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 Title Page
 Introduction
 Mechanical phases of the experimental...
 Results of the main research work...
 Characteristics of the flow field...
 Experiments on resuspension...






Group Title: Technical report – University of Florida. Coastal and Oceanographic Engineering Program ; 35
Title: Deposition of fine sediments in turbulent flows
CITATION PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00075013/00001
 Material Information
Title: Deposition of fine sediments in turbulent flows
Series Title: Technical report – University of Florida. Coastal and Oceanographic Engineering Program ; 35
Physical Description: Book
Creator: Partheniades, Emmanual
Affiliation: University of Florida -- Gainesville -- College of Engineering -- Department of Civil and Coastal Engineering -- Coastal and Oceanographic Program
Publisher: Dept. of Coastal and Oceanographic Engineering, University of Florida
Publication Date: 1977
 Subjects
Subject: Coastal Engineering
Sedimentology   ( lcsh )
University of Florida.   ( lcsh )
Spatial Coverage: North America -- United States of America -- Florida
 Notes
Funding: This publication is being made available as part of the report series written by the faculty, staff, and students of the Coastal and Oceanographic Program of the Department of Civil and Coastal Engineering.
 Record Information
Bibliographic ID: UF00075013
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved, Board of Trustees of the University of Florida

Table of Contents
    Title Page
        Title Page
    Introduction
        Page 1
    Mechanical phases of the experimental equipment
        Page 1
        Page 2
    Results of the main research work on the degree and rates of desposition
        Page 2
        Page 3
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
    Characteristics of the flow field in the annular channel-ring system
        Page 14
        Page 15
        Page 13
    Experiments on resuspension rates
        Page 16
        Page 15
        Page 17
        Page 18
        Page 19
        Page 20
Full Text






UFL/COEL/TR-035


DEPOSITION OF FINE SEDIMENTS

IN TURBULENT FLOWS



By



Emmanual Partheniades


January 1977

















COASTAL AND OCEANOGRAPHIC

ENGINEERING LABORATORY

University of Florida

Gainesville, Florida 32611



Prepared Under
The Initiation Grant No. G.K.. 31259
NATIONAL SCIENCE FOUNDATION
Washington, D.C.


1

















FINAL TECHNICAL REPORT


1. Introduction

At the conclusion of this award a major phase of research work on the
depositional behavior of cohesive sediments has been completed. The bulk of
this work was accomplished by August 1973 and it is contained in detail in
our Technical Report No. 16 (4)*. A copy of that report was forwarded to
the National Science Foundation in the spring of 1973 and another copy is
herewith attached. The project remained inactive during the principal inves-
tigator's leave of absence from September 1973 to September 1975. ,Limited
experiments on resuspension rates were conducted between January and June 1976.
The entire project can be; categorized according to the following major aspects:
(a) The mechanical aspect of the experimental equipment, (b) The primary
research work on the degree of deposition and the rates of deposition of the
depositable part of a sediment, (c) Flow characteristics in the experimental
apparatus which resulted as byproducts of the previously mentioned main
researchworkand (d) thepreliminary results on the rates of resuspension
of the deposited sediments.
This is a summary of all four phases. For the details of the first
three phases the reader is referred to the attached copy of Technical
Report 16 (4).

2. The Mechanical Phases of the Experimental Equipment

The experimental equipment was already designed, constructed, instru-
mented and calibrated prior to the initiation of the NSF project ENG 71 -
02310 (GK-31259). In fact several experiments had already been performed.
The only addition after the initiation of the project was the false bottom
which permitted a direct measurement of the bed shear stresses and, therefore,


Numbers in parenthesis indicate reports and papers based on the research
supported by this grant and listed in the "Summary."

















FINAL TECHNICAL REPORT


1. Introduction

At the conclusion of this award a major phase of research work on the
depositional behavior of cohesive sediments has been completed. The bulk of
this work was accomplished by August 1973 and it is contained in detail in
our Technical Report No. 16 (4)*. A copy of that report was forwarded to
the National Science Foundation in the spring of 1973 and another copy is
herewith attached. The project remained inactive during the principal inves-
tigator's leave of absence from September 1973 to September 1975. ,Limited
experiments on resuspension rates were conducted between January and June 1976.
The entire project can be; categorized according to the following major aspects:
(a) The mechanical aspect of the experimental equipment, (b) The primary
research work on the degree of deposition and the rates of deposition of the
depositable part of a sediment, (c) Flow characteristics in the experimental
apparatus which resulted as byproducts of the previously mentioned main
researchworkand (d) thepreliminary results on the rates of resuspension
of the deposited sediments.
This is a summary of all four phases. For the details of the first
three phases the reader is referred to the attached copy of Technical
Report 16 (4).

2. The Mechanical Phases of the Experimental Equipment

The experimental equipment was already designed, constructed, instru-
mented and calibrated prior to the initiation of the NSF project ENG 71 -
02310 (GK-31259). In fact several experiments had already been performed.
The only addition after the initiation of the project was the false bottom
which permitted a direct measurement of the bed shear stresses and, therefore,


Numbers in parenthesis indicate reports and papers based on the research
supported by this grant and listed in the "Summary."










enabled a refinement of the description of the entire flow field and of the
operational procedures.

The components of the basic experimental equipment consist essentially
of a system of a rotating annular channel 8 in. wide and 30 in. mean radius
containing the water-sediment mixture and a rotating ring positioned within
the channel and in contact with the water surface. The simultaneous rotation
of the channel and ring in opposite directions generates a uniform turbulent
shear field free of floc-disrupting elements. By proper instrumentation of
the blades supporting the ring and the false bottom the shear stresses on the
ring and the bed can be measured directly. Moreover, by properly adjusting
the speeds of the channel and ring the effect of the rotation-induced second-
ary currents on deposition can be eliminated so that the sediment deposits
uniformly across the width of the channel. The system thus simulates an
"endless straight channel."
The details of the design, instrumentation and operation are contained
in the attached copy of the T.R. 16 (4). Figures 1 and 2 show schematic
views of the annular channel and ring,respectively,with their pertinent
dimensions. Figure 3 shows aiview of the false bottom for measuring bed
shear stresses in the channel.

3. Results of the Main Research Work on the Degree and the Rates of
Deposition

For given flow conditions the two important depositional characteristics
are: (a) the degree of deposition, that is the fraction of the total suspended
sediment at the beginning of the run which eventually deposits permanently
on the bed and (b) the rates of deposition of the depositable portion of the
sediment. In a closed, self-contained flow system the degree of deposition
is represented by the ratio.

C C C
0 eq = C** 1- = 1- C*
CO eq CO eq


where C = the steady state sediment concentration attained after sufficiently
eq
long time defined as "equilibrium concentration," and CO = the initial con-
centration at the beginning of the run.
It has been found that the ratio C = C I/C0 defined as a "relative
eq eqd shear stress by the logarithmic
equilibrium concentration" is related to the bed shear stress by the logarithmic


. _I










enabled a refinement of the description of the entire flow field and of the
operational procedures.

The components of the basic experimental equipment consist essentially
of a system of a rotating annular channel 8 in. wide and 30 in. mean radius
containing the water-sediment mixture and a rotating ring positioned within
the channel and in contact with the water surface. The simultaneous rotation
of the channel and ring in opposite directions generates a uniform turbulent
shear field free of floc-disrupting elements. By proper instrumentation of
the blades supporting the ring and the false bottom the shear stresses on the
ring and the bed can be measured directly. Moreover, by properly adjusting
the speeds of the channel and ring the effect of the rotation-induced second-
ary currents on deposition can be eliminated so that the sediment deposits
uniformly across the width of the channel. The system thus simulates an
"endless straight channel."
The details of the design, instrumentation and operation are contained
in the attached copy of the T.R. 16 (4). Figures 1 and 2 show schematic
views of the annular channel and ring,respectively,with their pertinent
dimensions. Figure 3 shows aiview of the false bottom for measuring bed
shear stresses in the channel.

3. Results of the Main Research Work on the Degree and the Rates of
Deposition

For given flow conditions the two important depositional characteristics
are: (a) the degree of deposition, that is the fraction of the total suspended
sediment at the beginning of the run which eventually deposits permanently
on the bed and (b) the rates of deposition of the depositable portion of the
sediment. In a closed, self-contained flow system the degree of deposition
is represented by the ratio.

C C C
0 eq = C** 1- = 1- C*
CO eq CO eq


where C = the steady state sediment concentration attained after sufficiently
eq
long time defined as "equilibrium concentration," and CO = the initial con-
centration at the beginning of the run.
It has been found that the ratio C = C I/C0 defined as a "relative
eq eqd shear stress by the logarithmic
equilibrium concentration" is related to the bed shear stress by the logarithmic


. _I




















HORIZONTAL
FLANGES











VERTICAL
STIFFENERS


3 X 2 in. PLEXIGLASS
WINDOWS EVERY 90


Fig. 1. Schematic Views of Annular Channel.





3


r
'.~~t :f

9':
r

































REINFORCING


CROSS-SECTION ENLARGED




Fig. 2,. Schematic Views of Annular Ring.


_ I


MEMBERS



































































iv-3 "Support for Annular Plexiglass False Bottom.





















5


.. ,~ ,~f~c.~ w.. .- ---- -`~ -' L1L ,-- 'L











normal law:
y
Sw2
= 1
Ceq= e 2 dw (1)
eq 2

-00

where


log [(*- 1)/(T* 1) ] (2)
b b 50
y =s ,
cx


where T* = T/T T = the average bed shear stress across the channel
b b bmin b
width, Tbminthe value of b at which C just becomes zero, (* 1) =
bmin b eq b 50
the value of (T* 1) at which C /C0 = 0.50 and a1 = the geometric standard
deviation.
Figure 4 shows the plot of Ceq versus /(b Tb 1)s_ for seven
different cases and for sediments ranging from kaolinite to natural bay de-
posits containing montmorillonite and illite. This plot led to equations
and 2 with a = 0.49 for all soils. It was determined that ( Tb 1) is re-
lated to Tb according to Fig. 5. Further experiments showed a close cor-
bmin
relation of Tbin with the cation exchange capacity, CEC (Fig. 6).
It can thus be concluded that all the physico-chemical factors controlling
the degree of deposition can be represented by one and only one parameter, namely
T bin which can readily be determined in the laboratory. From Fig. 5 the
parameter (Tb 1)j can be determined and finally Fig. 4 for given b gives Ceq
The depositable portion of the sediment is represented by CO C The
eq
fraction of that portion deposited at time t is represented by C* =(Co co Ceq)

where C = the instantaneous sediment concentration at time t. All experiments
have conclusively shown that the variation of C* with time follows the loga-
rithmic normal law:
T

S C C C { e- w2/2dw (3)
C = = e
CO Ceq
C


6


--







































0.1 I

(r I) / (b- 11)50

Relative Equilibrium Concentration C in Percent Against Bed Shear Stress
eq
Parameter (Tb 1)/(rb 1)50.


99
98

95

90

80

70
60
50
40
30

20


0



04
L)


10

5

2
I
0.01


Fig. 4.


10


I























































1.6


in (dynes/c)
Tbmin(dyfnes/cm)


Fig. 51,. Relationships Between Tbmn, (Tb
Sbmin b


- 1)50 and Tb0.
50 b 50


2


I

0.9

0.8

0
S0.7


S0.6


o 0.5



0.4
"Nw


00


0.3


0.2


g' t. r,


tr
.r
r
;j
t


j.
r
-$II
1 ,






















S* Boy mud D
o 2 Maracaibo
Sediment -0.025(CEC)
_ "' bmin= 1.85 e
-o



,E


T 0.9 (Tb -')5
*"---^-------

0.7 .

0.6 ..--

0.5
0 5 10 15 20 25 30 35

CEC (milliequivalents per hundred grams) "

Fig. 6. .Relationships Between (T 1)50, bmin and Cation Exchange
Capacity (CEC).


;* : .

." -' '' / *-,^ ; '^ ,t^ '. :- p ; / .. J- / L '' .!*. *
141


40








'
fc :










where


T = log (-) (4)
a t
2 50



a2 is the standard deviation, w = a dummy variable and t50 = the time at
which C = 0.50. In terms of the error function Eq. 6 may be alternatively
expressed as:


C* = + 1 erf (--) (5)
2 2 2


The time rate of change of C*, which is directly related to the deposition
rates, is


dC* 0.434 -T2
dt =exp (-) (6)
dt rZf t L2


Thus for the true rates of concentration change only two parameters are
*
needed,tamely a and t Figure 7 shows a typical example of C --t plot, whereas
2 50
the entire experimental series are discussed in detail in (4, 10) and in
summaryin(7,8). Attempts to correlate the parameters t50 and a2 to the flow
parameters, Tb and the depth h, and to the initial sediment concentration,'Co led
to the following preliminary conclusions (Figure s):
(1) t50 increases with T* reaching a maximum for values of Tb ( = bmin)
b bmin
between 1 and 1.5. From then on it decreases with increasing T*
(2) For the same Tb, t50 seems to increase with increasing depth; how-
ever, there is considerable overlapping.
(3) a2 increases initially with increasing T* reaching its maximum
b
value also between 1 and 1.5. From then on it appears to remain constant or
to slightly decrease with increasing T*b
(4) The depth effect on a2 seems to be much smaller and less systematic
than on t50.
Tentative explanations for the observed trends have been presented in

(3, 4, 10). Similar trends have been observed in suspensions of kaolinite
in salt water and of natural sediments from the San Francisco Bay and Maracaibo

Estuary.


10

















99

98




98 ------------ -- -- -------___
690


0 --- -------_ --_



60 -











60-- -- --_----------O distilled 1080 6 1.07 8.6
50L

40



20 1---- Symbol Material Co(ppm) Depth(in.) T tso(min)

1.0- -- 0 Kaolinite 1080 6 1.23 36
10
in 1080" 6 1.41 3.8
5 0 distilled 1080 6 107 8.6

2 water 1080 6 1.33 13.3

0 -0- O. 0.5 5 10 50 I00


t/t5o

Fig. 7. Fraction of Depositable Sediment Concentration C* Deposited at Time t,
in .Percent, Versus Time Parameter t/t50, for Kaolinite in Distilled Water.


0

H C
H
*
0~


- -----z.-nrr rs~ *r-..:~-~l-~ ~.,-.I.. .-- ... ~.... ...-, ......... .....


V.VV


I


%0.9








































IV. a, a r


1.0


1.5
T*
^b


2.0


2.5


1.5
Tb*


Logt50 and 02 Versus

Distilled Water.


Tb for Kaolinite in
b


12


1.5, I


1.0


0
4-
a 0.50
0


0.0 -


u


3.0


Fig. 8.


U.5











Although no strict quantitative relations linking the parameters t50
and a2 to the pertinent flow variables have yet been reached Eqs. 3 and 4
are still subject to calibration using data fromfield observations. In this
sense the outlined results on the deposition rates constitute a considerable
step forward to the solution of the general problem of fine sediment trans-
port.

4. Characteristics of the Flow Field in the Annular Channel-Ring System

The details in the channel have also been investigated. Figure
9 shpws an example of velocity profiles. The flow field clearly consists
of two relatively thin zones of sharp velocity gradients at the neighborhood
of the bed and of the ring, whereas in the central and major portion of the
flow field the velocities remain very nearly constant. Near the bed the
velocity distribution follows very closely the logarithmic velocity distri-
bution law:


u = 5.75 log y + 9.6 (7)
u*

or, in its more general form,



u log _- (8)
u* K Y0


where K = 0.40, i.e., practically the same as for flow in pipes and open
channels, and yo, which represents the virtual distance from the theoretical
bed is 0.021 in., which is a logical value to expect corresponding to the
roughness of the deposited bed.
The flow uniformity within the central and largest portion of the flow
field implies a predominantly homogeneous turbulent structure with a constant
diffusion coefficient E. This conclusion has been experimentally confirmed
by suspended sediment concentration measurements which followed the law:

W
C = exp [- (y- a)] (9)
C E
a


13






























































































0 10 20 30 40 50 60 70


U (cm/sec)


Fig. 9.


Velocity Profiles for 6-1/4 in. Depth.


14


80 ,I
1 ** ^


'";








;. ,~ .^ 1



*5'-








*Fc






80


i


-s


r


* CI

r
,


I .










where y = the distance from the bed, a = a reference distance, w = the average
s
settling velocity of the sediment, e = the vertical eddy diffusivity and C a
the sediment concentration at y = a. Finally the study led to a new defini-
tion of the concept of the wash load (2, 5). This new definition provides
a unified view of the hydrodynamic behavior of the entire suspended sediment
load.

5. Experiments on Resuspension Rates

The objective of this experimental phase,which has not yet been completed,
was the discovery of the main characteristics of resuspension of deposited
sediment and of the derivation of a law linking the erosion rates of the
deposited sediment to the pertinent flow variables and soil properties. In
this sense it is an extension of the early work of the principal investigator
on erosion rates (Partheniades, E., "Erosion and Deposition of Cohesive Soils,"
J. Hydr. Div., ASCE, V. 91, No. HY1, Proc. paper 4204, January 1965). Prior
to the resuspension studies experiments were performed with uniform size sand
in order to determine the conditions for incipient motion, i.e. to repro-
duce Shields'curve for such a motion. The results are shown in Fig. 10 for
the indicated six sand sizes.
It is clearly seen that for R > 20 the two curves practically coincide
whereas for R > 20 they gradually deviate, maintaining,however, the same
e
general shape. Although extensive additional experiments and further refine-
ment are anticipated,the agreement between the two curves, particularly if
one considers the subjectiveness in defining the "incipient motion" is indeed
remarkable and reconfirms once more the elimination of the effects of the rotation-
induced secondary currents on the near-bed flow structure which controls the
erosion and deposition processes.
Two types of beds were tested. The first, defined as "stratified" was
formed by allowing the suspended sediment to deposit at shear stresses slightly
less than the Tbmin. The second, defined as "uniform" was formed as uniform
fluid mud outside the channel in liquid state and then poured into the channel
and leveled.
The stratified bed displayed rates of erosion which decreased with time,
as expected, since the inter-particle cohesive forces and the floc size and
strength increase with depth. Fig. 11 shows an example of concentration-time
variation for a stratified bed. It is seen that erosion may eventually


15











Although no strict quantitative relations linking the parameters t50
and a2 to the pertinent flow variables have yet been reached Eqs. 3 and 4
are still subject to calibration using data fromfield observations. In this
sense the outlined results on the deposition rates constitute a considerable
step forward to the solution of the general problem of fine sediment trans-
port.

4. Characteristics of the Flow Field in the Annular Channel-Ring System

The details in the channel have also been investigated. Figure
9 shpws an example of velocity profiles. The flow field clearly consists
of two relatively thin zones of sharp velocity gradients at the neighborhood
of the bed and of the ring, whereas in the central and major portion of the
flow field the velocities remain very nearly constant. Near the bed the
velocity distribution follows very closely the logarithmic velocity distri-
bution law:


u = 5.75 log y + 9.6 (7)
u*

or, in its more general form,



u log _- (8)
u* K Y0


where K = 0.40, i.e., practically the same as for flow in pipes and open
channels, and yo, which represents the virtual distance from the theoretical
bed is 0.021 in., which is a logical value to expect corresponding to the
roughness of the deposited bed.
The flow uniformity within the central and largest portion of the flow
field implies a predominantly homogeneous turbulent structure with a constant
diffusion coefficient E. This conclusion has been experimentally confirmed
by suspended sediment concentration measurements which followed the law:

W
C = exp [- (y- a)] (9)
C E
a


13
















0.1


Re = 250
7)


Fig. 10. Entrainment Function Relationship Comparison with Shields' Curve.


S# 16
S# 20
x # 35
^ 50
#80
# 80
v# 100




PRESENT EXPERIMENT









ORIGINAL SHIELD'S .CURVE







S.= Fluid Density

d50= Medium Grain Diameter

Ss = Specific Gravity of Grain

Fs = Entrainment Function

SU = Friction Velocity






I I110 I I I I I 1 1111 I 1 11111
I 10 ,.,. in( i0


In


II
LL


0.01


0.001


6l


I fvv


Iw.


Iy










where y = the distance from the bed, a = a reference distance, w = the average
s
settling velocity of the sediment, e = the vertical eddy diffusivity and C a
the sediment concentration at y = a. Finally the study led to a new defini-
tion of the concept of the wash load (2, 5). This new definition provides
a unified view of the hydrodynamic behavior of the entire suspended sediment
load.

5. Experiments on Resuspension Rates

The objective of this experimental phase,which has not yet been completed,
was the discovery of the main characteristics of resuspension of deposited
sediment and of the derivation of a law linking the erosion rates of the
deposited sediment to the pertinent flow variables and soil properties. In
this sense it is an extension of the early work of the principal investigator
on erosion rates (Partheniades, E., "Erosion and Deposition of Cohesive Soils,"
J. Hydr. Div., ASCE, V. 91, No. HY1, Proc. paper 4204, January 1965). Prior
to the resuspension studies experiments were performed with uniform size sand
in order to determine the conditions for incipient motion, i.e. to repro-
duce Shields'curve for such a motion. The results are shown in Fig. 10 for
the indicated six sand sizes.
It is clearly seen that for R > 20 the two curves practically coincide
whereas for R > 20 they gradually deviate, maintaining,however, the same
e
general shape. Although extensive additional experiments and further refine-
ment are anticipated,the agreement between the two curves, particularly if
one considers the subjectiveness in defining the "incipient motion" is indeed
remarkable and reconfirms once more the elimination of the effects of the rotation-
induced secondary currents on the near-bed flow structure which controls the
erosion and deposition processes.
Two types of beds were tested. The first, defined as "stratified" was
formed by allowing the suspended sediment to deposit at shear stresses slightly
less than the Tbmin. The second, defined as "uniform" was formed as uniform
fluid mud outside the channel in liquid state and then poured into the channel
and leveled.
The stratified bed displayed rates of erosion which decreased with time,
as expected, since the inter-particle cohesive forces and the floc size and
strength increase with depth. Fig. 11 shows an example of concentration-time
variation for a stratified bed. It is seen that erosion may eventually


15






0.18

0.17

0.16

0.15 *

0.14

0.13-

012 "
0.12

z 0


WU 0.10




.j 0.08



EL .(STRATIFIED)
o 0.06--
Z
w 0.05 -. Time in minutes
a:
0. Time in hours
0.04

0.03 -

0.02 Fig. 11. Rate of Resuspension for a Stratified Bed as a Function of Time.

0.01 -
1.11 1 i I111.11111 I \ I 1Iii I '
0 I 2 3 4 5 6 7 8 9 10 1 12 13 14 15 16 17 18 19 20 21
; r '- .TIME (HOUR AND MIN.)


22 23 24










stop altogether in which case the bed surface is covered by flocs with inter-
particle bonds strong enough to resist the disruptive shear stress near the
bed and consequently any further erosionceases. This is equivalent to the phenom-
enon of "shielding" of coarse bed whereby the bed surface is covered with
sand or gravel large enough so that they cannot be moved by the flow.
For uniform bed the erosion rates remain constant with time with the
exception of a comparatively short initial time period during which some loose
surface particles are removed at higher rates. Fig. 12 gives an example of
erosion rates for uniform bed.
The erosion rates increase with increasing bed shear stresses, as expected.
The following table summarizes the results of three erosion tests on uniform
beds made of commercial kaolinite clay.


Table I. Erosion Rates for Uniform Bed of Kaolinite Clay

Bed Shear Stress Depth dC/dt Erosion
T 0 Rates

dynes/cm2 psf inches ppm/hr grms/ft2/ht

4.13 0.0086 6 7.962 0.113

4.45 0.0093 6 10.370 0.147

4.83 0.0100 6 11.481 0.163


The following table II gives for comparison similar results of erosion
studies on natural silty clay deposits from the San Francisco Bay composed
predominantly of montmorillonite with some illite (Partheniades, E., "Erosion
and Deposition of Cohesive Soils," J. Hydr. Div. ASCE, V. 91, No. HY1,
Proc. paper 4204, January, 1965).
It should be noted first that in series III the bed was stratified
and that the indicated erosion rate applies to the upper layer of weaker flocs;
second that the bed of series II, albeit of approximately the same density
and water content as that of series I (both uniform and at field moisture),
displayed considerably higher resistance to erosion due to cementation by
iron oxides. In any case the erosion rates between the present and past
results are comparable and the trend of their variationwith the bed shear stresses
similar. The erosion depth was about uniform across the width of the annular
channel.


18


_ _____










Table II. Erosion Rates for San Francisco Bay Mud

Bed Shear Stress T Depth Erosion Rates Exp. Series

psf in. grms/ft2/hr

0.0070 6 0.176 I

0.0103 6 0.338 I

0.0100 6 0.174 II

0.0091 6 0.506 III


It is planned to continue the erosion experiments, upon a hopeful
approval of a proposal to the N.S.F. on Estuarine Sediments, for both uniform
and stratified beds. These studies will give a generalized relation between
sediment erosion and bed shear stresses to be used as "sediment source" func-
tion in any mathematical model of fine-sediment transport. The derived
equation on sediment deposition would then be used a "sediment sink" function
in such a model.


19
































50 -- ---- -- ------- i- -"_ __,_ ___ __ ___'"_ ___'


550-- ---
% i
500


400

250 ..-- -- -.......-- -- -- _...C __ .


? 3


w 10---1



S50
oo I i i i __ l l I_ _l l I 1 1 1 i l l i l it I i I




0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46

TIME (HOURS)


;50
--1600


500

450

-t- -- 400












47 48 49 50
300


47-4-----200


-i - 15 0


Fig. 12 Rate of Resuspension for a Uniform Bed as a Function of Time.




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