1. Watershed Water in a river system drains into a main river. The land area that supplies water to a river system is called a watershed. Watersheds are sometimes known as drainage basins.

2. Divides One watershed is separated from another by a ridge of land called a divide. Streams on each side of the divide flow in different directions. The Great Divide is the longest divide in North America, it follows the line of the Rocky Mountains.

3. Formation of Ponds and Lakes Ponds and lakes form when water collects in hollows and low-lying areas of land. Some ponds and lakes are supplied by rainfall, melting snow and ice, and runoff. Others are fed by rivers or groundwater.

4. Water Zones

5. Aquifers Any underground layer of permeable rock or sediment that holds water and allows it to flow is called an aquifer. Can range in size from a small patch to an area the size of several states. Provides water for millions of people, as well as crops and livestock. Groundwater may travel hundreds of kilometers and stay in an aquifer for thousands of years before coming to the surface again.

6. Wells, Pumps, and Pressure

7. Wells, Pumps, and Pressure cont. People can obtain groundwater from an aquifer by drilling a well below the water table. – When the bottom of the well is in a saturated zone, the well contains water. – If the water table drops below the bottom of the well, the well will run dry. Mechanical pumps bring up the groundwater. – Artisan well, water rises on its own because of pressure within an aquifer. – Some aquifers, groundwater becomes trapped between two layers of impermeable rock or sediment. – This water is under great pressure from the water extending back up the aquifer. – If the top layer of rock is punctured, the pressure sends water spurting up through the hole.