Groundwater

Summary

This video explores the global water cycle, focusing on freshwater sources and aquifers. It highlights the distribution of the Earth's water, with most being in oceans and the rest in glaciers, rivers, and groundwater. The video explains the key features of aquifers, including porosity, permeability, and the water table, and how groundwater flows. It also covers the effects of over-pumping and contamination, as well as the impact of pressure differences in aquifers. Additionally, it touches on confined and unconfined aquifers, artesian wells, and the importance of understanding geology in managing water resources.

Takeaways

• 🌊 97% of the world's water is in the oceans, leaving just 3% as freshwater.
• ❄️ 70% of the planet's freshwater is locked in glaciers and ice.
• 💧 Only 0.006% of Earth's freshwater is found in lakes and rivers, and it's not evenly distributed.
• 🌍 Groundwater makes up about 30% of the world's freshwater supply and is crucial for human consumption and agriculture.
• 🪨 Aquifers are underground layers where groundwater is stored. Their quality depends on rock porosity and permeability.
• 💦 For an aquifer to function effectively, the ground must be both porous (able to store water) and permeable (allow water to flow).
• ⛏️ If water is extracted faster than an aquifer can recharge, it can cause the aquifer to dry up and reduce its future capacity.
• 📉 A cone of depression forms around a well when water is pumped faster than the recharge rate, lowering the surrounding water table.
• 💨 Groundwater moves slowly, but it flows downhill under the influence of gravity and pressure differences in the earth.
• 🏞️ Confined aquifers are separated from unconfined ones by an impermeable layer of rock, and water in these aquifers can rise under pressure when tapped by wells, leading to artesian wells and springs.

Q & A

What percentage of the world's water is fresh, and where is most of it found?

Only 3% of the world's water is fresh, and about 70% of that fresh water is trapped in glaciers and ice on land.

What percentage of the world's fresh water is found in lakes and rivers?

Lakes and rivers make up only 0.006% of the planet's fresh water supply.

What is groundwater, and how much of the U.S. fresh water usage comes from it?

Groundwater is water that soaks into the ground and fills the spaces in rocks and soils. It accounts for about one-third of the U.S. fresh water usage.

What are the key ingredients for a good aquifer?

A good aquifer requires rocks with high porosity and permeability, and it should be located in an area with significant rainfall.

What is porosity in relation to rocks?

Porosity refers to the amount of open space in a rock that can be filled with air or water. The more porous a rock, the more water it can contain.

What is permeability, and why is it important for groundwater flow?

Permeability is the degree to which pore spaces in a rock are connected, allowing water to flow through it. High permeability is essential for groundwater to move freely.

What happens if groundwater is pumped out of an aquifer faster than it can recharge?

If groundwater is pumped faster than it can recharge, the aquifer may dry up, and the rock's porosity could decrease, reducing its future water-holding capacity.

What is the 'cone of depression,' and how does it form?

The 'cone of depression' is a drop in the water table around a well caused by excessive pumping, where water is extracted faster than it can be replenished.

What is the difference between a 'gaining stream' and a 'losing stream'?

A gaining stream is one where groundwater flows into the river, while a losing stream is one where water from the river soaks into the ground, recharging the aquifer.

What is an artesian well, and how does it work?

An artesian well taps into a confined aquifer under pressure. Water from the aquifer rises naturally to the surface due to the hydraulic pressure in the system.

How does over-pumping an aquifer close to the ocean affect the water quality?

Over-pumping freshwater aquifers near the ocean can reduce the pressure that keeps saltwater at bay, causing saltwater intrusion into the aquifer and contaminating the freshwater supply.

What is hydraulic fracturing (fracking), and why is it used in oil and gas extraction?

Hydraulic fracturing, or fracking, is a technique used to release oil and gas trapped in impermeable rock layers by injecting high-pressure water and chemicals to fracture the rock and increase permeability.