WATER POLLUTION CONTROL RESEARCH SERIES  16050 ERS 08/71
DEPOSITION OF  FINE SEDIMENTS
                           IN TURBULENT FLOWS
            U.S. ENVIRONMENTAL PROTECTION AGENCY

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          WATER POLLUTION CONTROL RESEARCH SERIES
The Water Pollution Control Research Series describes the
results and progress in the control and abatement of pollution
in our Nation's waters.  They provide a central source of
information on the research, development,  and demonstration
activities in the water research program of the Environmental
Protection Agency, through inhouse research and grants and
contracts with Federal, State,  and local agencies,  research
institutions, and industrial organizations.

Inquiries pertaining to Water Pollution Control Research
Reports should be directed to the Chief, Publications Branch
(Water), Research Information Division, R&M,  Environmental
Protection Agency; Washington,  DC  20460.

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           DEPOSITION  OF FINE SEDIMENTS IN TURBULENT FLOWS
                                   by

                         Emmanuel  Partheniades
                            Ashish J.  Mehta
        Department  of Coastal and Oceanographic  Engineering
        University  of Florida, Gainesville,  Florida  32601
                                 for the

                  Office of Research and Monitoring

                    ENVIRONMENTAL  PROTECTION AGENCY
                          Project  #16050 ERS
                              August 1971
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 - Price 60 cents

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                  EPA Review Notice


This report has been reviewed by the Environmental
Protection Agency and approved for publication.
Approval does not signify that the contents necessarily
reflect the views and policies of the Environmental
Protection Agency, nor does mention of trade names or
commercial products constitute endorsement or
recommendation for use.

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                              ABSTRACT


     Basic laboratory investigations were carried out to study the
role of flow parameters on the deposition of fine cohesive sediments
in a turbulent flow-field.  The study utilized a special apparatus
consisting of a system of a rotating annular channel  and ring.  The
results obtained have confirmed earlier conclusions that the
percentage of the total sediment that a given flow can maintain
in suspension depends only on the bed shear stress and is independent
of the initial sediment concentration.

     The percentage C1, of the depositable sediment deposited at time
t has been found to vary with time according to the law C1 = alogt
+ g, where the coefficient a appears to be independent of the flow
conditions and sediment concentration, while the coefficient g is
a function of the bed shear stress only.   Both a and  g are expected
to depend on the physico-chemical properties of the sediment and
the water environment.  It follows that the deposition rates are
proportional to the depositable sediment concentration and inversely
proportional to time.

     This report was submitted in fulfillment of Project Number
16050 ERS, under the sponsorship of Environmental Protection Agency.
                               111

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                           CONTENTS
 Section                                             Page
   I   Conclusions                                      1
  II   Recommendations                                  3
 III   Introduction                                     7
  IV   Previous Investigations                          9
   V   Experimental Apparatus                          15
  VI   Operational Procedure                           23
 VII   Results of Investigation                        27
VIII   Acknowledgements                                35
  IX   References                                      37
   X   Publications and Patents                        41
                               v.

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                              FIGURES
                                                     Page
 1.   ANNULAR CHANNEL                                 16
 2.   ANNULAR RING WITH STIFFENERS                    17
 3.   FALSE BOTTOM AND SUPPORTS                       18
 4.   TURN TABLE ASSEMBLY                             19
 5.   MECHANISM SUPPORTING ANNULAR RING               21
 6.   BASIC EXPERIMENTAL APPARATUS                    22
 7.   OPERATING CURVES                                24
 8.   VARIATION OF RELATIVE EQUILIBRIUM
     CONCENTRATION C  /CQ WITH BED SHEAR STRESS      28
 9.   VARIATION OF RELATIVE DEPOSITABLE
     CONCENTRATION (C0-C)/(CQ-Ce ) WITH TIME         30
10.   VARIATION OF COEFFICIENT a WITH CHANNEL
     DEPTH AND INITIAL CONCENTRATION                 31
11.   VARIATION OF COEFFICIENT B WITH BED
     SHEAR STRESS                                    32
                              VU

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                               SECTION I

                              CONCLUSIONS

     The following are the main conclusions of that part of the
present study supported by the EPA.

     1.  For given geometry, sediment, water quality and flow
conditions, the suspended sediment concentration reaches, after a period
of relatively rapid deposition, a constant value Ceq, herein called
equilibrium concentration.  This equilibrium concentration is found
to be a constant fraction of the initial concentration, C0, at the
start of each test; i.e. the ratio Ceq/C0 is independent of C0 and is
a function of flow conditions only, which implies that each flow
can maintain in suspension a constant percentage of the total
initial sediment.

     This very fundamental conclusion is in agreement with the earlier
preliminary results obtained by Partheniades (11) in an open flume
with a natural silty-clay sediment taken from the San Francisco
Bay.

     2.  The relative equilibrium concentration, Ceq/C0 is found for
various depths to be strongly related to the bed shear stress, TJ-, by
a logarithmic-normal relation.

     3.  The percentage C' of the depositable sediment deposited at
time t is fourtd to vary with time according to the law

              C1  = alogt + g

where the coefficient a appears to be independent of the initial
suspended concentration C0 for C0 less than 10,000 ppm, which
corresponds to the maximum sediment concentration encountered in
most estuaries.   For higher concentrations, a seems to decrease
with concentration, suggesting a reduction in the deposition rates.
10,000 ppm thus seems to mark the concentration above which the
settling of particles is hindered.   A slight variation of a with
depth is also observed; however no conclusive law for the dependence
of a on depth has yet been obtained.

     The coefficient B appears to be  independent of both the
concentration and depth and seems to  depend on the bed shear stress
only.

     The law described above pertains to measurements corresponding
to the bed shear stress greater than  the minimum bed shear stress

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Tbmin> at which Ceq becomes equal  to zero

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                              SECTION II

                            RECOMMENDATIONS

     The present study was carried out to investigate the role of
flow parameters on the deposition rates of a commercial kaolinite
clay, suspended in distilled water, in a turbulent flow field.
A significant extension of this study is required before a complete
knowledge of the behavior of cohesive sediments depositing under
turbulent conditions is acquired.  Various sediments, under various
ambient environments need to be studied.  Also, the effect of
secondary currents generated in the flow field need to be analyzed.
To this end, the following objectives and recommendations are in order:

     1)  An important objective is an investigation of the effect
of bed roughness on the equilibrium concentration and on the depos-
ition rates.  The strong dependence of these two important depositional
characteristics on the bed shear stress raises the question as to
whether the way in which the shear stress is transferred from the
boundary to the fluid is also of importance to sedimentation.
Such a transfer may take place either by molecular viscous action in
the case of a smooth bed, or by the drag resistance of the roughness
elements.  It should be mentioned at this point that recent results
of turbulence studies, conducted by Partheniades and Blinco (14)
showed conclusively that the turbulence intensities in open channel
flows depend on the bed shear stress, the distance from the
boundary and on the kinematic viscosity of the fluid, but not on
the roughness.

     The effect of roughness on deposition must be studied experiment-
ally by inserting in the channel plexiglass annular bottoms with
roughness elements glued on them.  Three or four roughness sizes
should be used.

     This phase should also involve detailed velocity profiles taken
by a 4 mm miniature propeller meter listed in Section V and
considerable turbulence measurements with a hot-film anemometer for
smooth and rough boundaries.  The average bed shear stress should be
directly measured by an instrumented false bottom as described in
Section V.   The main objective of these measurements would be to
compare the structure of flow, particularly in the neighborhood
of the bed, with that in an open channel and in a closed rectangular
duct.  The experiments of this phase should be conducted at the
operational speeds of the channel and ring so that the sediment
deposits unifromly.  In (17) it was explained how the simultaneous
rotation of the channel and ring generate two cells of opposing
secondary currents cancelling each other's effect on the distribution
of deposited sediment across the width of the channel.  Although
preliminary experiments at M.I.T. have indicated the existence of

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an almost constant bed shear stress distribution at these speeds,
the question as to the effect of these secondary currents on the
turbulence characteristics and the velocity distribution near the bed,
i.e. on the overall flow structure near the boundary, remains open.
It is expected that the recommended measurements will answer this
question and will indicate how closely an endless straight conduit
or a turbulent Couette flow is approximated at the operational
speeds.

     2)  A systematic study of the effect of secondary motion on
the distribution of the boundary shear and on the depositional
characteristics should be next conducted.  The first step of this
phase would be a study of the transfer of the shear stress from the
ring to the channel bottom for various relative speeds and depths.
The false annular bottom, described in Section V, must be used for
the measurement of the average bed shear stress.  Velocity profiles
and local bed shear stresses should then be measured by a micro-
propeller meter, a Prandtl tube and a Preston tube in order to deter-
mine the secondary flow effect on the spacial shear stress distri-
bution, and on the velocity profiles.

     This recommendation is motivated by the following previous
observations.  It has already been stated that any deviation
from the operational speeds strongly affects the depositional
characteristics.  This is indicative of a strong effect of the
unbalanced secondary currents on deposition.  Surprisingly however,
the early M.I.T. experiments indicated that the ring shear stress
depends only on the algebraic difference of rotational speed between
the channel  and the ring but is little affected by the absolute speed
of either component.  This conclusion was verified in the experiments
in University of Florida.  This means that the secondary currents may
have a weak effect on the total boundary shear force on either the
ring or the channel; however, they may strongly alter the spacial
distribution of the bed shear stresses.  In the light of the strong
dependence of deposition and erosion on the boundary shear stress,
it appears that the secondary currents affect deposition by creating
zones of low local shear stresses.  However, no measure of secondary
flows nor any quantitative relationships between secondary flow and
shear stress distribution have been established to date.  It is the
long range purpose of this phase of the recommended project to provide
a relevant quantitative measure for the secondary current effect on
boundary shear stress distribution and to investigate the relation-
ships between the local shear and the velocity profile near the bed.
It is realized that this is a very difficult task since it involves
essentially a three-dimensional turbulent flow.  For this reason,
it can only be hoped to approach the problem in terms of correlation
of gross flow variables.   Substantial turbulence measurements should
also be carried out for a preliminary study of the effect of secondary
currents on  turbulence characteristics, in combination with phase 1.
Moreover, the three-dimensional aspects of the flow should be

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investigated using a triaxial array hot-film probe for measurements
of turbulence intensities and time-average local velocities in the
three directions.

     3)  The third recommended objective deals with an investigation
of the role of sediment properties on deposition.  Very little is
known about the role of the physico-chemical  characteristics on the
hydrodynamic behavior of fine cohesive sediments.  A rigorous
literature review by Partheniades and Paaswell on the credibility
of channels with cohesive boundary showed that certain commonly
used soil mechanics parameters, such as cohesive shear strength,
compression index and Atterberg limits, for the prediction of the
behavior of a dense clay mass to an external  load, do not sufficiently
describe the soil resistance to erosion (9,18,19).  At this point,
however, the rather limited state of knowledge does not permit a
forecast of detailed experimental procedures. -The project should
start with pilot observations of deposition of various commercial
clays, mixtures of pure clay materials and natural cohesive soils
for constant flow conditions.  Techniques should then be tried
for obtaining an index or indices representative of the average
magnitude of the interparticle physico-chemical forces, to be cor-
related with the depositional characteristics of the sediment.

     4)  In addition to the above, a number of short duration
problems may be investigated.  The following are a few examples:

     a.  Hydrodynamic behavior of very fine sand and cohesion less
         silt.

     b.  Depositional characteristics at very high concentration.

     c.  Detailed measurements of grain size distribution of sus-
         pended sediment at equilibrium concentration.

     d.  Pilot sedimentation experiments in an open flume and in
         a closed rectangular duct.

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                             SECTION III

                            INTRODUCTION

     The importance of investigating phenomena related to the deposition
of fine cohesive sediments in turbulent flows is clearly evident from
the usefulness of the results of such an investigation in engineering
practice.  Challenging situations in this context arise in the problem
of shoaling in estuaries, channels, and in irrigation canals, due to
geological sediments carried by the flow.  Frequently the control of
such shoaling is important, as for example when the question of
maintaining a navigable waterway or of-sustaining a specific environ-
ment for aquatic life is involved (21).  Other situations where the
hydrodynamic behavior of cohesive sediments plays an important role
include the design of stable channels, and the transport of industrial
effluents through flows, carrying with them various chemical pollutants.

     Fine sediments are composed predominently of silt and clay and
range in size from a fraction of a micron up to a few microns.
Particles in that size range are strongly subjected to the effects of
the inte^particle physico-chemical forces, which may far exceed the
effect of the gravitational forces.  Some of these inter-particle
forces are attractive while others are repulsive (22).  Their net
effect may be either repulsive or attractive depending on the
physico-chemical properties of the water environment and the adsorbed
ions.  In the first case the individual fine particles remain
dispersed, so that the finer portion, smaller than one micron, may
remain indefinitely in suspension due to Brownian motion, whereas
a very slight degree of agitation could prevent even the heavier
silt particles from settling.   In the second case, which is more
common of the two, .the particles tend to attach themselves to each
other forming agglomerates, or floes, whose sizes and settling
velocities may become several  orders of magnitude higher than those
of the individual particles.  This phenomenon, known as flocculation,
is the main cause of rapid deposition of suspended fines, a well-
known occurrence of which is due to the presence of a slight salinity
in water (6,13).

     Estuaries, and especially deep estuarial channels are favorable
sites for the deposition of fine sediments coming from either landward
or seaward sources.  The two main factors that enhance such a deposition
are the low flow velocities, or low bed shear stresses, and the
increased salinity.  The latter contributes to the deposition by
favoring the process of flocculation and also by generating slow
upstream salinity currents which are associated with stratified
as well  as mixed estuaries (3,4,12).

     In the last three decades, there have been significant con-
tributions to the development of important theories leading to

                                 7

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semi-theoretical equations relating the rate of transport of coarse
sediments to -the flow conditions and to the mechanical  properties of
the sediment.  These theories are based on the phenomenological  laws
of turbulence.  The validity of these theories, the most important
of which describes Einstein's bed-load function (1), is limited to the
transport of bed-material load, i.e. to sediment sizes  adequately
represented in the bed of the channel, and to uniform flows in channels
in equilibrium.

     The state of knowledge of fine sediments is much more limited.
The hydrodynamic behavior of fine cohesive sediment suspensions
is complicated by the flocculation effect, since the basic settling
unit is a floe rather than an individual  particle.   The floe size-
distribution depends not only on the physico-chemical properties of
the sediment but also on the flow conditions themselves.   This dual
dependence makes the processes of erosion, transport and deposition
of fine sediments rather complex and quite distinct from the corres-
ponding processes of a coarse sediment.   It is necessary therefore,
to discover the important flow parameters and soil  properties, which
control the initiation,  degree and rates  of deposition  and erosion and
to establish quantitative functional relationships  among these
variables.

     Extensive investigations conducted by Partheniades and co-
workers during the past  several  years have revealed important
and conclusive information regarding the  effect of  flow parameters on
deposition, and about the physical  mechanism of erosion and deposition
of cohesive soils.  These results, contained in ref.  (2,9 to 16)
are summarized in Section IV.  The present experimental  phase is
essentially a continuation of the earlier studies and is concentrated
on investigating the role of flow parameters on the time-deposition
rates.   The results obtained to-date are  reported and discussed
in this report.

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                               SECTION IV

                         PREVIOUS INVESTIGATIONS

     In order to understand the process of shoaling in navigable
channels and attempts to control it, basic research on the depositional
behavior of fine sediments was begun in the late fifties.  The
sequel is a summary of the approach taken by various investigators,
dealing with the transport of fine sediments, and leading to the
present study.

     Erosion, transport and deposition of sediment is controlled by
two groups of variables:  a)  the flow parameters, describing the
hydraulics of the system, and b)  the sediment properties.

     Mclaughlin (8) derived the general fundamental  equation for the
transport of fine sediments based on the conservation of sediment
mass.  For one-dimensional flow, this equation reduces to the
following form:
             + U= D      + (       j    + D
          3t     ax    y sy^   v ay     ' ay    x ax

where C = the total concentration of sediment, U = U(y) = the time
average flow velocity as a function of the vertical distance y from
the bottom, Dx Dy = the turbulent 'diffusion coefficients in the x
and y directions respectively, x = the Cartesian coordinate in
the direction of flow and w = the average settling velocity of the
sediment.  The solution of Eq. 1 requires the following initial
and boundary conditions:

     a)  There is no net rate of transport in the y direction across
the surface.  The mathematical formulation of this condition is:


          Cf )      - - (rr  c)                               (2)
              y=y0        y    y=y0

where y  = the total depth of flow.

     b)  At the bed, the material eroded and re-suspended must be
entrained into the main flow by turbulence.  Dobbins and Mclaughlin
(8) used the following mathematical expression:


          E = - (y |y) at y-                               0)

where E = rate of erosion.  Partheni.ades (10) has a more detailed
discussion of this boundary condition.

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     c)  At time t = 0 the concentration distribution is known, i.e.
C = C0(x,y) is known.

     In addition to the initial  and boundary conditions, the settling
velocity, w, must be known.   This is essentially the greatest diffi-
culty in the problem since w, as stated in the introduction, depends
on both the flow conditions and the physico-chemical properties of
the sediment.  Mclaughlin studied theoretically and experimentally
the settling velocity distribution and the factors affecting it.
However, his work was limited to settling in quiescent water.

     The first systematic large scale studies on fine sediment
deposition in turbulent flows were conducted by Krone (5.,6,7)
in an open flume.  He used a silty-clay type of sediment from the
San Francisco Bay commonly known as Bay Mud and composed of about
equal proportions of silt and clay.  For low concentrations (less
than 300 ppm) the following experimental deposition law was derived:
          C        r   wat
          T- ^ exp [ - 
           o
'0
(i  -  r)
      c
                                      (4)
where wa = apparent settling velocity,  T^ = the average bed shear
stress, TC = the critical  bed shear stress above which no particle
can stick to the bed and C0 = the initial concentration.

      For high concentration, the following logarithmic law is
obtained:
          log C = - Klogt + Constant

where K is a function of the depth of flow, yn, and the
                                      (5)

                                 ratio  
                                       Tc
     It should be noted that in Eqs. 4 and 5, the concentration, C,
tends to zero with increasing time; which means that both equations
are valid for velocities low enough for the entire initial sediment
to deposit.  Krone also conducted interesting studies on the effect
of shear stress on the maximum floe size in a laminar flow between
two rotating concentric cylinders.  He derived the following
relationship:

               = - [' -5T (Ar) c, ]                            (6)
when rmax = the radius of the largest floe assumed to be spherical,
T = the shear stress at the boundary of a laminar shear field,
Ar = the roughness of the surface of the floe and Cf = the shear
strength of the floe.

     Eq. 6 verified by Krone's experiments, permits an estimate of
the shear strength of the floes, if their size and the shear stress
are known.
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     Partheniades  (11) investigated both the erosional and deposition-
al behavior of fine sediments.  His studies were conducted in an
open flume with the same sediment type as used by Krone (6).  The
deposition experiments indicated that the suspended sediment concentra^
tion approaches a  constant value, which may be referred to as
"equilibrium concentration".  Limited evidence at that time suggested
that this equilibrium concentration Ceq is, for given flow conditions,
a constant percentage of the initial concentration, C0, at the start
of the run.  Moreover, a critical velocity limit was found above
which an appreciable amount of sediment remains in suspension,
whereas, at velocities slightly below that critical limit, all the
suspended sediment deposits quite rapidly.

     The importance of the findings by Partheniades led to further
studies on-the depositional phenomena at M.. I.T.  The experiments
were conducted in  a special apparatus.  Its main components were
an annular channel with outer and inner diameters of 36 in. and
28-3/8 in. respectively, containing the water-sediment suspension,
and an annular ring, positioned within the channel and in contact
with the water surface.  A simultaneous rotation of the channel
and ring in opposite directions generated a turbulent flow field.
The advantages of  the channel-ring system in comparison with the
conventional flume are the following:  the flow is uniform at
every section; there are no floe disrupting elements in the water,
such as pump blades and, moreover, the floes are not affected in
zones of high shear stresses, such as in return pipes and diffusers.
The apparatus can  be instrumented so that the average shear stresses
on the channel and ring can be readily evaluated.   Also,  the
equipment permits  a quick and precise variation of the flow
parameters over a  range much wider than in a flume.  Finally, due to
the relatively small water volume, a large number of tests with
various fluids, sediment types and sediment concentrations can
be performed inexpensively and in a relatively short period of
time.  The effect  of the rotation-induced secondary currents on  the
uniformity of deposition was practically eliminated by properly
adjusting the speeds of the channel  and ring for uniform  sediment
deposition across  the width of the channel.  For these operation
speeds, the bed shear stress distribution across the channel  width
was found to be almost uniform.   The details of the instrument and
its operation are  described in references (2,17).   A commercial
kaolinite clay was used as the sediment with a grain size distribution
ranging from a fraction of one micron to 50 microns.  Inasmuch
as the experiments at M.I.T. and also at University of Florida have
been concentrated on the role of the flow variables on deposition,
the type of sediment and the water quality were kept constant.  The
results of the research are summarized in the sequel.

     1.   For given geometry, sediment, and flow conditions, the
suspended sediment concentration reaches, after a period  of relatively


                                  11

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rapid deposition, a constant value, Ceq, referred to as equilibrium
concentration.  This equilibrium concentration is a constant fraction
of the initial concentration, C0; i.e.  the ratio Cen/C0 is
independent of C0 and is a function of the flow conditions only;
therefore, each flow can maintain in suspension a constant percentage
of a given initial amount of the sediment.

     2.  The ratio Ceq/C0 for various depths seems to be strongly
related to the bed shear stress, T^, according to a logarithmic-
normal relation (15).  For the particular sediment and geometry
of the channel of the experiments, this relationship is found to be
                 logAP
CQ    0.49/2^
                GO
- Q-^2 [logAP^-1.764]2}d(logAPu)    (7a)
and


AP^ = log(2.38 x ]Qk x Tb-834 - 65)                            (7b)



where T^ is expressed in Ibs.  per square foot.

     3.  The initiation and rates of erosion of cohesive sediments
have also been found to depend strongly on the  bed shear stress (11).
Moreover, the basic research studies have shown that the stresses
at which erosion begins for a given sediment are considerably higher
than the stresses at which the same sediment in suspension deposits
entirely.  This last experimental conclusion is in complete agreement
with field observations in irrigation channels  (18,19).

     4.  The conclusions cited so far point out the mode of transport
of cohesive sediments and the nature of the equilibrium  concentration
to be different from that for a coarse sediment.  It has been well
established that in flows over a movable cohesionless bed there is
a simultaneous deposition and erosion of particles.  A constant
concentration of sediment in such flows is attained when the number
of particles eroded is equal to the number of particles  deposited
per unit area and per unit time.  If the suspended load  is suddenly
increased by an additional amount of sediment of similar mechanical
composition to the one already in suspension, the concentration
will drop soon to its original equilibrium value, since, for some
time, more particles will be deposited than scoured.  The constant
value of Ceg/C0 in the case of fine sediments suggests that
interchange of bed and suspended material does  not take  place.
Such an interchange is also excluded by virtue  of conclusion (3).
Moreover, experiments in the rotating channel at M.I.T.  in which
the suspended sediment at equilibrium concentration was
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gradually flushed out, has directly confirmed this conclusion.  The
constant equilibrium concentration  of sediments  in  suspension does  not,
therefore, represent the point of saturation of the sediment
transport carrying capacity of the flow.  It simply represents the
proportion of sediment with weak enough interparticle bonds, such
that the settling floes of that part of the sediment cannot resist
the high disruptive shear stresses near the bed.   The part of sediment
which can form floes large enough to settle to the bed and with
sufficiently strong bonds to resist breaking and re-suspension,
deposits permanently without being resuspended.
     5.  The ratio Ceq/C0 ceases to be a unique function of the
average bed shear stress for any speed combination other than the
one resulting in uniform deposition.  This suggests that the rotation-
induced unbalanced secondary currents also control the equilibrium
concentration.

     6.  Mechanical analysis has revealed that at equilibrium
concentration, the suspended sediment contains the entire grain size
range of the original sediment.  From this observation, it was
concluded that the degree of flocculation and the strength of the
inter-particle bonds play a dominant role in the deposition process
rather than the particle size, and that there is little correlation
between absolute size and intensity of inter-particle forces.

     7.  Limited data from the M.I.T. experiments showed that the
deposition rates are also strongly controlled by the bed shear
stress.  The following two tentative expressions were developed
for the instantaneous concentration, C(t) by two different approaches
(15):
C(t) = CQf(Tb)
                              10
                                            (8)
and
        C1 =
     VC(t)

     Co-Ceq
= - 0.592 + 0.135 log CQ + 0.455 log  t
(9)
where t is in minutes and 15 is in Ibs. per square foot.   Differentiat-
ing Eq. 9 with respect to time, the following equation for the rate
of deposition is obtained:
        dC(t) _   0.198
        ~dt         t
                                                        (10)
In Eq. 10 the shear stress, Tb, enters implicity through Ceq/C0.

     It should be noted that in all experiments, the suspended
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sediment concentration was directly and accurately determined by
filtering a sample through a membrane.   For this purpose.  Millipore
filtering equipment was used.
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                              SECTION V

                       EXPERIMENTAL APPARATUS

     The experimental apparatus and accessory equipment are as
described below.

     a.  Basic Experimental Apparatus

     The basic equipment, consisting of a system of a rotating channel
and a ring similar in principle and in operation to that designed
at M.I.T. (17), consists of the following basic components:

     1.  An annular channel 8 inches wide, 18 inches deep and 60
inches average diameter, to contain the water-sediment suspension,
shown in Fig. 1.  It is made of fiberglass 1/8 inch thick with four
plexiglass windows 3 inches by 2 inches at the lower part of its
outside wall to permit visual observation.  Laterial rigidity is
provided by top and bottom flanges and vertical stiffeners.

     2.  An annular, 1/4 inch thick, plexiglass ring of the same
average diameter as that of the channel and slightly less than 8
inches wide, shown in Fig. 2.  This ring is positioned within the
channel and in contact with the water surface.  A plexiglass
reinforcing stem .has been glued at the center of the ring, forming
a T-shaped cross-section, to minimize deflection between supports.
Simultaneous rotation of both components in opposite directions by
means of two concentric shafts, each driven by a separate variable-
speed motor, generates a uniform turbulent flow field.  The
operational speeds of the channel and ring were evaluated for the
sediment deposition to be uniform across the channel (see Section
VI).

     3.  An annular plexiglass, 1/8 inch thick, false bottom pictured
in Fig. 3.  It has the approximate horizontal  dimensions of the ring
and is to be placed inside the annular channel supported by
four removable cylinders , which in turn will be supported on knife
edges on four special removable supports, also shown in Fig. 3.  Thus
the frictional resistance to the rotation of the false bottom will be
minimized, and its tangential movement due to flow-induced shear
stresses will be resisted and sensed by an instrumented thin blade.
Calibration of the blade using static loads will permit a direct
estimate of the total shear force exerted on the bottom.

     4.  The supporting frame including the two concentric shafts
and ring support shown in Fig. 4.  It is made of 3 inch by 3 inch
by 5/16 inch tubing.  The 3 inch outside diameter hollow shaft is
supported on the two indicated plates through ball bearings.  The
one-inch diameter inner shaft is supported also by two ball bearings
inside the outer shaft.   A turn-table attached to the outer shaft

                                 15

-------
Small Plexiglass
Windows Every 90C
                 1'
                  '
                        -76'

18%'
i
                  Fig.  1 Annular Channel
                          16

-------
                                   STIFFENERS
                                       >/" T
                                       /I6   I
CROSS-SECTION UJ-(L) ENLARGED
   Fig. 2 Annular Ring with Stiffeners
                  17

-------
Fig.  3 False Bottom and Supports

-------
CONTINUOUS
REFILLING

FUNNEL
DRAIN


SUSPENSION
COLLECTOR
                                                BEARING  FOR
                                                INNER  SHAFT
                                                SLIPPING 8 BRUSH
                                                BLOCK  ASSEMBLY
                                  DRIVING  MOTORS
STRAIN  GAGES

RING  SUSPEDING
BLADE

INTERMITTENT
REFILLING  FUNNEL

FIBREGLASS  CHANNEL

FIBREGLASS  STIFFENER

SAMPLE"TAP

SAMPLE  BOTTLE
                                                                          TURNTABLE
                                                                          OUTER  SHAFT
                         Fig.  4  Turntable  Assembly
                                             19

-------
supports the annular channel, and a mechanism shown in detail  in Fig.
5 is used to support the annular ring, suspended from four flexible
stainless steel blades.   These blades are rigidly secured at the top
by clamping fixtures attached to four stiff radial  stainless steel
arms, which are in turn  attached to the 1-inch diameter inner shaft
through the device shown in Fig. 5.  The blades are instrumented
with strain gages whose  signal is transmitted to a strain indicator
through a set of slip rings.   To adjust the ring to touch the water
surface for a given depth of water in the channel, a fine and coarse
height-adjustment mechanism is provided by the clamping fixture,
which attaches the entire ring assembly to the inner driving shaft.
The fixture is made of two components which consist of a steel  collar
fitting closely to the inner shaft.  The collar slides on the shaft to
the desired height and is locked there by a set-screw which seats
into counter sunk holes, vertically spaced 1  inch apart on the inner
shaft.  The outer component is attached to the ring assembly and
through threads over the inner collar and provides a fine vertical
adjustment.

     Fig. 6a shows a general  picture of the entire assembled basic
experimental apparatus,  which, has worked perfectly.  Fig. 6b
shows a more detailed picture of the annular channel with the ring
inside it.

     b.  Accessory Equipment

     In addition to the  described basic experimental apparatus,  the
following accessory equipment and material is provided.

     1.  Kent 265 Miniflow Velocity Kit with  high and low speed
velocity probes of 10 mm diameter.  It is supplemented with a 4  mm
diameter miniature current meter.  These meters are to be used for
measurement of local flow velocities inside the channel.

     2.  Two variable-speed motors with speed regulators.

     3.  Mi Hi pore filtering  equipment with the necessary filtering
membranes,  for measurements of concentration  of suspended sediment.

     4.  Kaolinite clay, a commercial variety, tradenamed Peerless
No. 2, mined and processed by Dixie Clay Company, in Bath, South
Carolina.
                                 20

-------
      4.00
                               2"
                      Nut

                      Set Screw


                     Set covities
                   " Shaft
              SCALE  1:2
 o
	'
XN
 O
                                                          o^
                                                          o)!
                                                Arm  Connection
                                           A*-
                                                  0.03"
                                                 Blade  Support
                                                        Blade
                                                        3.03' thi
Fig.  5 Mechanism  Supporting Annular Ring


                              21

-------
                 a.  General  View
b.  Annular Channel  with Ring in Operational  Position

      Fig.  6 Basic  Experimental Apparatus
                     22

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                              SECTION VI

                         OPERATIONAL PROCEDURE

     The special annular channel and ring apparatus was designed to
obtain a uniform turbulent flow field at each section of the annular
channel as was mentioned perviously.  This was done (also see Section
IV) by rotating the channel and ring in opposite directions, so that
the generated cells of secondary currents were neutralized (17).  For
this purpose, the ring and channel speeds were calibrated, as
described below.  The method of taking concentration samples is also
outlined.

Operating Curves

     Since the idea was to obtain a uniform flow field in the channel
so as to have no secondary radial flow, and consequently a uniform
sediment deposition across the width of the channel, small plastic
beads of 1.06 specific gravity were placed at the bottom of the
channel, which was filled to different depths with water, and the
ring was positioned on its surface.  A simultaneous rotation of the
ring and the channel in opposite directions caused the beads to move
toward the inside or the outside wall of the channel, depending on the
strength of the secondary current.  If the channel rotated too fast,
the beads moved toward the outside wall.  On the other hand, if the
ring rotated too fast, the beads moved toward the inside wall.  At
the proper speed combination therefore, the beads stayed uniformly
across the width of the bed.  It was later verified by the actual
measurement of the depth of deposited sediment bed across the width
of the channel that the beads did in fact represent the sediment,
for the purpose of its uniform deposition, adequately.

     In Fig. 7, the speed combinations obtained by the foregoing
procedure for various depths are shown.  These are the operating
curves for the ring-channel system and they were adhered to through-
out the present experimental phase.  A deviation from these curves
would of course result in non-uniform sediment deposition due to
secondary currents.  This aspect of secondary current has been covered
in some detail in (17).

Sample Extraction

     Four stop-cocks were provided in the channel as observed in
Fig. 6a, for extracting concentration samples from the channel.  The
tubes and bottles provided below were used to collect the sample
while the channel was in operation.

     Initially, to begin a given test run, the ring and channel were
rotated at high speeds to ensure complete suspension of the material
inside.  Then the speeds were suddenly lowered to those corresponding
                                    23

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   22



   20
Q.
cr
   12

Q
UJ
UJ  10
CL
IT)
                            3456


                             CHANNEL  SPEED  IN  R . P. M.
                  Fig.  7  Operating Curves

-------
to a point on ttie operating curve of Fig. 7.  This was accomplished
in less than 10 seconds and at this point a stop-watch was used to
commence the time of deposition.
                                 25

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                              SECTION VII

                        RESULTS OF INVESTIGATION

     The experimental investigation was concerned with a detailed
study of the time-deposition rates (20).  Three different channel
depths of 6, 9, and 12 inches were conveniently selected and used
with initial sediment concentrations ranging from about 1000 ppm
to about 25,000 ppm.  The bed shear stress was varied over a wide
range, but was kept above the minimum value, tbmin at which Ceq
becomes zero.

     The independence of the relative equilibrium concentartion, Ceq/
C0 from C0, and its dependence solely on the bed shear stress,  was
once more verified.  The data obtained for all depths and concentrations
are summarized in Fig. 8 on a logarithmic-normal paper, indicated by
a straight line with random scattering.  The bed shear stresses
have been computed from the experimental equation derived previously
(15):

        T,  = [4.20 x io'5   1ML]1-20                       dD
where T^ is the bed shear stress at the center of the channel  in
psf, AU is the sum of the absolute velocities of the channel  and
ring in rpm, d is the depth and- b is the width of the channel.

     Fig. 8 leads to following equation relating the relative
equilibrium concentration to the bed shear stress:
.
Co
where M'is the geometric mean, i.e. the logarithm of T
Ceq/C0 = 0.50, and a is the standard deviation.  For the type of
sediment and the water quality used M' = 0, Tbmin = 1-60 dynes/cm2
and a - 0.49.

     The dotted line in Fig. 8 represents the average Ceq/C0
versus rb-Tbmin relationship of the earlier limited results of
M.I.T. (16,17).  The two lines are very nearly parallel  with almost
identical a values and thus confirm the validity of the functional
form of the Eq. 12.  At the present time, it is not known whether
the difference in the values of the means in the two cases is due
to a variation of the constant factor in Eq. 11 or to slight

                                   27

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yy
98
95
90
80
70
60
^o
^ 50
40
ro O
03 0 30
2" 20
O
10
5
2
1
0.5
0.2
O.I

















JoglTb-
Ceq_/l









. a v r\ <















r log(Tb-Tbmin)-M'i
CO J(T y27T*"K l 2 l CT
~
fbmin==l '60 dynes/cm , M'= 0.0
(T =0.49
	




















,










X














0
Ax










X
T
1


F


^

,





o


/
r-'
L



n

Tl


X
^v
T




/
Ref. (l 5)
X
/
^
x/O





x- 	 ^
^
X
(Y
X
0





V



o











I>
J
X
x

x^























I
{log(rb-Tmin)|l/x



X

^











X


><


x

^
s
d










J
\




^
- r


/x

/-

;
X '
p
(^) '  '
_^uj(r
nfe


I/ /s>
i



pp












c








ya
o



















/
^
1






-C
3













>-











Symbol Depth (in) Co(ppm)Range
O 6 1005-21180
D 9 1150-18390
O 12 1007-25930





1




1
/
]














O.OI
O.I
10
                                  7- 	 7-                 2
                                   b   bmin (dynes/cm  )
          Fig. 8 Variation of Relative Equilibrium Concentration C  /C  with  Bed Shear Stress

-------
differences in the chemistry of the water or of the admixtures of
the sediment used.  It should be noted at this point that the
depositional behavior of cohesive sediments is extremely sensitive
even to slight changes in water temperature, to differences in the
chemical constituents of the sediment, and to the dissolved ions.

     Fig. 9 shows an example of the time-concentration relationship
for the 6 inch depth and for an initial concentration of 9570 ppm.
C(t)_is the average instantaneous suspended sediment concentration
at time t.  It can be observed that the time-concentration lines are
nearly parallel for all bed shear stress values and initial sediment
concentration C .  The general empirical relationship thus has the
form:

               1 - C(t)/C

          C' = 1 - Ceq/CQ  = a 1Q9 t + *                       (13)

     It should be noted that 1-C  /C  represents the proportion of
the total depositable sediment, or tRe degree of deposition, whereas
l-C(t)/C  indicates the fraction of the original sediment deposited
at time t.  Therefore C' is the fraction of the depositable sediment
deposited at time t.  Obviously the left hand member is expected to
vary from zero to unity.  The coefficient a is the slope of the lines
and the coefficient 3 is the value of C1 at any arbitrary time,
selected equal to 1 minute, since this wa3 the minimum time after the
beginning of each run at which dependable measurements were obtained.
For a given depth, a is independent of the bed shear stress, T, .
Eq. 13 is valid for a time interval from 0.5 minute  up to the time
at which equilibrium concentration is attained, i.e. when C1 is
equal to unity.

     Fig. 10 shows a plot of a versus C  for all three depths.  It
is seen that a remains independent of concentration up to about C
= 10,000 ppm.  From then on it decreases gradually and linearly
with C .  For the 6 inch depth a decreases from 0.32 to 0.27, cor-
respon9ing to an increase of C  from 10,000 to 20,000 ppm, i.e. a
decreases by 17% for an increase of C  by 100%.  Since a smaller
a implies a lower deposition rate, it seems that a concentration of
10,000 ppm marks the beginning of hindered settling, without the
same hinderance affecting the relative equilibrium concentration
C  /C .  It should be noted, however, that even the highest observed
cBrlcentrations of a suspended fine sediment in natural waters are
well below that limit, so that for practical purposes a can be con-
sidered as being independent of C .  A small but systematic varia-
tion of a with depth is observed.  A doubling of depth causes an in-
crease of a by 20% without any effect on the relative equilibrium
concentration.  Tfie reason for this increase is currently under study.

     Finally, Fig. 11 shows the variation of 3 with bed shear stress
for all three depths and for the entire range of initial concentrations

                               29

-------
            1.0
                 i   I  1  i I
                                                                               I   I   1111.
            0.9
                                                          A
                                                                         O
CO
O
            0.!
            0.3
           0.2
                 j	i  1	LL
              Q5.6 .7.8.9 I
                                               O
A
                                                A
                                                    A
                                                         O
             A
                                                                          A
                                                               A
         Depth  6 in
                                                                    A
                                       c-c(t)  =0.32 logt
                                       Co Ceq
Symbol
*
O

V
Co(ppm)
9570
9570
9570
9570
9570
9570
TL (dynes/cm1)
1.89
2.62
3.00
3.33
5.69
6.67
0
0.14
0.21
0.36
0.58
0.75
0.83
                                                                           i
 4  5  6 7 8 910

      TIME  (minutes)
20
30  40 50 60708090100
200   300
                   Fig.  9 Variation of  Relative Depositable Concentration [C -C)/(C  -C   }  with Time

-------
   0.5
   0.4
   0.3
a
   0.2
   O.I
   0.0
       0
                                            Q =  -5.22X l66Cn+K
Symbol
O

D

O
Depth(in)
6

9

12
C0 ( ppm) Range
| 1005- 10630
^ 10630 -21180
r 1015 - 10750
I 10750.18390
, 1007 - 10910
1 10910 - 25930
a
0.32
0.36

0.33

K
0.375

0.415

0.445
5000     10000      15000
             C0( ppm)
20000
25000
30000
      Fig. 10 Variation  of Slope  a with Channel Depth and Initial Concentration

-------
IAJ
0.9
0.8
0.7
0.6
05
Q4
O3
0.2
3
O.I
0.09
0.08
0.07
1
0.05
0.04
0.03
0.02
QOI
0


















(3= 0.24(7



f^
V_7

^

^ e






G
e

/
/
fi^







o
X
B
H












b 1



} c
^
























0.812
 bmin'


y










()
X
4
r
D<
6
0
e
(5
e
e
0

(
C
MZ




/m
~^i,
ft ^
K H
r?M f*>
y v_7
1(3
i i
1 n
^
^Ti}
[X
y
AfC5
AA^

^
M


^
r


























;pth (in) Approx. Co(ppm) Range
9 12
Symbol
Q Q 1000 - 1100
B 0 4000-5000
H (3 9000 11000
H ^ 15000- 16000
! ^ 18000- J9000
H 0 20000 220OO
 % 2500026000
l i























































1 02 0.3 0.4 0.5 O60.7 1.0 2 3 4 5 6 7 8 9 10
b~ bmin
Fig.  11  Variation  of Coefficient 3 with Bed Shear Stress
                   32

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The random scattering suggests that  6  Is  Independent of  the depth
of flow  and of the initial sediment  concentration, and depends only
on the bed shear stress, according to the  relationship:
or
                    0.812
                                                              05)
Accordingly, Eq. 13 can be modified as
             - C(t)/C0          t        Tb        K
                     U_    I   L    .i/U      -i \ 
-------
of the concentration of the depositable sediment, C0-Ceq, decreases
with increasing bed shear stress in accordance with. Eq.  12.
Moreover, the average strength, size and settling velocity of the
floes which eventually reach the bed and which constitute the
depositable sediment concentration are expected to increase with
increasing bed shear stress.  Therefore, the average settling rate
and the percent of deposition at any arbitrary time are  expected
to be functions of the relative equilibrium concentration, which
in turn depends entirely on the bed shear stress.  It follows that
g should also be a function of T|>   The initial concentration C0
could affect 3 by increasing the rate of floe formation, since the
probability of particle collision is expected to be proportional to
C0.  The observed independence of g from C0,however, suggests that
the time of floe formation is negligibly small  in comparison with
the average time of deposition of floe.
                               34

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                           SECTION VIII

                         ACKNOWLEDGEMENTS

     The assistance of the staff of the Coastal Engineering
Laboratory at the University of Florida, where the tests were con'
ducted, is greatly appreciated.

     The support of the project by the Environmental Protection
Agency is sincerely acknowledged.
                                  35

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                              SECTION IX

                              REFERENCES

 1.  Einstein, H.A., "The Bed-Load Function for Sediment Transportation
     in Open Channel Flows", TecPinjcal Bulletin No.  1026, September,
     1950.                   -

 2.  Etter, R.J. and Hoyer, R.P., Partheniades, E.  and Kennedy,  J.F.,
     "Depositional Behavior of Kaolinite in Turbulent Flow",  J.  of
     Hydr. Div. , ASCE. Vol. 94, No.  HYS.pp. 1439-1452, November,
        ~
 3.  Harleman, D.R.F., and Ippen, A.T., "Salinity Intrusion  Effects
     in Estuary Shoaling", J. of Hydr. Div., ASCE, Vol.  95,  No.  HY1 ,
     pp. 9-27, January, 1969.

 4.  Ippen, A.T. (editor), "Estuary and Coastline Hydrodynamics",
     Chapters 10, 11, 12, 13, 14, 15, McGraw-Hill, 1966.

 5.  Krone, R.B., "Second Annual Progress Report on the  Silt Transport
     Studies Utilizing Radio-isotopes", Hydr.  Engr. Lab,  and Sanitary
     Engr.  Res. Lab., Univ.  of Calif,, February, 1959.

 6.  Krone, R.B., "Flume Studies of the Transport of Sediment in
     Estuarial Shoaling Processes", Final Report, Hydro.  Engr.  Lab
     and Sanitary Engr. Res. Lab., Univ.  of Calif. , Berkeley, June,
     1962.

 7-  Krone, R.B., "A Study of Rheologic Properties of Estuarial
     Sediments", Final Report, Hydr.  Engr.  Lab,  and Sanitary Engr.
     Res. Lab. , Univ. of Calif. , September, 1963.

 8.  McLaughlin, R.T. , "Settling Properties of Suspensions", Trans.
     ASCE,  Vol. 126, Pt. 1,  pp.  1734-1767,  1961.

 9.  Paaswell, R.E.  and Partheniades, E., "Erosion of Cohesive  Soils
     and Channel Stabilization", Pt.  II:   Behavior of Cohesive  Soils",
     Report No. 19,  Dept. of Civil Engr., State  University of New
     York at Buffalo, October, 1968.

10.  Partheniades, E. , "The  Present State of Knowledge  of the Behavior
     of Fine Sediments in Estuaries", Tech. Note No.  8,  Hydro-
     dynamics Lab. ,  M.I.T. ,  Cambridge, Mass.,  June, 1964.

11.  Partheniades, E., "Erosion  and Deposition of Cohesive Soils",
     J. of Hydr. Div., ASCE, Vol. 91, No. HY1 , pp. 105-138,
     January, 1965.
                                      37

-------
12.   Partheniades, E.,  "Field Investigations  to  Determine  Sediment
     Sources, and Salinity Intrusion  in  the  MaracaiBo  Estuary,
     Venezuela", Rep.  No. 94, Hydrodynamics Lab. ,  M.I.T.,  Cambridge,
     Mass., June, 1966.

13.   Partheniades, E.,  Discussion  6f Salinity Intrusion  Effects  in
     Estuary Sholaing",  by Harleman, D.R.F.,  and  Ippen,  A.T. ,
     (Proc. Paper 6340,  Jan., 1969).  J.  of Hydro.  Div. , ASCE,
     Vol.  96, No. HY1 ,  pp.  264-269,  January,  1970.

14.   Partheniades, E.,  and Blinco, O.H.,  "Effect of Boundary Resistance
     on Turbulence in  Free Surface Flows",  Technical  Report, Dept.
     of Coastal  and Oceanographic  Engineering, University  of Florida,
     Gainesville, Florida, February, 1970.

15.   Partheniades, E. ,  Cross, R.H.,  and Ayora, A.,  "Further
     Results on  the Deposition  of  Cohesive  Sediments", Proc.
     Eleventh Conf. on  Coastal  Engr. , Vol.  1, Ch.  47, pp.  723-742,
     September,  1968.

16.   Partheniades, E. ,  and Kennedy,  J.F., "The Depositional Behavior
     of Fine Sediment  Suspensions  in a  Turbulent Fluid Motion",
     Proc.  Tenth Conf.  on Coastal  Enqr. ,  Vol .  II,  Ch. 41 ,  pp. 707-
     729,  Tokyo, Japan,  September, 1966.

17.   Partheniades, E.,  Kennedy, J.F. , Etter,  R.J.  and Hoyer, R.P.,
     "Investigations of  the Depositignal  Behavior  of  Fine  Cohesive
     Sediments in an Annular Rotating Channel",  Rep.  No. 96,
     Hydrodynamics Lab., M.I .T, Cambridge,  Mass.,  June,  1966.

18.   Partheniades, E. ,  and Paaswell, R.E.,  "Erosion of Cohesive  Soils
     and Channel Stabilization" Pt.  1:  State of Knowledge", Report
     No. 19, Dept. of  Civil  Engineering,  State University  of New
     York  at Buffalo,  October,  1968.

19.   Partheniades, E. ,  and Paaswell , R.E.,  "Erodibility  of Channels
     with  Cohesive Boundary", J. of  Hydro.  Div. , ASCE, Vol. 96,
     No. HY3, pp. 755-771,  March,  1970.

20.   Partheniades, E. ,  and Mehta,  A.J., "Rates of  Deposition of  Fine
     Cohesive Sediments  in  Turbulent Flows",  Proc.  14th  Conf.
     Assoc.  of Hydr.  Res.,  Paris,  France,  V.  4,  D3-1 ,  pp.  17-26,
     August, 1971.

21.   U.S.  Government, Secretary of the  Interior,  "The  National
     Estuarine Pollution  Study",  Report to the  U.S.  Congress
     Pursuant to Public Law 89-753,  The Clean Water  Act  of 1966,
     Doc.  No. 91-58,  March  25,  1970.
                                    3Q
                                    O

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22.  Van Olphen, H. , "An Introduction to Clay Colloid Chemistry",
     Interscience  (Wiley), New York, 1963.
                               39

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                           SECTION X

                    PUBLICATIONS AND PATENTS

Partheniades, E., and Mehta, A.J., "Rates of Deposition  of Fine
Cohesive Sediments in Turbulent Flows",  Proc.  14th Conf.  Int.
Assoc. of Hydr.  Res., Paris, France, V.  4, D3-1 ,  pp.  17-26,
August, 1971.
                            41

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1

5
Accession Number
rt Subject Field & Group
02J
SELECTED WATER RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
Organization
           Department of Coastal and Oceanographic Engineering
    Title
           Deposition of Fine Sediments in Turbulent Flows
1Q Authors)
Par Lheiiiades , Emmanuel
Mehta, Ashish J.
16

21
Project Designation
EPA Project
#16050 ERS
Note
 22
    Citation
 23
    Descriptors (Starred First)
     ^Sedimentation,  -^Deposition, *Sediment Transport, ^Sedimentation Rates,  Turbulence,
     Hydraulics,  Fluid Dynamics, Water Properties, Turbulent Flow, Mixing
 25
Identifiers (Starred First)

 *Sediment Deposition Rates,  *Kaolinite Clay
 27
Abstract
  Basic laboratory  investigations were carried out to study the role of  flow
 parameters  on the deposition of fine cohesive sediments  in  a  turbulent flow field.
 The study utilized a special apparatus consisting  of a system of  a rotating annular
 channel and ring.  The results obtained have confirmed earlier conclusions that the
 percentage  of the total sediment that a given flow can maintain in suspension depends
 only  on the bed shear stress and is independent of the initial sediment concentration.
       The percentage C', of the depositable sediment deposited at  time t has been found
 to vary with time according to the law C1 =  alogt +  p, where the coefficient Q-
 appears to  be independent of the flow conditions and sediment concentration, while the
 coefficient p is a function of the bed shear stress only.   Both QI  and p  are expected to
 depend on the physico-chemical properties of the sediment and the water environment.
 It follows  that the deposition rates are proportional to the  depositable sediment
 concentration and inversely proportional to time.    (Partheniades-University of Florida)
Abstractor
 Emmanuel Partheniades
                          Institution
                          University of Florida, Gainesville,  Florida
 WR: 102 (REV. JULY 19691
 WRSIC
 r 0. S. GOVERNMENT PRINTING OFFICE: 1972 Wt-W? (350)
                                          SEND TO:  WATER RESOURCES SCIENTIFIC INFORMATION CENTER
                                                  U.S. DEPARTMENT OF THE INTERIOR
                                                  WASHINGTON, D. C. 20240

                                                                           * GPO: 1969-359-339

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