Explain the process of saltwater intrusion with neat sketches. Give examples from India.

Understanding Saltwater Intrusion

Saltwater intrusion occurs when the hydraulic pressure in coastal aquifers decreases, allowing denser saltwater to displace freshwater. This can happen due to several reasons, leading to both coastal and inland intrusion.

Causes of Saltwater Intrusion

• Over-extraction of Groundwater: Excessive pumping of groundwater reduces the freshwater head, creating a pressure gradient that draws in saltwater.
• Sea Level Rise: Global warming and climate change contribute to rising sea levels, increasing the hydraulic pressure of seawater and facilitating its intrusion.
• Reduced Freshwater Recharge: Decreased rainfall, reduced river flow, and urbanization limit the replenishment of freshwater aquifers.
• Hydrological Connectivity: Permeable geological formations and fractured rocks allow for easier movement of saltwater into freshwater zones.
• Coastal Morphology: Low-lying coastal areas and the presence of estuaries increase vulnerability to saltwater intrusion.

The Process of Saltwater Intrusion (with Sketches)

The process can be visualized in two main scenarios:

1. Coastal Intrusion:

(Image source: Wikimedia Commons - Illustrative example. Actual sketch should be hand-drawn for exam purposes)

This sketch depicts a coastal aquifer. The freshwater table is normally higher than the saltwater table. Over-pumping lowers the freshwater table, creating a cone of depression. This allows saltwater to move inland, contaminating the freshwater aquifer.

2. Inland Intrusion:

(Image source: USGS - Illustrative example. Actual sketch should be hand-drawn for exam purposes)

This sketch shows how saltwater can intrude along riverbeds and channels, particularly during periods of low flow. Reduced freshwater discharge allows saltwater to travel further inland, impacting water quality.

Impacts of Saltwater Intrusion

• Agricultural Losses: Salinization of agricultural land reduces crop yields and can render land unusable.
• Drinking Water Scarcity: Contamination of freshwater sources makes water unsuitable for drinking and domestic use.
• Ecological Damage: Saltwater intrusion alters coastal ecosystems, impacting mangrove forests, wetlands, and biodiversity.
• Infrastructure Corrosion: Saline water corrodes infrastructure, including pipelines and buildings.
• Economic Impacts: Reduced agricultural productivity and increased water treatment costs lead to economic losses.

Examples from India

State	Location	Specific Impact	Contributing Factors
West Bengal	Sundarbans Delta	Extensive agricultural land salinization, loss of mangrove forests.	Sea-level rise, reduced freshwater flow from the Ganges, over-extraction.
Gujarat	Coastal Saurashtra region	Drinking water scarcity, reduced agricultural productivity.	Over-pumping of groundwater, limited rainfall, geological formations.
Tamil Nadu	Nagapattinam & Cuddalore districts	Salinization of groundwater, impacting agriculture and drinking water.	Cyclone-induced storm surges, sea-level rise, over-extraction.
Kerala	Alappuzha & Ernakulam districts	Intrusion into backwaters and paddy fields, affecting rice cultivation.	Reduced freshwater flow, sea-level rise, land subsidence.
Puducherry	Karaikal region	Severe groundwater contamination, impacting drinking water supply.	Over-extraction, proximity to the sea, geological vulnerability.

These examples demonstrate the widespread nature of saltwater intrusion in India and its diverse impacts across different coastal regions.