Frio River at Concan, TX
USGS 08195000
Geo 4325
Spring 2013
Exercise 2
By Brittany Whalen
March 1st, 2013
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Table of Contents
I.
Gage Basics
pg. 3
II.
Calculation of Velocity
pg. 3
III.
Sediment Competence
pg. 4
IV.
Calculation of Manning’s Channel Roughness Coefficient
based upon the Manning’s Equation.
pg. 5
V.
References
pg. 7
VI.
Appendix
pg. 8
A. USGS Annual Mean Discharge (Calendar Year).
B. USGS Annual Peak Discharge
I.
Gage Basics:
Name of USGS gage: Frio River at Concan, TX
Number of USGS gage: 08195000
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Area:
389 mi²
1,008 km²
Lowest Elevation:
1,204 ft
3,118 m
Highest Elevation:
2,400 ft
732 m
Long Term Mean Annual Flow: 124 ft3/sec
Largest Peak Discharge: 162,000 ft3/sec Date: July 1st 1932
Mean Annual Peak Discharge: 6,710 ft3/sec
II. Calculation of Velocity
A. Determination of W: D ratio (USGS 2013):
Gage is in a sub humid region using a W:D of 12.
Stage at 0 ft3/sec: 2.0 ft.
Depth:
Long Term Mean Annual Flow; Stage ___4___ft
Depth:
___2___ft.
Largest Peak Discharge: Stage ___34.4___ft
Depth: ___32.4___ft.
Mean Annual Peak Discharge: Stage ___7___ft
Depth: __5__ft.
B. Calculations of the stream width for the three discharges based upon the W:D ratio of
12.
Long Term Mean Annual Flow; W= ___24___ft
Largest Peak Discharge: W =___388.8___ ft
Mean Annual Peak Discharge: W = ___60____ ft
C. Calculation of the Stream Cross sectional area (A) for the three discharges.
Long Term Mean Annual Flow; A= ___48___ft2
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Largest Peak Discharge: A =___12597.12___ft2
Mean Annual Peak Discharge: A = ___300____ ft2
D. Average Stream Velocity for the three Discharges by V = Q/A
Long Term Mean Annual Flow; V = Q/A = __124__ ft3/sec / __48__ft2 = _2.58___ft/sec
Largest Peak Discharge: V = Q/A = _62,000_ ft3/sec / _1259.72_ft2 = _12.8__ft/sec
Mean Annual Peak Discharge: V = Q/A = _6,710__ ft3/sec / __300__ft2 = _22.3__ft/sec
E. Estimated Peak Velocity (V*):
Long Term Mean Annual Flow; V* = V/0.8 = __2.58__ft/sec / 0.8
= _3.23_ ft/sec
= _98_ cm/sec
Largest Peak Discharge: V* = V/0.8 = __12.8__ ft/sec / 0.8
= _16.1_ ft/sec
= _490_ cm/sec
Mean Annual Peak Discharge: V* = V/0.8 = __22.3__ft/sec / 0.8
= _28_ ft/sec
= _852_ cm/sec
III. Sediment Competence
A. Entrainment and Transportation Competence Using the Hjulstrom’s Diagram
(Charlton 2007):
Long Term Mean Annual Flow: entrainment competence _0.005_ mm,
Transport competence __6__mm
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Largest Peak Discharge: entrainment competence __<0.001__ mm,
Transport competence __200__mm
Mean Annual Peak Discharge: entrainment competence _<0.001__ mm,
Transport competence __>1000__mm
B. Determination of Tractive Force:
The stream slope based upon the two contour lines that straddle the gage was
determined using a 1:24,000 topo map.
Contour interval: __10__ ft. Horizontal distance: __6795__ ft.
Slope = rise/run or contour interval / horizontal distance = _10_ ft. /__6795_ ft. = 0.0014.
Calculation of Tractive Force by Using the DuBoys Equation:
Long Term Mean Annual Flow: τ = ρgds = ___83.63___ = ___0.17___ lb/ft2
Largest Peak Discharge: τ = ρgds = __1354.8__= __2.82__ lb/ft2
Mean Annual Peak Discharge: τ = ρgds =__209__= __0.43_ lb/ft2
The Maximize Size Sediment that is entrained upon Leopold’s 1964 Diagram
(Leopold, Wolman, and Miller 1964):
Long Term Mean Annual Flow: τ = ρgds = ___0.17___lb/ft2 = __17__ mm
Largest Peak Discharge: τ = ρgds = __2.82_lb/ft2 = __210__ mm
Mean Annual Peak Discharge: τ = ρgds =__0.43__lb/ft2 = __40_ mm
IV. Calculation of Manning’s Channel Roughness Coefficient based upon the Manning’s
Equation.
V = 1.49 R0.67 S 0.5 /n To solve for n, Manning’s Roughness Coefficient, n = = (1.49
R0.67 S 0.5 ) / V
R = hydraulic radius = A / P where A = cross sectional area = w X d
and P = wetted perimeter = 2d + w
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Channel Slope = S = __0.0014__
Long Term Mean Annual Flow: V =__2.58__, A =__48__ P = _28__
R = __1.71____,
n = 1.49(_1.71) ^0.67(_0.0014) ^0.50_ / _2.58__ = ___0.079__/ ___2.58_
= __0.03_
Largest Peak Discharge: V =_12.86_, A = _1297.12_ P = _453.6_
R = __27.77___,
n = 1.49(27.77) ^0.67(0.0014) ^0.50_ / ___12.86___ = _0.156_/ __27.77__ = __0.04__
Mean Annual Peak Discharge: V = _22.36_, A = _300_ P = _70_
R = _4.28__,
n = 1.49(4.28) ^0.67(0.0014) ^0.50_ / ___22.37_ = __0.147_/ __22.36_
=_0.006_
V. References
Charlton, R.O. 2008. Fundamentals of Fluvial Geomorphology. New York, NY: Routledge.
Leopold, L.B., M.G. Wolman, and J.P., Miller. 1964. Fluvial Processes in Geomorphology. New
York, NY: Dover Publications.
U.S. Geological Survey (USGS 2013). 2013. Texas Water Service Center.
http://tx.usgs.gov/ (Last accessed 1 March, 2013).
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