Wednesday, February 13WATER ISSUES: BASIC PRINCIPLES AND SUPPLIESWater•70% of Earth’s surface is water.Hydrologic (Water) Cycle•Water in oceans, lakes, streams, etc. evaporates.•Water from the land goes through transpiration. •Clouds carry water inland, and the water condenses in the atmosphere.•Water comes down to the ground as precipitation.•Ice and snow melt.•Water from this precipitation (either melting or surface runoff) becomes part of the groundwater, infiltrates, and becomes part of groundwater discharge. Where Is the Water?•97% of water is saline (salt water) in oceans. •Only 3% of the water on Earth is freshwater. •About 30% of this is groundwater.•About 69% is in icecaps and glaciers.•Surface water is 0.3% of all freshwater, and mainly comes from lakes (87% of this 0.3%).Meeting Human Needs for Water Supply•Variation is important to meet human needs.•We can go for about 30 days without food but not long at all without water. •India has seasonal variation in rainfall. •Winter (January - February) is very dry, but the monsoon season (June - September) is very wet. Watersheds•area of land that drains to form a river or lake•also called drainage basins•separated by geological features•mountains, plateaus•open watersheds•eventually drain to sea•most watersheds are these•closed watersheds•do not drain to seaWater Resource Problems and Issues - Overabundance•floods - loss of life and property•some historic floods in the US:•Mississippi River, 1927•165 million acres were inundated•246 fatalities and over 600,000 people were made homeless•Flood Control Act of 1928 was passed - levees, reservoir maintenance and management to Army Corps of Engineers (COE), with cooperation from local agencies. •Mississippi River, 1993•Johnston, PA, 1889•New Orleans (Hurricane Katrina),