Dworshak Dam, Clearwater River, holds 12,384,000 acre- feet of water Idaho has 93,000 miles of rivers and streams

Deposition Erosion Development of a River System Divide Drainage Basins “Watersheds” are separated by divides

Lake Itasca, Minnesota: source of the Mississippi Mouth of the Mississippi: New Orleans, Louisiana Mississippi Fourth longest river in the world Average discharge 572,000 cfs

Amazon River Headwaters are in the Andes Mtns. Length: 3,969 miles During the rainy season, the Amazon may be 28 miles across. Drainage Basin = 2,669,882 square miles Discharge = 7,735,680 cfs (this is the flow of the Mississippi, Nile, and Yangtze Rivers combined) No bridges cross the Amazon

Define drainage basin… The area of land drained by a river and its tributaries.

Mississippi River Drainage Basin Continental Divide Appalachian Mtns

Longitudinal Profile of Rivers From headwaters to mouth Landform features change due to the energy of the river Ultimate goal of nature is to erode to sea level (base level)

Base level is the lowest point of a river found at its mouth.

Running Water Moves because of gravity. Velocity or speed of flow is dependent on: –Slope (gradient) –Channel dynamics like: shape, size and roughness –Volume of water (discharge expressed in cfs )

River Erosion Erosion happens by: –lifting loose particles –abrasion –dissolving Paria Canyon, AZ (Photo by Tom & Susan Bean) Big Wood River Canyon, ID Niagara Falls, NY (Photo by David Ball)

Pothole

Transport of Sediment Three types of “Load” a river carries: –dissolved load Mainly supplied by groundwater Mineral salts –suspension load Largest amount Makes color “muddy” Silt and clay-sized particles –bed load Sand sized and larger particles Move along river bottom by turbulence Saltation Ohio River during 1997 Flood (Photo by Mark Lyons)

Deposition of Sediment Occurs when stream velocity/energy decreases Particles are sorted according to size Erode on the outside and deposit on the inside of a meander.

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Deposition Features Alluvial Fan Delta Death Valley, CA Dominate in arid & semi- arid regions The mouth of a river dumps the sediment into the slower water

Delta Formation TERRA Satellite, JPL/NASA Close-up, Miss. Delta, TERRA, JPL/NASA A BC Gulf of Mexico Mississippi Drainage Basin

River Valley Development Develops in stages Stages are characterized by landform features –Youth: V-shaped valleys, waterfalls, rapids, high relief erodes more –Mature: narrow flood plains, meanders Equilibrium –Old: Oxbow lakes, large meanders, wide flood plains, low relief deposits more Yellowstone River, WY Green River, WY

Rivers erode V shaped canyons… they are trying to erode down to base level

Glaciers erode U shaped valleys because they fill the valley…

Oxbow Lake Formation Erosive action causes the the river channel to move laterally. Meander develops a cutoff from main river channel. Oxbow lake forms as old channel is abandoned. Meander develops due to low energy of river.

Cut-off and Oxbow Formation on a Stream Table - YouTube

Stages of a River… ____________ –The river is eroding down to reach base level _____________ –Meanders begin to develop because downward and lateral erosion is equal ____________ –The river is eroding side to side because it is close to base level

Apacheta cliff in Arequipa

Review Where along the river system (head or mouth) would the river have the most kinetic energy? What part of the river system involves the formation of deltas? What are the three types of load a river carries? Which type of load gives the river its color?

And More Review In a river meander, where is the river flowing the fastest? Along a river meander, where is erosion and deposition the most active? Identify each. Stream valleys are _____shaped while glacial valleys are ____ shaped.

Last Part of the Review Identify if the features listed are the results of erosion or deposition Waterfall DeltaCut bank on the outside of a Oxbow lake meander V-shaped valley Which stage of a river would have the greatest amount of energy? Which stage of a river would have the greatest amount of discharge? Which stage of a river would have the widest floodplain?