Micro-level Aquifer mapping & Aquifer management Plan for Coastal Aquifer system, Tamilnadu

Dr. D.Gnanasundar, Dr. M.Senthilkumar & Sh. N. Rameshkumar

Central Ground Water Board South Eastern Coastal Region, Chennai Ministry of Water Resources, River Development and Ganga Rejuvenation Government of Regional & Micro-level aquifer mapping Aquifer Mapping Objectives: 1. To decipher the vertical & lateral extent of the is a scientific process wherein a Aquifer Disposition – (2D & 3D) along with their combination of Geologic, Geophysical, characterization. hydrogeological & Chemical studies 2. To formulate Aquifer Management Plans (Field & Laboratory studies) – applied to 3. To facilitate sustainable management of GW characterize resources at regional & local level through • the quantity, Participatory Groundwater Management. • quality &

• sustainability of groundwater. Tamilnadu & UT of Puducherry Approach Regional Aquifer Micro-level Mapping aquifer mapping

Decipher Aquifer Units within Principal Aquifers

Conceptualization of the aquifer system

Aquifer management Plan through Numerical Modelling

Information on aquifers to farmers, State Govt. stakeholders for sustainable GW management Regional aquifer mapping Regional & Regional Aquifer System, Tamilnadu Micro-level aquifer mapping

Pondicherry coastal aquifer Cuddalore coastal Aquifer Sandstone Alluvium sand Cuddalore coastal aquifer Alluvium sand

sandstonesandstone Bay of Bengal Jayankondam aquifer Bay of Bengal Alluvium sand Alluvium sand

Specific Issues Micro-level aquifer mapping 1. Coastal aquifer – forms a part of Cauvery Basin.

2. Intensively irrigated area by Groundwater

3. Depressurization of the aquifer for mining activity.

4. Groundwater is pumped for drinking water supply to Chennai city

during lean periods.

5. Extension of the aquifers into the sea. Regional Aquifer Mapping & Aquifer management Plan : 1948 sq.km Aquifer Mapping Location : 200 km south of Chennai. Recharge zone (Cuddalore dt, TN)

Micro-level Aq.mapping : 428 sq. km

Sandstone

Sandstone

Alluvium

Vellar river Strike : North East – South west Dip : South East GW flow : South East (along the dip direction) 2 – D Aquifer Disposition Outcome by data gap analysis A” A north south (Aquifer 1/unconfined) Recent alluvium Sand/sandstones clay clay Cuddalore Sandstone – Mio-pliocene sandstones (Aquifer 2/Confined) potential aquifer lignite • Ferruginous, • Friable Eocene sandstones • Medium to coarse (Aquifer 3/Confined) grained with clay • continuous or discontinuous clay intercalations. Eocene sandstones (Aquifer 4/Confined)

Pebble west Inference : Multi-layered aquifer system B East ? Inf. required 40 m B’ clay msl

40 m lignite clay 80 m clay lignite 100 m Lignite at 80 m bgl

120 m clay Open cast mine – Outcome by data Gap analysis Hydrogeological studies

Long term Piezometirc head behaviour of aquifer – II

Piezometric head (m) Kudikadu PZ

Exploration carried upto 400 bgl. Period in months

1. Exploratory Drilling were carried out at 18 locations & 2. Additional 22 Piezometers were constructed to Zone wells (Pz) tapping aquifer unit –III & IV micro-monitor the behavior of Groundwater Heads of Different Aquifer Units. Aquifer Disposition inferred from E-Log Outcome from geophysical study Principal Aquifer : Sandstone

Aquifer Units : 4 nos Age: sangolikuppam

Sst. Aquifer – I (Sand/Sandstone)

clay Mio-pliocene Sst.

Aquifer – II Inference : (Sandstone) Multi-layered aquifer system (down to explored depth of 400 m) clay Lignite (marker bed)

Sst. Aquifer – III clay (Sandstone) Sst.

clay Eocene

Sst. Aquifer – IV (Sandstone) Outcome from exploratory drilling Aquifer Aquifer disposition inferred from Litholog Formation Units Recent - (exploratory drilling at Pachacharapalayam site) Alluvium 18 nos of additional exploratory wells were

Aquifer I Aquifer - I drilled. Mio-pliocene (unconfined) CGWB Rig - Cuddalore (Gl – 73m bgl) sst. Mio-pliocene sandstone Clay Clay (Cuddalore formation) Aquifer -II Mio-pliocene Aquifer – II - Cuddalore (107 – 122 m bgl) (confined) sst.

Eocene - lignite/CLay Lignite/clay (122 – 126 mbgl) Marker bed Principal aquifer (Sandstone) Aquifer - III Aquifer - III Eocene - Sandstone ) (126 – 244 mbgl) (Confined s

Eocene Litholog at drilling site Clay Clay sandstone (Neyveli formation) Aquifer - IV (263 – 364 mbgl)

Aquifer -IV Eocene - Inference : Sandstones (Confined) Multi-layered aquifer system (down to explored depth of 364 m) Outcome from Pz head analysis Pacharap alayam Piezometric Heads of Aquifer - III

40 Laterite Ayekuppam Kothandarajapuram

20 Aquif er -I SST Aquif 0 SST er -I msl Q= 10 lps -20 SST Bay of Bengal Aquif Clay Clay er -I -40

SST Aquif Aquif Clay discontinuous SST -60 er -II Q = 14 lps er -II

Clay

-80 Lignite/clay Lignite

SST Clay

-100 SST Lignite ?? Clay

-120 SST Lignite

Aquif Q = 29 lps SST -140 er -III Lignite SST

-160 SST Aquif head in Pzmsl er – Aquif III er -III -180

-200 Clay

-220 Q= 48 lps Clay

-240 Inference: 1. The variation of Piezometic heads reaffirms the presence of 4 aquifer -260

SST Aquif units & its nature (unconfined/confined) within the principal aquifer. (Aq-1 – -280 er -IV unconfined, II, III & IV – Confined)

-300 2. The Pz head (long tern hydrograph) infers distinct recharge & discharge -320 mechanisms in all 4 aquifer units.

-340 3. Individual aquifer management plan for each aquifer unit is required. Outcome

Micro-level aquifer mapping (Aquifer Information System) Less potential zones Aquifer – I (Unconfined)

Aquifer – II (confined)

Aquifer – III (confined)

Aquifer –IV I (confined)

Less potential zons Less potential zones Aquifer – I (Unconfined) Domestic & irrigation Aquifer – I (Unconfined) irrigation

Aquifer – I (Unconfined) Industrial & irrigation Aquifer – I (Unconfined) Drinking water supply to chennai city

To be shared to farmers, local administration for participatory GW management. 3 D Aquifer Disposition ( Block), , Tamilnadu Outcome

Aquifer Unit – I (unconfined) west east

Bay of Aquifer Unit – I (unconfined) Bengal Mio-pliocene sandstone Aquifer Unit – II (unconfined) Mio-pliocene sandstone Aquifer Unit – III (unconfined) Eocene sandstone

Aquifer Unit – IV (confined) Eocene sandstone 0 m

scale 300 m 0 km 10 km Pacharap alayam Outcome from hydrochemical studies

40 Laterite Ayekuppam Groundwater quality of all four aquifer units Kothandarajapuram

20 Aquif er -I SST Aquif 0 SST er -I msl

-20 SST Bay of Bengal

Clay EC : 250 µS/cm Clay Aquif -40 er -I

SST

Aquif SST unconfined er -II Aquif -60 EC : 120 µS/cm er -II

Clay

-80 Lignite/clay Lignite

SST Clay -100 SST confined Lignite ?? Clay

-120 SST Lignite

Aquif EC : 550 µS/cm SST -140 er -III Lignite SST confined -160 SST Aquif er – Aquif III er -III -180

-200 Clay

-220 EC : 1000 µS/cm Clay

-240

-260 Inference:

SST Aquif -280 er -IV 1. Again re-confirms the presence of four distinct

-300 aquifer units 2. All the 4 aquifer units have potable GW (insitu -320 Brackish GW exists as pockets near coasts) -340 Regional Conceptualization Cuddalore Coastal Aquifer. Multi-layered aquifer system (Seven Layer model) Depth of Outcome of the Study Layer – 1 (sand/sandstone) Occurrence Layer – 2 (clay- discontinuous) 20 – 120 m Q (10 – 45 lps) Layer- 3 (Sandstone) Q (10 – 40 lps) Layer – 4 (Clay/lignite – discontinuous) Q (8 – 40 lps) Layer – 5 (Sandstone) 20 - 180 m Layer – 6 (Clay – discontinuous) Q (5 – 15 lps) Layer – 7 (Sandstone)

40 – 240 m Recent alluvium and sst... Abstraction for Domestic & Irrigation Mio-pliocene sandstone User aquifer for Irrigation. 40 – > 400 m

Depressurization for mining activity

Abstraction for drinking water Explored depth : 400 m supply to chennai city

0 km 31 km 72 km Numerical Modelling for Aquifer Management Plan: Model Grid, Boundary conditions & input parameters. 7 layer model Finer gird Total model area : 1948 sq. km. (250 m x 25 m) Variable head boundary () Total Cells : 34629 nos Columns and Rows : 51 and 97 Layers : 07 nos Coarser grid : 1000 x 1000 m Finer grid : 500 x 500 m (Grid pattern is based on the data availability & objective of the model) River flows during rainy season only - River (Ponnaiyar, Gadilam & Vellar) flows for 40 days in a year - No significant base flow to the river. Perumal eri/tank (10 km width & 3 Km

wide) taken as General Head boundary

Constant Head Boundary (Sea) Boundary Head Constant

Coarser Grid Coarser 1000 m 1000x ) m ( (water in tank remains almost same throughout).

GW Flow equation

Variable head boundary (Vellar River)

Hydraulic conductivity (Kx) values as input : K = 30 – 40 m/day Method : Finite Difference Method Specific Yield : 12 – 14 % (unconfined, Aquifer – I) (FDM) Storativity : 0.003 to 0.000093 ( confined aquifer II, III & IV) Recharge rate: 12 - 14 % of the annual recharge (1290 mm/yr). Outcome from numerical modelling studies Groundwater withdrawal from aquifer units (I,II,III & IV) from 1000 Cuddalore coastal aquifer system Cumulative effect of groundwater 800 withdrawal for irrigation, mining Total activity, drinking water supply & Pumpage domestic purpose (MCM/yr) 600 Total annual Groundwater withdrawal from all Aquifer Units : 1213.58 mcm 400 Pre-pumping For Irrigation Total annual pumping from Neyveli mine : 133.10 mcm 200 Mining activity

1950 1960 1970 1980 1990 2000 2010 Period in years

Aquifer Hydrogeologic Unit Irrigation Industrial Domestic (GW withdrawal in mcm/yr) ------Sand/sandstone Upper Cuddalore (Aq-I) 393.0 0.8 30.0

Sandstone Lower Cuddalore (Aq-II) 611.65 1.2

Sandstone Upper Neyveli (Aq-III) 31.0 133.10

Sandstone Middle Neyveli (Aq-IV) 12.79*

Sandstone Lower Neyveli (no groundwater withdrawal) ------Total 1035.69 135.10 42.79 ------*Groundwater withdrawal for drinking water supply to Chennai city during lean periods. Aquifer Management Plan (Cuddalore coastal aquifer) Outcome from numerical modelling

Groundwater withdrawal as Impact on Aquifer Units S. No Management Options on Dec 2013 Aquifer Aquifer Aquifer Aquifer mcm/year Unit –I Unit –II Unit -III Unit-IV All Aquifer Units 1. Future projection upto 1213.58 No significant Head decline Head Decline No significant year 2025 with present change 0.10 to 0.20 m /yr 0.10 to 0.15 m/yr change rate of groundwater pumping. 2. Drought Occurrence once 1213.58 No significant No significant No significant No significant in four years with present change change change change rate of pumping. Aquifer I & II 3. 350 mcm/year increase in 1213.58 Head decline Head decline No significant No significant irrigation pumping from 0.10 to 0.20m /yr 0.20to 0.30 m /yr change change AQ-I & II (1213.58 + 350 mcm) 4. Increase in groundwater 1213.58 No impact Head decline 0.10 No Impact No Impact pumping for industrial activity to 0.20 m/yr along the coastal tract by 100 (impact 0 – 5 km mcm from aquifer-II (proposal along the coastal for SEZ zone and textile sipcot) tract) Aquifer Management Plan – (Cuddalore Coastal Aquifer) Outcome from numerical modelling

Groundwater withdrawal as Impact on Aquifer Units S. No Management Options on Dec 2013 Mcm/year (Aquifer Unit –I) (Aquifer Unit –II) (Aquifer Unit -III) (Aquifer Unit-IV) Aquifer Unit III 5 Increase in annual groundwater 1213.58 No impact Cone of depression Cone of depression No Impact pumping for mining activity by 60 increased by 200 m. increased by 200 m. mcm from Aquifer-III (Neyveli pumping : (impact around 10 (impact around 10 km (133 + 60 mcm) (proposal for 133.10 mcm/yr) km radius) radius) expansion of mine (mine III) 6 Increase in annual groundwater 1213.58 No impact Cone of depression Cone of depression No Impact pumping for mining activity by 130 increased by 400 m. increased by 400 m. mcm from Aquifer-III (Neyveli pumping : (impact around 10 (impact around 10 km (133 + 130 mcm) (proposal for 133.10 mcm/yr) km radius) radius) expansion of mine (mine III & IIIA) Aquifer IV 7 Increase in annual groundwater 1213.58 No impact No impact No Impact No Impact withdrawal by 6 mcm from Aquifer – IV (12.79 + 6 mcm/yr) (Drinking water supply : 12.79 During drought period in chennai mcm/yr)

• With the present prevailing scenario (1213.58 mcm/year), the aquifer is safe and no threat of seawater intrusion exists. • Aquifer – I & II are vulnerable to seawater intrusion (0 – 5 km from coast) if the annual GW withdrawal increases by 350 mcm. Aquifer Management Plan (for Aquifer – III)

• for monitoring the threat of sea water intrusion • 0 – 10 km inland coast : The safe Pz head is to be maintained as - 40 m to - 50 m w.r.to msl. • Pz head below - 80 m bmsl shall invite sea water intrusion. Pumping well Piezometer

Pre-pumping condition ( - 2 m) Present Pz head Present Pz head (-10 m) Safe Pz head (- 50 m)

Unsafe Pz head (- 80 m)

Aquifer - III

35 km 17.5 km 0 km

Major issues : Pumping for safe mining of lignite (depressuration) & pumping for irrigation by farmers at pockets. Aquifer management plan Groundwater flow simulation ( Groundwater Model) – Cuddalore Coastal Aquifer • With the present prevailing scenario (1213.58 mcm/year), the aquifer is safe and no threat of seawater intrusion exists. •Rainfall Recharge • Aquifer – I & II are vulnerable to seawater

Neyveli Lignite Mine intrusion (0 – 5 km from coast) if the annual GW BayFirst of Bengal withdrawal increases by 350 mcm.

Groundwater Flow {vertical & Lateral Flow}

clay Aquifer - I Aquifer -I (Sandstone) (Sandstone) unconfined clay Aquifer - II Aquifer -II (Sandstone) clay (Sandstone) Lignite confined

clay clay Aquifer -III Aquifer - III (Sandstone) (Sandstone) clay confined Aquifer - IV clay Aquifer - IV (Sandstone) Sixth layer (Clay) Aq – IV Probable Basement (4500(Sandstone) m) (Vertically exaggerated)(Granitic Gneiss) Reversal in hydraulic gradient (sea water intrusion) may take place if annual groundwater withdrawal exceeds by 700 mcm for Aquifer – I & 900 mcm for Aquifer – II. As annual estimation of GW withdrawal from the aquifer is a Management strategy for Aq-1 & II voluminous exercise, sustainable management of the Cuddalore coastal aquifer can be done by monitoring the GW head (Piezometers) fitted with high frequency Automatic WL • Thanks…….