1. Chapter 5 Sediment Yield

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学而时习之，不亦说乎！
5.1 Introduction
Soil erosion rate is the gross amount of soil moved by water and wind.
Soil loss is the soil moved off a particular slope or field.
Sediment yield is soil delivered to a point under evaluation.
Kirkby, M.J. and R.P.C. Morgan. Edited. Soil Erosion. John Wiley & Sons.
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5.1 Introduction
75% of upland erosion is deposited at the base of hillslopes, in flood plains, and within river channels.
25% of sediment is discharged into the ocean.
Read table 9.1 on page 173 calculate the sediment concentration (kg/m2)
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5.1 Introduction
Sediment concentration of Yellow river is 61 times larger than that of the Mississippi river.
Why?
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5.1 Introduction
Mississippi river
Yellow river
Humid zone
Vegetated
Soil conservation
Semiarid region
Agriculture
Denuded
Deep loess highly susceptible to erosion
Severe storm
Steep slope
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6. 5.2 Sediment movement and measurement
Sediment discharge is defined as the quantity of sediment per unit time carried past any cross section of a stream.
Measurement:
Sampling and relating it to streamflow
discharge
Sediment deposit surveys
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7. 5.2 Sediment movement and measurement
Factors affect the sediment yield
Supply of material-erosion
Physical characteristics of the sediment
Characteristics of the channel-morphological-stage roughness steepness
Streamflow discharge
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8. 5.2 Sediment movement and measurement
+++ Total sediment transport 
Supply rate
Sediment size
Sediment transport
Wash load
Bed material load
Transport capability
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9. 5.2 Sediment movement and measurement
100
Sediment
Streamflow
Coarse
Fine
Flat
Steep
Degradation
Aggradation
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10. 5.2 Sediment movement and measurement
By particle size
Bed material load
Wash load: mm or smaller
By method of transport
Suspended load
Bed load
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11. 5.2 Sediment movement and measurement
Suspended load is the sediment supported yb the upward components of turbulent currents and transported in suspension.
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12. 5.2 Sediment movement and measurement
The settling velocity of particles less than 0.1 mm in diameter is proportional to the square of the grain diameter.
Settling velocity  diameter2 d< 0.1mm
The settling velocity of particles larger than 0.1 mm in diameter is proportional to the square root of the grain diameter.
Settling velocity  diameter1/2 d> 0.1mm
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13. 5.2 Sediment movement and measurement
Settling velocity
W = (s-  )D3/6
F = CD D2 2/8
2 = 4 (s-  )gD / 3CD 
G. G. Stokes 1851
F = 3 D
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14. 5.2 Sediment movement and measurement
Settling velocity
= (s-  )gD2 / 18  D< R<0.4
= 1.72[(s-  )g D / ]
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15. 5.2 Sediment movement and measurement
Bed load
Bed load is the sediment that moves by saltation, rolling, or sliding in the bed layer, on or near the bed.
Bed layer: a flow layer, several grain diameters thick (usually taken as two grain diameters thick immediately above the bed).
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16. 5.2 Sediment movement and measurement
Duboy’s (1879) equation
for low velocities and small grains:
Tf = WWDS
Where Tf = tractive force; WW = specific weight of water; D = depth of water; and S = stream gradient.
for high velocities and large particles:
Competence = CV6
Where C is a constant.
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17. 5.3 Sediment delivery ratio
A percentage of the onsite eroded material that reaches a given measuring point.
Df = Ys/Te
Where
Df = sediment delivery ratio;
Ys = sediment yeidl at a point (wt·area-1·yr-1);
Te = total erosion from the watershed above the point at which sediment yield is measured (wt·area-1·yr-1).
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Further reading
钱宁，万兆惠. 1983，泥沙运动力学，科学出版社。
American Society of Civil Engineers Sedimentation Engineering.
M.Selim Yalin Mechanics of sediment transport. Pergamon Press.
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19. Watershed management-- 14
钱 宁 Ning Chien
1922 born
1943 graduate
1948 master degree
1951 doctor degree
1955 back to China
1979 cancer
pass away
H. A. Einstein
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