3

Factors affecting erosion and deposition

Velocity Gradient – rise over run Channel shape Channel roughness Discharge – amount of water flow per

unit time, as discharge increases, load increases.

4

Velocity

5

Velocity

6

Channel shape and roughness

SemicircularFlow fast

Wide channelFlow slow

Rough bottomFlow slow

7

Channel shape and roughness

Narrow channelFlow fast

Wide channelFlow slow

8

Changes from Upstream to Downstream

Profile Cross-sectional view of a stream Viewed from the head (headwaters or source) to the mouth of a

stream Profile is a smooth curve Gradient decreases downstream

Factors that increase downstream Velocity Discharge Channel size

Factors that decrease downstream Gradient Channel roughness

Stream Erosion• Stream erosion (and deposition) controlled by flow velocity and discharge

– Stream velocity controlled by stream gradient (slope), channel shape and channel roughness• Maximum velocity near center of channel

– Floods involve increased velocity and discharge (volume of water passing a particular point in a stream over time)

• Higher stream velocities promote erosion and transport of coarser sediments

– Erosion of very small particles difficult due to molecular binding forces

Do Now

Do ES1301-How Does Stream Flow Change over Time?

This activity can be found on my website under “Files From Class.”

Monday, April 29, 2013

Objective #2 You are going to learn the similarities and

differences between deltas and alluvial fans

DEPOSITION

Definition

Deposition- the process in which sediment is laid down in new locations The end result of erosion

Water Deposition

Alluvial fan- fan shaped deposit of sediment on land Usually form when a stream slows down and

enters a flat plain Delta- sediment from a stream deposited

where a river enters a large body of water Triangular shape

Alluvial fan and Delta

Sediment Deposition• Delta - body of

sediment deposited at the mouth of a river when flow velocity decreases– Surface marked by shifting distributary channels

– Shape of a delta depends on whether its wave-dominated, tide-dominated, or stream-dominated

Sediment Deposition• Alluvial fan - large, fan- or cone-shaped pile of sediment that forms where stream velocity decreases as it emerges from a

narrow mountain canyon onto a flat plain

– Well-developed in desert regions, such as the southwestern U.S.– Larger fans show grading from large sediments nearest the mountains to

finer sediments farther away

DO NOWNow you should access ES104 from the

“Files From Class” section of my website. This investigation will focus more on

deltas.