APES Chapter 9 - Water Resources

• Water is abundant

• Freshwater is rare (<3%)

• Usable freshwater is rarer still (<23% of that 3%)

  Ground Water

• Exists in the soil (soil water) and in a multitude of small spaces found within and between porous layers of rock and sediment called aquifers

• Water Table - the upper most level at which the water in an area completely saturates the soil or rock

• Unconfined Aquifers - an aquifer made of porous rock covered by soil (water can easily flow in or out)

• Confined Aquifers - an aquifer surrounded by a layer of impermeable rock or clay (impedes water flow into/out of aquifer)

• Artesian Wells - wells created by drilling a hole out of a confined aquifer

• Groundwater Recharge - water from precipitation can percolate into the soil and make its way into an aquifer

• Confined aquifers can only be recharged if there is an opening in the impermeable layer

• Impervious surfaces - pavement or buildings that do not allow water penetration that reduce groundwater recharge and increase flood risk

• Water infiltration in urban areas can be increased by:

  • Reducing impervious surface area (increase public transport, building up not out)

  • Using permeable pavement

  • Increasing vegetation in urban areas

• Groundwater resources are threatened when depletion exceeds recharge - causes cone of depression, recharge rate decreases

• When an aquifer neighbors an ocean, groundwater depletion can cause saltwater intrusion

• Saltwater Intrusion - movement of salt water into freshwater aquifers

Atmospheric Water

• Drought - a prolonged period of abnormally low rainfall, leading to water shortage, reduced plant growth, reduced recharge, and increased risk of fire

• Can have long-term implications for:

  • Water Security (unconfined aquifers are easily depleted, may force use of water in confined aquifer)

  • Soil Quality (increased erosion results in loss of topsoil and organic matter)

• Desalinization - the process of removing slat from saltwater

• While a promising technology for increasing freshwater resources, it can be energy intensive and its waste products are challenging to manage

Global Water Use

• 70% of the world's freshwater is used for agriculture (animal agriculture and crops)

• Flood Irrigation

  • Easy, inexpensive, and low tech

  • Only 50% water efficient

  • Waterlogs the soil and can lead to salinization (especially in arid environments)

• Furrow Irrigation

  • Easy and inexpensive

  • Only 60% efficient

  • Waterlogs the soil nearby the root zone and can lead to salinization (especially in arid environments)

• Spray Irrigation

  • More expensive and less energy efficient

  • 70 to 90% efficient (depending on method)

  • Can also lead to waterlogging, but is less commonly used in arid environments

• Drip Irrigation

  • Cost and labor intensive to set-up and maintain

  • Challenging for annual crops

  • Over 95% efficient

• Hydroponic Agriculture - the cultivation of crop plants under greenhouse conditions with their roots immersed in a nutrient-rich solution, but no soil

  • Uses up to 95% less water than traditional irrigation

  • Super productive, year-round yields

  • Energy-intensive

  • Not appropriate for gains and several other major crops

• Roughly 20% of the world's freshwater is used for industry:

  • Generating electricity

  • Cooling machinery

  • Refining metals and paper

• Roughly 10% of the world's freshwater is consumed for household use (varies significantly with level of development and local climate)