Physical Characteristics of Streams

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Physical Characteristics of Streams

• What is a stream?
• water -- usually freshwater
• moving
• in a channel

Close up look of streams stream
2
What makes a stream channel?

• The stream itself.
• Start water moving and it will form a channel.
• So, where does the water come from?

Yellowstone Steve
3

• Aristotle -- thought water vapor condensed in the
  soil
• Middle ages -- thought water came from the ocean
• Palissy, 16th century
• More springs in the mountains
• Water not salty
• Pierre Parroult, 1674
• Seine River in France
• Rain 6X stream flow
• Stream water comes from rain
• Where does the rest of the water go?

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Hydrologic Cycle
10-20 of precipitation Pine forest gt hardwood
forest
5
Surface runoff stomata
6
Evapotranspiration (ET) Interception Transpirati
on Evaporation
7
Runoff Surface Subsurface
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P ET RO
Precipitation
Evapotranspiration
Runoff
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Global Hydrologic Cycle
Land
Oceans
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Global Hydrologic Cycle
Land
Oceans
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Global Hydrologic Cycle
ET16
P23
RO7
Land
Oceans
7/23 30 On average, 30 of precipitation ends
up as runoff
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On average, 30 of precipitation ends up as
runoff Highly variable! Endorheic basin (no
outlet) ET 100, no runoff Parking lot ET
small, RO ? 100
Humbolt River, NV Carson Sinks Parking lot
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Runoff varies spatially
Evapotranspiration
Runoff
100
80
RO
60
Percent of precipitation
40
ET
20
Deleware R., NJ
0
Red R., ND
Sudbury R., MA
Neches R., TX
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Runoff also varies seasonally
15
80
Mean daily discharge
70
Coweeta WS 32, 1991
60
50
40
Discharge (L/s)
30
20
10
0
J
F
M
A
M
J
J
A
S
O
N
D
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Runoff can even vary daily
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So, the short answer is that streamflow is the
excess of precipitation over evapotranspiration
RO P - ET
So, now we have water in the stream, flowing
downhill
Escher
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Water flowing downhill
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Total Energy Potential Energy (Z) Kinetic
Energy (V) TE1 PE1 KE1 TE2 PE2 KE2 TE1
TE2 (First Law of Thermodynamics) PE2 lt PE1
Moving downhill
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TE1 PE1 KE1 TE2 PE2 KE2 TE1 TE2
First Law of Thermodynamics PE2 lt PE1 Moving
downhill So, KE2 gt KE1??? Does velocity
increase downstream?
Little Stony Mississippi
We have to include heat. When a stream does
WORK, KE and PE are converted to heat.
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Streams do 3 kinds of work
Transportation -- carrying material
(load) Erosion -- creating load Deposition
-- when a stream cant do work it doesnt have
enough energy to carry its load
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Transportation
I. Dissolved load Chemicals in solution --
solutes No work required Doesnt settle out
II. Solid load Particles Settle out if no
motion gt 0.45 µm (by definition)
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I. Dissolved load May cause color, but water
stays clear
II. Solid load Causes water to be turbid, that
is, to lack clarity
blackwater river New River, Wolf Creek
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Solid load
1. Floating load -- less dense than water
New River
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Solid Load
2. Suspended load particles in the water column
It takes work to keep the suspended load in
suspension. This work is the result of
turbulence, the chaotic movements of water
molecules.
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There must be turbulence in order to have
turbidity.
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Solid Load
3. Bed Load Moves along the stream bed, at
least occasionally in contact with the bottom
Little Stony
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CompetenceThe largest particle a stream can
carry at a certain flow
Little Stony 2
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Solid Load1. Floating2. Suspended3. Bed
In practice, difficult to separate
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ErosionBrings material into the stream
1. Corrosion -- chemical weathering creates
dissolved load
St. Elena Canyon
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Erosion
2. Corrasion -- Mechanical wearing away of
particles
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The larger the particle, the greater the force
needed to move it ????
Cohesion of small particles
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Factors affecting erosion
Geology Rock type, topography
Climate
Rainfall
Soil
Vegetation
Erosion
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How does rain affect erosion?
????
Erosion
Rain
HWC 2 Sediment vs Q
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How does precipitation affect erosion?
Desert
Grasslands
Erosion
Forests
100
150
50
Annual Precipitation (cm)
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Factors affecting erosion
Geology Rock type, topography
Climate
Rainfall
Soil
Vegetation
Erosion
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What happens when a stream loses velocity?
Less velocity Less turbulence Less ability to
carry suspended load Deposition
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How can a stream lose velocity?
1. Decrease in gradient stream comes out on a
plain alluvial fan
RMP fan, Lawn Lake Desert fans
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2. Stream enters standing water Delta
deltas
3. Stream enters lower gradient river
deltas Lake Peppin Waterton River Ain and Rhone
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4. Stream goes around a bend Point bar
Point bars
5. A flood -- stream goes out onto floodplain
flood floodplain
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Erosion, transportation, and deposition These
are the processes that shape the stream channel.
42
In order to make a 0.001 molar solution of
Ca3PO4, I would add 215 mg of this chemical to 1
liter of distilled water. What would be the
phosphorus concentration in this solution? Note,
this could be a trick question as Ca3PO4 is
essentially insoluble. In actuality, you would
end up with a liter of distilled water with 215
mg of white powder on the bottom. But just for
funzies, lets pretend that this much stuff
easily dissolves in water.
Easy way Since this is a 1 millimolar (0.001
molar) solution of Ca3PO4, it is also 1 mM P,
which is 31 mgP/L.   Or Molecular weight of
Ca3PO4 is 215 g, and 31 g of this is phosphorus.
So Ca3PO4 is 14.4 phosphorus. Multiply
0.144215 mg/L to get 31 mgP/L.
43
Your boss has asked you to analyze a bunch of
water samples for SRP (soluble reactive
phosphorus PO4-P. These samples were all taken
from undisturbed small streams, so you know the
SRP levels will be low. The first thing you
need to do is make a standard solution, and you
decide that 100 µgP/L would be a good stock
solution to start with. Explain how you would
make this solution using NaH2PO4 and standard
laboratory equipment -- a balance that weighs to
the nearest mg and volumetric flasks ranging from
10 mL to 1 L.
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Molecular weight of NaH2PO4 is 120. 100 ?g P
(120 ?g NaH2PO4 / 31 ?g P) 387 ?g NaH2PO4 But
our balance only weighs to nearest mg. So weigh
out 100 times this much (38.7 mg), add it to 1 L
of distilled water, and dilute it 1001 (add 10
ml of the solution to a 1 L flask and fill the
flask to 1 L).
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Morphology and other physical characteristics of
streams
I. Gradient -- the slope of a stream
Stream profiles 3
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This ideal concave shape graded stream
Ideally, streams reach grade due to a balance
between erosion and deposition.
deposition
erosion
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Convex profiles and waterfalls can occur where
there are changes in rock type.
Elevation
Elevation
Distance
Distance
L. Tenn 2 waterfalls 2
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II. Channel Pattern

• Straight
• Meandering
• Braided

straight, Florida meandering 3 braided 3
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III. Drainage network
Horton 1940s Strahler 1950s
Stream Order
Actually reach order
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Drainage patternsDepends on rock type
Dendritic flat rock strata Rectangular
faulted rock Trellised folded strata
Patterns James River
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IV. Stream size

• Stream order
• Different map scales
• Different areas of the country
• Streams of similar order may have different size

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Streams in U.S.
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Width
Compare the New River at McCoy Falls with
Narrows Width is a good descriptor of a site but
not of a stream in general.
New River

• Depth
• Same problem

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4. Length
Length (mi) of the ten largest rivers of the
world
1 Amazon 3,900 2 Congo 2,900 3 Yangtze 3,600 4
Mississippi 3,890 5 Yenisei 2,800 6 Lena
2,660 7 Paraná 1,500 8 Ob 3,200 9 Amur
2,900 10 Nile 4,160
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5. Watershed area
Watershed the area drained by a stream
watershed 2
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6. DischargeThe amount of water flowing down
the river
Ten largest rivers of the world
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DischargeNormally measured in L/s or m3/s

• Measuring discharge
• Flow continuity equation
• QWDV
• Qdischarge
• Wwidth
• Ddepth
• Vvelocity

velocity
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Measuring discharge b. Weir or flume
Weirs and flumes 5
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Measuring discharge c. Stage recorder
Stage recorder 2
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Discharge is not constant Hydrograph a graph
of discharge vs. time Storm hydrograph base
flow storm flow rising limb falling limb
recession curve Annual hydrograph Utah North
Carolina
hydrographs 3
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80
Mean daily discharge
70
Coweeta WS 32, 1991
60
50
40
Discharge (L/s)
30
20
10
0
J
F
M
A
M
J
J
A
S
O
N
D
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IV. Stream Size1. Order2. Width3. Depth4.
Length5. Watershed area6. Discharge
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• Velocity
• (Physical characteristics of streams)

Easy to make point measurements rubber
duckie current meter Spatial variability cross
section depth
velocity profiles
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Velocity varies width depth
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Manning EquationAn empirical equation that shows
what factors affect velocity
V velocity R hydraulic radius RA/P Sslope
(gradient) nManning roughness coefficient
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Hydraulic Radius (R)
RA/P Across sectional area (width
depth) Pwetted perimeter
If P?W
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So, for most streams velocity is a function of
depth, gradient, and roughness
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Manning roughness coefficients
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VI. Type of flow
Laminar Smooth, straight channel Very low
velocity All water molecules going in the
same direction Parallel streamlines
Turbulent chaotic movement eddies
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Reynolds Number, NR
?density of water Vvelocity Rhydraulic radius
(depth) ?viscosity
NR small (lt 300) laminar flow NR large (gt2000)
turbulent flow In between -- transitional
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Reynolds Number, NR

• Typical stream
• ? 1.0 g/mL
• V 20 cm/s
• R 50 cm
• 0.0114 Ns/m2
• NR 87,600

Typical streams are turbulent
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• Unusual stream
• ? 1.0 g/mL
• V 2 cm/s
• R 5 cm
• 0.0114 Ns/m2
• NR 876
• Still above the 300 for laminar flow.
• To get NR down to 300 we would need to reduce V
  to 0.68 cm/s. With a Manning n of 0.05 and
  keeping depth at 5 cm, the slope would have to be
  0.6 cm/km!