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II. Section 2 Water on the Surface. A. River Systems. Tributaries- the smaller streams and rivers that feed into a main river Watersheds- the land area that supplies water to a river system Divides- what separates one water shed from another
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A. River Systems • Tributaries- the smaller streams and rivers that feed into a main river • Watersheds- the land area that supplies water to a river system • Divides- what separates one water shed from another • Continental Divide- longest divide in North America, follows Rocky Mountains
B. Rivers and Floods • Flood- volume of water in a river increases so much that the river overflows it’s channel • As speed of a river increases so does its energy • Flooding river- uproot trees, wash away houses and bridges • Egypt- people welcomed the flooding of the Nile for fertile soil • In history floods have killed millions of people
C. Can Floods Be Controlled? • Dam- a barrier across a river that may redirect the flow of the river to other channels or store water in an artificial lake • Can open a dam’s gate during dry season to release stored water • During floods water can rush through and break or over the dam • Levees- long ridges alongside the channel • Can make matters worse downstream of a flood- surge of water
D. Bodies of Freshwater • Ponds usually smaller and shallower than lakes • Sunlight usually reaches the bottom of a pond where in a lake parts are too deep • Ponds and lakes form when water collect in hollow and low-lying areas of land
E. Ponds • Plants grow throughout the pond because sunlight can reach the bottom of the pond • Though photosynthesis these organisms create oxygen • Some ponds only appear in the Spring then evaporate in Summer • Some may freeze during winter
F. Lakes • The bottom is usually filled with mud and algae • Lake formation • Cutoff river meander • Ice age depressions • Deep valleys formed by movement in the crust • Volcanic craters • Man made- reservoir- a lake that stores water for human use • Plants do not live at the bottom of lakes • Home of large boney fish
G. Changes in a Lake • Undergo changes with season • Cool water becomes more dense with the change of the season and mixes with the warmer water • This change is called lake turnover- refreshed the supply of nutrients throughout the lake • Eutrophication- nutrients in a lake build up- algae grows and builds up on the surface • This happens because organisms are constantly releasing waste products
G. Changes in a Lake 6. When the layer becomes so thick it blocks sunlight- no photosynthesis 7. Organisms die and oxygen decreases 8. Lakes bottom becomes completely filled with plants and a grassy meadow takes the place of the lake
H. Icebergs • Glacier- a mass of ice and snow that moves slowly over land • When a glacier reaches a seacoast an iceberg forms • Although they are in the ocean they are made up of freshwater • Only 10% of an iceberg is visible the rest is under water • International Ice Patrol tracks icebergs-created after Titanic