ENVS200-WK7.1-water2

Groundwater Overview

  • Groundwater: essential resource, but often underappreciated.

Student Learning Objectives

  • By the end of the week, students will be able to:

    • Describe differences between aquifers and aquitards and the nature of the water table.

    • Differentiate between types of wells and springs.

    • Explain depletion/damage of groundwater.

    • Discuss negative consequences of groundwater overuse, dam impacts, and water transport.

Groundwater Basics

  • Porosity: Ability of rocks/sediments/soils to contain fluid.

  • Permeability: Ability of soils/rocks to allow fluids to pass through.

Groundwater Flow

  • Geology and geometry control behavior of groundwater.

  • Aquifers: High permeability/porosity; facilitate easy water flow.

  • Aquitards: Low permeability; slow or impede water motion.

Global Groundwater Distribution

  • Depicts groundwater availability by oceans and surface flow recharge.

  • Indicates where water supply is sufficient vs. insufficient per capita.

Accessing Groundwater

  • Groundwater accessed through:

    • Natural springs: where water table meets surface; often in valleys; surrounded by wetland vegetation.

    • Human-made wells: drilled to access groundwater.

Types of Wells

  • Ordinary Wells: Holes into aquifers where water seeps up to the level of the water table.

  • Artesian Wells: Wells in a pressurized aquifer where water rises to surface without pumping.

Future Challenges of Water Resources

  • Freshwater usage is unsustainable due to:

    • Over-extraction faster than natural replenishment.

    • Pollution and waste of resources globally.

  • 1 in 10 lack access to clean water.

Surface Water vs Groundwater

  • Surface water: freshwater from rain/melted snow,

    • 34% of reliable runoff is used:

      • 70% for irrigation.

      • 20% for industry.

      • 10% for domestic use.

  • Indirect usage accounts for significant water footprint (e.g., food production).

Causes of Water Scarcity

  • Caused by:

    • Dry climates, droughts, overuse, inefficiency, faster usage than replenishment.

  • Shared water basins among countries can lead to conflict.

Water Quality and Quantity Issues

  • Groundwater quality & quantity threatened:

    • 1.2 billion lack clean drinking water.

    • Overuse can lead to pollution, lowering water tables, and seawater intrusion.

Consequences of Groundwater Overuse

  • Over-pumping impacts:

    • Limits food production and raises prices, deepening socio-economic gaps.

    • Forms cones of depression in aquifers, lowering local availability.

    • Saltwater intrusion near coastal areas poisons freshwater supplies.

    • Compaction and subsidence damage infrastructure.

Mitigating Groundwater Issues

  • Strategies for addressing groundwater depletion:

    • Recharge wells with treated water to combat salt intrusion.

    • Monitor and manage aquifer compaction to avoid irreversible damage.

Large Dams and Water Transfer

  • Dams built to block river flow and create reservoirs:

    • Helps control floods, generates electricity, and supports recreation.

  • Disadvantages include displacement of communities, ecological damage, and finite lifespan.

Desalination

  • Process of removing salts from seawater:

    • Methods: Distillation, reverse osmosis.

    • High cost and environmental impacts like brine waste.

Current and Future Water Resource Strategies

  • Need for conservation, increased desalination reliance, and interbasin water transfers.

  • California's water project exemplifies statewide effort to redistribute water supply.