Chapter 11River Systems and

Landforms

- Rivers are the great circulatory systems of the Earth

- They are the great transporters of weathering, mass wasting and erosion

--- in this role they move nutrients [all to often they move too much nutrient – eutrophication and hypoxic conditions]

- Beyond water supplies, rivers give us transportation; waste dissipation; irrigation;supplies for processing and fabrication; cooling; can devastate us when they flood

River Systems and LandformsFluvial Processes and Landscapes

- stream related processes are termed fluvial

- fluvial processes are driven by insolation and gravity- processes both degrade (erode) and aggrade (deposition) the landscape- alluvium is the material transported and deposited

- fluvial processes behave both predictably and unpredictably  

  

  Base Level of Streams- concept of John Wesley Powell - the level below which a river or stream cannot erode the landscape – variable both spatially and temporally as local base level - sea level is the hypothetical ultimate base levelThe Drainage Basin System - landscape drained by a river or stream is a drainage

basin- drainage divides separate basins

[think of the continental divides east and west]

- Drainage basins are open systems

Powell’s Journey to Base Level

Figure 11.2

Ultimate and Local Base Levels

Figure 11.3

A Drainage Basin

Figure 11.4

Drainage Basins

Figure 11.5

Drainage Patterns- an arrangement of channels flow(s) determined by

slope; rock resistance; climate; hydraulic variability; relief; infiltration; etc

* The example shown for Huntington, WV – Portsmouth, OH is a dissected drainage resulting from relatively easy erosion on a topography featuring many ridges and convoluted hill slopes

* p. 368 I am not making testable for you, but look at it. I like Fig 11.9(g) Deranged stream flow

[it actually looks like an ink-blot test]

Highly Dissected Drainage

Figure 11.8

Drainage Patterns

Figure 11.9

Streamflow Characteristics  - Water above base level has potential energy. As it flows

to base level energy is converted to kinetic energy

--- kinetic energy is available to do work and is measured from discharge (Q) as

Q = wdv

--- most commonly we call the result of this work erosion and takes place all along stream

cross section [also might hear terms borrowed from glaciers – plucking and

scouring]

 

Stream Transport 

- materials are transported either through:

(1) dissolved load – in solution

(2) suspended load – fine grain material carried by the water column

(3) bed load – dragged along bottom by traction or “bounced along” by saltation

- type and volume of material transported is dependent on velocity (v) and were capacity is exceeded aggradation will take place

Fluvial Transport

Figure 11.12

Braided Stream

Figure 11.13

Stream Deposition  - Floodplains – flat, low-lying areas paralleling a stream channel

that are periodically flooded; where flooding deposits silt load, a natural levee may form

- Stream terraces – formed where a new local base level is formed; stream returns to downward cutting; these parallel the stream channel in a step-like formation

- River deltas – at stream base level velocity decreases rapidly; sediment load is dropped; material forms a depositional plain (delta); an estuary is formed

- Rivers without deltas – rivers need not form deltas or estuaries; where continent shelves angle steeply; where sediment loads are light (Amazon; East River, NYC)

Floodplain Features

Figure 11.21

Flooding and Morris, Manitoba

Figure 11.22

Ganges River Delta

Figure 11.24

Nile River Delta

Figure 11.25

Mississippi River Delta

Figure 11.26

Mississippi River Delta

Figure 11.26Copyright © 2006 Pearson Prentice Hall, Inc.

Floods and River Management  Floods and Floodplains   - a flood occurs when flow exceeds stream channel

ability to adequately pass it downstream [text examples 1999 Hurricanes Dennis, Floyd and Irene

and the flooding of North Carolina and the problem of flooding in Bangladesh]

- urban flooding is a particular problem as its surfaces are impermeable (no infiltration); its streets and runoff systems are designed to move large amounts of rainfall out of the city quickly… out of the city means into the river following a rainfall event

Urban Flooding

Figure 11.29

Weir and Bypass Channel

Figure 11.1.1