Mullipattu are clustered in

Fig. 9. Combinational map of SGWD and GWPZ. Fig. 10. Vulnerable combination firrkas

JOUR.GEOL.SOC.INDIA, VOL.99, OCT. 2023 1423

Table 4. Representative GWPZ for each firrka before and after the and have a lesser number of lakes and ponds. Kelur is considered for
reclassification further study. The changes of groundwater level depend on the lakes
Firrka GWPZ SGWD Combina- Vulnerable and land use pattern where the drainage is insignificant. Kelur firrka
tional consist of charnockite as a lithological unit. The aquifer in the region
Agrapalayam M SC SC-M Not Vulnerable is made of topsoil, weathered rock and fractured rock which is
Arni GM SC SC-GM Not Vulnerable unconfined. During monsoon, the water table is as high as 3 to 10 m
Chengam M OE OE-M Vulnerable below ground level; during the summer, it is as low as more than 15 m
Cheyyar M SC SC-M Not Vulnerable below ground level. Open wells are used for irrigation during the
Dusi M SC SC-M Not Vulnerable monsoon, and tube wells are used during summer. The net available
Kahalani M OE OE-M Vulnerable groundwater resource in 2020 was about 26.7608 Mcm, of which
Kalasapakkam M SC SC-M Not Vulnerable
36.1427 Mcm is drafted, resulting in 135% of extraction (Over
Kalasapakkam Rf M S S-M Not Vulnerable
Exploited). Thus, Kelur firrka (Fig. 11), with an area of 129.7849
Kalavai GM C C-GM Vulnerable
Kaniyambadi PM C C-PM Not Vulnerable km2, is considered the smaller vulnerable area suitable for future
Kannamangalam M SC SC-M Not Vulnerable modelling studies.
Kelur M OE OE-M Vulnerable
Kolappalur M OE OE-M Vulnerable CONCLUSION
Mambakkam GM SC SC-GM Not Vulnerable This study adopts a novel sequential step to choose the smaller
Mandakolathur M SC SC-M Not Vulnerable vulnerable area using a GWPZ map and SGWD category map. As the
Mullipattu GM OE OE-GM Vulnerable GWPZ map is categorised pixel-wise, it must be converted to a single
Nayadumangalam M SC SC-M Not Vulnerable
representative category for each administrative boundary by
Polur M SC SC-M Not Vulnerable
Pudupalayam PM OE OE-PM Not Vulnerable considering the mode as a central value of the frequency of category
Sandavasal M OE OE-M Vulnerable pixel counts in that administrative boundary. Similarly, SGWD
Sathyavijayanagaram GM SC SC-GM Not Vulnerable categories for the same administrative boundaries (firrka) are created
Thachambadi GM OE OE-GM Vulnerable as a map. For a fair comparison, the administrative boundary above
Thandrampat M SC SC-M Not Vulnerable 95% of the area preserved after curtailing with the basin boundary is
Vadathandalam M C C-M Not Vulnerable considered for the next step. Curtailment can be avoided if the GWPZ
Vakkadai GM SC SC-GM Not Vulnerable map is generated with the same administrative boundary. But in this
Vinnamangalam GM S S-GM Not Vulnerable
study, the GWPZ is adopted from the previous studies with watershed
GM - Good skewed moderate, M - Moderate, PM -Poor skewed moderate, S boundaries, so the curtailment of firrkas with SGWD is carried out.
- Safe, SC - Semi Critical, C - Critical, OE - Over Exploited This reduced the number of firrkas to 26 from 56 firrkas covering the
entire river basin boundary. Firrka-wise representative GWPZ
the central foothill region where the Jawadhu hills are projected like a categories based on the central tendency resulted in the moderate
finger. category in all 26 firrkas. So the moderate category is reclassified into
The firrka Mullipattu is not considered as its drainage comes from Good-skewed-moderate (GM), moderate (M), and poor-skewed-
the upstream firrkas, Kelur and Sandhavasal, which are considered moderate (PM) based on assumption with the frequency of Poor,
for any groundwater management practice application. Sandavasal and Moderate and Good category pixel count percentage and ratios. After
Kelur require modelling studies to focus on the groundwater level reclassification, 26 firrkas were segregated as 16 under M, eight under
decline. Both have a considerable increase in groundwater draft for GM and two under PM. SGWD category map for the 26 firrkas is
irrigation and domestic use. Kelur firrka has lakes as the recharging segregated as 8 under overexploited, 3 under critical, 13 under semi-
units with smaller drainage canals connecting each other, and critical and 2 under safe category. These two maps, Representative of
Sandavasal firrka has the main drainage from Senpagathope reservoir GWPZ category and SGWD category, are combined to get a combined

Fig. 11. Identified smaller vulnerable area

1424 JOUR.GEOL.SOC.INDIA, VOL.99, OCT. 2023

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Vishnuvardan Narayanamurthi, Annadurai Ramasamy, Professor,

Research Scholar, SRM Institute of SRM Institute of Science and Tech-
Science and Technology, Kattanku- nology, Kattankulathur, Chengalpattu,
lathur, Chengalpattu, Tamil Nadu, Tamil Nadu, India. He improvised
India. He carried out data collection, the article and the methodology.
methodology, analysis of the results Preparation of various maps was
and article drafting. carried out by VN under the guidance
of AR.

1426 JOUR.GEOL.SOC.INDIA, VOL.99, OCT. 2023