405^

INTERCHANGE OF STREAM AND
INTRAGRAVEL WATER IN A
SALMON SPAWNING RIFFLE

SPECIAL SCIENTIFIC REPORT-FISHERIES Na 405

Marine Biological Laboratory

rf-^ 1 :; \%z

WOODS HOLE, MASS.

This work was financed by the Bureau of Commercial
Fisheries under Contract No. 14-17-008-96, with funds
made available under the Act of July 1, 1954 (68 Stat. 376),
commonly known as the Saltonstall-Kennedy Act.

UNITED STATES DEPARTMENT OF THE INTERIOR, Stewart L. Udall, Secretary

FISH AND WILDLIFE SERVICE, Clarence F. Pautzke, Commissioner
Bureau of Commercial Fisheries, Donald L. McKernan, Director

INTERCHANGE OF STREAM AND INTRAGRAVEL
WATER IN A SALMON SPAWNING RIFFLE

by

Walter G. Vaux

Contribution No. 82, College of Fisheries, University of Washington

United States Fish and Wildlife Service
Special Scientific Report- -Fisheries No. 405

Washington, D. C,
March 1962

CONTENTS

Page

Introduction

Theory of interchange and intragravel oxygen resupply 2

Transport processes:

Stream-intragravel interchange 3

Ground-water oxygen transport 6

Intragravel oxygen balance '

Field verification of the slope-interchange mechanism 8

Experimental apparatus and procedure 8

Results ^

Q

Discussion °

a
Summary '

Acknowledgments ^^

Literature cited ^"

iii

INTERCHANGE OF STREAM AND INTRAGRAVEL
WATER IN A SALMON SPAWNING RIFFLE

by Walter G. Vaux

Fisheries Aid

Fisheries Research Institute

University of Washington

Seattle, Washington

ABSTRACT

Dissolved oxygen is supplied to intragravel water in a salmon spawning riffle
through (1) interchange of water from the stream into streambed gravel, and (2)
ground-water flow. The primary variables that control interchange are gradients
in the stream profile, permeability of the gravel bed, and dimensions of the bed.

The delivery of dissolved oxygen to intragravel water and the way in which rate
of delivery is affected by stream profile, permeability, and dimensions of the bed
are explained.

INTRODUCTION

While buried in the gravels of streams for
6 to 9 months, eggs and larvae of the Pacific
salmon (Oncorhynchus) are subjected to various
environmental factors causing mortality, such
as floods and freezing (Royce, 1959). Other
important factors that affect mortality are
dissolved oxygen content and rate of flow of
intragravel water* that bathes buried salmon
eggs and larvae (Wickett, 1958).

Oxygen dissolved in intragravel water is
consumed by biological and chemical proc-
esses and must be resupplied by diffusion,
ground-water flow, or circulation between
aerated stream water and water in the gravel.
The circulation between stream and intra-
gravel water is called interchange and is
either an upward or downward flow.

The Fisheries Research Institute started
studies of interchange in 1948 under the direc-
tion of Dr. William F. Thompson. These
studies were interrupted in 1949 and were not

resumed until 1957 when they became part of
a project to study effects of logging on produc-
tivity of pink salmon (Oncorhynchus gorbuscha)
in streams of Southeastern Alaska.* In 1957
the occurrence of interchange was qualita-
tively demonstrated in a spawning riffle by
injecting dye into the gravel through stand-
pipes and detecting the appearance of dye at
the surface of the gravel downstream from
the point of injection. In 1958 and 1959 pre-
liminary studies were conducted by the writer
in a small flume at the University of Wash-
ington Chemical Engineering Laboratory to
identify some of the variables that control
interchange. During the summer of 1959
studies conducted in a pink salmon spawning
riffle in Indian Creek in the Kasaan Bay
area of Southeastern Alaska (fig. 1) provided
qualitative verification of the dependence of
interchange on stream gradient and pro-
file.

The study of interchange is being continued.
In addition to field investigations, a quantitative

'The term "intragravel water" refers to water oc-
cupying interstices in gravel beds.

* Contract with Bureau of Commercial Fisheries,
U,S. Fish and Wildlife Service.

Figure 1,— Location of study streams, Hollis area.

laboratory study of the dependence of inter-
change upon stream gradient and profile and
gravel permeability is being carried on by
the writer as a thesis research program at
the University of Minnesota Department of
Chemical Engineering.

The primary purpose of this paper is to
present a theory of interchange. Results of

field experiments demonstrating interchange
are also described.

THEORY OF INTERCHANGE AND
INTRAGRAVEL OXYGEN RESUPPLY

The initial source of oxygen that is dis-
solved in intragravel water is the atmosphere.
The purpose of this discussion is to describe

the processes that operate to transport
free gaseous oxygen from the atmosphere
to intragravel water of salmon spawning
riffles.

Transport Processes

Stream-intragravel interchange. — The steps
involved in physical transport of free oxygen
to intragravel water are:

1. Dissolution of oxygen through air- water
interface into stream water.

2. Transport of oxygenated water to the
stream bottom.

3. Interchange of oxygenated water from
the stream into the porous gravel interior.

These steps are diagrammed in figure 2.

Since this Is a series process, the rate at
any point will control the entire process.

Rate of oxygen dissolution in standing water
is dependent upon temperature, surface area,
and difference in partial pressure of oxygen
dissolved in water and oxygen in the atmos-
phere. It is normally a slow process and may
be controlling. The dissolution of oxygen in
turbulent stream water, however, is a rapid
process compared with subsequent steps and
is normally not controlling. This is shown by
the near- saturation oxygen level in surface
water of unpolluted streams.

Dissolved oxygen, present at the stream
surface, may be transported to the stream
bottom through diffusion or turbulent water
current. In the case of standing water, for in-

stance a pool or pond, the water is motionless
or in laminar flow. Here the transport of dis-
solved oxygen is mostly by diffusion, and a
downward movement of oxygen is due to dif-
ferences in oxygen concentration between
highly oxygenated surface and poorly oxy-
genated bottom water.

On the other hand, a stream or river of the
kind used by salmon for spawning will usually
be in turbulent flow (Russel, 1942), which is
characterized by continuous swirling, eddy
crosscurrents, and complete mixing. Conse-
quently, oxygenated surface water (saturated
with dissolved oxygen) is mechanically car-
ried to all depths of the stream (O'Connor and
Dobbins, 1956). Turbulent transport is a rapid
process and is not controlling.

For oxygenated water to enter the stream-
bed a force must exist to induce flow across
the gravel boundary. Consider a stream flow-
ing over a smooth- surfaced gravel bed of
constant permeability and gradient. Turbulent
conditions do not exist at the thin water layer
adjacent to the stream bottom (McCabe and
Smith, 1956), and there is no reason to expect
interchange. For interchange to occur there
must be inherent factors in the surface water,
streambed surface, or streambed interior
affecting interchange. The factors that pos-
sibly control interchange include (1) stream
surface profile, (2) gravel permeability, (3)
gravel bed depth, and (4) irregularity of the
streambed surface.

If the stream surface profile is not curved,
if the gravel bed is of constant permeability

Air

Stream

\ o\ . \ Gravel a \ •

Figure 2.- -Oxygen transport through stream to gravel bed.

3

and depth, and if the stream bottom is smooth,
no interchange should occur. If gradient,
permeability, or bed depth vary in the direc-
tion of intragravel flow, however, interchange
should occur. Each of the three variables may
cause a change in total intragravel flow inde-
pendently of the others.

D'Arcy's law of flow related fluid flow
velocity in a porous gravel bed to permeability
and the energy change within the bed, viz..

V =

k (Ah)

(1)

where V is the average flow velocity, k the
gravel permeability and Ah the loss in specific
energy through the bed length L (Scheidegger,
1957; King and Brater, 1954). To describe the
flow of water within a streambed, the energy
change and bed length may be combined, giv-
ing.

V = - k sin e

(2)

where e is the angle of the energy line, that
is, the rate at which energy is lost in the
direction of flow (American Society of Civil
Engineers, 1949).

In the discussion that follows it will be as-
sumed that the energy line and stream surface
profile or hydraulic gradient are approxi-
mately equal, that is, they have the same
slope and curvature. In extreme cases, for
instance hydraulic jump, slopes of the energy
line and stream profile differ greatly; how-
ever, cases to be considered here are as-

sumed to have nearly uniform flow. Hence, 9
will be the slope of the stream surface pro-
file in the direction of intragravel flow. Per-
meability, defined by equation (1), is the
property of gravel permitting fluid flow and
is affected by gravel particle size, size dis-
tribution, porosity, organic content, and par-
ticle shape.

Consider the intragravel channel of unit
width and depth, the upper face of which is
the gravel surface and the bottom face and
sides of which are impermeable boundaries.
Axial flow within this channel follows the con-
tinuity equation (Lapple, 1951).

W = Ap V

(3)

where W is the mass flow rate (weight of
water flowing per unit time), A the channel
cross-section area, p the water density, and
V the average intragravel velocity. By sub-
stitution of equation (2) in (3)

W = - k Ap sin e

(4)

Since the channel cross-section area is as-
sumed to be constant, any increase in mass
flow rate must enter the channel by inter-
change across the gravel surface.

Interchange may be measured by the vari-
able, I, the flow rate of stream water entering
the gravel per unit area of gravel surface.
The interchange flow into the intragravel
channel must equal the change of axial intra-
gravel flow, W. Considering flow along an
increment of length, A L (fig. 3), (intragravel

Stream bottom *%, ^ ^

V. "c^r^

Interchange

Figure 3. --Interchange and intragravel flow to a channel section.

4

flow rate in) - (intragravel flow rate out) = I
(width of channel x length of channel) or, since
the width is assumed to be one unit, A W = !•
AL which may be expressed as first derivative,

1 =

dW

dL

(5)

celeration or deceleration of intragravel flow.
A convex surface causes a faster intragravel
flow velocity downstream. Since, by definition,
the lower boundary is impermeable in this
model (fig. 4), water must enter the intra-
gravel channel, by necessity through the gravel
surface, to provide the additional mass flow.

Applying this to equation (4),

I = - k Ap cos 6

6,6
"dL

(6)

Since kAp is positive, and fori9 < -y-, cos 6 is
positive, hence the sign of 1 and the direction
of flow depends upon the sign of-^ . Three

cases may be considered;

1. If the stream surface profile is a straight

line (not necessarily horizontal), _ = 0 and

dL

there is no interchange.

6.6

2. If the surface profile is concave,-^i^ is

dL
positive, 1 is negative indicating a flow out of

the gravel.

3. If the surface is convex, -^2_ is negative,

dL

I is positive indicating a flow into the gravel.

In other words, a curved stream surface
due to change in profile slope forces an ac-

Cooper (1959) reported that under constant-
gradient smooth-bed surface flow conditions,
intragravel flow lines were generally parallel
to the bed with some interchange near the
surface. He also stated that interchange in
the upper 1-foot stratum was greatly in-
creased if large rocks were placed on top of
the bed, and that extensive downward inter-
change could be expected if a hump of gravel
was formed by a female salmon digging an
egg pocket. In either case — piled rocks or a
hump in the stream bed — the water surface
is forced to a convex profile and conditions
provide a force for downward interchange.

While the curvature of the stream profile
induces interchange through controlling intra-
gravel flow velocity, a second effect is the
centrifugal pressure due to curved flow. It
may be shown, however, that usually the
centrifugal effect is negligible.

Varying permeability of streambed gravel
is a second cause of interchange. In a stream
in which gravel permeability changes, although
the stream gradient remains constant and has

Convex profile

/

Concave profile

Stream

Impermeable layer

Figure 4, --Longitudinal stream profile showing surface-induced interchange when gravel is

underlain with impermeable layer.

a planar gravel surface, the intragravel flow
velocity will necessarily increase or decrease.
If an area of low gravel permeability occurs
between two areas of high permeability, inter-
change will occur as shown in figure 5.

Looking again at the continuity equation (3),
a third cause of interchange is suggested: a
change in intragravel flow area or, in effect,
gravel bed depth. As gravel depth increases
in the direction of flow (assuming constant
slope and velocity) the total intragravel flow
must proportionately increase, and there will
be interchange into the gravel.

A fourth possible source of interchange is
the roughness and irregularity of the stream-
bed. It is surmised that the composite effect
of surface irregularities and fluid inertia
causes a channeling of surface water into the
gravel bed.

Since interchange may be either an upwell-
ing, a downdraft, or not present at all, it is a
controlling variable in the oxygen transport
process from air to gravel interior.

Of final consideration is the actual intra-
gravel flow of water. By D'Arcy's law, intra-
gravel flow velocity depends upon stream
gradient and permeability. Since both stream
gradient and permeability may vary to restrict
or freely permit intragravel flow, they are
also controlling variables.

Ground-water oxygen transport. — The
mechanisms of ground-water oxygen trans-
port are:

1. Dissolution of atmospheric oxygen In
standing surface water (lakes, ponds) or rain.

2. Diffusion of oxygen to lower levels of
standing water.

3. Seepage of oxygenated water through
soil to the intragravel strata.

This process is shown in figure 6,

Ground-water oxygen transport is subject
to controlling variables in each step of the
series process. Diffusion of oxygen through

1

->

t^trpnm

jr \

/ \

o / ^ c.

^^

Low permeability^

High permeability

x^i^igh permeability

Bed rock

Figure 5.- -The influence of varying gravel permeability on interchange.

Seepage

Figure 6.— Ground-water oxygen transport.
6

standing water is extremely slow; the flow
rate of water through soil is restricted
through low permeability; and dissolved
oxygen in soil water is subject to biochemical
oxygen demand.

Intragravel Oxygen Balance

At any instant, a given volume of spawning
gravel may be assumed to be in a steady state
with regard to supply and removal of dis-
solved oxygen; that is, dissolved oxygen is
supplied and removed at a constant rate.
Intragravel dissolved oxygen sources are
stream water and ground water having high
dissolved oxygen content. Depletion is a re-
sult of biochemical oxygen demand and dilu-
tion with ground water having low dissolved
oxygen content. Periphyton on and near the
gravel surface also has an influence on oxygen
balance, producing oxygen in the presence of
sunlight and consuming oxygen during periods
of darkness. Its influence on intragravel dis-
solved oxygen levels is poorly understood.

Consider the ideal intragravel system pic-
tured in figure 7.

Here interchange (i), ground water (g), and
intragravel flow (a) are supplying dissolved
oxygen at different concentrations and flow
rates. Oxygen is leaving the system through
intragravel flow (f), and biochemical oxygen
demand (B), (and upwelling if Wi is negative).

A complete oxygen balance over an intra-
gravel volume may be expressed as:

WiCi + WaCa + WgCg = WfCf + VB

Where

W is the volumetric flow rate,
3
m. wa_ter. ^ ^^^ dissolved oxygen

sec.

concentration.

g.

oxygen

; V the
cm. "* water

volume of gravel, cm. ; and, B the
biochemical oxygen demand,

S: oxygen

cm. 3 gravel sec. '

By careful measurements, stream profiles
and gravel permeabilities (Pollard, 1955) may

Wi-Cl

OO OO OOOOOOOOOOOOOOO

Wo- Co

Wf.Cf

Wg.Cg

Figure 7. --Intragravel oxygen balance.

WiCi is rate oxygen enters spavming bed through interchange.
WaCa is rate oxygen enters spawning bed through intragravel flov
WgCg is rate oxygen enters spawning bed through ground water.
WfCf is rate oxygen leaves spawning bed through intragravel flow

VB is rate oxygen leaves spawning bed through biochemical oxygen demand.

be determined and through such physical
studies, the dissolved oxygen supply to intra-
gravel strata may be quantitatively predicted.
Qualitatively, intragravel dissolved oxygen
levels will be increased by interchange and
will be lowered by ground-water dilution and
biochemical oxygen demand (Hobbs, 1937).

FIELD VERIFICATION OF

THE SLOPE -INTERCHANGE

MECHANISM

The occurrence of interchange has been
previously reported (Cooper, 1959). In the
field of intragravel flow, investigators
have described the conditions under which
interchange occurs; however, the mechanism
of water flow from stream to gravel has not
been defined.

From ground-water and intragravel flow
studies in Indian Creek in 1957 and 1958,
techniques for qualitatively detecting inter-
change flow were developed. After the theory
of interchange was proposed, work was started
to verify the proposed slope-interchange
mechanism.

Experimental Apparatus and
Procedure

The technique of tracing interchange was to
trace the intragravel flow of dyed water
through a study area. Water was tagged with
dye, and its flow mapped by appearance in
standpipes placed in the stream at various
locations and depths. The standpipes used
are described by McNeil (1962).

Downdrafts were detected by (1) placing a
capsule filled with fluorescein dye on the
stream bottom and observing the movement
of dye into the streambed, and (2) Introducing
dye through a standpipe 6 inches below the
gravel surface and observing its movement
to greater depths in adjacent standpipes. Up-
welling was traced by introducing dye 18
inches below t'le gravel surface and observ-
ing its movement to adjacent pipes nearer the
gravel surface and to the gravel surface. For
each location where interchange was observed,
shape of the stream surface was determined
with a transit and stadia rod.

Results

Observations were made in several convex
and concave riffles of Indian Creek, In most
cases, to provide a point of zero intragravel
velocity, a pool bounded one end of each study
section. Observed direction of interchange in
concave riffles was invariably an upwelling
of intragravel water. In convex sections, that
is, where the stream gradient increased in
the direction of flow, interchange was from
stream to gravel (downdraft).

In tracing intragravel flow, it was observed
that upwelling occurred in certain sections
having constant gradient. Upon examining con-
ditions surrounding these points of upwelling,
it was noted that small irregularities in the
stream bottom created waves on the water
surface. Points of upwelling were directly
below troughs of waves.

Influence of waves upon interchange was
investigated in more detail by tracing the
direction of interchange beneath large waves
created by placing large rocks on the stream-
bed. Results showed that upwelling occurred
beneath the troughs of waves and downdraft-
ing occurred beneath wave crests.

While change in slope over a riffle provides
uniformity in the direction of interchange over
a large area, waves may control the direction
of interchange at a point. As part of the Indian
Creek study, wave configuration was changed
by moving rocks on the stream bottom. By
changing positions of large rocks, a point
initially below a wave crest would lie under
a wave trough. Changing stream surface pro-
file in this manner caused a reversal in the
direction of interchange.

DISCUSSION

Observed dependence of interchange on
stream profile was in accordance with the
proposed profile-interchange relationship;
where the stream gradient was convex, inter-
change was downward; where the stream pro-
file was concave, upwelling occurred.

Change in stream gradient over a long
distance, for instance 10 feet, provides a
unidirectional interchange over a large area.
However, the point interchange driving force,
inherent in waves, induces a comparable total

flow over a smaller area. Beneath the wave
are adjacent areas of upward and downward
flow which provide a rapid circulation of water
over a small area.

It is to be noted that the assumption of equal
hydraulic and energy gradients no longer ap-
plies. Although there is no apparent basis for
predicting the direction of interchange beneath
a wave, there is certainly an energy dissipa-
tion through the wave. For the general case
of equal energy and hydraulic gradients up-
stream and downstream from a wave there
must necessarily be a point of inflection in
the energy line and, in turn, adjacent areas of
downward and upward interchange.

Another consideration in comparing profile
and point interchange is the location of points
of interchange in the stream. Assuming con-
stant gravel permeability, interchange due to
the axial profile can be expected to be in
the same direction across the stream. On the
other hand, the occurrence and size of waves
vary with velocity of flow. Accordingly, point
interchange can be expected to be low in calm
water near the stream shore and most exten-
sive at midstream points where turbulence
is greatest.

Finally, how do conditions causing inter-
change change with time and variations in
stream discharge? Changes in the direction
and extent of interchange will result, essen-
tially, from changes in the stream surface
configuration, the interchange driving force,
and an increase or decrease in gravel per-
meability.

Interchange over a large area will be in-
fluenced by changes in stream surface con-
figuration through stream discharge fluctua-
tions and shifting of the stream bottom. The
extent of interchange will be governed through
variations in gravel permeability resulting
from siltation, gravel compaction, organic
content, and gravel shift.

Point interchange, too, will depend upon
stream discharge, in this case, however,
through its effect on surface wave configura-
tion. During low stream discharge the water
surface is comparatively calm and point inter-

change will be reduced accordingly. Relative
dissolved oxygen levels tend to verify this:
McNeil (1962) has shown through extensive
intragravel dissolved oxygen sampling that
the intragravel dissolved oxygen content in-
creases with stream discharge, and Wickett
(1958) has proposed that low oxygen levels of
intragravel water are associated with periods
of low stream discharge.

SUMMARY

Studies of interchange of stream and intra-
gravel water were conducted in 1957, 1958,
and 1959 as part of a project that is supported
by the Bureau of Commercial Fisheries to
study the effects of logging on pink salmon
production. Interchange was first qualitatively
demonstrated in a salmon spawning riffle in
Indian Creek in Southeastern Alaska. Then,
experimental research was carried on at the
University of Washington Chemical Engineer-
ing Laboratory to determine variables that
control interchange and, finally, additional
field studies in Indian Creek provided a quali-
tative verification of dependence of inter-
change on stream gradient and other factors.

The theory of interchange postulates that
steps involved in physical transport of free
oxygen to intragravel water are (1) dissolu-
tion of atmospheric oxygen into stream water,
(2) transport of oxygenated water to stream
bottom, and (3) interchange of oxygenated
water from the stream into the porous gravel
interior. Factors controlling interchange are

(1) gradients in stream surface profile,

(2) gravel bed permeability, (3) gravel bed
depth, and (4) bed surface configuration.

This theory was partially verified in the
field as follows:

1. Interchange was traced by following in-
tragravel movement of dyed water through a
study riffle. Water was tagged with dye, and
its direction of flow mapped by appearance in
standpipes placed in the stream at various
locations and depths.

2. Downward interchange was detected by
(1) placing a capsule filled with fluorescein
dye on the stream bottom and observing dye

downdraft, and (2) introducing dye through a
standpipe 6 or more Inches below the gravel
surface and tracing its movement by detection
in standpipes at greater depths.

3. Upward interchange from gravel to
stream was followed by introducing dye below
the gravel surface and tracing its direction of
flow through appearances in pipes at lesser
depths and at the gravel surface.

Direction of interchange depends on stream
surface profile and bed surface configura-
tion:

1. Direction of interchange in that part of a
riffle with a concave surface (stream gradient
decreases in direction of flow) was upwards —
intragravel to stream.

2. Direction of interchange in that part of a
riffle with a convex surface (stream gradient
increases in direction of flow) was down-
wards— stream to intragravel.

3. Direction of interchange under the
troughs of standing waves created by irregu-
larities in the streambed was upwards; intra-
gravel to stream. Direction of interchange
under crests of waves was downwards—
stream to intragravel.

ACKNO W LEDGMENTS

The writer wishes to acknowledge the guid-
ance of William L. Sheridan and William J.
McNeil in the field studies. He is also in-
debted to William F. Royce, Robert L.
Burgner, and Charles O. Junge, Jr. of the
Fisheries Research Institute and to Eugene P.
Richey of the Department of Civil Engineering
of the University of Washington for helpful
suggestions and criticism in the preparation
of this paper.

LITERATURE CITED

AMERICAN SOCIETY OF CIVIL ENGINEERS.
1949. Hydrology handbook. Prepared by
the Committee on Hydrology of the
Hydraulics Division, American Society
of Civil Engineers, Manuals of Engi-
neering Practice, no. 28, 184 p.

COOPER, A. C.

1959. Discussion of the effect of silt on
survival of salmon eggs and larvae.
In Proceedings of the Fifth Symposium,
Pacific N.W., on slltatlon, its sources
and effects on the aquatic environment,
p. 18-22, U.S. Public Health Service.

HOBBS, DERISLEY F.

1937. Natural reproduction of Quinnat sal-
mon, brown and rainbow trout in certain
New Zealand waters. New Zealand Ma-
rine Department, Fisheries Bulletin
No. 6, 104 p.

KING, HORACE WILLIAMS, and ERNEST F.
BRATER.

1954. Handbook of hydraulics for the solu-
tion of hydraulic problems, revised by
Ernest F. Brater. 4th ed. McGraw Hill,
New York, 1 vol. with 10 separately
paged sections, 7 p. index.

LAPPLE, CHARLES E.

1951. Fluid and particle mechanics. Uni-
versity of Delaware, Newark, Dela-
ware, 353 p.

McCABE, WARREN LEE, and J. C. SMITH.
1956. Unit operations of chemical engi-
neering. McGraw Hill, New York, 945 p.

McNEIL, WILLIAM J.

1962. Variations in the dissolved oxygen
content of intragravel water in four
spawning streams of Southeastern
Alaska. U.S. Fish and Wildlife Service,
Special Scientific Report — Fisheries
No, 402, 15 p.

O'CONNOR, DONALD J., and WILLIAM E.

DOBBINS.

1956. The mechanism of reaeration in
natural streams. Proceedings of the
American Society of Civil Engineers,
vol. 82, part 6, no. 1115, 30 p.

POLLARD, R. A.

1955. Measuring seepage through salmon
spawning gravel. Journal of the Fish-
eries Research Board of Canada, vol.
12, no. 5, p. 706-741.

10

ROYCE, WILLIAM F. SCHEIDEGGER, ADRIAN EUGEN.

1959. On the possibilities of improv- 1957. The physics of flow through porous

ing salmon spawning areas. Trans- media. University of Toronto Press,

actions of the Twenty-fourth North Toronto, Canada, 236 p.

American Wildlife Conference, p. 356-

„,, WlCKbl 1, W. h".

1958. Review of certain environmental fac-
tors affecting the production of pink
RUSSEL, GEORGE EDMOND. and chum salmon. Journal of the Fish-

1942. Hydraulics. 5th ed. Henry Holt and eries Research Board of Canada, vol.

Co., New York, 468 p. 15, no. 5, p. 1103-1126.

MS #1031

11

GPO S2»124

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