Geomorphology and Groundwater salinity of Coastal aquifers

Dr. C.P. PrijuScientist B, Groundwater Division

CWRDM, Kozhikode

Introduction

Salinity – Major groundwater pollution in coastal regionsEncroachment of sea water to aquifers - surface and subsurface pathwaysHigh mineral content – saltsExcessive use (pumping) of groundwater in coastal regionInfluence of hydrogeological and geomorphological factors of the areaChanges in climate, land use pattern altering rate of groundwater rechargeInfluence of tidal oscillations and sea level rise

Coastal Geomorphology of Kerala

Divided into three geographical regions - Highlands (>80 m), Midlands(6-80m) and Lowlands(< 6m)Lowlands (coastal plain) – mainly river deltas, backwaters and seashoreCoastal geomorphic units – beaches, beach cliffs, stacks, islands, shore platforms, spits, bars, beach ridges, estuaries, lagoons, inlets, mudflats, tidal flats and deltaic plainsMajor landforms – backwaters and lagoons, sea inlets has major role in saline water ingress to aquifersCoastal landforms – made of sand and alluvium, generally elongated parallel to the coastStrandlines (ancient shorelines) and beach ridges mainly made upof sand form good freshwater aquifers

Geomorphological features of the Central Kerala coast

Schematic section of the coastal land

Hydrogeology of Kerala

Physiography and geological setting – major control on occurrence and movement of groundwaterGeologically mainly underlain by crystalline rocks with sedimentary formations and coastal alluvium in the mid and low land regionsGroundwater occurrence - phreatic, semi-confined and confined conditionsTertiary and coastal plain aquifers – sedimentary formationsTertiary Vaikom and Warkali beds- potential freshwater aquifersCoastal alluvium (thickness few meters to 100 m) – ground water in phreatic and semi-confined conditions (depth to water table < 1 m to 6 m)

Stratigraphic succession of Kerala

AGE FORMATION LITHOLOGY

Recent Alluvium Sand, Clay, riverine alluvium etc.

Sub-Recent Laterite Derived from crystallines andsedimentaries

Tertiary

WarkaliQuilonVaikom

Alleppey

Sand stone, clays with ligniteLime stone, marl and claySandstone with pebbles, clay and ligniteCarbonaceous clay and fine sand

Undated Intrusives Dolerite, Gabbro, Granites,Quartzo-feldspathic Veins

ArchaeanWayanad groupCharnockitesKhondalites

Granitic gneiss, Schists etc.Charnockites and associated rocksKhondalite suite of rocks and its associates

Groundwater and seawater intrusion

Ghyben-Herzberg relation

z = 40 x h, where h = water level above sea levelz = thickness of fresh water below sea level

Saltwater intrusion due to drawdown and upconing

Unconfined aquifer

Confined aquifer

Aquifer geometry in Island and coastal marine environments

Marine Island Coastal marine environment

Groundwater salinity-Interpretation tools

Hydrochemistry- Chloride vs. Water level elevations- Chloride vs. Conductivity- Piper Diagram

Geo-electrical Investigation- Schlumberger Array- Wenner Array (2D Resistivity profiling)

Chloride vs. Water level elevations

Hydrochemical Tools

Chloride vs. Conductivity

Piper Diagram

Vertical Electrical Sounding – Schlumberger array

Geophysical Tools

Vertical Electrical Sounding – Wenner Array

Resistivity profile of a coastal formation showing brackish

and saline water zones -Wenner method

2D Resistivity image of a coastal aquifer showing fresh water plumes and saline

intrusion