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1. In this session we explain:

2. MAIN SOURCES OF WATER

3. Surface Water Lakes, reservoirs, rivers Rivers dammed to create reservoirs Reservoirs store water during heavy rain/snow Lake Tuscaloosa Dam

4. Aquifers (Groundwater) Primary source of drinking water Porous consolidated rock or unconsolidated soil Groundwater fills spaces Wells and pumps used to remove water Aquifer

5. There are six ways to increase the supply of water to a community: withdrawing water from groundwater aquifers ; withdrawing water directly from nearby rivers or lakes; building dams to create reservoirs to store runoff; improving the efficiency of water use through water conservation; transporting water from a distant area by means of aqueducts , and converting salt water to fresh water (desalination) Many of these choices affect other communities For example, suppose one town takes water from a river upstream. This decreases the amount of water available to towns downstream. Lar ge pumps are used to supply water to a community.

6. 1. withdrawing water from groundwater aquifers 2. withdrawing water directly from nearby rivers or lakes

7. 3. building dams to create reservoirs to store runoff 4. improving the efficiency of water use through water

8. 6. converting salt water to fresh water(desalination) 5.transporting water from a distant area by means of aqueducts

9. Surface Water Surface water refers to water found on Earth's surface, such as: Rivers Lakes Streams Reservoirs (artificial lakes created by dams)

10. Seasonal Variability : River flow changes significantly from season to season More water in rainy seasons Much less in dry seasons → This inconsistency makes rivers unreliable as a steady, year-round water source. Limitations of Rivers as a Direct Water Source

11. Figure A large reservoir was created from the Colorado River at the Glen Canyon Dam, Arizona. DAMS large structures built to block the flow of a river and create a reservoir. Role and Benefits

12. Δ Disadvantages and Environmental Impacts of Dams 1- Displacement of Wildlife and People Reservoirs often flood large areas. This leads to: → Loss of animal habitats. → Relocation of human communities. → Submersion of farmlands and forests. 4- Sediment Buildup in Reservoirs Rivers naturally carry sediment (sand, silt, clay). When a dam blocks the river: → Sediment settles at the bottom of the reservoir. → Over time, this reduces storage capacity for water. → The reservoir can gradually fill up, making the dam less effective. 2- Loss of Cropland Productive agricultural land gets submerged under water. This can reduce food production in nearby regions. 3- Disruption of Fish Migration Many fish species migrate upstream to spawn (reproduce). Dams block this natural movement, leading to a decline in fish populations. Some dams install fish ladders to help, but they're not always effective.

13. Groundwater as a Water Supply Source What Is Groundwater? Groundwater is water stored beneath Earth's surface in porous sediment. It fills spaces between particles in soil, sand, gravel, or cracks in bedrock. Accessed by drilling wells and pumping the water to the surface.

14. Best Aquifer Materials: Loose, porous sand and gravel - store large volumes and allow easy flow. Fractured bedrock - especially when full of connected cracks. What Is an Aquifer? An aquifer is any underground layer of rock or sediment that stores and transmits groundwater. To be a good aquifer, the rock must have: → High porosity (space to hold water) → Good permeability (allows water to flow through)

15. 1. Unconfined Aquifers 2. Confined Aquifers Directly connected to the surface above. Separated from the surface by an impermeable layer (called an aquiclude). Recharge (refilling) happens when surface water seeps down through the soil. This barrier blocks surface water from recharging the aquifer directly. These are the most common and easiest to access. Recharge happens far away, often over tens or hundreds of kilometers. Example: The sand layer in basic groundwater models. Types of Aquifers Rural areas Small Towns and some cities • Most homes have private wells that tap directly into aquifers • Multiple large wells are used to pump water from deep aquifers • This forms a major part of the municipal water supply.

16. serious consequences can occur: Land Subsidence (Sinking Ground) As groundwater is withdrawn, supporting pressure is lost, causing the land to sink. This is known as subsidence. Example: Edwards Air Force Base, California Overuse of groundwater caused the land to sink more than 2 meters. Resulted in damaged runways, even affecting facilities once used by space shuttle.

17. Advantages Disadvantages Reliable and abundant in many regions Overuse can cause land subsidence Protected from surface pollution (especially confined aquifers) Recharge can be slow or distant Used widely in rural and small communities Some aquifers may eventually dry Can be tapped year-round Pumping costs (energy and infrastructure)

18. They can be tens or even hundreds of kilometers away. In many areas where groundwater has been used for a long time, the land surface subsided (sunk down). This is because so much water has been withdrawn. One example is Edwards Air Force Base in California. The land there hassubsided more than two meters. This has damaged some of the runwaysonce used by the space shuttle.

19. Aqueducts In some areas water use is greater than local supplies. Water must be brought in from distant areas where there is lots of water. This is the case in California. About two thirds of California’s precipitation falls in the north. However, about two thirds of the population lives in the south. A system of reservoirs in northern California supplies southern California with water. This water is transported through a system of large surface pipes and channels. They are called aqueducts. Over long distances, the water in the aqueducts flows downhill under gravity. In some places, enormous pumping plants must raise the water up over hills and mountains.