1. Channel Networks
The drainage basin, or watershed, is the surface around a channel that "sheds water and sediment into that channel"
Streams that get their water from overland or groundwater flow, and not from other streams, are first -order streams
A second-order stream
begins at the junction of
two first order streams
If two second-order streams join, a third- order stream is formed
Skip 233 right to 237 left, resume 237 right "a critical power”

2. Stream Power
Skip 233 right to 237 left, resume 237 right "a critical power"
Critical Power is that rate of useful energy necessary to transport the existing [sediment] load
If more Kinetic Energy, erosion (degradation) will result
If there is too much sediment for the available energy, deposition (aggradation) will result

3. Driving and Resisting Forces
Driving forces: gravity propelling water downslope
Resisting forces: friction within the fluid (water), and friction between water and the channel boundary
Conversion of Potential Energy into Kinetic Energy

4. Conservation of Mass (Continuity) The Role of Cross Section Area
Mass is neither created nor destroyed
Inputs = outputs
Inputs and outputs for fluid
flow are discharge
Vel (V) x Area(A) = const.
All this means is that discharge is constant, flow rate remains the same from 1 xs to the next. Unless you are in a losing/gaining reach, where inputs do not equal outputs. Water is incompressible, so the same amt of water must go through a smaller space as a bigger one. (Continuity applies to all fluid flows, even air. Continuity is not true in aerodynamics, where air flow becomes compressible when approaching Mach 1)
V1A1 = V2A2
If area gets smaller, velocity gets larger

5. Gilbert’s Fluvial Process
Joined John Wesley Powell survey in Utah, 1874
First suggested the concept of “graded streams”
A stream’s form is defined by its ability to transport load, and that a “graded” stream condition will exist when the stream can just carry the load supplied to it
“The transportation of debris by running water”, USGS Prof. Paper 86, Grove Karl Gilbert, 1914
Grove Karl Gilbert

6. Gilbert: The Role of Stream Slope
If a stream …
reaches a point where the slope is less, it
becomes overloaded and part of the load is dropped,
making a deposit.”
“If a … stream reaches a point where
the slope is steeper …
it [goes faster and erodes] more load...”
Graphic by Peter Wilcock
Text by G.K. Gilbert, “Hydraulic
Mining Debris in the Sierra Nevada”
USGS Prof. Paper 105, 1917.

7. Sediment Sources, Storage, and Yields
Most stream sediment from creep, soil erosion, mass wasting
Called “Colluvium”
River incision of bed-rock important after dramatic increase in elevation above sea-level.
Steep streams form vee-shaped channels
Most streams transport limited: supply exceeds removal ability. = "Alluvial Streams"
Most streams store sediment, only about 5 to 7 % of sediment input removed by main trunk.
Meandering covers bed load with point bar and floodplain deposits.

8. Downstream Changes in Alluvium Grains
6_5
Downstream Changes in Alluvium Grains
Character of detrital sediments depends on time, distance, and energy. For example, in streams:
Particles are large and
irregular, and consist of
a variety of minerals,
including the least
resistant.
Particles are mid-sized
and of intermediate
roundness, and include
resistant and nonresistant
minerals.
Particles are small and
nearly spherical, and
consist mainly of the
most resistant minerals,
such as quartz.
HIGHLANDS
LOWLANDS
NEAR-COASTAL

9. Active and Relict Alluvium
Active: that sediment that can be removed and carried by the stream that now covers it.
Anything deeper
or coarser is relict
See Figure 11-8

10. Floodplain Morphology
Scrollbars
floodplain
meander scar
floodplain
oxbow
Splay
floodplain
cutbank
colluvium
pointbar
chute
yazoo
Splay : pile of sediment on floodplain from a levee breach
Scroll-bars (aka Scroll marks) an asymmetrical ridge and swale topography on the inside of the bends due to loop migration.
Meander scar a crescentic cut in a bluff or valley wall produced at a cut bank

11. Fluvial Deposits
Table 11-2

12. Loop Cutoff and Oxbow Formation
Floods allow shortcuts. A shortcut is a short lateral path for the same drop, i.e. a steeper gradient. Shortcuts lose less energy to friction, and they cause oxbows.
Figure 11-10

13. Crevasse Splay Skip Climatic Change and Aggradation.
Scroll marks, point bar scars

14. Terraces Remnants of former floodplain
River adjusts to uplift or drop in ultimate base level (sea-level) by downcutting
Any spot is higher, water falls further to get to that spot, has accelerated more, so is faster.
Stream cuts off meander loops, straightens, uses a smaller, lower, floodplain
Older, higher floodplain now a “terrace”

15. River meanders across floodplain
Repeat
River meanders across floodplain
Base level drops,
or region uplifts.
Water goes faster, stream cuts down into channel, straightens, new lower floodplain narrower.
Old, unused floodplain a terrace
Further incision cuts a new terrace

16. Depositional and Erosional Terraces
Alluvial Stream
Bedrock Stream

17. Deltas Consists of three types of beds
Occur where stream hits slow water
Competence decreases to nearly zero, suspended load is dropped
Deposits build out into lake or sheltered sea, extending the length of the river
Consists of three types of beds
Topset beds - horizontal, surface delta
Foreset beds - delta slope
Bottomset beds – horizontal, bottom sea or lake

18. Deltas have strata deposited in a characteristic geometry
Topsets, Foresets and Bottomsets
Actually much more complex: many distributary channel deposits

19. The Mississippi River Delta changes location with time
General trend: Delta builds Seaward.
If Floodwaters happen to reach
the sea via a shortcut, they flow faster in
the shorter (steeper) path, cutting a
new channel. The old channel is abandoned.

20. topsets
foresets
birdsfoot
A fan-delta in a lake
bottomsets

21. An Alluvial Fan in Death Valley Sudden drop in competence
Fast, steep bedrock stream hits flat plain

22. Colluvial Fans
Small Scale
Large scale
Bulk of stream load