Runoff and Rivers

•How Rivers Shape Our Landscape

How do rivers form?

• River: A large natural stream that empties into a large body of water such as a lake or ocean.

• Runoff: precipitation that returns to the sea– erodes stream/valley– transports sediments (erosion!!!!!)– deposits sediments

River Vocabulary• Capacity: the maximum amount of sediments that a

stream can move (transport)• Stream Load: amount of material a stream can

move (transport). Depends on capacity and type of land.

• Suspended Load: Sediments such as clay that are suspended (floating) in the water.

• Deposition: laying down of sediments• Sorting: deposition by size and density

• the biggest and heaviest (rocks) are always deposited first• silt and clay (very small) settles last

Load: How do rivers transport sediments?

• Three ways a river can carry its load:– Solution: stuff dissolved in the water– Suspension: particle of silt/clay/mud “floating” in

the water– Bed load: heavy stuff (rocks) that roll, bounce or

slide along the bottom

River Calculations

• Gradient-the slope of a river expressed in feet/mile• Velocity-speed expressed feet/second. This can be

calculated by timing a piece of wood floating over a certain distance and then dividing the distance by the time

• CSA (Cross Sectional Area): width x avg. depth• Discharge: velocity x CSA

• Dsi

River Features• Deltas: Fan-shaped area of

deposition at the mouth of a river• Levee-Man made or natural wall

along a river bank that controls flooding

• Tributary-A large stream or small river that flows into an area’s main river.

• Divide-High area that separates drainage basins (ex. Continental Divide)

Satellite image of tributaries

River Drainage Patterns

• Dendritic: Like tree branches. In areas with some hills.

• Radial: In a circle. Mostly from flowing off a mountain.

• Rectangular: Flat areas.

River Features

• Alluvial Fan: Fan shaped deposits of river transported material called Alluvium.

• Normally found at the base of a mountain. Gold can be found here!

River Features

• Flood Plain: A flat area on either side of a stream, enclosed by a river valley, that floods during periods of excessive rainfall.

Rivers can erode and deposit• A meandering river moves

faster on the outside curve than the inside curve.

• Meander: A loop-like bend in a stream’s path.

• Erosion occurs on the outside curve called the Cut Bank.

• Deposition occurs on the inside curve called the Point Bar.

Oxbow Lake• Oxbow Lake: A lake that forms

when a meander is cut-off from the main stream. Is in a curve shape.

Old Rivers vs New RiversWell-Developed Drainage

(Lots of tributaries) Few tributaries

Wide Valleys V-shaped valleys

Floodplains, Meanders and Oxbows Waterfalls and Rapids

Low Gradient Steep Gradient

Side-cutting Down-cutting