SOME FACTORS INFLUENCING THE TURBIDITY OF WATER ...

SOME FACTORS INFLUENCING THE TURBIDITY OF

WATER COLLECTED BY RIVER INTAKES

by

William J. Cosgrove, B.Eng.

A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfilment of the requirements for the degree of Master of Engineering.

Department of Civil Engineering, McGill University, Montrea.l. April 1962

TABLE OF CONTENTS

CHAPT ER 1 - PREVIOUS WORK... • • • • • . • • • • • • • • • • • • • • • • • 1

CHAPTER 11- OBJECT OF EXPERIMENT •••••.••••••••••••• 6

CHAPTER 111- APP ARA TUS • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 8

CHAPTER lV - PROCEDUR.E. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 20

CHAPTER V- OBSERVATIONS ••••••••••••••••••••••••••• 30

CHAPTER Vl- DISCUSSION OF RESULTS •••••••••••••••••• 70

CHAPTER Vll- CONCLUSIONS •••••••••••••••••••••••••• •. 99

APPENDIX -

( i)

PREFACE

The author wishes to express his sincere gratitude

to his Director of Research, Professer Andrejs Pakalnins,

Department of Civil Engineering and Applied Mechanics,McGill

University for his encouragement and helpful supervision;

to Professer V.W.G. Wilson, also of the Department of Civil

Engineering, for his advice on modifications to the apparatus

and for the assistance of his staff in the erection thereof;

to Mr. Curtis Meyer B.Agr.Eng., for his assistance in pre

paring the apparatus and throughout the sampling.

Montreal, Quebec.

April, 1962.

William J. Cosgrove

1

CHAPTER 1

PREVIOUS WORK

During the month of August, 1957, Mr. Robert J.

Lindsay, a graduate student of the Civil Engineering

Department at McGill University, carried out experimenta

with Model River Intakes. The resulta of the experimenta

were submitted as his thesis entitled "The Details of Water

Intakes- Their Effect on the Turbidity of Water",presented

to the Faculty of Graduate Studies and Research of McGill

University in August, 1960.

The summarized object of the experimenta was to

determine:

"Primarily

That irrespective of particle theory, a reduction

in turbidity can be obtained by preferential positioning of

the mouth of an intake in relation to the direction of the

approaching current, and,

"Secondarily

The extent to which the theory of discrete

particle movement is applicable to such an investigation."

As a result of the experimenta it was concluded

2

that:

"Where turbulent conditions of flow exist adjacent

to an intake, the position of the mouth of the intake in

relation to the direction of the approaching current can

affect a reduction in the turbidity of the water withdrawn

from the source provided that the ratio between the intake

velocities and the velocity of the current be substantially

lesa than unity.

"The reduction in turbidity affected is a function

of both intake position and the ratio of these velocities,

and not of intake position alone; therefore, if suitably

modified, the theory of discrete particle movement is

applicable to the present investigation."

"The reduction in turbidity affected is inversely

proportional to the ratio between the intake velocity and

approaching current velocity irrespective of the position of

the intake.n

"The reduction in turbidity affected by an upstream

or downstream positioning of the intake is about three times

more than that produced when the intake is pla.ced straight

out and at 90° to the approaching current."

The first of these conclusions would appear to con

tradict the findings of Vito A. Vanoni who stated in 1946

that "When the sampling velocity is lower than the local

stream velocity, the fluid streamlines curve away from the

3

sampler tip. Because of their greater inertia, the sediment

particles follow paths of less curvature than the fluid with

the result that sediment is transferred to the fluid entering

the sampler and the apparent concentration is increased.

When the sampling velocity is greater than the stream velocity,

the curvature is towards the sampler, and a tendency to

decrease the amount of sediment collected would therefore be

expected.n 1

Table 1 on Page 5 lists the experimental resulta of

Mr. Vanoni which were the basis of the above statement.

It should be noted that in these experimenta the

weight deviation of individual samples from the mean was as

high as 10%, although the deviation of the average weight of

three consecutive samples from the mean did not exceed 3%. Similarly, Mr. R.J. Lindsay reported variations in turbidity

which ranged from -15% to +15% for the most part, while the

range of probable error at the same flume velocity was ± 12% for a single reading. In the latter case, however,

duplication of readings reduced the probable error to an

average of ! 5%. 2

The probable errors found in both researches are small

when compared with those found by Benedict, Albertson, and

1. Vito A.Vanoni Assoc. M.A.S.C.E., "Transportation of Suspended Sediment by Water", Transactions of the American Society of Civil Engineers, Volume 111, 1946, page 67.

2. Lindsay, op. cit., P• 161

4

Matejka, and reported in 1955.3 In accordance with their

report, a single sample collected at any given time might

have varied by 83.5% from the true mean, and the standard

deviation of the variations at one station would be ! 48.8%

for 95.5% of the time, and at another station ! 22.0% for

95.5% of the time.

3. Paul c. Benedict, Maurice L. Albertson, and Donald Q. Matejka, "Total Sediment Load Measured in Turbulence Flume.", Transactions, American Society of Civil Engineers, Volume 120, 1955 p. 457.

5

TABLE 1

EXPERIMENTAL DETERMINATION OF THE ~~·~'ECT OF THE SAMPLING VELOCITY ON THE AMOUNT OF SEDIMENT COLLECTED.4

No. Observations

1 2

3 c ë

Definitions-

Us - 1.00 --u

0.99 1.04 0.99 0.95 0.97 1.06 •••• •••• • • • •

us - 0.86 --u

1.08 1.05

0.98 0.9~ 1.0 0.90 1.00 0.99 1.05 0.91 1.10

Us = 0.75 u

1.13 0.99 0.95 0.99 1.oo 0.97 • ••• • • • • ••••

Usju is the ratio of sampling velocity to the velocity

of the stream at the sampling point; ë is the average sediment

concentration, in grams per liter, for the series of samples;

cjë3 is the ratio of C to the average concentration obtained

when the sampling velocity is equal to the stream velocity; and

cjë is the ratio of the sediment concentration for individua1

sample to c.

4. Vanoni, op. cit., p.2

CHAPTER 11

OBJECT OF EXPERIMENT.

6

In view of the apparent confl.ict of the resulta obtained

by Messrs. R.J.Lindsay and V.A. Vanoni, and especially

taking into consideration the probable errors which are re

latively large when compared ta the variations in turbidity

determined, it wes concluded that future investigations

shauld be carried out in such a manner as ta reduce the pro

bable errors ta a minimum. Since the research of R.J.Lindsay

was directly concerned with water intakes, and since his

conclusions were based on a great many more observations than

those of Mr. Vanoni, it may be assumed that his conclusions

are more likely ta be correct for this specifie case, and an

attempt sbould be made ta verify them.

The intake mouthpiece used in the experiment of Mr.

Lindsay was of the same shape for all three positions in

vestigated. The intake mouthpiece had a port opening of an

area equal to 6.3 times the area of the int~ke conduit itself.

In arder ta determine whether the port velocity and the shape

of the mouthpiece itself influences the amount of turbidity

which is carried into the intake, a series of measurements

were made with a mouthpiece praviding a greatly reduced port

velocity.

7

Finally it should be noted that no theory has been

advanced concerning the flow of water into intakes. It was

therefore decided to make an attempt to observe the flow and

to explain the quantitative experimental resulta.

In summary, therefore, the objecta of the present ex

perimenta are:

1. To investigate by introducing more refined

experimental methods the conclusions reached by R.J.Lindsay,

namely: a) that intake position alone does not affect a

reduction in turbidity and

b) that provided the ratio of intake velocity to

current velocity is substantially less than

unity, the intake position may be varied to affect

a reduction in turbidity.

2. To investigate what effect the shape of the mouth

piece in general, and the relative size of the port opening,

in particular has upon the apparent turbidity of the

collected water.

3. To derive an explanation of the quantitative results

obtained under 1. and 2. above by observations of the flow

patterns.

CHAPTER 111

APPARATUS

8

In order to facilitate comparison of resulta of these

experimenta, with the resulta obtained previously, it was

decided insofar as was possible, to use, the equipment

employed by R.J.Lindsay in his experiment. Figure 1

illustrates schematically the apparatus used for these ex

perimenta. A detailed description of the equipment ia as

followa:

Item 1.

A horizontally driven centrifugai pump with a rated

capacity of 10 cfa.

Item 2.

A aupply reservoir measuring 11 1 - 2" in length,

71 -8" in width, with a depth of about 6 1 -6". After the ex

perimenta were underway and for the reasons described in

Chapter 4- Procedure, this reservoir was reduced to approximately

61 -0" in length by introducing a baffle plate, and the width at

the bottom was reduced to approximately 4 ft. by means of a

sloping plywood bu1khead which rested on the bottom and against

one wall of the tank.

Item 3.

A weighing assembly consisting of a acale balance

and weighing tank with a capacity of about 5,000 lbs. The

contents of the weighing tank could be returned to the main

Control Valve

1 1Mixing IBasin( 7)

' ~--1 L~

......._ ___ _ Flume (5)

Weighing Assembly(3)

---"'-- -"'--

..

..

( 8)

~- . --1 ~

Supply ir (2) rump~ Reservo

L -

Note- Not to SQa le Figure s i n brackets (3) refer to apparatus item number in text.

Fig.l- Schematic Diagram of Apparatus ~

11

uJ l :J .J LL

12

reservoir through a connecting line.

Item 4. A steel-framed f1ume of rectangular cross section

which could be bulkheaded to form a receiving or mixing basin

of any desirable capacity and into which the effluent from the

overhead delivery line could be diverted. The steel flume,

being of very sturdy construction, could also be used to

support the test flume and receive any spillage therefrom

during the course of the experimenta.

Item 5. Experimental flume. This was the same flume

which had been used by R. J. Lindsay in the experimenta pre

viously mentioned. This flume was of trapezoïdal cross

section having a bottom width of 1 1 - O", a top width of 3'-0"

and a depth of l'- O". It had originally been pre-fabricated

in two sections of 8 ft. lengths and assembled in the

laboratory. Afterwards, the flume was dismantled and stored

in the laboratory. It was re-assembled for the purpose of

this experiment. Plates 1, 11 and lV illustrate various

aspects of the flume in position.

Item 6.

Intake pipes. The two intake pipes used by

R.J.Lindsay in his experiment, were made available for the

purposes of this experiment. Each was fitted with a bell·

mouth attachment 1~ ins. long having a port diameter of 1.813

in. The two pipes were identical in every respect except that

one provided a 90° bend for observations upstream and down

stream whereas the other was entirely straight. A third

mouthpiece was made with a bell-mouth attachment ll in. long

but having a port diameter of 5 in. The three mouthpieces

are illustrated on Plate 111.

Item 7.

Bulkheads for Steel Flume. The original bulk-

heads were manufactured of 1 in. marine plywood and later

stored in the laboratory. These were re-constructed in their

original position 4 ft. apart in a section of the steel flume

to provide the necessary receiving or mixing basin at the out

let from the de li very line. The plywood was fastened on 2'tby

4't studs, the two bulkheads wedged against the aides of the

steel flume and the joints caulked with plasticine and oakum.

The bulkheads were braced with 2n by 4n struts placed between

them and drawn up tight against these by six !" steel reinforc

ing rods with threaded ends which passed through each bulkhead

and were bolted on the outside of the supporting studs. As

the experiment progressed, and for reasons outlined in Chapter

4- Procedure,the mixing reservoir was divided into two basins

by means of a plywood baffle. This baffle was made reasonably

watertight in order to eliminate the carrying of sediment

into the outside portion of the basin, but it was not

attempted to eliminate all leaks. This baffle is illustrated

by Plate lV.

15

z -cil ( al

l!J z )(

16

Item 8.

Intake Overflow. In the previous experiment, an

overflow weir was used which required the vertical upward

flow of the sediment laden water before its discharge.

Although calculations had been very carefully done in arder to

insure that the upward velocity would always be sufficient to

carry the sediment, nevertheless it was decided for the

purpose of this experiment to eliminate the weir and to dis

charge the flow freely through the intake conduit. The

conduit was placed so that there was always a continuous dawn

ward slope from the intake itself to the discharge end of the

conduit and the flow regulated by means of a clamp. The model

intake conduit is shawn on Plate 1 and in colour on Plate V.

Item 9.

Receiving Flume. The original receiving flume

which consisted simply of an open-bottom box, was found to be

still in the laboratory although it had been somewhat modified

for the purposes of another experiment. Openings in this box

were closed up and it was placed in its original position where

it served to prevent splashing of the discharge from the flume

and to direct it into the storage reservoir. This discharge

flume is also shawn on Plate 1.

Item 10.

A Gurley Current Meter, (Priee Pattern) of the con

ventional bucket wheel type was used to measure flume

velocities.

PLATE V

Arrow indicates Intake Discharge.

PLATE Vl .5" Mouthpiece facing downstream, with current meter in position behind it.

17

18.

In Plates 11 and Vl, the current meter can be seen mounted in

position behind the 5" diameter mouthpiece which is facing

downstream.

Item 11.

Turbidimeter: The turbidity was measured using

a Turbidimeter manufactured by the Hach Company of Ames,Iowa.

u.s.A. This instrument employa two photo-electric cells with

light sources. Through a comparison of the intensity of

light passing through the sample as compared with the light

passing through distilled water, it registers the turbidity on

a meter scale which is graduated to give turbidity directly in

accordance with the silica standard. This meter is shown in

Plate Vll.

CHAPTER FOUR

PROCEDURE

20

With the apparatus assembled as indicated in Plate 1,

the slope of the flume, the discharge of the pump and the

positioning of the gate valve which controlled the flow in

the supply piping were adjusted to minimize spillage, main

tain sufficient submergence of the intake pipe, and create

the desired flume velocity.

The velocity in the intake conduit was adjusted by

raising or lowering the discharge end of the conduit and by

opening or closing a clamp which was placed on the discharge

end of the conduit. For each position of the madel intake,

a series of readings was taken with five different ratios of

intake conduit velocity to flume velocity. In general these

ratios varied between 0.16 and 2.0. Five combinations of

intake and position were used; namely: 5" diameter mouthpiece

facing upstream and facing downstream; 1.813" mouthpiece

facing upstream, downstream and straight out. In most cases,

ten samples were taken, metered and averaged to produce a

reading for each combination of velocity ratio and intake

position.

Samples were collected in comroon galvanized steel pails.

The sample from the intake contained all of the sediment-bearing

water which was discharged from the intake during the period

21

of the observation. The corresponding sample from the flune,

consisted of two individual samples collected into one pail

by briefly intercepting a part of the discharge from the

flume in the pail a.t the beginning and the end of each period

of observation. The large samples in the pails were stirred

vigorously and a smaller sample taken which was placed in the

Turbidimeter and metered immediately.

At the beginning of ea.ch run an empty standard bottle

was filled with clea.r tap water and the empty sample bottle

was placed in the meter. The meter gwitch was then closed

and the meter current was varied by means of a. rheostat to

produce a zero reading on the silica scale. To obtain the

turbidity of a. sample, the sample bottle was filled with a

well-stirred sample from the sampling pail, the exterior of

the sample bottle was carefully dried, the bottle shaken and

inserted in position in the meter, and the meter switch closed

to give a turbidity reading directly from the scale.

As stated earlier, the flume velocity was measured

using a Gurley Current Meter. When placed in a flowing stream,

the buckets of this meter rotate at a speed which is pro

portional to the velocity of flow and every rotation (or

multiple thereof) transmits a signal to the headset worn by

the observer. By noting the frequency of the signal over a

known period of time the velocity of flow can be determined

from a calibration curve supplied by the manufacturer for each

22

instrument. During this experiment, the velocity was measured

at the beginning of each run and especially while the flow was

being adjusted, until it was constant at the desired figure,

and it was also measured at the end of each run. The meter was

removed from the flume while the sampling was being carried out.

The velocity of flow in the intake conduit was

determined by weighing the water which was discharged from the

conduit over a known period of time and dividing the equivalent

volume of water by the cross-sectional area of the intake con

duit. To save time, the weight of water which would have to be

discharged over a five-minute period, in order to create the

velocity of 1 ft. per second in the intake conduit, was cal

culated. By adjusting the discharge end of the intake conduit,

it was possible to arrive at multiples or fractions of this

weight and thereby set the intake discharge velocity at its pre

determined value. When the intake velocities were low, the

quantity of water actually discharged over the period of the

observation was measured, and the exact discharge velocity com

puted precisely.

Artificial turbidity of the water being circulated

through the system was created by the introduction of two

different types of sediment in the mixing basin. One of these

was magnesium silicate (talc) having a nominal particle aize of

149 microns. This was the same material as used by R.J.Lindsay

23

in his experiment. The actual particle aize variation for this

material before it was mixed with the water, was not determined.

In addition to the talc, pure silica {sand) was also used in

this experiment. The particle aize distribution as determined

by the supplier (Dominion Silica) is shown in Figure 2.

A sample of the suspension was analized in the soils

laboratory of the Department of Civil Engineering, McGill

University. The resulta of this analysis are shown in Table 2.

There was much deposition of sediment both in the mixing basin

and in the storage reservoir, and the resulta of the hydrometer

analysis indicated that it was the heavier fraction of the

sediment which was settling out. In an attempt to keep all of

the sediment in suspension and thus maintain uniform turbidity

in the flume, both the mixing basin and the storage reservoir

were reduced in aize through the introduction of baffles as

described in Chapter 3 - Apparatus. Plate Vlll indicates the

excellent degree of turbulence which was achieved in the storage

reservoir. Plate lX indicates the affect of placing the baffle

in the mixing basin and thereby reducing its effective volume

by one-half. At the end of the period of the experiment a

second hydrometer analysis was performed and the resulta thereof

are expressed in Table 3. It is to be noted that the improve

ments made in the two basins increased the diameter of the

largest aize particle in suspension from .04 to .19 milimeters.

r-

-

~.g Q)

c-S r-i ..::tV\

•CV"\

24

~ - i--- / - v ·-- -- -

1 0 r:il

·-r-- - ~ -- ~ cl;

+----E-1 rx:l 0:::

---- - ~·- E-1 -

~ H lïl

1 ·- ~-

E-1

~ o _

1 / ffi p.,

l ·~

/ H E-1 cl;

~-1 / ~ 1

l 0

-- - - ·-_y SCREEN SCALE RATIO 1.414

~~ ~~ ~.g ~.g ~.g Q) Q) ~ -.::t~ ~

V\S cos c- ==t 0' 0 -.::to 00 c-o C\JCO (\J'V\ r-iO r-i V\ ~Rl • -.::t •...o •r-i •r-i

GRAIN SIZE DISTRIBUTION OF SILICA SAND USED IN EXPERIMENT

Figure 2

100

90

80

70

60

50

40

30

20

10

0

z cl; p.,

25

In an attempt to investigate the pattern of flow around

the intakes, observations were made of the flow of dye around

the intake in the various positions. A long thin tube was

filled with a dye solution which later was released into the

stream immediately upstream or downstream from the intake to

obtain the flow pattern. In order to study the flow pattern

in two dimensions, the intake mouthpieces were raised to the

surface and small quantities of magnesium silicate were added

to the surface of the water upstream from the mouthpiece. The

pattern which the magnesium silicate formed in flowing past the

mouthpieces was photographed. Sketches were also prepared of

the dye pattern below the surface as well as the magnesium

silicate pattern on the surface adjacent to the intake.

26

z -

15l

27

(.!]'

z -x

TABLE 2

HYDROMETER ANALYSIS OF SUSPENDED SEDIMENT AT BEGINNING OF EXPERIMENT.

E1apsed time

2'

4'

10'

20 1

40'

8o•

Hyd. rdg.

1.0005

1.0002

1.0001

1.0

0.9999

0.9999

True Hyd. rdg.

1.001

1.0007

1.0006

1.0005

1.0004

1.0004

z: cm

16.8

16.88

16.90

16.93

16.96

16.96

Water temperature 19.5°0 Hydrometer correction +.0005

2.89

2.05

1.30

.921

.696

.498

Ana1ysis by S.J.Windich, Soi1s Laboratory McGi11 University, October )rd, 1961.

28

Dmm

.0416

.0295

.0187

.0133

.0100

.0071

TABLE 3

SOIL MECHANICS LABORATORY HYDROMETER ANALYSIS OF SUSPENDED SEDIMENT AT END OF EXPERIMENT.

E1apsed time

l:..t 4:

t' l'

2•

6•

22 1

34'

50'

Hyd. True z ~ rdg. hyd. rdg. cm tmin

1.0005 1.0006 7.644 5.53 1.0005 1.0006 7.644 3.91

1.0004 1.0005 7.670 2.77

1.0002 1.0003 7.722 1.965

1.0000 1.0001 7.744 1.133

1.0000 1.0001 7.744 0.594

1.0000 1.0001 7.744 0.478

.9999 1.0000 7.80 0.394

Water temperature 22° C Hydrometer correction +.0001

Analysis by S. J. Windich, Soils Laboratory McGil1 University October 31st, 1961.

29

Dnnn

.19

.11

.064

.039

.017

.oo6

.004

,003

CHAPTER V

OBSERVATIONS

A. Flow Pattern Observations

30

On October 8th, 1961, beginning at about 1 p.m., a series

of observations were carried out in an attempt to observe the

pattern of flow around the mouthpiece. A mixture of bright

orange common household dye was prepared. This was sucked into

a thin glass tube approximately five feet in length and held

in the tube by sealing the upper end of the tube until the

lower end was positioned near the intake. The dye was then

allowed to flow out of the tube by gravity and the pattern which

it traced was noted.

( i) Flow Patterns, 1.81.3" diam. Mouthpiece ttstraight-out••

The first observations were made with a flume velocity

of one foot per second, (1 fps) the small intake in its

straight-out position and with the flow approaching 0 fps thera

in. There appeared to be a great deal of turbulence around the

port of the mouthpiece and the thread of dye released just up

stream from the port diffused immediately into a ribbon

approximately two inches in width. No pattern of flow was

observed around the mouthpiece. However, when the mouthpiece

was raised to a partially submerged position, and a small

quantity of magnesium silicate was distributed on the surface

of the water just upstream from the mouthpiece, the flow pattern

was observed to be as sketched in Figure .3.

0)

p. G-t

r-i

1» +-) ..-i ()

0 r-i Q.)

:> Q.)

§ r-i rx...

~ 0

..-i tl() Q.)

0:::

- -------

Intake velocity 0 fps

Flow pattern around 1.813" diam. mouthpiece 11 straight-out" (i Actual Size)

Figure 3

31

Flume velocity 1 fps


All dye placed in shaded area entered intake

Flow pattern around 1.813 11 diam. mouthpiece

(i Actual Size) facing upstream

Figure 4


Intake velocity ......._ ____ ___, 0 fps

..--... 0/~ Envelope of wake --

Flow pattern around 1.813 11 diam. mouthpiece facing

(i Actual Size) upstream

Figure 5

PLATE · X

Showing dye-filled tube used to trace flow pattern below surface.

PLATE Xl

3la

Illustrating flow pattern around 1.81311 diam. mouthpiece facing upstream, flume velocity 1 fps, intake velocity 0 fps.

32

(ii} Flow Patterns, 1.813" diam. Mouthpiece Facing Upstream.

At 2:30p.m., the small mouthpiece was placed in

position facing upstream, the flume velocity was established

at approximately· one foot per second and the intake velocity

at approximately five feet per second. Dye was released from

the glass tube in several trials and the flow pattern was

observed in each case. It was noticed that dye placed in an

area represented by the shaded area in the sketch of Figure 4

all entered the intake mouthpiece.

The velocity in the intake was then reduced until it

approached zero feet per second. Under this new condition the

zone of influence noted above seemed to disappear. While some

of the dye appeared to enter the intake, the pattern indicated

that there was considerable turbulence in the port itself and

the pattern shown in Figure 5 suggested itself.

Further experimenta were carried out using the same

mouthpiece in a partially submerged condition and under the

same conditions of velocity. Exactly the same pattern of flow

was noticed when magnesium silicate was spread on the surface

upstream from the mouthpiece with the exception that the

streamline outline of the turbulent area behind the mouthpiece

hugged the mouthpiece more closely when it was submerged then

it did at the surface. This is illustrated in the sketch of

Figure 6.

An attempt was made to observe the flow pattern by

releasing a quantity of magnesium silicate from a position below

33

the surface of the water but this method was not successful.

Moreover, because the capacity of the glass tube was small,

the period of time during which the dye indicated the flow

pattern was very short and it appeared almost impossible to

photograph the pattern during such a short period of time.

Since it had been observed that the flow pattern on the surface

was very similar to the flow pattern of the submerged mouthpiece,

photographs were taken of the surface pattern when magnesium

silicate was spread on the surface of the water upstream from

the mouthpiece. These photographs are shown in Plates Xl to

XVll incl. on Pages 31a, 35a, 36 and 37.

(iii) Flow Patterns, 5" diam. Mouthpiece Facing Upstream

The five inch diameter mouthpiece was then substituted

for the smaller one and placed in the upstream position with the

intake velocity at five feet per second and the flume velocity

remaining at one foot per second. Dye was used to determine the

flow pattern. It was observed that all of the dye placed in the

cross-hatched area shown in Figure 7, entered the intake. Dye

placed outside of the hatched area mostly bypassed the intake

although, in some cases, very small quantities appeared to enter.

The intake velocity was reduced to almost zero feet per

second. The flow pattern around the mouthpiece changed and it

was observed that both dye and talc which was also applied in

the same manner were carried right into the mouthpiece where

there appeared to be a great deal of turbulence. When the mouth-

34

piece was raised to a partially submerged position and

magnesium silicate was added to the surface of the water up

stream from the mouthpiece, the talc was seen to collect inside

the mouthpiece as shawn in Figure 8.

(iv) Flow Pattern, .5n diam. Mouthpiece Facing Downstream.

The five inch diameter mouthpiece was then turned to its

downstream position. With an intake velocity of five feet per

second and a flume velocity of approximately one foot per second,

it was observed that none of the dye or at least no observable

quantity of the dye which was added upstream from the intake was

carried into the zone of influence downstream from the intake,

Dye which was added within the zone of influence (aee Figure 9)

flowed upatream to the intake where it was diffused, some of it

entering the intake, but the greater part of it entered into

the turbulent portion of the zone of influence, along the edgea

of which aome of it was returned to the flume flow. The same

pattern was observed when the intake velocity was reduced to

zero, except that the upstream velocity towards the intake within

the influence zone appeared to be reduced and diffusion took

place more quickly. It appeared that there was greater turbulence

within the zone of influence when the intake velocity approached

zero.

With the intake in the partially submerged position, and

the intake velocity approaching zero feet per second, talc was

added to the surface upstream from the inta.ke mouthpiece.

Flume velocity 1 fps ,/ 35 Flume velocity 1 fps

velocity ~----L-,fp s ___&{ ~Intake velocity

"- 0 fps Pool '~. >!'

of taï"C\j

Enve lope \!:::( , of wake ..........,-.......J

Flow patterns around partially submerged 1.813 11 diam. mouthpiece traced by floating talc. (! Actual size)

Figure 6



All dye placed in shaded area entered intake

Flow pattern around 5" diam. mouthpiece facing upstream. (i Actual size)

Figure 7

C' 1 __) Intake velocity Intake velocity

}

Flumë velbcity 1 fps

Intake submerged pattern traced with dye

fps

~ (_ \ Flume velocity 1 fps

Intake partially submerged pattern traced using talc

Flow pattern around 5" diam. mouthpiece

Figure 8

0 fps

35a

PLATE Xll Illustrating flow pattern around 1.813" diam. mouthpiece facing upstream, Flume velocity 1 fps, intake velocity 0 fps.

Illustra tin facin

36

PLATE XlV Illustratin flow pattern with 1.813" diam. mouth upstream, f1ume ve1ocity 1 fps, intake ve1ocity

facin

37

Illustra tin downstream,

PLATE XVll attern around small mouth ieee facin down-

38

By far the greatest portion of the talc bypassed the

intake and the zone of influence behind it. However, the

small amount which was captured by the wake of the mouthpiece

remained within the zone of influence for a comparatively long

time (longer than one minute). Essentially the same pattern

was observed when the intake velocity was increased to five

feet per second, except that the flow towards the intake conduit

within the mouthpiece, was rouch better defined.

It was observed that the streamline along the contact edge

between the wake behind the mouthpiece and the flow in the

flume appeared to oscillate back and forth, that is to say that

a particle on the far side of the mouthpiece would flow upstream

along the stream line entering the cone, passing the center

thereof and then flow downstream on the near slde of the mouth

piece. This is illustrated in Figure 10.

(v) Flow Pattern, 1.81311 diam. Mouthpiece Facing Downstream.

The sma11 mouthpiece was then substituted for the

large facing in a downstream position and the flow pattern was

traced using dye for intake velocities of five feet per second

and approaching zero feet per second with the flume ve1ocity at

approximately one foot per second. The patterns observed were

similar to those observed with the five inch mouthpiece except

that the size of the zone of influence was reduced. These

patterns are illustrated in Figure 11. The smal1 mouthpiece

was then raised so that it faced downstream in a partia11y sub-

39

merged position and the flow pattern on the surface was

traced with floating talc added upstream. Once again, some

of the talc (a small percentage) was captured by the wake of

the mouthpiece. The captured talc entered the mouthpiece it

self where when the intake velocity was very low, it lay for

some two minutes until it was absorbed by the intake or carried

out of the wake and into the stream flow by the oscillatory

effect noted in the description of the observations concerning

the five inch mouthpiece. In the case where the intake velocity

was five feet per second, there was a very strong flow towards

the intake conduit and ali of the captured talc entered the

mouthpiece almost immediately.

B. Sedimentation Measurements

In order to determine the rate of settlement of the

turbidity in still water, a sample from the fiume was left

standing in the sample bottle in the turbidimeter and the

turbidity of the sample was read at five-minute intervals from

12:30 p.m. to 2:00 p.m. on September 25, 1961. The res~lts of

this series of measurements are given in Table 4.

c. Hldraulic Characteristics of 5" d am. Mouthpiece

It was observed on September 26th, 1961 during the

first experimenta with the 5 inch diameter mouthpiece that a

hydraulic jump was set up approximately ten inches downstream

40

from the face of the large mouthpiece, regardless of whether

the mouthpiece faced upstream or downstream. In arder to

minimize this jump the depth of flow was kept at the maximum

which was possible without causing overflow of the mixing

basin.

D. Quantitative Observations

The quantitative results of the experimenta follow in

Tables 5 to 31, Pages 43 to 69.

Flume

Intake velocity 0 5 fps

-Flow pattern around 5" diam. mouthpiece (submerged) facing downstream (i Actual Size)

Figure 9

Flume velocity 1 fps 2

Intake velocity 0 5 fps ----

..........._

41

Successive positions of a particle of talc captured by the 5" diam. intake partially submerged (i Actual Size)

Flume velocity 1 fps ~

Intake ~ 5 f~---./"

Dye placed in hatched area flowed into intake

Figure 10


Dye placed in hatched area flowed upstream into intake

Flow patterns around 1.81) 11 diam. mouthpiece facing downstream (submerged) (! Actua1 Size)

Figure 11

42

TABLE 4

Variation of turbiditz with time of undisturbed samp1e in turbidimeter, September 2$th, 1961.

Ti me Turbidity Reduction

12:2.5 p.m. 82.5 ppm

tt 75 ppm

12:30 750 75

12:3.5 tt 67.5 75

12:40 tt 600

12:4.5 11 50

.550 25

12:50 11 525 13

12:5.5 tt 512

1:00 tt 25

487

1:0.5 " 37

4.50 13

1:10 tt 437 12

1:1.5 tt 425 13

1:20 " 412 12

1:25 tt 400

1:30 tt 387 13

12 1:3.5 tt 37.5

0 1:40 tt 37.5

12 1:4.5 tt 363

0 1:.50 tt 363

1:.55 tt 350 13

0 2:00 tt 350

43

TABLE 5

OBSERVATIONS- September 26th, 1961.

10:2.5 a.m. F1ume Turbidity - B25 ppm.

1st. Run F1ume 2 fps

Intake 1 fps .5" mouthpiece facing upstream.

Time F1ume Intake Reduction % Remarks Turbidity Turbidity ppm ppm

10:2B a.m. B10 B10 0 0 F1ume 1st.

10:41 n B5o 790 +60 +7.4 Intake 1st.

10:4.5 " Boo B10 -10 -1.2 F1ume lst.

10:49 n B40 Boo +40 +4.8 Intake 1st.

10:.54 " Boo BlO -10 -1.2 F1ume 1st.

10:.57 tt Boo Boo 0 0 Intake 1st.

11:00 tt Boo 790 +10 +1.2 F1ume 1st.

11:0.5 tt B25 77.5 +50 +6.1 Intake 1st.

11:07 " Boo Boo 0 0 F1ume 1st.

11:10 " B25 92.5 0 0 Intake 1st.

Total +17.1

Mean = +1.7%

44

TABLE 6


2nd. Run Flume 2 fps 5" mouthpiece facing downstream

Intake 1 fps

Ti me Flume Intake Reduction Remarks Turbidity Turbidity ppm ppm

11:35 a.m. 780 780 0 0

11:39 n 800 775 +25 +3.2

11:41 tt 775 790 -15 -1.9

11:44 tt 800 825 -25 -3.2

11:47 tt 775 775 0 0

11:52 n 800 825 -25 -3.2

11:.5.5 " 800 810 -10 -1.2

11:.50 tt Boo 775 +25 +3.2

12:00 noon 800 Boo 0 0

12.03 p.m. Boo 790 +10 +1.2

Total +1.9

Mean = +0.2%

4.5

TABLE 7


lst. Run F1ume 3 fps Small Mouthpiece facing downstream

Intake 1 fps

Ti me F1ume Mean Intake Reduction % Remarks Turbidity Turbidity ppm ppm

2:10 p.m. 82.5

2:12 tt 82.5 825 82.5 -2:13 tt 825

2:18 " 880 Zero

2:20 n 88.5 885 900 -15 reading

-1.7 on meter re-set

2:22 n 885

2:25 n 885 887 885 +2 +Oo2

2:27 ft 890

2:29 n 890 890 890 -2:31 " 890

2:35 " 900 887 885 +2 +0.2

2:37 n 875 Total -1.3

Mean • -0.3%

46

TABLE 8


2nd. Run

Time

2:48 p.m.

2:51 n

2:54 n

2:55 n

3:00 n

3:03 n

3:06 " 3:08 n

3:13 n

3:15 n

Flume 3 fps Small Mouthpiece facing downstream

Intake i fps

Flume Mean Intake Reduction % Remarks Turbidity Turbidity ppm ppm

890 895 845 +50 +5.6

900

890 882 850 +32 +3.6

875

885 885 865 +20 +2.3

885

890 887 865 +22 +2.5

885

885 887 860 +27 +3.1

890

Total +17.1

Mean = ... 3.7%

47

TABLE 9


)rd. Run

Time

3:.52 p.m.

3:.54 tt

3:.5.5 tt

3:.56 tt

3:.59 tt

4:01 tt

4:03 " 4:0.5 tt

4:09 tt

4:11 tt

F1ume 3 fps Sma11 straight Mouthpiece

Intake 0 • .5 fps


875 882 870 +12 +1.4

890

900 892

88.5 87.5 +17 +1.9

900 887 87.5 +12 +1.4

87.5

875 875 875

875

890 89.5 87.5 +20 +2.2

900

Total +6.9

Mean = +1.4%

48

TABLE 10

OBSERVATIONS- October 18th, 1961.

Trial Run

Time

9:32 p.m.

9:35 " 9:37 " 9:40 tt

9:42 " 9:45 " 9:47 n

9:49 n

9:52 " 9:54 n

9:56 n

9:59 "

Flume Vel. 2 fps Small Mouthpiece facing downstream.

Intake Vel. 2 fps


685 660 665 -5 -o.8

635 637 620 +17 +2.7

640 620 615 +5 +0.8

600 600 650 -50 -7.7

600 600 575 +25 +4.3

600 600 600 -600 587 575 +12 +2.1

575 575 575 -

575 575 575 -

575 565 560 +5 +0.9

555 552 560 -8 -1.4

550 Total +0.9

Mean = +0.08

TABLE 11

OBSERVATIONS- October 23rd, 1961.

lst. Run F1ume Ve1. 2 fps Sma11 Mouthpiece facing downstream.

Intake Ve1. 1 fps

49

Ti me Flume Mean Intake Reduction % Remarks Turbidity Turbidity ppm ppm

9:25 a.m. 920 910 870 +40 +4.6

9:28 " 900 910 925 -15 -1.6

9:30 tt 920 900 875 +25 +2.8

9:34 tt 880 877 840 +37 +4.2

9:36 tt 875 867 880 -13 -1.5

9:39 tt 860 845 870 -25 -3.0

9:43 tt 830 840 875 -35 -4.1

9:45 ft 850 850 850 ...

9:48 tt 850

825 837 875 -38 -4.5

9:50 tt

827 840 -13 -1.6 9:53 " 830

Total -4.9

Mean = -o.5%

50

TABLE 12

OBSERVATIONS- Ootober 23rd, 1961.

2nd. Run Flume Vel. 2.0 fps Small Mouthpieoe faoing downstream.

Intake Vel. O.$ fps

Time Flume Mean Intake Reduction ~ Remarks Turbidity Turbidity ppm ppm

10~15 a.m. 780 775 790 ....15 -1.9

10:17 tt 770 775 760 +15 +1.9

10:19 tt 780 770 770 ...

10:21 tt 760 767 770 -3 -0.4

10:23 n 775 767 770 -3 -o.4

10:26 lt 760 767 765 +2 +0.3

10:28 n 775 770 780 -10 -1.3

10:31 " 765 757 750 +7 +0.9

10:33 tt 750 750 770 -20 -2.6

10:36 " 750 750 770 -20 -2.6

Total -6.1

Mean= -o.6%

51

TABLE 13


3rd. Run Flume Ve1. 2.0 fps Sma11 Mouthpiece facing downstream.

Intake Ve1. 4.0 fps

'l'ime Flume Mean Intake Reduction '/, Remarks Turbidity Turbidity ppm ppm

10:47 a.m. 725 737 710 +27 +3.7

10:49 lt 750 740 725 +15 +2.0

10:51 tt 730 740 725 +15 +2.0

10:54 tt 750 737 725 +12 +1.6

10:56 tt 725 725 725 - 5 -0.7

10:59 n 725 730 725 + 5 +0.7

11:01 n 735 730 725 + 5 +0.7

11:03 " 725 725 735 -10 -1.4

11:06 n 725 730 725 + 5 +0.7

11:08 tt 735 730 725 + 5 +0.7

11:09 lt 725

Total +10.0

Mean= +l.O%

TABLE 14

OBSERVATIONS• October 23rd, 1961.

4th. Run Flume Vel. 2.0 fps Smal1 Mouthpiece facing upstream.

Intake Vel. 4.0 fps

52

Time F1ume Mean Intake Reduction % Remarks Turbidity Turbidity ppm ppm

11:30 a.m. 675 675 690 -1.5 -2.2

11:31 tt 675 .582 680 + 2 +0.3

11:33 tt 690 682 67.5 + 7 +1.0

11:3.5 tt 67.5 687 67.5 +12 +1.7

11:38 tt 700 68.5 67.5 +10 +1 • .5

11:39 tt 670 670 67.5 ... 5 -0.7

11:42 tt 670 670 680 -10 -1.5

11:44 tt 670 67.5 690 -1.5 -2.2

11:47 If 680 67.5 695 ·20 -3.0

11:50 " 61].0 677 67.5 + 2 +0.3

11:51 tt 685

Total -4.8

Mean = -o.5%

53

TABLE 1,5


$th. Run

Time

3:15 p.m.

3:17 tt

3:19 tt

3:21 tt

3:25 rt

3:27 n

3:28 tt

3:31 tt

3:32 tt

3:35 tt

3:36 tt

Flume Vel. 2.0 fps. Sma11 Mouthpiece facing upstream.

Intake Vel. 2.0 fps.

F1ume Mean Intake Reduction % Remarks Turb1d1ty Turbidity ppm ppm

625 632 635 -3 -o.5

640 640 660 -20 -3.1

640 645 640 + 5 +0.8

650

635 642 640 + 2 -0.3

637 640 - 3 -o.5 640

638 640 ... 2 -0.3 635

632 6$0 -18 -2.7 625

630 640 -10 -1.6 635

635 635

640 - s -o.8

640 638 635 + 3 +0 • .5

Total -7.9

Mean = · -o.8%

54

TABLE 16


6th. Run

Time

F1ume Ve1. 2.0 fps Sma11 mouthpiece facing upstream.

Intake Ve1. 1.0 fps

F1ume Mean Intake Reduction Re marks Turbidity F1ume Turbidity in ppm Turb. ppm Turbidity

ppm ppm

3:50 p.m. 565 563 575 -12 -2.1

3:52 11 560 563 580 -17 -3.0

3:55 tt 565 567 570 -3 -o.5

3:57 tt 570 565 565

3:59 ft 560 563 580 -17 -3.0

4:01 ft 565 570 565 +5 +0.9

4:03 11 575 573 580 -7 -1.2

4:06 " 570 575 570 +5 +0.9

4:08 n 580 575 565 +10 +1.7

4:09 lt 570 575 570 +5 +Oo9

4:12 n 580

Total -5.4

Mean = -o.5

55

TABLE 17

OBSERVATIONS- October 23rd, 1961

7th Run. F1ume Vel. 2.0 fps Sma11 mouthpiece facing upstream

Intake Ve1. 0.5 fps

Ti me

4:20 p.m.

4:23 lt

4:25 " 4:27 lt

4:29 tt

4:31 n

4:33 " 4:35 tt

4:37 tt

4:39 n

4:42 rt

F1ume Turbldity pp Ill

560

565

570

570

565

570

580

580

570

570

570

Mean Flume Turb. ppm

563

568

570

567

567

575

580

575

570

570

Intake Turbidity ppm

570

560

560

560

570

570

565

580 580

580

Total

Reduction in Turb. ppm

... 7

+ 8

+10

+ 7

- 3

+ 5

+15

- 5 -10

-10

Mean=

% Remarks

-1.2

+1.4

+1.8

+1.2

-o.5

+0.9

+2.6

-0.9

-1.8

-1.8

+1.7

+0.2

56

TABLE 18

OBSERVATIONS- October 24th 1 1961.

1st.Run F1ume Ve1. 2 fps Sma11 mouthpiece straight-out

Intake Ve1. 4 fps

Ti me

10:32 a.m.

10:35 tt

10:38 tt

10:40 tl

10:42 tt

10:44 " 10:46 rt

10:48 rt

10:50 rt

10:52 " 10:54 "

F1ume Turbidity ppm

690

530

555 540

535

575 560

560

540

570

550

Mean Flume Turb. ppm

610

542

547

537

555 565

558

550

555 560

Intake Reduction Rems.rks Turbidity in Turb. ppm ppm

) These read-565 +45 +7.4 ) ings were

) probably

570 -28 -5.2 taken be-fore flume

540 + 7 +1.3 conditions had become

540 - 3 -0.5 stable.

565 -10 -1.8

560 + 5 +0.9

565 - 7 -1.3

560 -10 -1.8

565 -10 -1.8

550 +10 +1.8

Total -1.0

Mean = -0.1

TABLE 19


57

2nd Run. Flume Vel. 2 fps Small mouthpiece straight-out

Intake Vel. 2 fps

Time

11:14 a.m.

11:16 n

11:18 lt

11:21 If

11:23 Il

11:25 ft

11:27 tt

11:29 tt

11:31 ft

11:33 n

11:34 11

F1ume Mean Turbidity Flume ppm Turb.

ppm

720

760 740

760 760

725 742

712 700

710 720

715 710

720 7.30

737 745

735 725

737 750

Intake Reduction % Remarks Turbidity in Turb. ppm ppm

775 -.35 -4.7

740 +20 +2.6

775 -.3.3 -4.4

7.30 -18 -2.5

740 -30 -4.2

715 -7.30 -10 -1.4

710 +27 +3.6

750 -15 -2.0

725 +12 +1.6

Total -11.5

Mean = -1.2

58

TABLE 20

OBSERVATIONS• October 24th, 1961.

3rd.Run Fiume Vel. 2.0 fps Sma11 mouthpiece straight-out

Intake Vel. 1.0 fps

Ti me Fiume l-1ean Intake Reduction % Remarks Turbidity Flume Turbidity in Turb. ppm Turb. ppm ppm

ppm

11:45 a.m. 700 702 720 -18 -2.5

11:47 " 705 700 715 -15 -2.1

11:48 tt 690 682 700 -18 -2.6

11:50 tt 675 677 715 -38 -5.6

11:52 tt 680 672 700 -10 -1.5

11:55 tt 675 670 680 -10 -1.5

11:57 tt 675 675 675

11:59 n 675 675 675 -12.01 p.m. 675 670 700 -30 -4.5.

12.03 tt 665 670 660 +10 +1.5

12.05 tt 675

Total -21.4

Mean= ... 2.1

59

TABLE 21


4th Run. Flume Vel. 2.0 fps Sma11 ro.outhpiece straight-out

Intake Ve1. 0.5 fps

Ti me

1:12 p.m.

1:14 tt

1:16 lt

1:18 11

1:20 n

1:22 tt

1:24 tt

1:26 n

1:28 tt

1:29 n

1:31 tt

Flume Turbidity ppm

600

600

600

600

600

600

600

600

610

600

600

Mean Flume Intake Turbidity Turbidity ppm ppm

600 600

600 595

600 625

600 625

600 610

600 600

600 610

605 600

605 595

600 600

Reduction % in Turb. pp m.

... + 5 +0.8

-25 -4.1

-25 -4.1

-10 -1.6

-10 -1.6

+ 5 +0.8

+10 +1.6

Total -8.2

J!.1ean = -o.e

TABLE 22


60

1st. Run F1ume Ve1. 2 fps Large ( 5n diam.) mouthpiece facing upstream.

Ti me

10:1.5

10:17

10:19

10:21

10:23

10:25

10:27

10:29

10:31

10:33

10:35

Intake Ve1. 4 fps

F1ume Turbidity ppm

a.m. 88.5

n 890 tt 87.5 tt 895

tt 845 n 835 tt 830

tt 835 tt 800

n 815

n 790

Mean F1ume Turb. ppm

887

882

885

870

840

832

832

817

807

802

Intake Turbidity ppm

900

890

875

900

840

84.5

8.50

82.5

82.5

Boo

Reduction in Turb.

ppm

- 3

- 8

+10

-30

-13

-18

- 8

-18

+ 2

Total

Mean =

% Remarks

-0.3

-0.9

+1.1

-3.5

-1.5

-2.1

-0.9

-2.1

+0.3

-9.9

-1.0

2nd. Run

Ti me

TABLE 23

OBSERVATIONS • October 25th, 1961

F1ume Ve1. 2.0 fps Large mouthpiece facing upstream

Intake Ve1. 2 fps

61

F1ume Mean Turbidi ty F1ume ppm Turb.

Intake Turb. ppm

Reduction % Remarks in Turb.

ppm ppm

10:43 p.m. 740

10:45 tt 735 725 +10

730

10:47 rt 710 720 755 -35

10:49 lt 720 730 -10

730

10:51 " 720 725 720 + 5

10:53 tt 680 700 720 -20

10:54 tt 715 697 730 -33

11:02 n 670 692 755 -63

11:04 tt 660 665 675 -10

11:06 lt 650 655 680 -25

11:08 tt 650 650 670 -20

Total

Mean =

* this reading not considered in total and mean.

+1.3

-4.8

-1.3

+0.7

-2.8

-4.7

-9.1 * Note long interval

-1.5 between

-3.8 readings.

... 3.0

-19.9

-2.2

TABLE 24

OBSERVATIONS - October 25th, 1961.

62

3rd. Run. Flume Vel. 2.0 fps Large mouthpiece facing upstream

Time

11:14 a.m.

11:16 lt

11:19 tt

11:21 n

11:23 ft

11:25 tt

11:27 lt

11:29 n

11:30 tt

11:31 ft

11:33 lt

Intake Vel. 1.0 fps

F1ume Turb. ppm

655

630

650

650

640

640

630

630

625

635

600

Mean Fiume Turb. ppm

642

640

650

645

640

635

630

627

630

617

Inta.ke Turb. ppm

640

650

660

650

640

640

625

6~5

630

625


+ 2

-10

-10

- 5

- 5 + 5

+ 2

... 8

Total

JVlean =

Rema.rks

+0.3

-1.6

-1.6

-o.a

-o.a +0.8

+0.3

-1.3

-4.7

... o.4

TABLE 25


63

4th Run. F1ume Ve1. 2.0 fps

o.5 fps

Large mouthpiece facing upstream

Time

11:46

11:48

11:51

11:53

11:55

11:57

11:59

Intake Ve1.

F1ume Mean Turb. F1ume ppm Turb.

ppm

a.m. 605 615

t1 625 620

tt 615 615

tt 615 620

lt 625 617

ft 610 610

tt 610 612

12:01 p.m. 615 617

12:03 11 620 622

12:05 tt 625 605

12:07 tt 585

Intake Turb. ppm

770

600

610

600

600

595

595

590

575

590

Reduction % in Turb.

ppm

-155-l}

+20 +3.2

+ 5 +0.8

+20 +3.2

+17 +2.7

+15 +2.4

+17 +2.7

+27 +4.3

+47 +7.5

+15 +2.4

Total +29.2

.lV1ean = +3.2

* This reading not considered in total and mean.

Remarks

TABLE 26

OBSERVATIONS- October 25th, 1961

5th.Run. Flume Vel. 2.0 fps Large mouthpiece facing downstream

Intake Ve1. 4.0 fps

64

Time Flume Turb. ppm

Melin Flume Turb.

Intake Turb.

ppm.

Reduction in Turb.

ppm

% Remarks

ppm

12:18 p.m. 570 575 -o.5 572 .. 3

12:21 tt 575 567 575 - 8 -1.4

12:23 tt 560 565 570 - 5 -0.9

12:24 ft 570 572 575 - 3 -o.5

12:26 ft 575 567 560 + 7 +1.3

12:28 n 560 560 575 -15 -2.6

12:29 tt 560 560 560

12:31 ft 560 555 570 -15 -2.6

12:33 tt 550 555 570 -15 -2.6

12:35 ft 560 555 570 -15 -2.6

12:37 lt 550

Total -12.4

Mean = -1.2

TABLE 27


6th. Run. F1ume Ve1. 2.0 fps Large mouthpiece facing downstream

Intake Ve1. 2.0 fps

65

Ti me F1ume Turb. ppm

Me sn F1ume Turb.

Intake Turb. ppm


ppm

Remarks

pp m.

12:45 p.m. 875 800 580

12:47 725 725 615

12:49 725 700 650

12:52 675 657 625

12:54 640

12:56 650 645 645

640 625 12:58 630

640 635 12:59 650

640 635 1:01 630

635 650 1:02 640

630 645

Total

Nean =

* These readings not included in Total or Mean.

+220 ~(

+110 * + 50 * + 32 *

...

+ 15 +2.3

+ 5 +0.8

+ 5 +0.8

-15 -2.3

-15 -2.3

-0.7

-1.0

TABLE 28


7th.Rnn. Fiume Vel. 2.0 fps Large mouthpiece facing dcwnstream

Intake Vel. 1.0 fps

66

Ti me Flume Turb. pp m.

Mean Intake Fiume Turb. Turb. ppm.


Remarks

ppm ppm.

1:12 p.m. 590 587 620 -37 -6.3

1:14 585 587 610 -27 -4.6

1:15 590 590 595 - 5 -0.9

1:17 590 595 610 -15 -2.5

1:19 600 600 610 -10 -1.6

1:20 600 600 615 -15 -2.5

1:22 600 600 600

1:24 600 607 625 -18 -2.9

1:26 615 617 600 +17 +2.7

1:27 620 615 600 +15 +2.4

1:29 610

Total -16.2

Mean = -1.6

TABLE 29


67

8th. Run. F1ume Ve1. 2.0 fps Large mouthpiece facing dol-rnstresm

Intake Ve1. 0.5 fps

Time F1ume }1ean Intake Reduction % Remarsk Turb. F1ume Turb. in Turb. ppm Turb. ppm ppm

ppm

1:37 p.m. 600 595 625 -30 -.5.0

1:39 .590 590 580 +10 +1.7

1:41 .590 595 600 - 5 -o.8

1:43 600 600 600 .. -1:45 600 600 600 -

1:47 600 58.5 590 - 5 -0.9

1:48 570 580 595 -15 -2.6

1:50 590 .590 .590

1:.52 590 590 .590

1:.54 590 .582 .580 + 2 +0.3

1:56 575

Total - 7.3

Mean = - 0.7

TABLE 30


lst.Run. Flume Vel. 2.0 fps Large mouthpiece facing upstream

Intake Ve1. 0.75 fps

Time F1ume 1-Iean Intake Reduction Remarks Turb. F1ume Turb. in Turb. ppm Turb. ppm ppm

ppm

12:54 p.m. 990 985 950 +35 +3.5

12:55 980 970 970

12:57 960 952 955 ... 3 -0.3

12:59 945 950 955 - 5 -0.5

laOO 955 940 950 -10 -1.1

1:01 925 935 860 +75 +8.5

1:03 945 947 905 +42 +4.4

1:04 950 935 875 +70 +7.5

1:06 92~ 922 900 +22 +2.4

1:08 925 900 905 - 5 -0.5

1:12 875

Total +23.4

Mean= + 2.3

68

TABLE ,21

OBSERVATIONS - October 26th, 1961

2nd.Run F1ume Ve1. 2.0 fps Large mouthpiece facing upstream

Intake Ve1. 1.5 fps

69

Ti me Flume Turb. pprn.

Mean F1umo Turb.

Intake Turb. ppm


% Remarks

ppm

1:30 p.m. B20 B20 B40 -20 ... 2.4

1:32 B20 B17 B40 -23 -2.8

1:33 B15 Bl7 B25 - B -1.0

1:3.5 B20 Bl5 B15 -

1:37 BlO Boo B25 -25 -3.1

1:39 790 792 B35 -43 -5.4

1:41 795 787 B20 -33 -4.2

1:43 780 7B5 Boo -15 -1.9

1:45 790 787 790 - 3 -0.4

1:46 785 782 795 -13 -1.6

1:48 780

Total -22.8

Mean = -2.3

CHAPTER Vl

DISCUSSION OF RESULTS

A. Apparatus and Methods.

10

Before proceeding with an analysis of the resulta obtained

in this experiment, it would be in order to carefully examine

the apparatus and methods used.

In actual practice a crib is generally built around the

intake mouthpiece to prevent its being damaged by partially sub

merged or floating debris. If the crib is not used, the mouth

piece may be protected by piles driven into the riverbed, up

stream from the mouthpiece. This crib or protective piling

might have an effect upon the hydraulic characteristics of the

intake. It may be suggested for an important intake, that

model studies using a properly scaled model of the intak~ be

carried out.

The fundamental part of the model used in this experiment

is the intake itself. The flume is only required to establish

hydraulic similarity between the intake mouthpiece of the model

and that of the prototype. Since the intake is below the sur

face thus having no wave-making quality, and since it occupies

a very small fraction of the cross-section of the stream and

thus has low-pressure resistance, Froude 1 s number may be

neglected. Friction forces predominate in determining the

characteristics of flow and therefore the Reynolds number should

be the same for both modal and prototype. This is confirmed by

71

Binder who states "For ••• f1ow in which bodies are fu11y

immersed in a f1uid {as vehic1es, submarines, aircraft and

structures) in such a fashion that free surfaces do not enter

into consideration and gravity forces are found by buoyant

forces, the inertia and viscous forces are the only ones which

need to be taken into account."5 Reynolds number is a dimen-

sionless number which expresses the ratio of

Where

The ratio

Inertia force Viscous force R = ;0 VL

--;;:-R - Reynolds number

L - any characteristic length

V - relative fluid velocity

?

?;a =

density of fluid

viscosity of fluid

1 ----fA- 7

Where: ~ = The kinematic viscosity

For water at 50°F. y = 1.410 x 10 -5

Therefore, assuming that the prototype has a diameter of

two feet which may be considered as representative of small in-

takes in rivers and that the average velocity in the stream is

2.5 ft. per second, the Reynolds number of the prototype:

R = V L -y = 2. x 2.0 c'

1. 10 x 10 -:;; = 365,000

5. "Fluid Mecha.nics 11 by R.C.Binder, Ph.D, Second Edition, Published by Prentice-Hall Inc., 1949 Page 8o.

72

For the model inta.ke used by R.J .Lindsay:

For the five inch diameter mouthpiece prepared by this observer:

R = 2.5 x 0.417 5 1.410 x 10 - = 74,000

Since all of these R values are we11 in excess of 2,000 and

thus indicate the turbulent range, it has been assumed that the

relationship between the models and the prototype is

sufficiently similar and special modifications to the model are

not necessary.

It will be noted that in the above calculations of the value

of Reynolds number for the models a flume velocity of 2.5 ft.

per second has been assumed. It was decided to use this vel-

ocity which is the same as the velocity assumed in the prototype

in order that the same size of particle may be used in the

model as it is assumed exista in the prototype. Hunsaker states:

"The settling of •••• sediment through water is controlled by

frictional forces because of the low ratio of mass to surface of

the individual particles".6 For a particle size of 149 microns

which is assumed to be average for the magnesium silicate used

in the experiment, Steel states that the settling velocity would

be about 15 millimeters per second or 0.049 ft. per second.?

6. "Engineering Applications of Fluid Mechanics" by J.C.Hunsaker and B.G.Rightmire first edition, McGraw-Hill Book Co.Inc., 1947, page 116.

7. "water Supply & Sewerage" by Steel,McGraw-Hill Book Co., third edition.

Thus, for the particle size in question, Reynolds number

R = 0.049 x 0.490 x 10 -3 1.410 x 10 -5 = 1•7

73

Since the value of Reynolds number is so low, it is

essential that the same value be kept for both model and pro-

totype. The simplest way to arrange this was to use the same

particle size in the model as it had been assumed to exist in

the prototype. This decision having been made, it followed

that it would be desirable to maintain the same flow velocity

in the flume as in the prototype in order that the ratio of

settling velocity to flow velocity would be the sam~ for both

the model and the prototype.

On page 39 it was noted herein that a hydraulic jump was

created some 10 inches downstream from the face of the five

inch diameter mouthpiece. The appearance of this jump would

indicate that this mouthpiece occupies too large a fraction of

the cross-section of the stream and thus has considerable

pressure resistance. The flow pattern around the model mouth

piece would therefore be expected to be somewhat different from

that around a prototype mouthpiece having the same shape but

occupying a relatively small fraction of the cross-sectional

area of the stream in which it is located. The effect which this

dissimilarity would have on the resulta of this experiment is

difficult to estimate.

In the conclusions of his paper, Vito A. Vanoni reports a

variation in the relative turbidity of sediment flowing in the

74

8 stream with depth from the surface of the stream. In these

experimenta the center line of the intake is fixed at a con

stant depth below the surface of the stream, and samples which

were taken through the intake therefore represent sorne function

of the apparent turbidity at that depth. On the other hand,

samples taken at the end of the flume to indicate the flume

turbidity were integrated samples since some water from all

depths was collected in the sampling peil. In the case of the

five-inch diameter mouthpiece, the intake sample would be an

integrated sample taken from 50% of the depth of the flow.

Since the variation in turbidity with depth depends upon the

variation in particle size, it would be necessary to carry out

additional comprehensive measurements for this particular flume

and particle aize in order to chart the actual variations. Once

aga in, it is difficult to determine the effect of this

phenomenon on the resulta of this experiment.

B. Probable Errors and Summarz of Resulta.

~e turbidimeter was read directly to 25 ppm although the

meter scale was graduated so that it could be interpreted to

the nearest 5 ppm. (see meter scale on Plate Vl). Since the tur

bidity readings during the experiment varied from approximately

550 ppm to 900 ppm, it therefore follows that the experimental

error in reading the meter would be less than ± 1% for a single

reading. The readings obtained actually showed a much greater

8. Vanoni, op.cit., page 2

75

variation which, it is assumed, were caused by variations in

turbidity with time at the sampling points. In order to pro-

perly assess the effect of these variations on the probable

error, the standard deviation was calculated for each series of

readings. The sample calculations in Table 31 illustrate the

method which was used to calculate the standard deviations.

After the calculation of the standard deviations, the

limits of uncertainty were calculated for each series of readings

following the method outlined in the A.S.T.M. Manual on Quality

Control of Materials, Part 11.9 The following table of

factors for calculating 95% confidence limita for averages is a

portion of a table presented in the A.S.T.M. Manual.

TABLE 30

Number of Observations in Sample, n

Confidence Limits

Confidence Limits, +

95 per cent Confidence Limits (P = 0.95)

Value of a

4 .............•.........•.. 1.837

1.388

1.150

0.999

o.B94

0.815

0.754

5 ••••.••.•..••••••••..••••

6 •••••••••••••••••••••••••

7 • . . • • . . . . . • • . . . . . . • . . . • • •

8 . . . . . . . . . . . . . . . . . . . . . . . . . 9 •••••••••••••••••••••••••

10 ••••••••••••••••••.••••••

9. ASTM Manual on Quality Control of Materials, American Society for Tes ting and Materials, Janue_ry, 1951, page 43.

76

Tables 32 to 36, inclusive, list the obaerved means for

each set of observations and the confidence limita calculated

for these observations. In order that the pattern of the re

sulta may be more readily discernible, the resulta for each of

these tables have been aummarized ln the graphs shown in

Figures 12 to 16 inclusive.

c. Discussion of ~uantitative Resulta.

Examination of the tables and graphs reveals that the mean

variation in turbidity in the intake sample from the turbidity

in the flume over the whole range of velocity studied for the

various intake positions is lesa than 1% for all positions. Ex

amination of the graphs for the five-inch diameter mouthpiece

facing downstream and the small diameter mouthpiece facing up

stream, does not reveal any significant trend towards reduction

of turbidity. On the other hand examination of the other

graphs indicates that we can atate with 95% confidence that a

reduction in turbidity will be obtained if the ratio of intake

velocity to flume velocity is less than 0.37 for a five-inch

diameter mouthpiece facing upstream,less than 0.18 for the small

diameter mouthpiece facing downstream, and less than 0.17 for

the small diameter mouthpiece in the straight-out position.

Furthermore, the rate of reduction of turbidity for values of

this ra.tio below those listed increased markedly with decrease

in the ratio.

F1ume Turb. ppm

572

567

565

572

567

560

560

555

555

555

!"lean

TABLE 31

Samp1e Ca1cu1ation of Standard Deviation.

A -555

17

12

10

17

12

5

5

A2

289

144

100

289

144

25

25

1016 101.6 60.8 4o.8

= 6.4 ppm

% Reduction, R

-cl.5

-1.4

-0.9

-0.5

+1.3

-2.6

-2.6

-2.6

-2.6

77

R2

0.25

1.96

o.81

0.25

1.69

6.76

6.76

6.76

6.76

TABLE 32

SUMMARY OF RESULTS

.5" Diam.. Mouthpiece facing upstream.:

F1um.e Intake Ratio 1 Ve1.fps Ve1. fps F

(F) (1}

2.0 4.0 2.0

2.0 1 • .5 0.75

2.0 0.7.5 0.38

2.0 o • .so 0.2.5

2.0 2.0 1.0

2.0 1.0 o.5

F1ume Turb. pp m.

84.5

800

944

614

696

634

Mean Reduct. tr in Turb. %

-0.99 1.28

-2.28 1.46

+2.34 3.33

+3.2.5 1.73

-2.21 1.54

-0.47 o.8

95% Confidence Limits

-1.97% -0.01

-3.38 -1.18%

-0.20% +4.84

+1.81% +4.66

-1.0.5% -3.37

+0.13% -1.07

Average reduction in turbidity = 1.81/6 = +0.30

No. of Samp1es

10

10

10

9

10

10

TABLE 33

SUMMARY OF RESULTS

5" Diam. Mouthpiece facing downstream:

F1ume Ve1.fps

(F)

2.0

2.0

2.0

2.0

2.0

Intake Ve1.fps

( 1)

1.0

4.0

2.0

1.0

o.5

Ratio 1 F

o.5

2.0

1.0

o.5

0.25

F1ume Mean Turb. Reduct. ppm in Turb.

%

793 -0.19

563 -1.24

671 -0.07

599 -1.62

591 -0.73

95% (J Confi

dence Limita

2.17 +1.~5 ' -1. 3 lb

1.25 -0.30 % -2.18

1.31 +1. 75 ::' -1.89 Jo

2.68 +0.41 % -3.65

1.76 +0.60 % -2.10 "

Average reduction in turbidity = 3.85/5 = -0.77

79

No. of Samp1es

10

10

5

10

10

TABLE 34

SUMMARY OF RESULTS

Sma11 mouthpiece facing upstream:

F1ume Intake Ve1.fps Ve1.fps

(F) ( 1)

2.0 4.0

2.0 2.0

2.0 1.0

2.0 o.5

Ratio 1 F

2.0

1.0

o.5

0.25

F1ume Turb. ppm

678

637

569

571

Mean Reduct. in Turb. %

-0.48

-0.79

-0.54

+0.17

Average reduction in turbidity =

() 95% Confidence Limits

1.59 +0.72% -1.68 °

1.25 +0.16% -1.74 °

1.57 +0. 78<11

-1. 72/o

1.51 +1.31% -0.97

80

No. of Samp1es

10

10

10

10

TABLE 35

SUMMARY OF RESULTS

Small mouthpiece facing downstream:

Plume Intake Ratio 1 Plume Vel.fps Vel. fps F Turb.

(F) (1) ppm

3.0 o.5 0.16 887

2.0 2.0 1.0 597

2.0 1.0 o.5o 866

2.0 o.5 0.25 766

2.0 4.0 2.0 732

Mean Reduct. in Turb.

%

+3.42

+0.09

-0.47

-0.61

+1.0

81

CJ 95% No. of

1.93

2.91

3.12

1.42

1.37

Confidence Samples Limita

+6.10 +0.74 % 5

+2.29 -2.11 % 10

+1.88 -2.82% 10

+0.46 -1.68 10

+2.03 -0.03 10

Average reduction in Turbidity = +3.43/5 = +0.68

TABLE 36

S~1ARY OF RESULTS

Sma11 mouthpiece straight-out:

F1ume Intake Ve1.fns Ve1. fps

(F)~ (1)

3.0 o.5

2.0 4.0

2.0 2.0

2.0 1.0

2.0 o.5

Ratio 1 F1ume F Turb.

ppm

0.16 886

2.0 551

1.0 731

o.5o 679

0.25 601

Mean t:r 95% Reduct. Conti-in Turb. denee

% Limits

+1.38 0.75 +2.42 +0.34%

-0.93 2.02 +0.71 -2.57%

-1.14 2.76 +0.94 -3.221&

-2.14 2.11 -0.54 -3.74%

-0.82 1.89 +0.60 -2.2~

Average Reduction in Turbidity = -3.65/5 = -0.73

82

No. of Samp1es

5

9

10

10

10

•

•

•

83

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+--+-++-+--- -f'*- ;::---6..--V---tf, ~- -- -~ +--- -+-1- ---, r-~. i- - ~ +--+-+--+--'---',1--t--, +--+1-+-t-t-' +-:--t-~1 ~-t-+--t----1FH-~-+-+-+-+--+---+--+--+--+~--~-....... r=t- -Lowe r- ~% Co-n-f-id m-e-e--+--lrlm!-u ... v +--r--+--;-,--r---7---i!--r--1

l--++-+-+-t---"--1 -+-no\, 5_._ 1-f-6-+-+-----;-~ ., ~ -- ' é_

1 1 1 1 1 1 1

1 1

00

• ·t ___,. -H-r+ t ~

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1 ' :" 1 : 1 : 1 _l

1

i+ +H-~ +- j- -+-+-ri-+r t-1

-r~

+ t-,

·~ ' 1

'r 1 1

1 1 i 1 1 , 1 1 1

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' --r-'-4 i L LI 1 -+----+-' ' 1 1

1 ~~ 1 1 1 i 1 ' 1 i 1 1 i 1

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r' ' ~~-1

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ITTh ()- V / / // // _//_/_//// / R 'A T it:RkA V P.

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1 1 1 i : 1 i : 1 : @ 1 1-r- 1 1 . !

P-n- - ~ t- ___,.~ -+ -~-+-+~- ___!___;_ -t- f- - +>-+++-r- -

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t--l- ----n -~l i _1_ ' ï"--:-r---T 1 1 i

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1

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+-i 1

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- p. ,_._ .... ---+---.-+ ----t---1------ . ~ ..,....ï-+- --- t--r- . t- t±i+' 1 -.. + ' ' 1 '

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1 : _ll_l__!__ ___]_ 1

t- ~--4-t- r-+-----+ 1 ~,__ -:--!+ 1

1 ' ' 1 ' l

88

It should be mentioned in regard to the curve for the

small mouthpiece facing upstream, that no readings were taken

for a ratio of intake velocity to flume velocity lesa than

0.25. In view of the fact that the strong tendency towards re

duction in turbidity for this mouthpiece in the downstream and

straight-out positions was not evident except at ratios below

0.25, and also since the general shape of the curve for the

mouthpiece facing upstream conforma with the general shape of

the ether curves, it is very probable that a similar reduction

in turbidity would be observed for this small mouthpiece facing

upstream at values of intake velocity to flume velocity ratio

of lesa than 0.25.

On the ether hand, the curve compiled from the resulta

for the five-inch diameter mouthpiece facing downstream does

not bear even general similarity to the four ether curves. It

was observed that the influence zone for this mouthpiece ex

tended some 8 inches downstream from the face of the mouthpiece.

It was also observed that a hydraulic jump occured approx

imately 10 inches downstream from this face. It is therefore

suggested that the experimental resulta for this mouthpiece

have been affected by the disturbence of flow conditions sur

rounding the mouthpiece, which disturbence is a direct result

of the failure to provide adequate depth and cross-sectional

area of flow in the model flume.

In comparing the resulta for the five-inch diameter

mouthpiece facing upstream with those for the small diameter

mouthpiece facing upstream, it may be readily seen that the

increase in mouthpiece diameter bas increased the value of the

ratio of intake velocity to fiume velocity at which a re

duction in turbidity may be affected while, at the same time,

it has magnified both the reduction in turbidity which may be

affected at values of the ratio lower than the critical value

and also the increase in turbidity which may be affected at

values of the ratio higher than the critical value. For a

mouthpiece of this shape, it should be made certain that the

intake would be operating on the low side of the critical

ratio throughout the greater part of its useful life.

D. Compariaon with Results of Previous Experimenta

The curves obtained by R.J.Lindsay showing variation in

turbidity with the ratio Intake Velocity/Flume Velocity have

been plotted on the corresponding graphs for these experimenta

together with point results from Mr. Lindsay's experiment.

Similarly, point results from the experimenta of Mr. Vanoni

which were previously listed in Table 1 have been plotted on

the graph for the small mouthpiece facing upstream.

In principle, the curves suggested by Mr. Lindsay agree

with those obtained in these experimenta. In general they in

dicate that a reduction in turbidity begins at a considerably

higher ratio of intake velocity to fiume velocity than has been

90

found by this experiment and they also indicate much more

marked increases or reduction in turbidity than has been found

by this experiment. It is likely that both of these differ

ences are the result of the wide variation in individuel

readings obtained by Mr. Lindsay.

The turbidity meast~ements made by Mr.Vanoni were taken

using a sediment sampler. These samplers were developed by the

United States Federal Inter-Agency River Basin Committee.

Figure 18 illustrates the u.s. DH-48 depth integrating hand

sampler. It is to be noted that the sampling tube is straight,

i.e. it does not have a flared inlet. Thus over the range of

values of the ratio of intake velocity to stream velocity which

were examined by Mr. Vanoni and bearing in mind that he found

deviations of ! 3% from the mean for a series of three con

secutive samples, it would appear that the elimination of the

flared mouthpiece has little significant effect upon the

apparent turbidity of the water carried into the intake.

One notable agreement between the results of Mr. Lindsay

and those of this experimenter is illustrated on the graph for

the small diameter mouthpiece in the straight-out position.

Although there is considerable difference in the positioning of

the curves, prepared from the resulta of the two experimenta,

nevertheless these curves do coincide at the point where the

ratio of intake velocity to flume velocity is equal to 1.0 and

also where the two curves intersect the ordinate axis, i.e.

91

where the ratio of intake velocity to flume velocity is equal

to o. Mention of the intersection of these curves with the

ordinate axis raises the question of whether it is correct to

produce these curves to intersect this axis. By this is meant,

not whether the slope of the curve should be extended but

rather whether there may be some dis-continuity in the reduction

of turbidity as the ratio of intake velocity to flume velocity

approaches 0 or, in effect, as the intake velocity approaches o. Assuming that the hypothesis derived later in this discussion

to explain these variations in turbidity, is correct, then the

main factor affecting a reduction in turbidity is the settle

ment of the sediment within the zone df. influence surrounding

the mouthpiece. So long as the rate of settlement with time is

constant, it may probably be assumed that the rate of reduction

in turbidi ty will likewise be consta.nt.

Using the data of Table 2, a graph has been prepared in

dicating the rate of reduction of turbidity with time for the

particular sediment used in this experiment. It may be seen

from this graph in Figure 18 that for at least twenty minutes

the rate of reduction of turbidity remains constant. For all

practical intenta and purposes an inlet time of 20 minutes

would indicate a flow of 0 fps with a corresponding ratio of in

ta.ke velo city to flume veloci ty of 0. The intersection of the

curves and the ordinate ~~is may, therefore, be justified.

Measured suspended load

Unmeasured suspended load _t

Flow

U.S. GOV 1 T. D.H. -48 DEPTH INTEGRATING HAND SAMPLER

Figure 17

Boo

700

t 600

500

300

200

100

~~~~~----~~--~--~~~~--~~---~~--~o 0 0

U\ (\J • .. s (\J •

r-i P.

.. (\J .-1

0 0 .. .-1

.. .-1

.. . . .. .-1 .-1 (\J

GRAPH SHOWING VARIATION IN TURBIDITY OF UNDISTURBED SAMPLE ~~TH TIME

Figure 18

92

93

E. Flow Pattern Observations

It may be readily seen from the sketches of the flow

pattern observations that the zones of influence of both the

large diameter and small diameter mouthpieces, whether they

face upstream or downstream, were much greater when the intake

velocity was 5 ft. per second, than they were when the inte.ke

velocity approached zero. As previously stated in Chapter 1,

Vanoni suggests that the sediment particles follow paths of

less curvature than the streamlines which curve away from the

sampler tip with the result that sediment is transferred to the

fluid entering the sampler. 10 In our case, and from our obser

vations, this would mean that the sediment was being trans

ferred into the zone of influence from the streamlines around

it. The following theoretical discussions therefore concern a

particle of sediment which, because of a greater inertia than

that of the streamline of water which carries it, separates

from the streamline and entera the cone of influence created by

the intake mouthpiece.

Consider a particle of sediment moving in the stream at

stream velocity 2.5 fps. The streamline carrying this particle

skirts the cone of influence created by the intake. The

particle being discrete, attempts to decelerate to 0.2 fps

which is the port entrance velocity of the small diameter mouth

piece with an intake velocity of 2.0 fps. If we neglect the

mean free path of the particle, the motion of the particle can

10. Vanoni, op. cit., page 77.

94

be predicted by mechanics. The fol1owing sketch indicates the

forces on the partic1e immediately upon its entrance into the

zone of influence.

D ~---·

~g vf = 0.2 fps

Where D = drag

vP = partic1e ve1ocity Vf = Flume ve1ocity

g = force of gravity

Considering the forward motion (i.e. motion in the same

direction as that in which the particle was originally moving)

the ve1ocity of the particle relative to the fluid has changed

from 0 to 2.3 fps, creating the corresponding drag. This drag

is the only force which can act to dece1erate the partic1e in

the direction of its movement.

It is assumed that the partic1e is a spere of diameter

490 x 10 -3 ft. and the water temperature is 50° F.

The mass of the partic1e, assuming a specifie gravity

= 2.6 in air, or 1.6 in water

= 6

= x .118 x lo-9 x 62.4 x 1.6

= 370 x lo-9 lb.

Reynolds number for particle under these conditions

R = 2.3 x .490 x lo-3 1.410 x 10-.5

= 79.5

95

Whence, from Binder 11

en = 1.25

D = 1.25 x pv2A 2

= 1.25 x (1.940 x 32.174) x 2.o2 x il x (.490 x lo-3)2 2 x

= 1.25 x 62.410 x 4xÎÎx 24 x 1o-6

Where Cn= drag coefficient

D = drag

V = partic1e ve1ocity

A = cross-sectional area of partic1e

By Newton F=D=ma

58.8 x 10-6 = 370 x l0-9 x a

V2 =

o.2o2 =

0.04 =

318s =

B =

=

a =

=

u2 + 2as 2 2.3 - 2 x

5.3 - 318s

5.26

.0165 ft.

0.2 inches

58.8 x 1o-6 370 x 10-9

58.8 x 103 37"0

159 x s

11. Binder op. cit., page 173.

= 159 ft/sec2

Where u = initial ve1ocity

v = final velocity

a = acceleration

s = penetration distance

96

The foregoing discussions show that the particle will

penetrate far enough into the zone of influence and will no

longer be influenced by the flow outside of that zone. The

behaviour of the particle within the zone of influence will

depend entirely upon the hydraulic characteristics of the

flow within the zone. If the flow within the zone of influence

is not too turbulent, then the particle w:lll tend to settle

out at a velocity of 0.049 fps. which was previously mentioned.

The lower will be the intake. velocity, the longer time the

particle will take to reach the intake conduit itself, and

therefore the greater the settlement and the greater the re

duction in turbidity.

The above theory substantiates the resulta which were

obtained for the mouthpieces facing in the upstream position,

where the apparent turbidity is first increased by the penetra

tion of discrete particles as described above into the zone of

influence of the mouthpiece. All dye which was placed within

this zone of influence entered the intake, indicating that all

of the water within the zone of influence also entera the in

take. However, as the intake velocity is decreased, thus

decreasing the ratio of intake velocity to flume velocity, an

increasing number of particles of sediment settle out of the

zone of influence to be carried away by the streamline adjacent

thereto, thus affecting a reduction in the turbidity within the

zone of influence. As the intake velocity continues to be

97

decreased, a velocity is reached B.t which the rate of settlement

out of the zone of influence compensates for the increase in

turbidity caused by the penetration of particles into the zone.

At the corresponding ratio of intake velocity to flume velocity,

which has be en described previously as the cri tica.l ratio, the

apparent turbidity within the zone of influence is equal to the

turbidity in the flume itself. At values of the ratio lower

than the critical value, which result from further decreases in

the intake velocity, there is actually a reduction in turbidity

caused by a greater rate of removal of sediment out of the zone

of influence than the rate of penetration of sediment into the

zone of influence.

The flow conditions around the mouthpiece facing dawn

stream are not stable nor do they suggest any apparent reason

for the increases in turbidity which were observed. It would

appear that particles of sediment are carried into the wake by

the action of the turbulence which was observed to exist along

the boundary layer separating the wake from the streamflow.

This wake created downstream from the mouthpiece is very similar

to that which was observed by Helmholtz and Kirchhoff to exist

behind the flat plate. Their observations and the theory which

they developed to expla.in them are described by Hunsaker and

Rightmire.

"Noting that motion downstream from a plate is highly

rotational, Helmholtz and Kirchhoff approximated the actual wake

by a region of dead water or motionless fluid separated from the

mainstream by an infinitely thin sheet of rotating fluid

particles springing from each edge of the plate.n 12

Although the authors later go on to explain that this

flow pattern can be no more than the first approximation to the

actual one because of its instability, nevertheless, their

theory suggests that flow conditions inside the zone of in

fluence or wake are less turbulent than outside the zone, and

therefore it would be expected that the longer a particle re

mained within the zone, the greater would be its settlement and

the greater the reduction in turbidity of the fluid entering

the intake.

Lack of sufficiently detailed observations makes it

impossible to suggest a theoretical explanation for the reduction

in turbidity of the water entering the mouthpiece in its

straight-out position. It is likely that sorne zone of influence

exlsts within the mouthpiece or immediately in front of it in

which, as in the two ether positions, there is less turbulence

than in the stream itself, and out of which sorne of the sediment

will settle.

12. Hunsaker and Rightmire, op. cit., pages 198 and 199.

CHAPTER Vll

CONCLUSIONS

99

Bearing in mind the limitations of the experiment as

outlined in the foregoing discussion, the following conclusions

may be drawn:

1. For the small-diameter mouthpiece, which is modeled

after mouthpieces commonly in use, variation in the position of

the intake, i.e. whether it faces upstream, downstream or

straight out, does not substantially affect the turbidity of the

water carried into the mouthpiece, for values of the ratio of

intake velocity to stream velocity which wov.ld normally be con

sidered desirable in pre.ctice.

2. For the small-diameter mouthpiece, and values of the

ratio of intake velocity to strea.m velocity of less than 0.2, a

reduction in the turbidity of the water carried into the mouth

piece in e.ll three positions will occur. This reduction in

turbidity will be somewhat greater when the mouthpiece is facing

upstream or downstream than when it is facing straight out.

3. The five-inch diameter mouthpiece, which had a much

greater cross-sectional area relative to the cross-sectional

area of the intake conduit ths.n the small-diameter mouthpiece,

accented the effects which were observed to occur around the

small·diameter mouthpiece. It can be said with 95% confidence

that for values of the ratio of intake velocity to stream vel

ocity lesa than 0.37, this mouthpiece will affect a reduction in

lOO

turbidity.

4. The reduction in turbidity in the upstream and dawn

stream positions of the mouthpiece is the ref.mlt of sedimen

tation within the zones of influence in front of or within the

intake mouthpieces in which there is less turbulence than in

the adjacent stream flow.

5. From a practical point of view the resulta of this

experiment indicate that:

a) For slow-moving streams and/or streams with·low

turbidity, the intake should be designed on an economical basis

without regard for the insignificant effect which the mouthpiece

design or position will have on the turbidity of the water

gathered into the intake.

b) For streams where during the spring break-up periods and

heavy summer and fall storms,the flow velocity and the amount of

turbidity carried reaches high values, the design and con

struction of a special intake mouthpiece may become economically

warranted.

c) For swiftly flowing streams of significant turbidity

and/or for highly turbid streams, it would be worthwhile to

study a mouthpiece similar in shape to the five-inch diameter

mouthpiece used in this experiment and placed facing upstream.

Since the effectiveness of the mouthpiece in reducing turbidity

depends upon the hydraulic characteristics of the mouthpiece,

model tests should be carried out using a true scale model of the

101

stream bed and the intake including its protective cribbing.

The construction of a special mouthpiece may be warranted

when the saving in treatment cost due to the reduced turbidity

is larger than the additional cost of constructing this

special mouthpiece, and of a larger diameter intake conduit.

Appendix A

BIBLIOGRAPHY

1. Steel, Ernest w., Water Supply and Sewerage, 3rd Edition, McGraw-Hill Book Co.Inc.,

5.

6.

8.

Hunsaker, J.c., and Rightmire,B.G., Engineering Applications of Fluid Mechanics, McGraw ... Hill Book Co. Inc., 1947

Binder, R.C., Fluid Mechanics, Prentice-Hall Inc., 1949.

Hydraulic Models, ASCE Manual of Practice No. 25, American Society of Civil Engineers, 1942.

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