JKEARNEY
NOTES
SHC 410
, 3/02/2020 SedimentTranspo
Movement & Effect of sedimentation :
deposition of
-
sediment Structures
scouring& of foundations
↳
→
.
.
↳ Canals
scouring sedimentation
→
.
↳ Reservoirs loss of
capacity
→
sedimenttransportoo.cc
Bed load boulders
Deposition {
rolling
* :
.
*
Suspended load suspended particles
:
water Colloidal water (difficult remove)
quality
← *
stays in to
:
roughness T )
* As Froude number increases (
more sediment can into suspension
go .
AMmountofmaterialtransporte.cl# → under
given conditions
Dependent
( interaction
on →
→
Quality &
Quantity of sediment
of stream to
Influences the
between )
Capacity transport
quality
& { Groupie # Sediment brought down depend on
of & of watershed
quantity Geology Topography
of rainfall Intensity
Duration & Distribution
sediment
Magnitude
*
.
, ,
Soil Moisture
Vegetal
* * cover
Grazing Surface
* * erosion
nation
24/7 Duration
Topootaµ¥¥¥¥
rainfall rainfall
Magnitude
8
Geology New grazing
i. ooo : :! ! LT Erosion .
Soil moisture
, Groupie of transport sediment
capacity stream to
→ a
Hydraulic
{ Slope Discharge Viscosity
* * *
Velocity
of
properties *
RoughnessRadius
* *
Density
the stream .
*
Hydraulic * Turbulence
cEE÷¥÷iEmois
of sediment
size &
gradation
inn roughness Tractive
forces
Q
radius
Hydraulic
Definitions
dice thick) above the bed
Bed
layer Flow
layer (2
grain
-
. .
Bed load Sediment that rolls / slides bed
along
→ .
i. e .
Contact Load .
Bed material → Sediment mixture of stream bed .
Bed material Part of total sediment
discharge } Cfoonupnodsqd of
grain sizes
the bed
discharge on .
Discharged
weighed
concentration unit volume of
.
→
Dry weight of sediment per
discharge
sediment moved
Load
by stream
- .
Sediment →
Quantity of sediment that
pass a 0 per
Discharge unit time .
Sediment
yield
→
Suspended load → Sediment supported
turbulence .
by upward components of
, Frictionformulao.Uniformflow.ee *
a-ureunuitynfotr.EE?onbat9Ees
/ 0pgµ
.
t } Gravity force in
pgtthxsinco flow direction
)
I #
← .
To×P×L } Shear force
↳ Perimeter
To
%
xPL=pgAL×sinco )
since sinlojretancofs .
} Shallow slope
To=pgA#
P
To=pgRSo
↳
boundry stress
mean .
, Forcesonpartickso
-
#
£§€Ecaag#
-
a-
-
to
00800000
* shear force on bed W' (Ps p)
xgxvs ( weight)
= -
force
* on a
grain .
Unit area :
Ap Areaotpartice
=
nr of particles a. Ape
Total area D 502
To A FD xttp D 50 size of
passing
ooo : 50%
D 502
* Point where a particle is about to move :
Cf angle of repose
-
To =
Tcr
* if To > Ter -
unstable
To shear force particles will move
by water &
-
.
Ten -
force required to move the particle .
xDf
'
Tcr A
Cps pg xtanc
-
x
Volume
Tcr_ A ( Q)
( ps ptg xD
- Itxgttpxtan
, Incipent hreshd lmotiono .co 400
To =p
xgxRx5←{ When Rett 7400 →
TCR =
0,056 x (Ps p
-
)gxD5O
↳ Flow is turbulent around the bed
material fully
.
Read value from
When Re* L 400 →
graph
↳ Tcr x (Ps
Pg xD 50
-
number ← Re* 1,14×10-6 Mls
U*yD5o_
2
Reynolds
=
V
=
,
t
kinematic
viscosity .
& U*
=p# Density of the fluid
f p
-
.
Shear
velocity
:{
HRS valid
Dso is
only when D= 1,65
=Ps
=
IEEE ↳
*
assumptions .
z¥
, falllsettlingjveloc.it# submerged
of sediment
gelatine density
diapmeter
Fallingeocity LIFE
f- ilgbd and D=
lPs#
Constant & function of CD
Assume - Sf for
t
=L and CD -2
large D
form factor and CD -
24
REI
Consider a
falling particle :
( Ps p
)xgxt=LzCDxPxAxVFs2
-
ps-plxgxtTDT3-ICDxpxltgdxUFSZVFSZ-kxbgxf.DE
(
)
thus
VFs=y/¥×tg×d
VF5-AxilgxdxD.AT/IzxITFallVelocity:-
given
Rough VFs=T/2zgD⑦
a) sediment - CD -2
b) Fine sediment →
6=24*2
yr-s-yftfxrffxg.AT
& Re*=VFSxD
T
:tFs=gy
o
, Scourestimationo
→
Complexities:
* Non
Homogeneous mixtures of water a sediment
-
* 3D flow patterns
*
Difficulty establishing actual geometries .
actual scour depths
*
Observing
*
Highly variable properties .
long term t short term @ Piers & abutments
enteral
^
p
Total scour =
EG t contraction + Local scour
Alluvial channel scour →
Cohesive bed channel scour →
Scouring : As
ooo
a
Velocity
river scours the
decreases
depth
→
increases
scour potential increases
Scourcountermeasureso
① Hydraulic countermeasures
River Berms
↳
training
↳ Bed armour
structures →
Spurs ,
Dykes ,
ing →
Riprap Gabi ons
,
ing
↳ Local scour armour →
② Structural →
Foundations
③
During maintenance →
{ EROSION If Hydraulic
Fwriaggestation }
:
