Geology Exam

Stream

any surface water confined to channel

forms when rainfall scours a channel

- in soft substrate

where water is moving faster

Tributaries

smaller streams that feed trunk stream

Drainage Patterns

depends on land surface topography, composition, and structure

• Dendritic - tree branches 

• Structurally controlled 

Drainage Basins 

total land area whose surface water drains into a stream 

Drainage divides

high topography that separates drainage basins

• headwaters

• Continental divides separate drainages that flow to different water bodies (e.g. to Gulf of Mexico versus Atlantic Ocean)

Straight Streams

Highest velocity @ headwaters - steeper topography

• Steep topography = steep gradient 

• Large change in elevation over a given horizontal distance 

• Low sinuosity

• Shapes ( V-shape valley, Slot canyon, Stair-step canyon)

Waterfalls and Rapids

Sudden topographic drop

• Erosion of softer rock “step” of resistant rock

• Faulting 

• Migrate upstream as the step is eroded 

Braided Streams

consisting of interfingering channels

sediment load (capacity) is very high and channel is very shallo 

sediment choke channel with sand and gravel bars

Braided Streams

where gradient drops

velocity drops 

sediment deposited within streambed 

braided stream

Meadering Streams

occupy only a small part of the floodplain

floodplains are often bounded by bluffs

During floods, entire flood plain may be immersed 

Natural levees form ridges parallel to the channel 

Meandering Streams 

Low gradient - flat topography 

High sinuosity - horizontal erosion 

Wide floodplain 

Meandering Streams

Erosion @ outside of curve - Fastest water

Deposits sediment along inside of next curve - point bar

• Curves become exaggerated

• Eventually abandoned, forming oxbow lake

Floodplains (features of rivers) 

Areas of flat ground bounding a river channel on either side

Usually narrow in mountain/hills but wide in low-land areas

Ex: Rio Grande in Colorado , Mississippi River

Levees

Natural levees

• ridges of sediment along a stream deposited by repeated floods

• creates a deeper stream able to carry more water

Deltas 

forms when a stream enters standing water 

The stream divides into a fan of distributaries 

Velocity slows; sediments drop out 

• Delta morphology is a dynamic balance of sediment load, waves and storms, tides, and slumping. 

shape: Bird’s foot , Arc-like, triangle-shaped

Delta

stream flows into standing water

slows 

sediment is deposited - Coarse —> fine 

Distributaries 

Mississippi Delta 

is sediment- sediment-dominated delta 

• Today’s Mississippi Delta covers an area of approximately 40,000 square km 

• Older sediment lobes have compacted and subsided below sea level 

Deltas

Development on deltas is at risk for subsidence

• Sediment starvation allows subsidence to quicken

• subsidence makes deltas more vulnerable to floodinh

• New Orleans is an example

• Ex. Nile River Delta

Alluvial Fans

build at canyon mouths

Sediment drops out as water spreads out from the mouth 

• Coarsest Material is dropped first, close to mouth 

• finer material is carried further, to distal edge of fan

Alluvial Fans 

sediment creates a conical, fan-shaped structure 

During strong flood, debris flow spreads across, smoothing fan surface

Alluvial Fans

Arid regions, streams flwo from narrow, steep channels onto flat valleys 

Water loses velocity 

Sediment deposited in fan-shaped deposit