Wednesday
March 2, 2011
(Stream Base Levels;
River Valleys)
The Launch Pad
Wednesday, 3/2/11
Name all
points
meander scar
yazoo tributary
meandering
stream
oxbow lake
meander scar
point bar
back swamp
alluvial deposits
natural levees
Announcements
??
Assignments For This Six-Weeks
Date Issued
Date Due
Video Quiz - Lakes, Rivers, and Other
Water Sources
2/27
2/27
WS - Running Water and Groundwater
(Part 1)
2/25
3/4
PowerPoint Project - Rivers
2/28
3/3
Formation of Natural Levees by Repeated Flooding
Figure 5.21
Running Water
The base level of a stream is the lowest point to which
that stream can erode.
There are two general types of base levels:
•ultimate base level, which is sea level.
•temporary, or local, base levels are lakes, resistant
layers of rock, or main streams that act as base levels
for their tributaries.
Any change in base level will cause a corresponding
readjustment of stream activities, such as deposition
and erosion.
A resistant layer
of rock can act
as a local
(temporary)
base level.
Because the
durable layer is
eroded more
slowly, it limits
the amount of
downcutting
upstream.
When a dam is built
and a reservoir
forms, the stream’s
base level is raised.
This reduces the
stream’s velocity and
leads to deposition
and a reduction of
the gradient
upstream from the
reservoir.
Figure 5.15
Running Water
A stream valley’s sides are shaped by three processes:
•weathering
•overland flow
•mass wasting
Some characteristics of narrow valleys:
•v-shaped
•downcutting toward base level
•rapids
•waterfalls
A Narrow, V-Shaped Valley
Figure 5.17 A
In this narrow, vshaped valley,
the rapids and
waterfalls
indicate that the
river is vigorously
downcutting.
Continued erosion and deposition
widens a valley.
Figure 5.17 B
A wide stream valley is characterized by
meandering on a well-developed
floodplain.
Figure 5.17 C
Running Water
Some characteristics of wide valleys:
•stream is near base level
•downward erosion is less dominant
•stream energy is directed from side to side
•floodplain
Features often include
•meanders
•cutoffs
•oxbow lakes
Erosion and deposition along
a meandering stream
Figure 5.10
A
meander
loop on
the
Colorado
River
Figure 5.18
Begin Worksheet
Running Water and
Groundwater (Part 2)