Three Categories of Streams

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Three Categories of Streams

• Ephemeral
• Flow only after precipitation (lt30 days per yr.)

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Three Categories of Streams

• Ephemeral
• Flow only after precipitation (lt30 days per yr.)
• Intermittent ( )
• Seasonal flow lasts gt 30 days
• Perennial ( )
• Flow continuously throughout the year
• Base flow generated from groundwater

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Stream Cross-section for Discharge Measurement
0.6 depth is the approximate mean velocity
0.2 depth
o
0.8 depth
The mean velocity at the 0.2 and 0.8 depths
approximates the mean velocity of the section
n Q ? widivi i1
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Vertical Velocity Distribution
0.6 depth
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Velocity distribution varies with stream width
and shape.
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Measuring Discharge
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Estimation of Velocity
Velocity is a function of a) stream gradient
(slope) b) volume of flowing water c)
viscosity of water d) channel
roughness Velocity can be estimated with
Mannings Equation V 1 R2/3
S1/2 n Where n Mannings roughness
coefficient S slope R hydraulic
radius (A/P) in m. V m/sec
Metric Units
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Stage Discharge Relationship
There is a constant relationship between water
depth (stage) in a stream and discharge. This is
determined by stream morphometry.
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What Happens to This Curve if the Stream
Overflows its Bank?
Bankfull
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What Happens to This Curve if the Stream
Overflows its Bank?
Bankfull
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Pressure transducer measures small differences in
water pressure as stage varies. Data can be
stored on a datalogger.
Datalogger Case
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Large snag from spring 1999 flooding. Note that
water is not flowing and is backed up from Lake
Monroe.
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This December 2001 flood damaged the recording
gear
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EQUATION Q C(ha)n Where Q predicted
discharge (cfs) C constant (32.12354) h
measured stage (ft) a stage at 0 discharge
(-1.049) n constant (0.843278)
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The excellent correlation between Q _at_ Brummetts
and Stephens creeks allows us to accurately
predict Q at Stephens Creek from the datalogger
results at Brummetts base station.
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Streams have 3 types of characteristic discharge

• Channel forming
• Deepens/widens channel until equilibrium
• Bankfull
• When water just begins to leave the channel
• Where flooding begins
• Effective
• Flow that attains the maximum sediment transport
  value over time

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Velocity distribution varies with meanders
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The energy in flowing water allows the stream to
do work.

• Solid Load
• Suspended Load fine sediments require low
  velocities to remain in suspension
• Bed Load coarser material moving along the bed
  usually lt5-10 of total load
• Dissolved Load
• Major anions HCO3, SO4, Cl
• Major cations Ca, Na

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The mass of suspended load exceeds that of
dissolved load
River Dissolved Load Suspended
Load Mississippi 23 77 Colorado 12 88
The reverse is true in lakes
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In disturbed watersheds, gtQ yields gtsoil erosion.
TSS will be our measure of this suspended load.
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The concentration of particulates peaks prior to
Qmax because particulates accumulate between rain
events and are washed away during the first flush.
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Relation between current velocity and size of
mineral particles that can be eroded from a
streambed.