LAND SUBSIDENCE DUE TO GROUNDWATER PUMPING

 LAND SUBSIDENCE DUE TO GROUNDWATER PUMPING

Introduction

Land subsidence is the gradual sinking or settling of the Earth's surface due to subsurface material movement. In the context of geology, it often occurs when large volumes of groundwater are extracted from underground aquifers, causing the ground above to collapse. This process is significant in regions dependent on groundwater for agriculture and domestic use.

The image below illustrates the phenomenon of land subsidence in California's San Joaquin Valley, caused by extensive groundwater pumping.

Quick Points:

1. Aquifer System Structure

The San Joaquin Valley contains layers of sand, gravel, and clay, which act as aquifers holding fresh water.

A critical layer, Corcoran Clay, separates shallow aquifers from deeper aquifers.

2. Groundwater Pumping

Farmers drill wells that penetrate deep aquifers below the Corcoran Clay layer to extract water.

Excessive pumping lowers the water table, reducing water pressure in the layers.

3. Clay Compaction Process

When water pressure decreases, the loose clay particles compact and lose their original structure, a process similar to stacking pancakes.

Healthy clay has a granular structure filled with water, whereas damaged clay, once compacted, cannot regain its original form.

4. Permanent Impact

The compaction is irreversible, reducing the ability of these layers to store water in the future.

As a result, the ground surface subsides (sinks) permanently, altering the land elevation.

5. Current Example

The newest affected area covers approximately 1,200 square miles near El Nido.

Satellite-based measurements by the U.S. Geological Survey (USGS) report subsidence rates of nearly one foot per year in some locations.

CONSEQUENCES:

Agricultural Impact: Loss of arable land and reduced water storage.

Infrastructure Damage: Roads, canals, and buildings can crack and collapse.

Water Resource Issues: Permanent reduction in groundwater storage capacity.

Image Source📷:

Doug Griswold / Bay Area News Group (as cited in the image).

Data: U.S. Geological Survey.