CRISIS NOTES

CRISIS NOTES - RiversandFloods 18:06 River: evaporation...

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Rivers and Floods 18:06 River: Most powerful agent of erosion Most water is from the oceans—raindrops are stripped of salts through  evaporation Why important? Balance of nature Sediment source for beaches Soil nutrition (we don’t allow our flood plains to flood!) Wildlife Source of fresh water Floods—we live on floodplains Flat land, nutritious soil, water availability, water transport (1/8 trucking, 2/5 train  cost) Issues Superfloods—circa 100 year cycle Levee breaks—point source of 1000 miles of flood waters (a flood plain is suppose to flood) Loosing beaches and barrier islands because of dams and channeling of rivers  (for shipping to deep waters) They are barriers against hurricanes!!! If we hold back sand behind the sand you have erosion greater than  deposition
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Water on earth Ocean 97.3 Fresh water 2.7 Groundwater 0.575 Rivers 0.001 (used for bathrooms/farms) Atmosphere 0.0001 Lakes 0.017 Ice 2.065 Downstream Changes High on profile: erosion>>deposition Low on profile: erosion=deposition except during floods Changes downstream: Width (>), depth (>), velocity(>),  discharge w*d*v (>) Amount of water moving at a given mile time Rivers are constantly shifting, never flood whole floodplain Where do you want your dance hall? The cliff or the point bar? Point bar! As rocks roll down hill they become smaller and more rounded
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Deposition on the inside turn Streams and rivers and continuously shifting their pathway High on profile-headward erosion All youthful streams Youthful stream:      steep walls, v-shaped streams, erosion greater than deposition Sediment transport-high on the profile Large pebbles, cobbles and boulders… are they moving? No. Conglomerate—sedimentary rock—used to be where a river was What evidence do you see of floods?  Look at the rocks. Aren’t moving now but they were before As we go down a stream we get to older and older portions The beginning of a mature stream As it is older it begins to broaden out and you get the first evidence of a flood  plain Restricted flood plain; note threes on natural levee
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CRISIS NOTES - RiversandFloods 18:06 River: evaporation...

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