Fluvial Geomorphology

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Fluvial Geomorphology GRG 338-C Streamflow
(Discharge)
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• Importance
• geomorphic significance (performs work)!
• hydrology
• water resources
• ecological

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Big Thompson River, CO
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Rio Pánuco, San Luis Potosi
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Rio Tamuin, San Luis Potosi
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Mississippi River bank erosion, upstream of New
Orleans
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Rio Moctezuma, San Luis Potosi
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• Importance
• geomorphic significance (performs work)!
• hydrology
• water resources
• ecological

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Lower Rio Panuco _at_ Panuco, Veracruz
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• Importance
• geomorphic significance (performs work)!
• hydrology
• water resources
• ecological

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• Importance
• geomorphic significance (performs work)!
• hydrology
• water resources
• ecological

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Flow Paths to Stream Channel
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• Sources of streamflow (discharge) have different
  travel times
• Runoff (throughflow)
• Ground water

Runoff
Ground water (base flow)
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• Hydrographs
• express the relationship between discharge and
  time
• single event hydrograph

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• Single event hydrograph
• shape a function of runoff and base flow

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Discharge (m3/s)
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5
1
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Time (hours, days, weeks)
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Source of streamflow determines the hydrograph
shape
Runoff
Ground water (base flow)
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Elements of a single event hydrograph
Peak
Rising Limb
Falling limb
Discharge (m3/s)
Base flow
Runoff
Base flow
Time (hours, days, weeks)
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Continuity equation for discharge (Q) Q (m3/s)
V (m) A (m2)
Depth (D)
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w
d
d
Q ?qi
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q1 0.64 m3/sec (5.0 0.85 0.15) q2 7.64
m3/sec (5.0 2.35 0.65) q3 30.9 m3/sec
(5.0 4.75 1.3) q4 46.0 m3/sec (5.0
5.75 1.6) q5 6.88 m3/sec (5.0 2.5
0.55) Q 92.1 m3/sec
v velocity (m/sec) d depth (m) w width
(m) Q, q discharge (m3/sec)
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• Q stage rating curve
• standard procedure for estimating Q

Q (cms)
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floodplain

• Q stage rating curve
• uniform x-sec. geometry

Qbf
Q (cms)
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• Q stage rating curve
• non-uniform x-sec.
• low high channel

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• Q stage rating curve
• non-uniform x-sec.
• low floodplain

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Guadalupe Valley at Cuero, TX
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Guadalupe valley at Cuero
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• Q stage rating curve
• single line
• assumes scour deposition during flood event

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Stage (m)
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75
50
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Q (cms)
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• Channel scour (erosion) and deposition
  (infilling) during Q event
• influences rating curve

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b.
a.
c.
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Scour lt deposition
c.
a.
b.
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Scour lt deposition
c.
a.
b.
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b.
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Stage (m)
c.
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a.
75
50
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Q (cms)
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Rising stage
Falling stage
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• Factors influencing the shape of hydrographs
• Precipitation characteristics
• Surface characteristics
• Basin characteristics

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• Factors influencing the shape of hydrographs
• Precipitation characteristics
• distribution
• intensity
• duration
• seasonality

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distribution
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• Factors influencing the shape of hydrographs
• Precipitation characteristics
• distribution
• intensity
• duration
• seasonality

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• Factors influencing the shape of hydrographs
• Precipitation characteristics
• Surface characteristics
• influence on runoff and baseflow!!
• Basin characteristics

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• b. Surface coverage
• Consider how influences infiltration and
  runoff!!!
• land use
• soils
• vegetation

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• Urbanization results in higher rates of runoff
  due to a reduction in infiltration
• influence on hydrograph??

Impervious cover
2.5 cm/hr
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Urban hydrology
Runoff high rates!
Ground water much lower!
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New Hydrograph due to increased impervious cover

• higher highs and lower lows
• steeper rising limb
• higher peak discharge
• steeper falling limb
• low base flow

Peak
Rising Limb
Falling limb
Discharge (m3/s)
Base flow
Runoff
Ground water
Time (hours, days, weeks)
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soils
Coarse-textured (gravel, sand)
Infiltration capacity (cm/hr)
Fine-textured (high clay content)
Time after onset of rainfall (hours)
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clay soil/geology
Sandy/gravel
Discharge (m3/s)
Time (hours, days, weeks)
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land use
Forest (original vegetation)
Infiltration capacity (cm/hr)
Corn field
Time after onset of rainfall (hours)
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agricultural (corn field)
forest
Discharge (m3/s)
Time (hours, days, weeks)
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• Factors influencing the shape of hydrographs
• Precipitation characteristics
• Surface characteristics
• Basin characteristics

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c. Influence of basin characteristics on
streamflow Assumes all other factors are
constant
area
Smooth vs. Flashy
slope
drainage density
shape
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• Streamflow Regimes
• discharge conditions over a year
• water year in U.S. (Oct 1. - Sept. 30th)

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• 1. Perennial streamflow regime
• humid regions flow all year long
• streamflow sustained by base flow between
  rainfall events

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Streamflow Regimes 1. Perennial
Supplied by precip. events
Supplied by base flow
Discharge (m3/s)
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• 2. Intermittent streamflow regime
• semi-arid seasonal flow
• base flow sustains streamflow during wet season

Canadian River, TX Panhandle
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2. Intermittent
Supplied by precip. events
Supplied by base flow
Discharge (m3/s)
Dry season no base flow
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• 3. Ephemeral
• arid flow only after a rainfall event

Monterrey, NL
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Streamflow Regimes 3. Ephemeral
Individual precip. events
No base flow!
Discharge (m3/s)
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• Flood Recurrence Interval (RI)
• Avg. years between floods of equal or greater
  magnitude
• Annual peak Q
• RI (n 1 / N)
• n years of record
• N rank of a particular flood event

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• Flood Recurrence Interval (RI)
• Avg. years between floods of equal or greater
  magnitude
• Annual peak Q
• RI (n 1 / N)
• n years of record
• N rank of a particular flood event

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July 3rd July 7th
Guadalupe River floodplain _at_ Cuero
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2002 1998 flood
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2002
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1998
2002
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