XII. Streams

A. The Hydrologic Cycle (components and pathways)

B. Stream Velocity (controls and results)

C. Drainage Patterns and Landscape Features (results of erosion and deposition)

D. Stream Valley Development (tectonic uplift and downcutting)

The Hydrologic Cycle See Fig. 12.3

Systems of streams and their tributaries that collect runoff Divide Ground Water

Drainage Basins

Great LakesDrainage Basin

Steam Profiles(Streams Shaping

the Land)

V-Shaped Valley

FloodPlain

What is this Drainage Pattern?(What does is tell of the geology?)

Valley and Ridge Province of PA(Trellis Stream Patters)

Stream Gradient

Slope of the land Sinuosity of stream

10 m/km 10 m per 1¼ km =

8 m/km

10 m

1 km

10 m

1 km

Meander Velocity

Higher velocities on outside of meanders causes erosion (cut bank)

Lower velocities on inside of meanders causes deposition (point bar)

Fig. 10.6

Channel Shape and Roughness

A. Narrow and Deep Less resistance Faster flow

B. Wide and Shallow More resistance Slower flow

C. Rough Streambed More resistance Slower flow

Stream Velocity Controls:

How much and what grainsize of sediment is Eroded and Transported

Where and what grainsize size will be sediment

Stream Erosion

Then, Erosion Solution (chemical weathering) Hydraulic Action (lifting) Abrasion (crushing and grinding)

Pg. 276 .

First, Weathering Fracturing

(mechanical) Loosening

(mechanical and chemical)

Solution (chemical)

Stream Transport

Dissolved Load Suspended Load Bed Load

Saltation Rolling, sliding

Pg. 276

(ions)

Stream Deposition

BraidedStreams

Alluvial Fan

e.g., Alluvial Fans

Fig. 12.14a

Fig. 12.14b

Erosion Dominated High gradients Less resistance Fast velocities

Deposition Dominated Lower gradients More resistance Lower velocities

Stream Deposition

Midchannel bars Fig. 12.7b

Point bars

Fig 12.9

Braided streamsFig. 12.7a

Deltas

Fig. 12.13

Reduction of velocity due to extreme widening

Deposition of silt and clay

Erosion and Deposition Transport

E.g., Meandering streams As meanders are

migrating Cutbanks eroding Point bars building

Sediment is moving downstream

Meander Cutoff

How does the gradient change with meandering and meander cutoff?

Meandering Streams

Identify Cutbanks Point bars Meander neck Oxbow lakes Areas of Erosion Areas of

Deposition

AA

BBCC

DD

EE

Flooding Overbank deposits Widening of stream

into flood plain Deposition of

sediment Coarse near stream Fine farther away

Natural Levees

Fig. 12.11Fig. 12.11

Graded Streams

Increased velocity and accelerated erosion.

Erosion acts to grade the Longitudinal stream profile to concave-upward curve

Base level:Lake or Sea

Same Base level

Drainage PatternsGeology controls stream patternsA. Uniformly Erodible

(e.g., flat-lying sedimentary rocks of the Midwest)

B. Conical Mountains (e.g., Volcanoes)

C. Fractured bedrock(shallow bedrock)

D. Resistant ridges of tilted sedimentary rocks(e.g., Valley and Ridge Province of Pennsylvania)

A. Dendritic

B. Radial

C. Rectangular

D. Trellis