Streams and Rivers

What is the hydrologic circle?

Movement of water between reservoirs

What is sheet flow?

Water that is neither absorbed or accumulates on the surface, but runs downslope

What are rills?

Small linear depressions representing the lowest order of stream flow

What is a stream/river?

Body of water that flows downslope along a clearly defined natural passageway

What is a channel?

Clearly defined passageway through which a stream flows

What are the characteristics of a stream?

Smooth, concave up, steeper slope near source, flatter slope near mouth

What is base level?

Lowest point to which a stream can erode

What things can disturb the equilibrium of a stream (or restore it)?

Discharge, sediment load, sinuosity, gradient

What is stream discharge?

Rate of water flow, volume of unit per time, varies seasonally

Can a stream control discharge?

No, it is an independent variable

What is the velocity of discharge?

Water flows in a stream as an elongated spiral, velocity is a variable in a curving cross section of the stream

What are the characteristics of discharge velocity?

Channel bed and banks plus surface air cause friction that slows flow, maximum flow is in the middle, curves offset the maximum flow towards the deeper side near outer bank

What is the sediment load?

Suspended, dissolved, and bedded sediment carried by steam, affects velocity and depth of water

Can the stream control sediment load?

No

What is the dissolved load?

Ions from mineral weathering

What is the suspended load?

Fine particles in water column

What is the bed load?

Larger particles that roll, slide and bounce

What is sinuosity?

Degree of curvature of stream path

Can the stream control sinuosity?

Yes, to offset discharge

What is the sinuosity index?

Length of stream divided by length of the valley, straight stream at 1

What is a meandering river?

Super curvy river, sinuosity above 1

What is a sinuous river?

River with sinuosity index of 1-1.5

What are meandering channels?

Sinuosity index greater than 1.5

How does erosion affect meandering channels?

Cuts banks: makes the neck between curves narrow, during floods, rivers take the shortest course through the neck, new straighter river course and abandoned ox bow lake

What are braided channels?

River beds with high sediments lows, steep profile and variable discharge

What is stream gradient?

Slope of stream bottom

Can streams affect their gradient?

Yes, to control sediment load

What is a graded stream?

Delicate equilibrium maintained by changing stream gradient

What does a stream typically look like upstream?

Too much load, too little discharge, braided pattern

What does a stream typically look like downstream?

Too much discharge, finer sediment load, meandering pattern

Why does a stream change gradient?

Response to seasons, changes in sea level, tectonic events

What is a floodplain?

The relatively flat valley floor adjacent to a stream channel

How is a floodplain made/maintained?

Built by erosion and deposition when a stream overflows its banks, occupied during previous floods and will be occupied again in future floods