1. Freshwater Resources Chapter 7

2. Water: A Vital Resource Water is fundamental to life as we know it. Water is fundamental to life as we know it. A total volume of 325 million cubic miles covers 71% of Earth’s surface. A total volume of 325 million cubic miles covers 71% of Earth’s surface. About 97.5% of this volume is salt water of the ocean and seas. About 97.5% of this volume is salt water of the ocean and seas. The remaining 2.5% is fresh water – water with a salt content of less.1% The remaining 2.5% is fresh water – water with a salt content of less.1% Evaporation from the oceans combines with precipitation to re-supply the small percentage continually through the solar powered water cycle. Evaporation from the oceans combines with precipitation to re-supply the small percentage continually through the solar powered water cycle. Thus, fresh water is a continually renewable resource. Thus, fresh water is a continually renewable resource.

4. Groundwater Most percolates into the soil layers, moving downward to become groundwater, which makes up 1/5 of Earth’s freshwater supply and plays a key role in meeting human water needs. Most percolates into the soil layers, moving downward to become groundwater, which makes up 1/5 of Earth’s freshwater supply and plays a key role in meeting human water needs. Groundwater is contained within aquifers, porous, spongelike layers of rock, sand or gravel that holds water. Groundwater is contained within aquifers, porous, spongelike layers of rock, sand or gravel that holds water.

6. Confined Aquifer (Artesian Aquifer) Exists when a water-bearing porous layer of rock, sand, or gravel is trapped between an upper and lower layer of less permeable substrate (often clay). Exists when a water-bearing porous layer of rock, sand, or gravel is trapped between an upper and lower layer of less permeable substrate (often clay). In such a situation, water may be under great pressure because it is trapped between these layers. In such a situation, water may be under great pressure because it is trapped between these layers.

7. Unconfined Aquifer A layer of less permeable substrate underlies unconfined aquifers. A layer of less permeable substrate underlies unconfined aquifers. There is no upper layer to confine them. There is no upper layer to confine them. The water they contain us under considerably less pressure than that of a confined aquifer. The water they contain us under considerably less pressure than that of a confined aquifer.

9. Groundwater Aquifers in the United States hold 30 times more water than all U.S. lakes and rivers. Aquifers in the United States hold 30 times more water than all U.S. lakes and rivers. Groundwater supplies almost 40% of freshwater in the U.S. Groundwater supplies almost 40% of freshwater in the U.S.

10. Groundwater The Ogallala aquifer lies between Texas and N. Dakota. Pumping up water from this aquifer has made this arid region of the U.S. into some of the most productive farmland in the country. The Ogallala aquifer lies between Texas and N. Dakota. Pumping up water from this aquifer has made this arid region of the U.S. into some of the most productive farmland in the country. Removal of water from Ogallala has occurred at a faster rate than recharge rate resulting in a drop in water table and subsidence (sinking of the land) in some areas. Groundwater depletion will bring an end to this type of farming. Removal of water from Ogallala has occurred at a faster rate than recharge rate resulting in a drop in water table and subsidence (sinking of the land) in some areas. Groundwater depletion will bring an end to this type of farming. Other areas of major subsidence include the San Joaquin Valley of California and Mexico City. Other areas of major subsidence include the San Joaquin Valley of California and Mexico City.

11. If water withdrawal is faster than recharge: Cone of depression.

13. Consequence of Overdrawing water from aquifers.

14. Saltwater Intrusion Where aquifers open into the ocean, freshwater is maintained in the aquifer by the head of freshwater inland. Excessive removal of water may reduce the pressure, so that salt water moves into the aquifer.

15. NJ has had to deal with saltwater intrusions that were putting salt water into farm irrigation wells. Solution: Build surface water reservoirs for irrigating farmland.