Chapter 11: Freshwater Resources

Chapter 11: Freshwater Resources

Overview

  • Freshwater is a limited resource; usage exceeds natural replenishment rates.

  • Recovery and purification methods exist, yet conservation is crucial.

Main Concept

  • Freshwater availability is becoming a crisis despite the planet's vast water coverage.

Water Availability

  • Finite Water Supply:

    • Total water on Earth: Approximately 1.4 billion cubic kilometers.

    • Glaciers hold about 35 million cubic kilometers.

    • Additional water is present in rivers, lakes, and living organisms.

  • Usable Freshwater:

    • Less than 0.004% of total water is usable by humans (freshwater with few dissolved ions).

  • Water Cycle:

    • Water is constantly moving through the environment via the water cycle.

    • Over 66,000 km³ of water vapor enters the atmosphere annually, equating to 17,000 trillion gallons.

Precipitation and Surface Water

  • Almost all precipitation ultimately falls into oceans; the remaining is surface water (lakes, rivers) or groundwater (aquifers).

Watersheds

  • Definition:

    • A watershed is the land area surrounding a water body where water (like rain) can flow and potentially enter that body.

  • Types of Watersheds:

    • Open Watershed: Flows eventually to the ocean.

    • Closed Watershed: Inland basins that do not drain to the sea.

Water Scarcity

  • Definition:

    • Water scarcity is having insufficient access to water supplies; it is a global crisis affecting many regions, especially in the Middle East, parts of Africa, and Australia.

  • Challenges:

    • Access to water may exist, but financial barriers prevent capture, purchase, or processing.

    • Over 2 billion people lack proper sanitation or access to fresh water.

Baseline Water Stress

  • Varies by region based on withdrawals compared to available flow:

    • Low (<10%)

    • Low to medium (10-20%)

    • Medium to high (20-40%)

    • High (40-80%)

    • Extremely high (>80%)

National Water Use (2020 Data)

  • Average daily water withdrawals by usage type (in million gallons per day, mgd):

    • Irrigation: 108,412 mgd

    • Thermoelectric: 80,213 mgd

  • Water Usage by Region:

    • Southeast: 71,991 mgd

    • Western: 64,633 mgd

    • Northeast to Midwest: 55,795 mgd

    • Public Supply: 35,575 mgd

    • High Plains: 31,780 mgd

Water Use in Developed Nations

  • Developed nations generally have higher per capita water usage.

    • U.S. average:

    • 2015: ~150 gallons/day.

    • 2023: ~82 gallons/day.

  • Investment in technology is prevalent in economically prosperous nations to mitigate water scarcity.

Global Water Access Issues

  • The UN estimates 3.5 billion lack access to clean water; 2.5 billion lack sanitation.

    • Example: Ganges River receives 1.1 trillion liters of raw sewage per minute, making it the second most polluted river globally.

Aquifers

  • Definition:

    • An aquifer is an underground region of permeable soil or porous rock saturated with water.

  • Infiltration:

    • Water from rain and snow enters the Earth, filling cracks and crevices in the aquifer, naturally filtering and providing clean water for municipal services.

  • Water Table:

    • The upper surface of the saturated zone in an aquifer; it fluctuates based on usage, season, and precipitation.

    • Measured in acre-feet: volume needed to cover an acre to a foot deep (1 acre-foot = sufficient for 2 families annually).

Aquifer Depletion and Challenges

  • Aquifers can weaken from water loss (due to drought or extraction), undermining their structure.

  • Urban environments hinder infiltration due to impermeable surfaces, raising flood risks and potential aquifer collapse (sinkholes).

Saltwater Intrusion

  • Definition:

    • The inflow of seawater into freshwater aquifers typically occurs when the water table dips below sea level, leading to aquifer contamination.

  • Mitigation:

    • Strategies required to maintain high aquifer levels to prevent saltwater intrusion.

Case Study: Orange County Water District (OCWD)

  • In Anaheim, California, drought conditions prompted the implementation of a controversial solution.

  • California Water Dynamics:

    • Water flows from northern California to southern regions, complicated by increasing climate change impacts reducing snowpack and precipitation.

  • Aquifer Characteristics:

    • Depth ranges from 90-900 meters (300-3000 ft); proximity to seawater induces saltwater intrusion.

Groundwater Replenishment Program

  • Initiated in 1975, involves injecting treated sewage into aquifers (~5 million gallons/day).

  • This program addresses both aquifer replenishment and wastewater management issues.

Wastewater Treatment

  • Treated sewage must be potable for environmental release, requiring rigorous treatment processes.

    • Communities rely on high-tech, energy-intensive methods (e.g., microfiltration, reverse osmosis).

    • Treatment stages:

    1. Primary Treatment: Screening large debris, settling solids.

    2. Secondary Treatment: Biological treatment, bacteria breakdown of organic matter.

    3. Advanced Treatment: Further purification for potable water release or groundwater injection.

Dam Pros and Cons

  • Advantages:

    • Provide dependable water sources, facilitate electricity generation, assist in flood control, and offer recreational opportunities.

  • Disadvantages:

    • May restrict downstream water supply, experience significant evaporative loss, and disrupt habitats.

Conservation Strategies

  • Emphasizing reduction in wastewater and adoption of water-efficient technologies is crucial:

    • Behavioral Changes: Turn off faucets when not in use, take shorter showers, run appliances only when full.

  • Technology Comparison:

    • Old vs. New:

      • Toilets: 6 gallons/flush → Low-flow toilets: 1.3 gallons/flush.

      • Showers: 3.8 gallons/minute → Low-flow shower heads: 2.3 gallons/minute.

    • Incorporating smart practices can greatly reduce household water usage.

Wastewater Recycling and Desalination

  • Wastewater Recycling: Pros include addressing water scarcity; cons involve negative perceptions and costs.

  • Desalination: Effective but costly and energy-intensive; converts seawater into potable water through reverse osmosis.

Importance of Water Management

  • ~1% of Earth's freshwater is surface water; crucial to manage this supply through reservoirs to mitigate downstream losses.

  • The balance between water conservation, technological advances, and behavioral changes is vital for sustainable freshwater resources.

Final Note

  • Continual efforts are necessary to address the fresh water crisis while considering environmental and social implications.