River Systems - Runoff

Running Water

• Integral part of sculpting the Earth’s surface• MOST IMPORTANT AGENT OF

EROSION• Indirectly results in the formation of

sedimentary rocks

Stream Formation

• Sheetflow or Sheetwash – overland flow of water

• Repeated precipitation events cause a preferential channel to form – downcutting

• Tributaries form & the main channel continues to grow up slope – headward erosion

• Streams increase in length by headward erosion – erosion occurring at the beginning of the stream

• Streams become wider through lateral erosion – mass wasting of the stream banks

• Streams become deeper through downward erosion of the channel by abrasion of the sand and gravel

Stream Morphology

Fig. 11.13

Stream Terminology• Stream System – main stream plus

tributaries

• Drainage Basin – area drained by main stream and tributaries

• Drainage Divide – area of higher elevation that divides drainage basins

• Function of size/scale

For Example:

Kickapoo CreekSangamon River Illinois River Mississippi River

Fig. 11.7

Stream Terminology• Stream System

• Drainage Basin

• Drainage Divide

• Function of size/scale

Fig. 11.6

Stream Subsystems

• Collecting System– Tributaries is head water region– Funnel water and sediment to main

channel– Primarily erosion and transport

• Transporting System– Main tributary– Main process is the movement of the

sediment and water– Erosion, transport, and deposition all

occur

• Dispersing System– Distributaries at mouth region– Primarily deposition of the sediment– Coarse sediment along the confluence– Fine particles carried further in to body

of water

Fig. 11.8

Drainage Patterns

Streamflow Dynamics

• Examine the physical and hydraulic properties of the stream

• Discharge• Velocity

– Gradient– Channel Properties

• Wetted Perimeter• Shape• Size• Roughness

• Sediment Load

DailyQuestion

Duplicate the chart to the right.

On the chart add lines that represent how the following properties change:

Discharge

Velocity

Cross-Section Area

Gradient

Channel Roughness

Base level

The property “drainage basin area” is provided as an example

Discharge (Q)

• Volume of water passing a given point over a specified length of time (length3/time), generally given in ft3/s or m3/s

• Calculated by:• Where A is the cross-sectional area (length2) & v is the

velocity of the water (length/time)

vAQ

Velocity

• The speed of the water at a given point along a stream• Directly related to a stream’s ability to erode and

transport material• High velocity water can carry heavier sediment• Is a function of

– Gradient– Channel Properties

• Wetted Perimeter– Shape– Size– Roughness

Stream Gradient• Slope or steepness of the

stream channel• Vertical drop (relief) of a

stream over a fixed distance• Controls the potential

energy of the water• Steeper the gradient – the

higher the velocity, the lower the gradient – the lower the velocity

• Meanders decrease the gradient by increasing the horizontal distance of the stream

Wetted Perimeter• The area in which water touches

the channel walls• Channel shape and size controls

the wetted perimeter• Most efficient streams have small

wetted perimeters• Roughness of the channel

controls the frictional resistance to water movement– A smooth channel decreases

frictional force– A rough channel increases frictional

force