Chapter 11
River 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 Landforms
Fluvial 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 level
The 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 steplike 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
Copyright © 2006 Pearson Prentice Hall, Inc.
Figure 11.26
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