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ANCHORAGE,ALASKAi 8 -'i 59AR.LIS
Alaska Resources
Ljbrk~lnfo~a~::~ervlces
SUSITN~'RESERVOIR SEDIMENTATION
AND \yATER CLARITY STUDY
Prepared for:
Acres American,Inc.
Suite 305
1577 "e"Street
Anchorage,Alaska
Prepared by:
Peratrovich,Nottingham &Drage,Inq.
1506 West 36th Avenue,Suite 101
Anchorage,Alaska 99503
and
Ian P.G.Hutchison"Ph.D.
Steffen Robertson &Kirsten
1510 W.Mississippi Avenue,Suite 210
Lakewood,Colorado 80226
November,1982
-~.
SUSITNA RESERVOIR SEDIMENTATION &WATER CLARITY STUDY
TABLE OF CONTENTS
LIST OF TABLES
LIST OF FI GURES
PAGE
iv
v
1.PURPOSE AND SCOPE
1 .1 BACKGROUND.-.
102 STUDY OF OBJECTIVES
1.3 SCOPE OF WORK
."'"1.4 STUDY APPROACH
2.SUMMARY
2.1 PAST STUDIES
2.2 SUMMARY OF CONCLUSIONS
2.3 RECOMMENDATIONS
3.REVIEW OF AVAILABLE LITERATURE
1
1
1
2
5
5
5
7
8
-
i;
i
4.SEDIMENTATION PROCESSES
4.1 GENERAL
4.2 SEDIMENT SETTLING CHARACTERISTICS
4.2.1 SETTLING VELOCITIES FOR SPHERICAL PARTICLES
4.2.2 EFFECT OF PARTICLE SHAPE ON SETTLING VELOCITY
4.2.3 EFFECT OF SEDIMENT CONCENTRATION ON SETTLEMENT VELOCITY
4.2.4 EFFECT OF FLOCCULATION ON SETTLING RATES
4.3 QUISCENT SETTLING IN THE RESERVOIR BASIN
4.4 RESERVOIR MIXING PROCESSES
4 .4.1 THE ANNUAL CYCLE
4.4.2 PARTICLE MIXING IN THE EPILIMNION
4.4.3 VERTICLE MIXING IN THE HYPOLIMNION
4.4.4 OUTFLOW AND INFLOW DYNAMICS
4.5 REINTRAINMENT OF SEDIMENT
4.6 TURBIDITY VERSUS SEDIMENT CONCENTRATION
-ii-
10
10
11
11
12
13
14
15
18
18
20
20
22
23
23
TABLE OF CONTENTS (continued)
5.WATANA RESERVOIR SYSTEM
5.1 CLIMATE
5.2 HYDROLOGY
5.3 SEDIMENT REGIME
5.4 RESERVOIR
6.ANALYSIS OF SEDIMENT BEHAVIOR
6.1 QUIESCENT SETTLILNG
6.2 INDUCED MIXING
6.2.1 WIND INDUCED MIXING
6.2.2 WIND AND THERMAL MIXING
6.3 SEDIMENT REINTRAINMENT
7.PROJECTED RESERVOIR TURBIDITY
7.1 PROJECTED SEDIMENT CONCENTRATION
7.2 PROJECTED TURBIDITY LEVELS
REFERENCES
APPENDIX A.BIBLIOGRAPHY OF ADDITIONAL INFORMATION SOURCES
-iii-
PAGE
25
25
25
25
26
27
27
29
29
30
31
34
34
34
35
Following Text
-,,
·./"""
Table No.
LIST OF TABLES
Following Page
4 .1
Comparison of Basin Characteristics
Particle Settling Rates
9
11
.f"""5 .1 Watana Reservoir Characteristics 26
,!,,"
I
6.1 Results of "DEPOSITS"Model Runs 27
rr-'
6.2 Results of Quiescent Settling Analy~s
r~
for the Watana Reservoir 28
F"
6.3 Duration of Wave Mixing to 25-Foot Depths 30
"""
6.4
6.5
6.6
Duration of Wave Mixing to 50-Foot Depths
Water Velocities·Induced by Convective Penetration
and Wind Shear for June-August
Hypolimnion Mixing Scale,June-August
-iv-
30
32
32
',~
,-~
LIST OF FIGURES
Figure No.
1 .1 Plan View Showing Watana Reservoir and Sampling
Stations Used
4.1 Depth of Particle Settling over Time
4.2
;-~
4.4
'II"""
4.5
5.1
..-,
5.2
.....
6.1
7-
6.2
I""'"
6.3
Comparison of Theoretical Values of K for Ellipsoids and
Observed Values for Ellipsoids and Several Other Shapes
Effect of Concentration on Fall Velocity of Uniform
Quartz Spheres
Sediment-Removal Function for Settling Basins..
Revised Turbidity Versus Suspended Sediment Concentration
Susitna River at Gold Creek -Sediment Concentrations
(Summer Values Only)
Susitna River at Gold Creek -Average Monthly Particle
Size Distribution
Particle Size Distributions Predicted by DEPOSITS Model
Predicted Reservoir Thermal Profile
Relationship Between Mixing Depth an Percentage of Reservoir
Area Affected by Mixing
-v-
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r
1
r
I
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l.1
1.PURPOSE AND SCOPE
1.1 Background
This report summarizes the results of the Phase 2 investigations aimed at
determinipg turbidity levels in the proposed Watana reservoir.The
Phase 1 studies were completed by R&M Consultants,Inc.,(January 1982).
These earlier studies deve£oped trap efficiencies for.the Watana and Devil
Canyon reservoirs.Total sediment accummulatlon for each of the
reservoirs was also estimated.An indication of what downstream river
turbidity levels were likely to be was also provided.These studies
included a brief description of the delta formation in the reservoir,the
likely behavior of glacial flour within the reservoir,and a general
discussion on the temperature regime.
The Phase 2 studies which are described here were initiated in order to
analyze in more detail additional data obtained on other lake systems
throughout the world and to attempt to predict,on a more quantitative
basis,likely turbidity levels in the Watana reservoir.
A plan view of the proposed Watana reservoir and the sediment and climatic
data stations on the Susitna River used in Phase 2 studies are shown on
Figure 1.1.
1.2 StUdy Objectives
The objective of the study is to estimate the range of sediment
concentrations and turbidity levels in the Watana reservoir for the
various months of the year.It should be stressed that the objective is
not to provide a detailed quantitative estimate,but rather to perform an
exploratory type investigation to determine order of magnitude estimates.
1.3 Scope of Work
The scope of
(Acres)dated
follows.
work was outlined in a letter to Acres American,Inc.,
April 19,1982.A brief summary of the proposed program
-1-
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MILES
'-----------------_..---._,.,-----_...,
'~~'\
l(e:~
SAMPLING STATIONS
GOLD CREEK
WATANA,
VEe
....
..PARAMETER
STREAMFLOW
SEDIMENT DISCHARGE
WATER TEMPERATURE·
STREAMFLOW
CLIMATE
WATER TEMPERATURE
STREAMFLOW
SEDIMENT DISCHARGE
FIGURE 1.1~,.~,Petatrovlch &.Nottingham,Inc.
e ,:.,',.,.'.''..•",.',.."".'.'.',.:~Engineering ConsultantsI~-"<-,----"",,,",~J';:'~,,,A """'.oJ ,,_J """·'eM"m,@:,~.JI ""m~,,<:.,~''e:~'~';1"'$"'"'~'oSb:1 \0:>'4J ~;~.J_'L,:.i'_.~.J_~:::~:J
,i"'"
(a)Obtain and review all additional data including:
o climatic data
o reservoir data
o sediment data
o literature survey
Verify the
relationship.
sediment concentration versus turbidity
(c)Conduct quiescent settling analyses for the reservoir.
(d)Quantify the wind and themal mixing characteristics of the
reservoir.
-(
(e)Estimate ranges of sediment and turbidity values for the
reservoir for each month of the year.
Limited input to these studies was
conducted by'Acres American,Inc.
baseline turbidity and sediment
collected by R&M (1982).
1.4 Study Approach
derived from~the thermal lake modeling
(1982),on the Watana reservoir,and
concentration data from Eklutna Lake
1""',
Under quiescent conditions,sediment with particle size greater than about
2 um that flows into the Watana reservoir would practically all settle
out.However,the reservoir water is continually subjected to internal
mixing induced by meterologic conditions such as wind and temperature,as
well as turbulence induced by inflowing and out flowing water.Because of
this mixing,many of the smaller particles would not settle,but would
remain in suspension and contribute to increased turbidity levels in the
reservoir.In addition,turbuler.ce in the water also reintrains sediment
that has settled out on the bottom of the shallow portions of the
reservoir perimeter,again contributing to increased turbidity levels.
-2-
The basic approach to the study involved a semi-quantitive evaluation of
the process described above,and consisted of several distinct tasks.
These include:
(a)Literature and Data Review
Literature and data relating to other glacial lakes under
similar condit!ons have been reviewed.Any useful information
which could be extrapolated to Watana has been abstracted and
summarized.Thfs information is then used to support some of
the conclusions drawn from ~he simplified sediment analyses.
(b)Description of the Lake Sedimentation Process
A detailed description of the likely sedimentation process has
been developed.It is based on current knowledge of the
Watana reservoir and documented descriptions of other similar
lakes and reservoirs.This description aided in the
determination of sediment types and turbulent mixing•analyses.
!
L
(c)
(d)
Description of the Watana Reservoir
All relevant data for the Watana reservoir has been assembled
and summarized.These data include a description of the
monthly inflows and sediment concentrations,sediment grain
size distributions,reservoir storage volumes and releases,
and monthly wind and temperature data.
Analysis of Sediment Behavior
The amount of sediment that would settle out under quiescent
conditions has been calculated for various sediment inputs,
reservoir elevations,and withdrawal rates.Following this,
quantitative assessments have been made of wind and
temperature induced mixing currents in the reservoir.Use has
-3-
.-
....
I--
It
f-~
(e)
been made of the thermal modeling conducted by Acres (1982).
Approximate turbidity-sediment concentration relationships,
previously developed by R&M (January 1982),have been updated
using additional Susitna River data,and also used in the
analysis.
Prediction of Reservoir Turbidity
Based on the assumption that reservoir mixing velocities of
the same order of magnitude as the particle settling
velocities would disrupt the settling process,typical ranges
of sediment concentrations in the Watana Reservoir,near the
outlet,have been estimated.These sediment concentrations
are converted to turbidity using the appropriate turbidity
sediment concentration relationships •
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2.SUMMARY
2.1 Past Studies
The Phase 1 studies conducted by R&M (January 1982)on the Watana
reservoir indicated the following:
Typical sediment gradations of Susitna River water in the Watana reservoir
area are 15 to 20 percent finer by weight than 2 microns,25 to 35 percent.
finer than 10 microns,and 95 to 100 percent finer than 500 microns (0.5
mm).The sediment trap efficiency of the Watana reservoir was estimated
to be between 70 and 95 percent with particles less than 2 microns
possibly passing through the reservoir.Under worse case sedimentation,
conditions of 100 percent trap efficiency,an estimated 472,500 acre.ft.
of sediment would be deposited in the reservoir over a 100-year period.
Turbidity in the downstream river would decrease significantly during the
summer months due to the large amount of sediment trapped by the
reservoir.It is likely that the turbidity pf water released in the
winter months when a stable ice cover exists would be near natural
conditions,as suspended sediment in the near-surface water would settle
out once the reservoir ice cover reduces surface disturbance and
essentially quiescent conditions occur.
2.2 Summary and Conclusions
Due to the complexity of glacial flour sediment behavior in large water
bodies,the general shortage of quantitative data,and little direct
experience with large glacial feed reservoirs,the conclusions drawn at
this time should be considered qualitative.However,the following
conclusions are considered defensible and provide order of magnitude
quantitative values that should allow project personnel to reevaluate the
effects of reservoir water clarity on other physical and biological
aspects of the Susitna project.
1.There will be some level of turbidity in the reservoir at all times.
-5-
.,-
! '
I
rr-
r,~
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2.It is likely that sediment particles less than 3 to 4 microns will
remain in suspension.This constitutes up to 20%of the summer
sediment input.Maximum turbidity levels at the outlet are on the
order of 50 NTtT's,which corresponds to a sediment concentration of
200 ~o 400 mg/l.Minimum turbidity levels will be in the order of 10
NTU's.This corresponds to a sediment concentration of 30 to 70 mg/l.
3.Order of magnitude tur~idity levels at the reservoir outlet during
each month appear to be primarily dependent on the travel time it
takes sediment slugs,delivered to the reservoir during previous
summers,to reach the reservoir outlet.Longitudinal mixing,
primarily induced by wind turbulence,will tend to mask the near
surface sediment slugs.Quantification of longitudinal mixing has not
been directly addressed within the scope of this task.
4."Wind m~x~ng is significant in retaining sediment less than about 12
microns in suspension for the upper 50-foot water layer •
5.Reintrainment of sediment from the shallow depths along the reservoir
periphery during severe storms will result in short-term high
turbidity levels.This will be particularly evident during the summer
refilling process when water levels will rise,resubmerging sediment
deposited along the shoreline during the winter.
6.In spite of some limitations,the data gathered from outside sources
supports the conclusion that Watana reservoir turbidity levels will be
in the range of 10-50 NTU's.
7.Preliminary results from the Eklutna Lake study show summer turbidity
levels in the near surface layers to be in the range of 20-40 NTtT's.
This generally agrees with the range of turbidity values predicted for
the Watana reservoir •
6 .'--
2.3 Recommendations
Should more reliable and accurate estimates of turbidity levels be
required,futher work is warranted to firm up predictions of sediment
concentration and turbidity in the Watana reservoir.Some of the major
weaknesses in the current data base and analytical approach include the
lack of knowledge of the electrochemical behavior of the sediment,the
role of phytoplankton and'its effect on turbidity,and the simplistic
nature of the analysis of ~he sedimentation process.To overcome these
deficiencies,the following study program is recommended:
(a)Conduct more detailed laboratory settling tests on river
sediment samples.
(b)Develop more reliable relationships between turbidities and ~\
sediment concentration incorporating the effects of
phytoplankton growths should this be regarded important,and
incorporating results from USGS summer field program to
measure sediment discharge....
(c)Apply a two-dimensional model to analyze the longitudinal
distribution of sediments deposition in the reservoir.The
model should incorporate the values of mixing velocities
derived from the Acres (1982)thermal modeling using a
diffusion type analogy.It is important to incorporate a
relatively long sequence (several years)of representative
inflow and sediment concentration data in these studies.This
will facilitate·a more accurate determination of turbidity
ranges likely to occur in the reservoir.
-7-
,~
3.REVIEW OF AVAILABLE LITERATURE
Under Phase I of the current reservoir sedimentation study,investigations
have been ongoing to retrieve any unpublished data or reports from those
references included in the Reservoir Sedimentation Report (January,1982)and
to search out,any additional information from sources worldwide.
Appendix B includes a bibliography of all additional reports of data obtained
from the literature search.It has been separated into two parts;the first
containing references from New Zealand Lake stUdies,the second listing
additional general references on reservoir sedimentation or the behavior of
fine particles in a water body.Efforts have been made not to duplicate those
publications referenced in the earlier reservoir sedimentation study (R&M,
January,1982).
Compilation of information from these sources has
Contacts in New Zealand have provided the most
Susitna.Table 3.1 summarizes the available
characteristics for major study sites.
been an on-going process.
relevant information for
basin and reservoir/lake
{I~
.' !
Lakes Tekapo,Pukaki and Ohau lie in adjacent mountain valleys at slightly
different altitudes.Each basin is a long,narrow glacial trough exposed.to
strong winds,primarily from the northwest,blowing down the valleys.Thermal
stratification is weakly developed and deep,and all lakes have a low chemical
content of the water (specific conductance at 25 0 C of 5.0-7.0 umhos/cm).
In general,the lakes are clearest in autumn as precipitation in the upper
basins falls as snow and inflow to the lakes is reduced.Turbidity increases
in the late spring as the snow melt period begins and flow increases.Inflow
to the lakes then carries a heavy silt load.The mean SECCHI disc readings
for one year were:Lake Ohau -9.36m (30.7 ft.),Lake Tekapo -4.99m
(16.31 ft.),and Lake Pukaki -0.51m (1.87 ft.).The maximum readings were
21.74m (71.31 ft.),7.0m (23.0 ft.),and 1.0m (3.28 ft.)respectively •
The literature reports that the differences in turbidity indicated by the
SECCHI disc readings are related to silt content,rather than to algal
production affecting light penetration.
-8-
L .
The variations in extinction depth appear to be due in part to the percent of
each drainage basin covered by glaciers.
However,at this time,limitations on the data preclude making direct
comparisons between the behavior of fine sediments in the proposed Watana
reservoir and existing New Zealand lakes.Additional supporting data on
climatic characteristics,ice regime,incoming sediment size distribution,and .~
seasonal turbidity or extinction depth for each lake are needed to complete
the analysis.
-9-
r'l-j-1 l'il 1-'-"···~··-·i·]}.
TABLE 3.1
COMPARISON OF BASIN CHARACTERISTICS
NEW ZEALAND
BASIN CHARACTERISTICS WATANA EKLUTNA PUKAKI TEKAPO .Q!!!!!
Drainage Area (m1 2 )5,180 119 545 565 463
Glacier Area (mi 2 )290 6.2 73 16.6 8.0
%of Drainage Area 5.9 5.2 13.4 '2.9 1.7
Annual Inflow (ac.fL)5,750,263 234,300 1,557,442 989,990 917,546
RESERVOIR/LAKE CHARACTERISTICS
Length (miles)48 7 14 15.5 10.5
Maximum Depth (feet)680 200 230 395 423
Mean Depth (feet)360 -154 ~226 243
Maximum Width (miles)5 0~7
Mean Width (miles)1.5 0.6 5.0 3.7 3.2
Surface Area (acres)37,800 3,420 24,460 21,500 13,340
Elevation of Water Surface (feet)2,185 871 1,624 2,322 1,696
Capacity,Total (ac.ft.)9,500,000 414,000 3,780,400 4,866,180 3,260,340
Average 8,330,000
Live 4,210,000 •213,271
Average 3,040,000
Maximum Drawdown (feet)140 60
Live Storage/Total Storage 0.44 0.52
Total Storage/Surface Area 251 121 155 226 244
Length/Average Depth 704 -480 362 228
Drawdown/Depth 0.21 0.30
Length/Average Width 32 11.7 2.8 4.2 3.3
Mean Water Residence Time 635 646 418 847 612
4.SEDIMENTATION PROCESS
4.1 General
Sediment inflow to the Watana reservoir is derived mainly from the
glaciers ..located in the upper portions of the drainage basin.The
sediment size generally varies from less than 2 microns (0.002 mm)to
1 mm.As the river flows into the reservoir J the coarse fraction of
sediment will settle out in.the upper reaches and form a delta deposit.
The finer particles will continue to flow into the reservoir where some
will settle.Some of the fine particles will not settle,others will be
reintrained and ultimately will be discharged from the reservoir through
the powerhouse or over the spillway.
Under quiescent conditions,as the water flows through the reservoir,
shear stress will be generated around the sides and along the bottom and
density strata boundaries.These will generate some turbulence within the
reservoir which will keep some of the smaller particles in suspension.
-it
Under actual conditions,a large reservoir such as Watana does not
experience these quiescent conditions.Continuous mixing processes are
generated by climatic influences on the lake's surface and by inflowig and
outflowing currents.These processes create a substantial amount of
additional turbulence within the reservoir which would tend to keep the
smaller fraction of the sediment in suspension.
Under actual conditions,a large reservoir such as Watana does not
experience these quiescent conditions.Continuous mixing processes are
generated by climatic influences on the lake's surface and by inflowing
and outflowing currents.These processes create a substantial amount of
additional turbulence within the reservoir which would tend to keep the
smaller fraction of the sediment in suspension.
The following sections describe the above-mentioned processes in more
.detail.Much of the information has been obtained from the work done by
Imberger and Patterson (1981).
-10-
4.2 Sediment Settling Characteristics
4.2.1 Settling Velocities for Spherical Particles
-
The behavior and rate of a particle settling in a fluid is not only
dependent on the fluid flow,but also on the characteristics of the
sediment particles.Fluid flow governs whether the sediment particle
will be entrained,transported,or eventually deposited.In time and
space,the eventual d~position of very fine particles is also
dependent on the physical characteristics of the sediment.Size of
the sediment particle is the most important property.However,the
specific weight and shape of the particle along with the
electrochemical characteristics of the fluid medium and concentration
of sediment in the fluid,directly affect the sediment fall
velocity.
of a sphere
18
w =
The classical relationship that defines the physics
falling within a quiescent fluid medium is Stokes Law.
gd2 •(21,-t)
"'"
-
w =settling velocity
g =acc.of gravity
d =particle diameter
~=kinematic viscosity
6s =sp.wt.of sediment
~=sp.wt.of liquid
The above equation assumes the drag coefficient on the particles is
constant and is therefore only valid for particle Reynolds numbers o~
less than 0.1.
,-PJlI"!o Table 4.1 lists the settling velocities calculated for particle sizes
ranging from 0.5 micron to 1 Mm.Values for the .1 mm to 1 mm range
(100 to 1000 microns)were obtained from curves for spherical
particles given by W.N.Graf (1971).All the above values have been
I-~
-11-
TABLE 4.1
PARTICLE SETTLING RATES
Particle Diameter Settling Velocity
of Spherical Particles Particle Reynolds No.(R)Assumed Settling Velocity
(S.G =2.5,T =40 0 F)of Spherical Particles of Glacial Particles
mm microns fps ~
1 3.1 x 10-1 61 2.7 x 10-1
0.5 1.5 x 10-1 14 1.3 x 10-1
0.2 4.9 x 10-2 2 4.3 x 10-2
~
0.1 100 1.6 x 10-2 0.3 .1.4 x 10-2
50 4.4 x 10-3 <.1 3.8 x 10-3
20 6.9 x 10-4 II 6.0 x 10-4
10 1.7 x 10-4 II 1.5 x 10-4
5 4.3 x 10-5 II 3.7 x 10-5
2 6.9 x 10-6 "6.0 x 10-6
1 1.7 x 10-6 "1.5 x 10-6
4.3 x 10-1 ..3.7 x 10-7.5 .Ii
Note:(1)Values for R;>.1 based on curves in Reference (7)by W.H.Graf (1971).
(2)Values for R ~.1 based on Stokes equation
(3)Settling velocities of~lacial sediment particles are based on
1/1.15 x velocity of spnerical particles.
.--1
,I ,,··r ~J .1 J
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calculated for a temperature of 40 0 F and assumed particle specific
gravity of 2.5.(1)
Figure 4.;shows the depth of settling with time in the upper active
layer for 2,5,and 10 micron size particles using the settling
velocities listed in Table 4.1.
The above analytic·te'chnique is for an ideal situation that would
reveal the maximum sett;Ling velocities that could be expected.As
prev iously discussed,even under quies cent conditions,the rate of
settlement would be less due to the influence of other physical
properties on the particle fall velocity.
Effect of Particle Shape on Settling Velocity
,.~
i,
Sediment grains are rarely spherical in shape and vary from a
rod-shaped particle to a disc-shaped particle.Glacial sediments tend
towards a platy-type shape,but.the shape is dependent on the parent
mineral and process of decomposition.•
Preliminary results from shape analysis of Susitna River sediments
show that finer sediments tend towards a platy-type shape due to the
,
relatively high percentage of mica and feldspar.
A study conducted by MeN own ,et al,(1951),determined the settling
velocities for various machine-shaped particles and related the
resistance factor f K'to the shape factor 'SF',as shown on Figure
4.2.These tests were run for Reynolds numbers less than 0.1,which
are representative of.particles less than sand size.The curves
represent theoretical results for ellipsoids (McNown &Malaika,
1950)•The numbers beside each data point give the shape factor
(b/c),and the shapes used are indicated in the Figure.
;R;~;~t-~;t;~;;;~~i~-i;~-~;taindicates that Susitna River Sediment may have a
higher mean specific gravity.
-12-
--'1 .
400350300250200
TIME (DAYS).
15010050
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I I I'I!,Ii!I I:,i I !!,!:,i I III'I I !I i [:i "!i
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E
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,DEPTH OF PARTICLE SETTLING·
OVER TIME'UNDER QUIESCENT CONDITIONS
,FIGURE 4.1
•.~J ,.,~..l J L.-,J
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0.9
0.125 0.25 0.5 1 2
Silape 'Klor,~
4 8 16
j
',II
COMPARISON OF THEORETICAL VALUES OF K FOR ELLIPSOIDS AND
OBSERVED VALUES FOR ELLIPSOIDS AND SEVERAL OTHER SHAPES
FOR REYNOLDS NUMBERS LESS THAN 0.1 (McNOWN,et al.,1951)
VANONI,V.A.(1975)SEDIMENTATION ENGINEERING
~PERATRO~9TTINGHAM &DRAGE INC•.'FIGURE 4'.2~..eNGINeeRI:'"CONSULTANTS
,..,
There is little difference between the theoretical values for perfect
ellipsoids and the observed values for ellipsoids and other shaped
particles.The values of 'K'based on the two ratios,a/;-bC and blc
are within 10 percent of the theoretical value for ellipsoids,thus
indicating that the axis ratios represent the principal hydrodynamic
features of the particle shape.These curves can then be used to
estimate settling velocities of nonuniform shaped particles occurring
in nature.The value for 'K'is equal to the ratio of the fall
velocity of a sphere with the same volume and weight as the particle
to the fall velocity of the particle.For example,comparing a 20-
micron sphere with an ellipsoid particle that has the same specific
gravity,volume,and a shape factor of blc =4 would produce a
resistance factor of 1.15 for the ellipsoid.This means that an
ellipsoid with the ratio of dimensions presented above would have a
fall velocity of 15 percent less than an equivalent spheroid.
In the particle size range being investigated here,there are few
particles that approach a spherical shape.As yet,no information is
available on the actual particle shapes.Fer purposes of this study,
therefore,it has been assumed·that a resistance factor of 1.15
applies.Table 4.1 lists the corresponding settling velocities for
these assumed glacial sediment particles.
Effect of Sediment Concentration on Settlement Velocity
The previous discussion addressed a single particle settling in a
clear infinite fluid.Influence of other particles falling within the
water column could retard or accelerate the settling rate of a single
particle.If the particle was one of"an isolated group of similar
particles,the settling rate of the particle group and hence,the
single particle would tend to increase.This situation approaches
that of flocculation.However,in the natural system that is
continuously being supplied by sediment,it is likely that a variable
spectra of sediment sizes would be found in the water column.When
this occurs,the interference between neighboring particles will tend
to reduce their fall velocity,which is often referred to as hindered
sett:ling.
'r-
I
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1 '
.--iI!JIIIf
I-~
McNow and Lin (1952)studied theoretically and experimentally this
phenomena,generating a relationship between the ratio of clear water
settling velocity (W o )and the particle velocity in a fluid with a
given sediment concentration (W c ).The curves shown in Figure 4.2 are
for an approximate theory based on the Oseen modification of Stoke's
theor-y for the motion of a sphere in a viscous liquid at a low
velocity.The curves apply for Reynolds numbers less than 2,which is
representative of most·of the particle size range.being considered for
this project.In refer.encing Figure 4.3,the influence of sediment
concentration on the fall velocity can be significant When the
sediment concentration is around 0.1 percent or 1000 mg/l.Susitna
River suspended sediment concentrations measured at Gold Creek
generally fall between 500 mg/l and 2000 mg/l when the discharge is
greater than 20,000 cfs.Concentrations within the reservoir,
however,are expected to be significantly lower.
As an example,if the inflow to the reservoir has a sediment
concentration of 1000 ppm,it would be expected that the settling rate
would be retarded by about 10 percent.The.solid lines on Figure 4.3
are representative for different particle Reynolds number.For
particle sizes of 50 microns or less,the Reynolds number is less than
0.1,therefore,the upper curve should be used for the Susitna
Project.
As the sediment concentrations within the lake generally will be
significantly lower than 1000 mg/l,the impact on settling velocities
will therefore be much less than 10 percent.For purposes of these
studies,therefore,the "effect of sediment concentration on settling
velocity has been neglected.
Effects of Flocculation on Settling Rates
If the mineralogy of the particles and the water chemistry are
compatible,electrochemical forces will tend to hold particles
together once they come in contact.Contact of particles and the
potential subsequent formation of an agglomeration,or floc,can be
-14-
~ttJ~rr !•I I I
1.0'...j..L~::=...-----~+---l--t--+--+-t-H_Hf--_+-+--+---f--_I___+___i-il~---1
I
i
!
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8 9
!
I
0.1 0.5 1 2 3 4 6
PERCENTAGE CONCENTRATION BY DRY WEIGHT,C,
(FOR QUARTZ SAND).
..
EFFECT OF CONCENTRATION ON FALL VELOCITY OF UNIFORM QUARTZ
SPHERES (McNOWN AND LIN,1952)
O.ft i
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1.6-------,...--~_.,..._r___r_r_1"'T"""'\""-r-r-~'--;---~~-..,________r___r-Ir__,...___,
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VANONI,VeA.(1975).SEDIMENTATION ENGINEERfN,
r,~
-
r~
!
--
...-c,
induced by internal IIlJ.x~ng of the fluid or by particles with higher
fall velocities overtaking and capturing slower particles.Once two
or more particles combine,the floc will settle at a higher rate than
any of the individual particles of the floc falling alone.Low levels
of turbulent mixing will tend to aid the formation of the floc;higher
levels will break the floc apart.There is therefore a limit to the
floc size depending on the level of turbulenoe within the system and
electromagnetic forces:When the relatively turbulent river water
initially enters "the .relatively quiesoent reservoir water,the
sediment particles will be dispersed in the water column.During this
initial period,the greatest opportunity for heavier particles to
encounter and adhere a smaller particle will occur.With time,the
particles will tend to stratify in similar particle sized bands and
therefore decrease the number of particle encounters.
To date,no studies have been done on the flocoulating characteristics
of the sediment in the Susitna River.However,metal shadowed
micrographs of sediment sampl~s from the Susitna River near Chase show
a significant amount of agglomeration.Petrhgraphic analysis revealed
that these were composed of denser materials (pyrite,iron oxides,
illenite)agglomerated onto lighter minerals (quartz,feldspar).More
thorough investigation of the processes of agglomeration and
flocculation would be needed to assess the impact of these processes
on sediment behavior,particularly settling rates.For purposes of
these stUdies,the effeot of flocculation or agglomeration have
therefore been neglected.
4.3 Quiesoent Settling in the Reservoir Basin
The approach used for estimating quiescent settling involved application
of a reservoir sedimentation computer model.The model,DEPOSITS,has
been developed by A.Ward (1979)for the design of sedimentation ponds.
It describes the sediment transport and deposition process in a reservoir
as a function of the basin geometry,inflow hydrograph,the "inflow
sediment graph,the sediment characteristics,the"outlet structures and
the hydraulic behavior of flow w~thin the basin.The model determines
-15-
basin trap efficiency,loss in storage due to sediment accummulation and
effluent suspended sediment concentrations.The model has been verified
with data from several different ponds and reservoirs located throughout
the nation,but not wi th a basin that has significant glacial flow and
sediment contribution.
In the model,flow wi thin the basin is idealized by plug flow concepts.
Plug flow assumes no mixing between plugs and routes the flow on a first
in,first out basis with each plug representing an equal time increment.
Settling of the sediment particles is described by Stoke's Law of
Settling.The reservoir bed is considered a perfect absorber of sediment
and resuspension or saltation of the particles is disregarded.The model
accounts for the variation in sediment concentration with depth by
sUbdividing each plug into four layers.Selective withdrawal,at the
basin outlet,from these layers is provided for in the model.
The basic inputs to the model include:
1)Inflow hydrography
2)Viscosity of the flow
3)Stage-area curve for the basin
4)Stage-discharge curve for the basin
5)Stage-discharge.distribution curve
6)Degree of dead storage or short-circulating
7)Sediment inflow graph or load
8)Particle size distribution and specific gravity of the
suspended sediment
For purposes of these studies,the model has been modified to accept
specified discharge values rather than a stage discharge curve.
Because it ignores dispersive mixing within the reservoir,the model will
tend to underestimate the minimum ?ischarge concentrations and
overestimate the maximum outflow concentrations.This must be taken into
account when interpreting the results of the model runs.
-16-
-.
-
,.~
ri~
-
,-
A second approach has been used to check on the results of the model
runs.It is described by H.T.Rouse (1948)and is based on work done by
Camp (1943).This approach is briefly outlined below.
The Watana reservoir is a relatively long (48 miles)and narrow (1 1/2
miles basin).For purposes of sediment deposition calculations,it can
therefore by treated as a channel.Water-flows into the upstream end,
passes through the channel-shaped basin,and flows out at the downstream
end.Storage changes take place which result in differences in the inflow
and outflow rates.As the sediment particles pass through the reservoir,
they gradually settle out.The velocity of flow through the basin
generates shear stress along the boundaries,and hence,turbulence within
the reservoir.This turbulence tends to reduce the rate of settling,
particularly of the small particles.
Camp (1943)evaluated the turbulent transport function for two-dimensional
flow.He assumed the water velocity is the same at every point in the
channel and that the mixing coefficient is also the same at all points.
The functional relationship he developed is as follows:
(qs)e
(qs)i =
w
tip
wL
Vy
in which
(qs)e =quantity of sediment of given particle size in effluent
(qs)i =quantity of sediment of given particle size in influent
w =fall velocity of the given particle size
tip =shear velocity
Vn g
1.49y 1/6
y =basin depth
n =Manning's roughness coefficient
L =basin length
V =mean velocity of flow in basin
-17-
4.4 Reservoir Mixing Process
It is shown on Figure 4.4.
This function
experimentally.
has been evaluated analytically and verified
-
As outlined by Imberger and Patterson in Fisher et al (1979),the major
m~x~ng processes occurring in the Watana reservoir are meterologic
conditions and the inflowing and out flowing water.These processes all
tend to generate turbulent eddies within the reservoir which continually
stir the sediment in the water.The basic processes are discussed
below.
4.4.1 The Annual Cycle
The annual thermal regime of the reservoir is currently being studied .,
by Acres (1982).Based op preliminary results from these studies,as
well as earlier thermal modeling also conducted by Acres (1982),the
reservoir's thermal regime appears to be relatively stable as compared
to more moderate climate reservoirs and lakes.
During the winter months (November through April),most of the water
in the reservoir would be at·40 C (40"F).In the upper layers,
temperatures would drop to OOC (32°F).During the spring and summer
warming period (May through July),surface temperatures would
gradually increase to approximately 9 to 10 0 C (48-50 0 F).The
reservoir would be reasonably well stratified with a thermocline
located up to 50 meters (165 feet)below the surface.Water
temperatures below depths of approximately 100 meters (328 feet)would
remain at 40 C.During the cooling periods (August through October),
the surface water would cool down.Overturning would take place in
the upper 100 meters as the surface.temperatures reach 4°C.During
this period,the upstream 10-mile reach of the reservoir which has
depths less than 100 meters would probably be SUbjected to complete
overturning.
-18-
I·I
I
I
I :
0.1
0.2
I I
I
I
!I
I
'·~-"""""jII':"'--WI1.l2-011Tr-I--=V:::::::::::'i-I-=:::;;;;=~
Vy -I'1
0.6·...r=:::::::::::::=+----6.~~~£....---4---l.-~.-I--~I--+-~-+-i
1-(qa)e tL-=~-.r==--j~n:t---=::::t:::::;;::;:::-iliTT-_·t-l---t41-H(qs)1 I
I I
i I0.411==--tjj~:::=::=rIIIIIT-II--r1111
I .\
!!
;,
l ...
0.01 0.10 Wy1l8
VnW
1.0 10.0
SEDIMENT-REMOVAL FUNCTION FOR SETTLING BASINS
ROUSE,H.(ed~),1950,ENGINEERING HYDRAULICS
-------
will tend to flow into the near surface layers of the reservoir which
are the same temperature.During the spring warming period,from May
to June,the river water would warm at a quicker rate than the
reservoir surface,and,therefore,continue to flow into the upper
layers of the reservoir.During the July to September period,river
water would start to cool more rapidly than the reservoir water.Flow
into the reservoir would gradually tend to enter at lower layers;and
towards September,the flow would be entering the reservoir in the
vicinity of the thermocline.As the lake water cools,the river
inflow would gradually move back to the surface layers.
Based on the above discussion,it is evident that the sediment
entering the reservoir will flow in near the surface most of the
year.The exception is during the late summer and fall months when it
would tend to flow into deeper layers near the thermocline.During
this period,the overturning that occurs in the upper layers of the
reservoir would provide some mixing of the sediment particles in these
layers and sGmewhat reduce the amount of sediment that settles out.
R&M (1982)is currently conducting studies on Ek1utna Lake,located
approximately 100 air miles to the south of Watana,in support of
ongoing model efforts.These studies indicate that Ek1utna Lake is
subject to complete overturning during the fall period.In addition,
sufficient mixing forces over the length of the lake surface result in
little variation in surface turbidity levels,regardless of the
distance from inflowing streams.Maximum turbidity is not always
recorded at the surface.Turbidity plumes below the surface have been
traced in the lake.
The observed behavior at Ek1utna Lake and predicted behavior of the
Watana reservoir still need to be.confirmed.The two are not
necessarily consistent in all respects.Data for a full annual cycle
at Ek1utna Lake will be needed to strengthen assumptions and.
conclusions about the similarity in behavior of the two systems.
-19-
4.4.2 Particle Mixing in the Epilimnion
.-,~
The major mixing forces active in the upper layers of the reservoir,
Fisher et aI,1979,include:
o penetrative convection
o wind induced mixing
o mixing induced by inflowing or out flowing water
These are discussed in more detail below.
'i~
~
I
-I
I
(a)
(b)
Penetrative Convection
The epilimnion would be subjected to diurnal temperature
fluctuations due to daytime heating and nighttime cooling.
The depth of penetration of the short wave radiation depends
on the water clarity,but in the absence of wind there is
always an identifiable temperature rise and stratification
layers during the sunlight hours.As night falls and
radiative heat losses begin to dominate the thermal exchange
at the surface,the surface layer cools and convective motions
mix the upper layers~Often these convective motions proceed
until they reach the mature thermocline where they begin to
erode the stable temperature structure.
Mixing Due to Weak Winds
A wind blowing ·over a lake exerts a stress on the water
surface that causes waves to form,break,and transfer
momentum to the water.The wave motion,especially when waves
are breaking,produces turbulence in the upper layer.This
turbulence then interacts with the mean shear in the upper few
meters to produce further turbulent kinetic energy.Often
this interaction produces a secondary motion as well as a mean
windward drift.Such secondary motions are called Langmuir
cells and they are distinguishable to an observer by the
-20-
characteristic slick pattern associated with the regions of
convergence.The net turbulent kinetic energy produced in
these upper few meters is then exported to the lower parts of
the epilimnion during turbulent diffusion or by the advective
motion associated with the Langmuir circulation.-In addition to this stirring of the surface water layers,the
wind will also cause the water to accelerate so that after a
short time the whole epilimnion will have a mean motion with a
velocity.The shear associated with this mean motion may then
further contribute to the production of turbulent mixing.~
(c)Reservoir Behavior Under Severe Wind Conditions
So far,the discussion of wind mixing in the epilimnion has
not taken·into account the motion of the water in the
reservoir.The wind stress will initiate motion and move the
water in the epilimnion in the direction of the wind.If the
water surface is to remain nearly horizontal,as it does,then
the water in the hypolimnion must counter this flow and move
in the reverse direction.A shear will develop across the
thermocline which will increase with time until the
thermocline has tilted sufficiently to set up a hydrostatic
pressure gradient which just balances the surface stress.At
this stage the motion changes from a whole basin circulation
to two closed gyres,one each in the epilimnion and the
hypolimnion,and the shear at the interface will decrease to a
very small value.All the work done by the wind is then
either dissipated internally or used to deepen the
epilimnion.The set up time is·proportional to the seiching
period of the thermocline which may be as much as two or three
days,giving the wind stress ample opportunity to develop an
appreciable shear across the thermocline.
-21-
-
Vertical Mixing in the Hypolimnion
Observations in large lakes using measured distribution of natural or
artificial traces indicate that vertical diffusive mixing in the
hypolimnion ranges from molecular diffusion to values up to 10-4 to
10-5 in m2 /sec (10-6 to 10-7 ft.2/sec.)(Fisher et al 1979,and
Hamblin,1982).In addition to this,sometimes relatively rigorous
mixing occurs.The only apparent explanation for this is that
although overall there is not sufficient kinetic energy to cause
mixing,there are portions of the lake at any particular time where
the energy density has been increased by some type of concentrating
mechanisms,allowing a local breakdown in the mixing of the
structure.The mixing is thus patchy and intermittent and quickly
collapses under·the action of buoyancy.Upon collapse ,the mixed
patches elongate and interleave with themselves and their
surroundings,leading to steplike vertical density structures.
4.4.4 Outflow and Inflow Dynamics
'--'1lJI'IlIiI
-
-
Local mixing is generated in the zone Where the inflow and outflow
occurs.Depending on the magnitude of the discharge,the outflow may
draw water from several layers within the reservoir.The velocity
field induced by the withdrawal will generate additional turbulent
mixing.However,for a reservoir as large and as long as Watana,this
mixing influence is expected to be limited to a small local area near
the power intakes.
A river entering a reservoir nearly always will be at a different
temperature,and thus density,than the surface water in the
reservoir.Upon entering the reservoir,it will thus push the
stagnant lake water ahead of itself only until buoyancy forces,due to
the density differences,have become sufficient to arrest the
inflow.At that point,the inflowing water will either flow over the
surface of the lake if it is warmer,or plunge and flow submerged if
it is colder.There are three distinct mixing regimes associated with
the inflow.
-22-
First,there is IlU.x~ng associated with the plunge line.Second,in
the case of the underflowing situation,the bottom roughness often
leads to mixing,called entrainment,at the interface between the
reservoir water and the inflow.Third,whenever the density of the
inf10wing water equals that opposite in the reservoir,then the
inflowing water will leave the bottom and intrude horizontally into
the reservoir.These intrusions may also occur along the surface if
the density of the inflowing water is less than that of the surface
water.
4.5 Reintrainment of Sediment
Along the shores1ine of the reservoir,the convective and wind mixing
effects will reach the bottom sediment.Some of these sediments will be
resuspended and reintrained in the water.The maximum particle size and,
hence,the amount of sediment that will be reintrained will depend on the
strength of the m~x~ng currents.During high wind periods,this
reintrainment can contribute substantially to turbidity in the reservoir
along the shore.
4.6 Turbidity Versus Sediment Concentration
Biological activity in .the lake is dependent on light penetration,which
in turn,is a function of the concentration of suspended matter.A
relationship is therefore required to convert predicted lake sediment
concentrations to turbidity.
R&M (1982)developed a regression equation relating to turbidity in NTU's
to sediment concentration in mgt1.The data was derived from measurements
at the Gold Creek and Vee stations.Subsequent to these studies,
additional data have become available at the Susitna River station near
Chase.A new regression equation has been developed combining all the
available data and is shown in Figure 4.5.
Much of the subsequent analysis in this report is based on this
turbidity-sediment concentration relationship because of limitations on
-23-
-
.,7'.•.•=-~.
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....,...~:f~f""'··t..:r."":"-
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=.=1"..:.::c·.~--
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-::.;..:......'T'+,.~.."7,..::.:...:;::
,d-I~--"T
:t:::
.-t-
~~.:''O.:::d.y::-
::::::._.~.::~.]:::...."~:J=:::::.....,.--.::i=~
40
f'~
--/-
6 ..":-"'-'
,
7 8 96
_._..i=-
.I----·--1-
-r-
''''':'''_--'-'
5
,
3 4
(mg/l)
,;.....
....--:-
.:,
,.
I ; I
3 4 5 6 7 8 9 100 2
SUSPENDED SEDIMENT CONCENTRATION
2
! i !
-=20}-
Z-
4_~'"''::.:'
~.-
5.~'-'--
E'-:-:-~;-:::_=~.
>.}--e
I:Da:10._.
7 _.~--
,.~
'1"'"".
I ,.....
TURBIDITV V8 SUSPENDED SEDIMENT
CONCENTRATION
~!;RATROVICHIN9TTlNGHAM~GIH££~IH~CONSULTANTS
FIGURE 4.5
&DRAGE,INC..
[ I
other available data.It is important to incorporate all additional data
from the USGS 1982 field sampling program as it becomes available.Weekly
measurement of turbidity and sediment concentration in the Susitna River
near Chase will provide data to verify the relationship presented here.
These results can then be modified to account for the variation in
behavior in.lakes and rivers.
-24-
,~
-
,!""
r'~
5.WATANA RESERVOIR SYSTEM
5.1 Climate
Wind-induced mixing is one of the principal ~x1ng processes occurring in
the Watana reservoir.Winds blowing over the reservoir surface produce
turbulence in the upper layers and can initiate water motion in the
direction of the wind.
To carry out detailed wind analysis,data from three weather stations in
the Susitna Basin were reviewed.Data on wind magnitude and direction
from the Watana weather station were selected for use in analysis.This
station most nearly represents conditions at the reservoir and also has
the most complete record.
5.2 Hydrology
Case C intermediate flow and power conditions,presented in Volume 4,
Appendix A,of the Susitna Feasibility Report,has been used to provide
baseline hydrology information for determining monthly reservoir operating
conditions.
5.3 Sediment Regime
Data from several sources has been compiled to define the sediment regime
in the Susitna River near the proposed dam site.Historical data from the
USGS on sediment concentration and particle size distribution has been
summarized on a monthly basis for input into the DEPOSITS model using data
collected at the Gold Creek Station.Figures 5.1 and 5.2 present average
monthly sediment concentration with maximum and minimum values,and
average monthly particle size distribution.The crosses on both figures
indicate values used in the DEPOSITS model.
-25-
~:~-§=-:.--~1-
3 ___~:---:.1:--:---_.
--;-'~~~--!~I"~c
-:;'~"".-,.~.
,~-'
, I
, I
:!
, I
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I ,'I ,-'-+-,~+i-:+'-'-.-!--'--.........+-I-+-+-'....+ .'.-;-+-+'-11,....+-;-1:-4t=c=tt~=t=:::Ldttttll =bItt!:,~:p=:ttj;~~~·;~~~~::$~I;;'~~.-H-\-r-
i
-H;-t-I'+-I,"';",+,,~~~I~~M -j-i-+-
I,+1''''':-1
1000 i:i!.I ',J,.........:I !I :i ,~!!Ii!i I!Ii,iii::-~.~--:=-~t ~=---~::.:-.~
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7_---..:t:=
6 ._--
-~,-:"",:r
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1
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I ,
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I 'i
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II i t I
AVERA
,,
,
I
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I "T I 1 !I i \,i
I I I i II!I I I I ,,I .':!
I I !
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I----t=--zo
t=<2a:
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W
(,)
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(,).,.100 ..
t-~.I===::.Z 9 ---.~_
5.
~~_t ----.
4 _c:::::=yo,...
L._-
-:-MINIMUNI_~_
.-~:..-'"
-_"nOSSES:-SHOWtv AI;UES..
.HSED -IN--:DEPOSITS .MODEL -:~t '-+-7+
...,..;..'-1-+-+-1
!I I I """II.I I I I .1 ,I I
I I I I I ,I,!,I I I I I I I I .!I ,!!I , I I
i 1 :i I I !I I I I !,I I I i I I I
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JUN .JUL AUG SEP 'I
I :
I i
-_.
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,-
I
I
I
L.
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iI.
FIGURE ~1
&DRAGE;.INC.1=
,SUSITNA RIVER AT GeLD CREEK .
-SEDIMENT CONCENTRATION-SUMMER VALUES
ONLY t-r952-'~9B~)~.
~DOES NOT INCLUi>E 19iH USGS DATA~
[.'.--)I J J
"
I]
I
]J 1 --J 1
1/11 I I j_I....__.::IIIIH¥~+'••••.'",,IIIIIII W11
..._..tIlr-:'.,'.n l
I jlmrn~
~I,'<A:'Xli 'I
11-_....v -.rmffim,v.....x·..---n/._._nJ---I"
fill fl~~+t~-I IT·fH1'
80
100111Tll1f :1 --j ,I!-,-,-.'---,r=~"=f=-'-"--•j"i -...--I'- .0_~.""--,=--,-I I [11r1i '1111;1/ii'l ;1':Inn pi .'j"]
H f"I .\'=-:'-_.--...--.I I.1 11 -'----...fj +j lil l I !!!IIl)~7',~"I"I"1;\;1il,-----,'11--'"..-...--I-!II !I!I';"~P:/lr t'1\".,.•............I'--....--.-.-,,h;;..".j.;t 'I j
90HJ"-i ·t .1-..---.-I j 1--..·------tU-~~,!~W'f ':-'1111
I I ..-.-'-.-.----wtml I!..I II "11 l'ill--II I~--..- -_...-'....1 --------_.-'''.;'I'I II'I ['.
--"fI~I "I .I'-I --j -..----_.V't I .Ii'
11.1 j I ~"j ~=~~:-:.~..---~:-.I:~illl;r-f-:-:?•.~--'-ht,~:'-"i r-J I'I
It
-I ......--..-.-.v .._......-.,;I~1 I I
.II...-----I-.----._..I ...-..-I L/,}I II Ii I I.
7...1 r :J -I-~_.-.J w-..J4J..+~.I,I j'.!I 11111
-"1 ,-.
-.I··,,~80 jl II ill!111l!1 " ,
I-50 .,I '1
1
I I -"~
a:I I I I'~<C 'I
Q,40 I ill ..'1-~'-1.1 ii"j I!I2:I I'I r
ffi •.J i ~'.~,:1
1
:I..,_
1&0 ,J\)~,U"f ,i'l ----- -X""CROSSESiS 0 "cu .EUS Cft ,'I',20 -F;'U$1'~I 'I-"',I I •..,.,.".•.I'j";--"...~.t~..99~~,I lJ--...:~----1-1 -EPdsIT"00 II'[Ii '.'.i'~!~,
.':y!!~!I:~'~I'11 .llv''_:. .I .==_,~.l),__,~'II ~ll1 jilli I ii'":~•.'II.:~'4 j iIn 'j ~llllllLi _if,II".---!/-----.---..-III .1·,I I'I,10f~k11 I LUfF.!!ft ----,-----...-..'1 !I!!I !!i .!!, I j I ,.--.---...",----.'i :,II:I·rwr !.I 11)Iljl/1 I II,.".""."I.I I ....-.--I lUI I t i ;11:r IIIIi II:I.'It-IH -H I,,I 11 -..ill,11 I~~a!.-.....'!;~f I I ;'1'1,Ii 1 II iI~
.802 .004 .008 .016 .031 .062 .12&0.26 0.50 1.0
I ..-"-'~SILT'----~--;;~';;';~';"LESIZE'(m~SAND'--I
.FIGURE 5.2'
~~RATROVICH.NOTTINQHAM &DRAGE,INC.I
~.ENQIN,EERI~~CONSULTANTS
SUSITNA RIVER AT GOLD CREEK
AVERAGE MDNTHLV PARTICLE SIZE DISTRIBUTION
During the summer of 1982,anextensive sediment sampling program was
carried out by the R&M Consultants,Inc.,and the USGS,to improve
understanding of the existing sediment regime.Samples collected on a
weekly basis through the summer months included turbidity,sediment
concentration,and bedload.Analysis of the turbidity samples is
complete,however,sediment concentration and bedload sample analyses have
not been completed at this time.When these results become available,
they should be incorporated into the statistical analysis of turbidity
versus sediment concentration to add strength to the correlation.
For this report,existing turbidity versus concentration values for the
Susitna River at Cantwell (Vee),at Gold Creek,and near Chase have all
been combined to revise the regression line presented in the earlier
report.Figure 4.4 shows the new regression line used to convert
predicted sediment concentration in the reservoir to turbidity.
5.4 Reservoir
Information on daily inflow to reservoir and proj ected powerhouse flows
used in determining monthly water retention time,flow-through velocities,
and live storage for the reservoir have been taken from the Susitna
Feasibility Report,Volume 4,Appendix A.Table 5.1 shows the resulting
monthly values of the above mentioned parameters used in this report for
modelling and analysis.
-26-
·-~1 T"-.
.J ]1 ,,".-]I --1 -J 1 .J -J ]])--I 1
TABLE 5.1
WATANA RESERVOIR CHARACTERISTICS
RETENTION .RESERVOIR
POWERHOUSE AVERAGE WATER SURFACE AT END STORAGE VELOCITY TIME LENGTH
INFLOW(efs)FLOW FLOW OF MONTH (tt.)(ae.ft.)(fps)(yrs)AT END OF
HONTH Ava.MAX.MIN.(ere)(ers)AVa.MAX.MIN.LIVE TOTAL LIVE TOTAL LIVE TOTAL MONTH
OCTOBER 4513.1 6458.0 2403.1 7370.5 5941.8 2177 2185.6 2122.5 3.98 X 10 6 9.27 X 10 6 .009 .004 .93 2.15 49.3 mUes
NOVEMBER 2052.11 3525.0 1020.9 8723.6 5388.0 2166 2173.2 2112.6 3.67 X 10 6 8.97 X 10 6 .009 .004 .94 2.30 46.11.
DECEMBER 1404.8 2258.5 709.3 11135.4 6270.1 2150 2155.9 2097.3 .3.22 X 10 6 8.51 X 10 6 .011 .004 .71 1.67 47.2
JANUARY 1157.3 1779.9 619.2 9535.0 5346.1 2133 2138.2 2081.2 2.75 X 10 6 8.04 X 10 6 .011 .004 0.71 2.08 46.9 miles
FEBRUARY .978.9 1560.4 602.1 9150.3 5064.6 2119 2122.0 2068.5 2.35 X 10 6 7.64 X 10 6 .012 .004 0.64 2.08 46.6 miles
MARCH 898.3 1560.4 569.1 6865.11 3881.9 2107 2110.0 2054.5 -2.01 X 10 6 7.30 X 10 6 .011 .003 0.71 2.60 46.4
APRIL 1112.6 1965.0 609.2 6176.9 3664.7 2097 2100.0 2045.3 1.73 X 10 6 7.02 X 10 6 .012 .003 0.65 2.611 46.2
MAY 10397.6 15973.1 2857.2 5767.5 6082.5 2106 2119.1 2045.2 1.99 X 10 6 7.28 X 10 6 0.023 0.006 0.34 1.24 46.4 miles
JUNE 22912.9 42841.9 13233.4 6099.7 14506.3 2139 2164.7 2075.9 2.91 X 10 6 8.21 X 10 6 0.028 0.010 0.28 0.78 47.0 miles
JULY 20778.0 28767.4 14843.5 5483.7 13130.9 2166 2190.0 2109.0 3.67 X 10 6 8.97 X 10 6 0.021 0.009 0.39 0.94 46.4 mUes
AUGUST 181131.4 31435.0.7771.9 9329.3 13880.3 2181 2190.0 2130.3 II .10 X 10 6 9.39 X 10 6 0.020 0.009 0.41 0.93 49.7 miles
SEPTEI-lBER 10670.4 172Q2.~~10158.7 10414.5 2182 2190.0 2126.8 II .13 X 10 6 9.41 X 10 6 0.015 .hQQ1 0.55 1.25 49.8 miles
AVERAGE 79112 42841.9 569.1 7983 .7741.5 2150 2190 2045.2 3.04 X 10 6 8.33 X 10 6 0.015 0.006 0.60 1.711 47.7 miles
(efs)(ere)(ers)(efs)(ere)(ft.)(ft.)(ft.)(ao.ft.)(ae.ft.)(fps)(fps)(yrs.)(yrs.)
6.ANALYSIS OF SEDIMENT BEHAVIOR
6.1 Quiescent Settling
a.DEPOSITS Model
In order to allow for an initital start-up period,the model was run for a
period of four average years.The resultant steady state discharge
sediment concentrations are summarized in Table 6.1.The discharge values ~
range from approximately 0 to 60 mg/l for the upper portion of a dead
storage area of 900,000 acre-ft.,and range from °to 100 mg/l for the
upper portion of a dead storage area of 5,290,000 acre-ft.
An additional run was done assuming all the volume below elevation 2,050
feet to be dead storage.In this run,the discharge was assumed to occur
uniformly over the full depth of the active storage zone,i.e.above 2,050
feet.The results are similar to those using a dead storage value of
5,290,000 acre-feet.As mentioned in Section 4.3,the.program neglects
dispersive mixing.The range of values stated using all the different
dead storage areas is therefore probably over estimated.
The amount of dead storage selected represents a range from a minimum
value of approximately 10 percent of the total storage to maximum level
equal to the annual average difference between total and live storage as
reported in Table 5.1.
The trap efficiency predicted by these model runs ranges from 94 to 96
percent,depending on the dead storage area.The inflow and predicted
outflow sediment gradation curves are shown in Figure 6.1.It can be seen
that only particles with diameters of 2 microns or less travel through the
reservoir under quiescent conditions.
As the model does not take into account horizontal mixing,and because it
is difficult to predict the actual amoupt of dead storage,it is not
possible to estimate the time variation of sediment concentrations at the
discharge point.
-27-
--_.---_....----..__._-----
-
,r--
1 i ]]--J J 1 1 -]~-~]]----J ~-J -J '1
TABLE 6.1
RESULTS OF "DEPOSITS"MODEL HUNS
SEDIMENT CONCENTRATION (mg/l)
INFLOW OUTFLOW
DEAD STORAGE
SIMULATION VOLUME SUMMER TRAP
CASE ACRE.FT.PEAK AVERAGE MAXIMUM AVERAGE MINIMUM EFFICIENCY (%)
Quiescent 900,000 1197 773 61 30 °96
5,290,000 1197 773 95 56 2 94
Volume below 2050'1197 773 94 54 5 94
Minimum 900,000 1197 773 211 84 2 93
Mixing 5,290,000 1197 773 213 121 2 87
Volume below 2050'1197 773 224 134 12 86
Maximum 900,000 1197 773 .316 124 3 90
Mixing 5,290,000 1197 773 316 179 2 81
Volume below 2050'1197 773 345 206 18 78
Note:•Assume uniform withdrawal over depths at discharge end of reservoir.All other runs assume withdrawal is
limited to upper 25%of depth at discharge end of reservoir.
.4 .6 .8 1.0
·MM -----------.-1
I----t----+--+--~·-···-·..
l-t-~-
8'0 8'0 100
.1 .2-.--...-·......."1'I-~......-·---
40
--~-·--·I-ljlHH 11 j
-.._-,-_.._-------_._---_.._-+--
~---I---t--+_4-<-~-
. 0 t::ttlttJ tttilitlt1lt11ttttl 11 t~111111111Ittr!1llllJ111AIIt1I11~\7tTrl Tr 11~'o
~--_...-_.----.-..--.---------MICRONS
PARTICLE SIZE .__.....
I Ii 1.1.'.'.'I..,'11:11:'IL!'.'.i.'.la"!II'IIIIH Illffi~1'111,1-+-+++-lJJ+1W,IWi IHlllTI@lflIUIUW1IIP lll[,ili\.}-tt-'HJ~'nrmi"l'\III rmnm~QUIE5C~N .SE1;';rI:-I.,.,d ,I!i !!1!P7APP ·OX!.CUI VE U.=;i'~G'~~MP~~:l (t~~3 ~P"'UTI.O 'Iill l!!.l'li!!'lH II!JIt i llil ilil if!:illi ill:.11",III11 i ~:II II iI 1111 1'1 Hi I!ii 'Ii I':Illi 11111;fli'..,'II,,II~I!:"',!I,,:III~I100jllKiill!.li~.::,~~jnl~~rI1Ij:rl ill.i;8(CillI1111 1111:Iii I '1111 '11 i lil'I'li -~IMF~O Ii I jI iII ill!i~li i~mwiii
I 1::/'1'1 11.lU2D "ulY.;:~V',r/I Ifl It!'F~.1/..I Ii ~j I ,,:11)rl .~I I I r I T ~rrH·....
901 -41'.!.U"!X'lji1U1ITW:~)~IMI~lrv U:J~r,!~:i iV =.:.~.-.".~-.II I II III [.Ii'I :..--....11'D I 1[1 11'I'l.....--.i !~Vi I .~"If G ·11 n~....__._ _II i !__.... ..,.....-.-·1,/,l -,.J ~'1'111 ~n:'-'~'ild~!~111·_"r~_.__..--..I I I 1 ...-.-• - 1 I I II I,..!..w-r---.----r ..-~~j I "lliill 111 II,l)I!1 ,
N 80 .lI:1"".'1 "7,1 .,f'::t .'l"jl I -..-----...---..- .I I 1;;~=~~...~=:::-.~-~I:.'~ij'l'IIII1 .'1''~I .:..r-::-..;=~:.~".-----.1-"-"-~:.-.-~-.___--
w .--..~'~j'1'1 I I.II I,MA,Xlf,II ~M'-.:-.-I.~:.~_~k...~.-...t
..I ..--..--.-~9'>t !1,..,'II,I IN""'"I.'.
o 7..I'J 1'//I j"M X,.".....- .I V'-1--....1 [111'[jli=~==.~1=..:--.--l~!I'- .II ..~[.I _I~_~___ . --'_1_--I I(J~I~I==-~~:.---I .1-1 -fI 1111 .lll~I I ,----I ..-.---!I'.i~11
80 II " ".1::..1 _.1·i III0..._.._._.~.·i'l~i';..-..--.....-__.._._1 ".',lv:;'...-r---..- - ......,t Iz ---...--..,I;t'1 ,.-'-"--..---..---...,I
c .----.........-.".1 I~.±~:;.-II ,.j I ---.-....-........-"".-.-.II .'..f I.1.::I:-1-.....-..t..;.~'ItTI'r r-m~j I ".
1-50 .:;.r-'b1~~..---r--"'--"-'"I·~I I'ij:,,='~--:i,Iift'till 11 ,.'...,I=;=~::::::.I .,I!~~~N~D A ~1
0
d~r 'ff Ilila40-I--'1 ;1 I I;:!)J.I ..,_,"''''c..~clof.)QO AC ~i!:fl jl II II .1 'I lid- -.'-...-..It-.....--1---....'-.,..,I 1 1~.1=I=i=~:::'.~--·1 j-t TIl .-11'I!I],-.j I Ii::::=":=~~_~~•i .11.-:'=".-.:..=t--l.~.--~-ll.l[t 1~~~'1 JIi I --.'11 111
--.'--....... . I 11 1'1 I I 1'-l.-.-..~1r"~l:Ja~t~1 ~:W ill_'j"W!eSO:::_~:_I~:~_~_~._~·__1 II I 11'1 -':1.!1,':~2-~.-.=·::---··-~-"llr:_:'-=-,:::r~.~f2~]'~Yf~~CtEI I'~III [11111a:'-r-.Ii I jj.:.!--:"I -.---.I)!"'A 'r.TO ~!,11 ' ,
I I .1-.-.....~,,.,W 1-.1---."..-_....;c--·.."-.........1"'.-.','","'-,:,-,-.,".'.1
Z 20 I I·:1'-"':-.c I'-_.:.1'.0'J.~~~ElO ':~5 'f il iii:-,....,~.•,.}',.--'.--'.'..•...,..1----,----".-.-..-.-.I-.•.•''- --.'.'I "j tl111.ll i 11.11.III"'0,=:~=',:~:;:ilrll illl •..I :~:=~~,.II ,~_,=_,......l~mlim II',
PARTICLE SIZE DISTRUBUTIDNS PREDICTED BVDEPDSITS MDDEL
~tP2
FIGURE 8.1.
PERATROVICH,NOTTINGHAM &DRAGE,INC.
EN~c .",'liNG C -":wTANr-''II
o ";;,"'"""-~V~:.fJ ';:;j>L-:-~;;,,,,I-\~0:;;!H,:,--,-;II a
')
.....
-
b.Camp Curves
The relationship shown in Figure 4.4 was also used to calculate the amount
of sediment that would settle out in the Watana reservoir.The monthly
sediment size gradation curves shown in Figures 5.2 and the corresponding
settling velocities contained in Table 4.1 were used.The integration of
the total amount of sediment which settles out was carried out using
particle sizes of·0.5,0.1 mIn,50,10,5,and 1 micron.Monthly reservoir
velocities were calculated by the following equation:
QL
v =
Vol
Where:
V =average longitudinal velocity through the reservoir (ft./s)
Q =average monthly outflow (ft.lIa)
K =length of reservoir (ft.)
Vol =average monthly reservoir volume (ft.3 )
Reservoir volumes were obtained from Table 5.1,and an average reservoir
length of 48 miles was used.Reservoir depths were calculated by
sUbtracting the average monthly reservoir stage from the minimum active
zone elevation of 1,950 feet,which is approximately 50 feet below the
power intake elevation.
The results of these analyses for the summer months are summarized in
Table 6.2.They demonstrate that a large proportion of the sediment would
settle out and that only particles of diameter of less than 3 to 4 microns
would leave the reservoir.
These results agree reasonably well with the DEPOSITS computer model
resul ts.The following sections describe how these results should be
modified to give a more realistic indication of sediment concentration by
incorporating the turbulent mixing in the reservoir.
-28-
TABLE 6.2
RESULTS OF QUIESCENT SETTLING ANALYSES
FOR THE WATANA RESERVOIR
Month
Percentage of Sediment
Inflow Running Through
the Reservoir -%
Approximate Maximum Size of
Sediment Particle Running
Through The Reservoir
(microns)
r""
May It 3
June 10 4
July 21 3
August 16 4
r~
September 17 3
6.2 Induced Mixing
Two approaches were adopted in quantitatively evaluating the mixing
induced by wind,thermal input,·and the inflow and outflow.The first
approach involved evaluating the effect of wind wave action only.For
each month of the year,the total period in which wave heights exceed
critical values was evaluated.The critical wave heights were those which
induce an orbital current of 2 x 10-4 ft./s at depths of 25 and 50 feet
respectively.
The second approach involved using the results of the Acres (1982)thermal
modeling of Watana Reservoir.The program was modified to print out the
shear velocities associated with wind and thermal mixing in t~e epilimnion
and with mixing induced by inflow and outflow in the hypolimnion.The two
approaches are discussed in more detail below.
6.2.1 Wind-Induced Mixing
The main objective of this analysis was to determine the impact of
oscillating wind-induced currents on small suspended particles.A
particle settling velocity of 2 x 10-4 ft./s was arbitrarily selected
for this study.It corresponds to a particle size of approximately 12
microns (see Table 4.1).
Equations for calculating oscillating wave velocities at depth for a
given wave height and period have been developed by the U.S.Army
Coastal Engineering Research Center (1977).These equations were
orbital velocities of 2·x 10-4 ft./s at depths of 25 and 50 feet
respectively.Effective wind fetches were calculated for the
reservoir for each 22 1/2 degree directional component.Using this
information in conjunction with the equations developed by the U.S.
Army Coastal Engineering Research Center (1981)for determining fetch
limited wave height and periods,and the critical wave heights
calculated previously,the corresponding critical wave speeds were
calculated.These winds speeds were calculated for each directional
component for each month during 1981,and for critical velocities
-29-
occurring at 25-and 50-foot depths respectively.
speeds and the resul ts of the monthly wind speed
analyses,the percentage of time the critical wind
in each month was calculated.For these analyses a
feet was used.
Using th~se wind
direction duration
speed is exceeding
water depth of 600
,-
The results of the analyses for the open water period are summarized
in Tables 6.3 and 6.4.The percentage durations reflect the
integrated duration of winds from all directions during that month.
seen,significant mixing to a depth of 25 feet occurs
and 55 percent of the time during the summer months except
month of August,when the prevailing winds were from the
significant reduction in mixing occurs at the 50-foot
The wave orbital.velocities above the indicated depths increase over
the value of 2 x 10-4 as one gets closer to the water surface.This
means that in the shallower layers,particles with settling velocities
much larger than 12 microns will be held in suspension by the wave
action.
The results of those 'analyses indicate that under certain conditions,
particles as large as 12 microns could pass through the reservoir.It
is important to remember that these analyses are based on 1981
recorded data and do not necessarily reflect average monthly
conditions.
Wind and Thermal Mixing
....
r·~!'
The dynamic reservoir simulation model,DYRESM,is a one-dimensional
(vertical)numerical model for the,prediction of temperature and
salinity in lakes and reservoirs.I t is a comprehensive model,and
attempts to model all the mixing mechanisms within the reservoir •
The model is provided with 6 hourly averaged input data,including ail"
and inflowing wate.r temperature,long and short wave radiation,and
-30-
Month
May
June
July
August
September
October
November
Month
TABLE 6.3
DURATION OF WAVE MIXING TO 25-FOOT DEPTHS
%of Month During Which Wind Waves Generate
Orbital Velocity Exceeding 2 x 10-4 ft/s
40
41
35
8
30
35
55
TABLE 6.4
DURATION OF WAVE MIXING TO 50-FOOT DEPTHS
%of Month During Which Wind Waves Generate
Orbital Velocity Exceeding 2 x 10-4 ft/s
May 4
June 2
July 1
August 0
September 1
October 0
,--November 12
.-_.~
.-~
-
II"'"
i I
evaporation.Withdrawal rates and changes in reservoir storage are
also specified.The model then simulates the vertical mixing due to
the meterologic forcing functions and turbulence introduced by the
inflowing and outflowing water.It is vertically layered and
calculates the temperature and salinity for each layer at the end of
each computational period.A detailed description of the model is
given by Imberger and Patterson (1981).Acres (1982)applied the
model to the Watana Reservoir for the May to October 1981 period.The
temperature profiles predicted by the model are shown in Figure 6.2.
Modifications have been made to the model in order to calculate and
print out the shear velocities induced by the mixing process.In the
epilimnion,the root mean square shear velocity of the velocities,
induced by convective penetration and by wind shear,and the
associated depth of mixing are calculated.This shear velocity is
assumed to be constant with depth over the calculated depth of
mixing.
Mixing in the hypolimnion is controlled by molecular diffusion and the
buoyancy frequency between the various reservoir layers,wind shear
transferred from the epilimnion,and the inflowing and out flowing
currents.The latter terms generally are several orders of magnitude
greater than molecular diffusion.The program prints out these
velocities for each of the reservoir layers for each calculation'time
period.
When interpreting the results,it should be remembered that the model
is one-dimensional,and that all the mixing parameters are averaged
within each layer over the entire width and length of the reservoir.
6.3 Sediment Reintrainment
As outlined in Section 4.5,reintrainment of particles around the edges of
the reservoir will occur,particularly during windy periods.Figure 6.3
illustrates the relationship between the mixing depth and the percentage
of the reservoir area in which water depths are less than the mixing
depth.This curve gives some indication of how much of the lake surface
would be subject to reintrainment.The 25-foot mixing depth calculated in
121011
WATER TEMPERATURE °C
4 5 6 7 8 9321250....-_--'-1-----t-_...l.-_-+-_---'-__.l-..-_....I..-_-+__L....-_+-_--.l-_--f
81243 ,
I
/
I
/
I
~/
)/
'•.:;:r-.-i';/-"-
81273
;X 4
I
i
-II
!
150 I
I
~
j
I
I
-I
I
I
-!
I
-I!
~X 1
I
200 -:x 2---------------1-------,-;-t'..........t-W-.L-----
J
I x 3
I
~-":E-
100 -l-----L----L --'---..........._
P5701.53
DC 30 SEP 82
SUSITNA HEP
RESERVOIR TEMPERATURE'MODEL
WATANA
FROM ACRES AMERICAN.INC•.
~alrOWlell.Nolllngllam •Drag••Inc.
~r-E;;gin.li:'f'i;'l9Consullants
FIGURE 6.~
,~
NOTE:CURVE VALID FOR RESERVOIR WATER LEVELS
BETWEEN 2050 AND 2200 FEET
I
20018016014012010080604020
OJ:;-.--l---t---I---+---+--+----f---+---+--O+--o
10
si
40
130
"'cr;'s>c::WeCbwUJI-
o:()
U.W
Ou.wLL.
CJ<
.<C <C
_I-1LI
2a:w<
(Jc::
Wa.
...............,_••0 _~':-~'"
.....
MIXING DEPTH (FT)
.
F;ELA7;CNSHIIl=BETWEEN MIXING Ceil=TH ANC
1=5:;:;C:=N,.AGE elF RfS5EiMVCIR Ai1EA AFFECTED
.ElV MIXING
!
Section 6.2 indicates that approximately 8 percent of the reservoir
surface area would be subjected to reintrainment of particles of sizes 12
microns and less,between 35 and 55 percent of the time during the summer
months (to be confirmed by reference to thermal model output).
Based on the above,it can be concluded that reintrainment would occur,
but that it would not present a major problem except during severe storm
events when the wave mixing depth exceeds 25 feet.
The results of the preliminary runs conducted on Watana using DYRESM model
summarized in Tables 6.5 and 6.6 indicate that under maximum wind
conditions,the shear velocity in the epilimnion and hypolimnion are
generally below 3 x 10-3 and 1.5 x 10-4 ft./s respectively.During calm
periods,these can drop to just above 3 x 10-4 and 3 x 10-5
respectively.The epilimnion values bracket the order of magnitude
numbers calculated using the wave equations as described in Section
6.2.1.
It should be noted that DYRESM Model runs to date have only been conducted
for the open water period.No data is available on the mixing that occurs
during the ice cover months.It is,however,not expected to be very
dissimilar to the values quoted above for the hypolimnion during calm
periods.
The DEPOSITS Model was updated to allow for the reduction in the
calculated settling velocities due to shear velocities.The effective
settling velocity was assumed equal to the quiescent settling velocity
minus the shear velocity.The upper quarter depth of the water plugs in
the model were subjected to the epilimnion shear velocity an the lower
three quarters to the hypolimnion velocity.As before,the inflow was
assumed to be well mixed over the full reservoir depth and all discharge
was taken from the top one-quarter depth.
The results'of these model runs are shown on Table 6.1.They indicate
that discharge sediment concentrations could range from below 50 mg/l
during quiescent conditions to over 300 mg/l during windy periods.
-32-
-
TABLE 6.5
ROOT MEAN SQUARE SHEAR VELOCITY OF VELOCITIES
INDUCED BY CONVECTIVE PENETRATION
AND WIND SHEAR
Month Average (fps)Maximum Minimum
F'"June 1.6 x 10-3 2.6 x 10-3 4.1 x 10-4
July 1.4 x 10-3 3.0 x 10-3 5.0 x 10-4
August 1.9 x 10-3 3.7 x 10-3 3.3 x 10-3
r~'
.-
TABLE 6.6
HYPOLIMNION MIXING SCALE
f··~
I"""
Month
June
July
August
Average (fps)
1.0 x 1O~4
6.3 x 10-5
1.1 x 10-4
Maximum
2.3 x 10-4
1.1 x 10-4
2.0 x 10-4
Minimum
5 8 10 -5• x
5.3 x 10-5
5 3 10 -5• x
As mentioned earlier,considerable care must be taken when interpreting
these results,as longitudinal dispersion in the reservoir is not taken
into account.Also,these values are only representative of conditions
near the dam.Higher concentrations could occur towards the upstream
reaches.
-33-
-i
rc,
of""
\
7.PROJECTED RESERVOIR TURBIDITY
All the anaytical work described above is based on limited data and very
idealistic models.In determining reservoir mixing velocities,the reservoir
has been treated as a one-dimensional body of water.This is a severe
limitation when one considers that the body of water is 48 miles long and
averages 1 1/2 miles wide.
In this section,an attempt is made to project expected reservoir turbidities
under post-project conditions.Because of the analytical limitations outlined
above,these projections must be regarded as tenta tive order of magnitude
estimates only.The values reported apply to conditions averaged over the
reservoir,and no attempt is made to distinguish between conditions at the
upstream and downstream ends respectively.
The first step in evaluating reservoir turbidity involves projecting likely
sediment concentrations in the lake by adjusting the values predicted by the
quiescent settling calculations for wind-and thermal-induced mixing.The
second step involves converting these concentrations to turbidity using the
curves presented in Section 4.6.
7.1 Projected Sediment Concentrations
It is assumed that sediment particles wi thin the reservoir will tend to
remain in suspension provided the mixing velocities are equal to or
greater than the particle settling velocities.This approach tends to
overestimate the sediment concentration in the reservoir,as some settling
will still occur even when the mixing velocity equals the particle
settling velocity.
7.2 Projected Turbidity Levels
Using the suspended sediment concentration versus turbidity relationships
given in Figure 4.4,the projected lake turbidities would be in the ranger
\
of 10-50 NTU's.
-34-
List of References for Sections 1,2,4,6 and 7
(1)R&M Consultants,Inc.,"Subtask 3.07 -Closeout Report -Reservoir
Sedimentation,"January 1982.
(2)Acres American,Inc.-New Report -Results of Temperature Modeling.
R&M Consultants,Inc.-New Report
Collection Program.
Results of Eklutna Data
(4)Fisher,H.B.,et al,"Mixing in Inland and Coastal Waters,"Academic
Press,1979.
(5)Imberger,J.,and J .C.Patterson,"A Dynamic Reservoir Simulation
Model -Dyresm:5,"Transport Models for Inland and Coastal Waters,
Academic Press,Inc.,1981.
(6)Simons,D.B.,and F.Senturk,"Sediment Transport Technology,"Water
Reservoir PUblications,Fort Collins,Colorado,1977.
(7)Graf,W.N•,"Hydraulics of Sediment Transport,"McGraw-Hill Book
Company,1971.
(8)McNown,et al.(1951)
(9)McNown &Malaika,(1950)
(10)McNown and Lin,(1952)
(11)Camp,T.R.,"The Effects of Turbulence on Retarding Settling,"
Proceedings Second Hydraulics Conference,University of Iowa,Studies
in Engineering,Bulletin 27,1943.
(12)Rouse,N•T• ,"Engineering Hydraulics,"John Wiles and Sons,Inc.,
1949.
-35-
.-
(13 )Acres American,Inc.-New Report on Thermal Modeling of Wa tana,
1982 •
.-~(14 )
(15 )
Acres American,Inc.,"Susitna Hydroelectric Project -Feasibility
Report,Volume 4 -Appendix A,Hydrological Studies,"Alaska Power
Authority,1982 •
.R&M Consultants,Inc.,-New Report on Data Collected From the Eklutna
Lake,1982.
(16)..Hartman,C.W.,and P.R.Johnson,"Environmental Atlas of Alaska,"
University of Alaska,April 1978.
(17)Hamblin,P.,Personal Communication,Canada lake for inland Water,
Burlington to Ontario,September 1982.
.,....
(18)U.S.Army Coastal Engineering Research Center "Shore Protection Manual
-Volume 1,II Department of the Army Corps of Engineers,1977.
U.S.Army Coastal Engineering Research Center "Coastal Engineerig
TeChnical Note -Revised Method for Wave Forecasting in Deep Water,n
CETN-1-7 3/1981.
-
'--r-
(20).Ward,AI,Maan,T.,Tapp,J.,"The DEPOSITS Sedimentation Pond Design
Manual,"Institute for Mixing and Mineral Research,Kentucky Center
for Energy Research Laboratory ,University of Kentucky,Lexington,
Kentucky,1979.
-36-
,'....
APPENDIX A
BIBLIOGRAPHY OF ADDITIONAL
INFORMATION SOURCES
.-
.-
.-
,-
,.,~
.-
-
i.
PART I
NEW ZEALAND LAKE STUDIES
Brodie,J .W.,and J.Irwin,1970,"Morphology and Sedimentation in Wakatipu,
New Zealand,II New Zealand Journal of Marine and Freshwater Research,4 (4):
479-96.
Study of the morphology of the lake floor has shown a system of current
channels developed by movement of underflows related to flood discharges
of inflowin~rivers,or turbidity currents generated by slumping of
previously deposited slope sediinents.For Lake Wakatipu,the surface
waters are reported to be clear at all times due the continuous sinking of
turbid inflowing water.
Irwin,J.,1968,"Observations of Temperatures in Some Rotorua District
Lakes,"New Zealand Journal of Marine and Freshwater Research,2(4):591-
605.
trwin,J,1971,"Exploratory Limnological Studies of Lake Manapouri,
South Island,New Zealand,"New Zealand Journal of Marine and Freshwater
Research,5(1):164-77.
Lake Manapouri develops thermal stratification by mid-summer 'and continues
into late fall.Near isothermal conditions exist in late winter.Water
temperatures below 200m is between 7.8 0 and 8.0 0 e throughout the year.
Surface temperature varies between 16.250 e in summer (January-March)and
8.0 0 e in winter (August -September).Tritium values suggest mixing has
taken place to at least 400m.
Irwin,J,1972,"Sediments of Lake PUkaki,South Island,New Zealand,"New
Zealand Journal of Marine and Freshwater Research,6(4):482-91.
Through most of the lake,excluding the delta slope,80-90%of bot tom
sediments are less than 8 microns.At great depths there is little
variation in spring and summer core samples.
---_._._---------
No information is given in the report on incoming suspended sediment size
distribution or climatic conditions for the lake.However,the lake is
reported to be turbid throughout the year with average depth of disc
disappearances of 0.5 me.ters.
Irwin,J.,1974,"Water Clarity Records From Twenty-Two New Zealand Lakes,If
New Zealand Journal of Marine and Freshwater Research,8(1):223-7.
Four lake types were studied:
1)associated with glacial activity
2)associated with volcanic activity
3).formed by wind
4)formed by landslide
Water clarity values are greatest in lakes of glacial origin,as these are
generally the largest and deepest.However,values are affected by
glacial silt.Smaller and shallower lakes formed by wind and volcanic
activity have lower water clarity values.
Irwin,J.,1978,"Bottom Sediments of Lake Tekapo Compared With Adjacent Lakes
Pukaki and Ohau,South Island,New Zealand,"New Zealand Journal of Marine and
Freshwater Research,12 (3):245-250.
After travelling 1.3 km into the lake,25 %of bottom sediments are less
than 4 microns in size.However,water clarity values are low for this
deep,glacially fed lake.Average depth of disappearance of the secchi
disc was 4.9rn in May 1971 and 1.6m in April 1974.
~
Irwin,J.,1978,"Seasonal Water Temperatures of Lakes Rotoiti and Rotoroa:jj,
South Island,New Zealand,II New Zealand Oceanographic Institute Records,
4(2):9-15.
Irwin,J.,and R.A.Heath,1972,"Winter Temperature Structure in Lake
Atiamuri and Ohakuri,New Zealand,"New Zealand Journal of Marine and
Freshwater Research,6(4):492-496.
"~
,-pBIlIl
Li!
I~Nin,J.,and V.Hilary Jolly,1970,"Seasonal and Areal Temperature
Variati on in Lake Waka t i pu (N ote),n .:;N:.:e;.:;w:......;;;Z:.:e;;:;a;,;;l;;:;a::.:n:.;:d:....-..;.J..;;o..;;u;.;;.r~ri:.::;a;,;;l;........;;o_f_.;.;M;;:;a;;;.r.;;;i~n;.;;e_.;;;a~n=d
.:.F.:.r-=e,::;s~hw,;,;;a::;;.t~e:;,;;r~R~e;.;;;s..;;e.;;;a;;;.r.;;;.c_h,4 (2 ):210-6
Irwin,J.,and R.A.Pickrill,in press,"Water Temperature and Turbidity in
Glacial-Fed Lake Tekapo,"New Zealand Journal of Marine and Freshwater
Research
Surveys of lake temperature and turbidity suggest a seasonal cycle of
lake-river interactions.Waters are clearest in early spring.Inflowing
water either interflows or underflows down-slope to the deepest basin.
Corio lis force deflects inflowing water to the east.Lake water
stratifies as summer progresses.Significant diurnal fluctuations result
from water travelling through wide braided delta channel.Turbid water,
at 5 times the lake concentration,enters the lake as interflow.Winter
is associated with near isothermal lake water at aOc but the lake remains
turbid.Cold inflowing water (2-3 0 C)underflows to deepest basin.
Jolly,V.H.,1975,"Thermal conditions,"New Zealand Lakes,V.H.Jolly and
J.M.A.Brown,eds.,Auckland University Press/Oxford University Press,p.90-
105.
of June to
lakes when
r~
!
!
Important thermal regime characteristics for the New Zealand
investigated show:
1)The coldest temperatures occur from the end
mid-August and full circulation for stratified
hofomictic would be at least three months •.
lakes
•?"",
i
-
2)Warmest temperatures are found from mid-December to mid-March,
but usually in January or February •
Thermoclines,particularily in large deep lakes,form late in
the warming period because of strong winds and develop very
deep epilimnia.
i
I
I ~
4)Many relatively deep lakes do not permanently stratify,because
of the turbulent waves created by winds blowing over long
fetches.
5)The annual temperature range is not as great as that observed
in most lakes in similar latitudes due to mild oceanic
climate.
Jowett,LG.,and D.M.Hicks,1981,"Surface Suspended and Bedload Sediment -
Clutha River System,"Journal of Hydrology,20(2):121-130.
Pickrill,R.A.,1980,"Beach and Nearshore Morphology and Sedimentation in
Fiordland,New Zealand:A Comparison Between Fiords and Glacial Lakes,"New
Zealand Journal of Geology and Geophysics,23:469-480.
Pickrill,R.A.,and J.Irwin,in press,"Sedimentation in Deep Glacier-Fed
Lake,Lake Tekapo,New Zealand,"Sedimentology
Major controlling processes of sedimentation in Lake Tekapo:
1)Single dominant inflow at head of lake has resulted in delta
progradation.
2)Underflows .appear to be predominant inflow mechanism during
spring freshets and floods.
Small changes in bed morphology can produce large changes in
sedimentation rates over short distances.Morphology controls
the direction and distance travelled by underflows.
4)Across lake variaton in sedimentation rates are controlled by
Coriolis force deflecting inflowing water.
.~,.
5)Seasonal cycle of sed.input controls temporal variations in
sedimentation rate and texture.
,--.~
6}Lake level fluctuations redistribute coarse sediment
downslope.
Rotational slumping redeposits delta sediments down lake.
Pickrill,R.A.,J.Irwin,and B.S.Shakespeare,1981,"Circulation and
Sedimentation in a Tidal-Influenced Fjord Lake:Lake McKerrow,New Zealand,"
Estuarine,Coastal and Shelf Science,12:23-37.
Stout,V.M.,1978,"Effects of Different Silt Loads and of Hydro-Electric
Developments on Four Large Lakes,"Verh International Verein Limnol,20:1182-
1185.
Brief review of key basin and lake characteristics for Lakes Tekapo,
Pukaki,Ohau,and Benmore including physical features,mean and maximum
SECCHI disc readings,and kinds of phytoplankton present.
Stout,V.M.,1981,"Some Year to Year Fluctuations in a Natural and in an
Artificial Lake,South Island,New Zealand,"Verh International Verein Limnol,
21:699-702.
Both chlorophyll a content and zooplankton populations have retained
similar seasonal patterns.However,turbidity of the water in both lakes
during spring and summer months has shown significant changes from year to
year due to climatic variations.
Thompson,S.M.,1978,"Clutha Power Development -Siltation of Hydro-Electric
Lakes,August,1976,"Environmental Impact Report on Design and Construction
Prooosals,New Zealand Ministry of Works and Development.
Report describes siltation problems in the Clutha River,processes causing
the problems and possible remedies.
Appendix 2 describes the method used·to determine the grain size
distribution in the total load of the river from the distribution of
sediment grain sizes on the lake bed.
PART II
GENERAL INFORMATION
Baxter,R.M.,and P.Glaude,1980,"Environmental Effects of Dams and
Impoundments in Canada:Experience and Prospects,"Can.Bull.Fish Aguat.
~,205:34 p.
Brylinsky,M.,and K.H.Mann,1973,"An Analysis of Factors
Productivity in Lakes and Reservoirs,"Limnology and Oceanography,
14.
Governing
18(1):1-
,.~
;.~
:,,
Data collected from 43 lakes and 12 reservoirs from the tropics to the
arctic showed that variables related to solar energy input have a greater
influence on production than those related to nutrient concentration.
-Morphological factors have little influence on productivity pel"unit
area.
Csanady,G.T.•,1978,"Water Circulation and Dispersal Mechanisms,"Abraham
Lerman,ed.,Lakes:Chemistry,Geology and Physics,Springer-Verlag Press,
New York,Pages 21-64
Conceptual model developed to describe lake hydrodynamics including
special cases for long and narrow basins with discussions on such things
as effect of bottom friction and coriolis force,coastal jets,and
spontaneous thermocline movements neal"shore.
Elder,Rex A.,and Walter O.Wunderlich,1972,"Inflow Density Currents in TVA
Reservoirs,"Paper 7,International Symposium on Stratified Flows,
Novosibirsk.
Irwin,J.,1975,'!Morphology and Classification,"V.H.Jolly and J.M.A.Brown,
eds.,"New Zealand Lakes,Auckland University Press/Oxford University Press,
Pages 25-56.
Kellerhals,R.,M.Church,and L.B.Davies,1979,"Morphological Effects of
Interbasin River Diversions,"Can.Jour.Civ.Eng.,6:18-31.
Kellerhals,R.,and D.Gill,1973,"Observed and Potential Downstream Effects
of Large Storage Projects in Northern Canada,"Proceedings of 11th
International Congress on Large Dams,Madrid,1973,Pages 731-753.
Kinnunen,Kari A.I.,1981,Itproblems Connected with Modeling Artificial Lakes
in Finland,"Unpublished Report,National Board of Waters,Finland.
Kinnunen,Kari A.I.,B.Nyholm,and J.S.Niemi,1981,"Ecological Model of a
Subarctic Lake,"Verh.Internat.Verein.Limnol"21:102-108.
o Variation of EPAECO model calibrated for temperature with ice cover
and effect of wind mixing on Finland Lake Paijanne.
o Max.surface temp.in early August (-18o C).
o Thermocline at 10-20m below surface-average max.depth at 30m in
mid-September.
-
o Bec.omes isothermal by early-mid November.
mid-May.
Stays isothermal until
o Effect of wind especially important in early summer when stratif.
period starts.Without wind consideration simulated temperature
stratification is too steep.
Kinnunen,Kari A.I.,J .S.Niemi,T.Frisk,T.Kyla-Harakka,1981,"Water ~
Quality Modeling at the National Board of Waters,Finland,"Unpublished
Report,National Board of Waters,Helsinki,Finland.
o
o
Evolution of the FINNECO model from the EPAECO model.
New model includes:mixing effect of wind
precipitation of phosphorous
new temp.correction
ice formation routine
denitrification process
/r""
I
!
o Investigation of some river water quality models.
Kjeldsen,0.,1981,"Sediment Transport Studies in Norwegian Glacial Streams,
1980,"Report 4-81,Norwegian Water Resources and Electricity Board,Oslo,
Norway.
Kjeldson,0.,and G.0strem,1977,"Sediment Transport Studies in Norwegian
Glacial Streams,1975,"Report 3-77,Norwegian Water Resources and Electricity
Board,Oslo,Norway.
Kuenen,Ph.H.,1968,"Settling Convection and Grain-Size Analysis,"Journal of
Sed.Petrology,38:817-831.
Lambert,A.,and K.J.Hsu,1979,"Non-Annual Cycles of Varve-Like
Sedimentation in Walenese,SWitzerland,"Sedimentology,26:453-461.
o multiple layers deposited in lake bed represent continuous-fed
turbidity currents generated by hyperpycnal inflow during river-flood
stages.
o Currents with bottom velocities up to 50 em/sec.were detected during
summertime even when the lake is thermally stratified.
f"'"i
l
Lambert,A.,and S.M.Luthi,1977,"Lake Circulation Induced by Density
Currents:An Experimental Approach,"Sedimentology,24:735-741.
Saltwater was continuously fed into a tank of freshwater to model
turbidity underflows caused by flood-stage discharge.
In most cases the height of lake water dragged along by the underflow is
about equal to the underflow thickness.Maximum return velocity occurs in
the lower (denser)parts of a lake basin.
Lee,Dong-Yang,W.Lick,and S.W.Kang,1981,"The Entrainment and Deposition
of Fine-Grained Sediments in Lake Erie,"J.of Great Lakes Research,7(3)224-
233.
o Provides quantitative data on the entrainment rates.Variations
depend on shear stress,water content and type of sediment (size and
mineralogy).Vertical variation in thin surficial layer active in
deposition -entrainment produce different entrainment rates.
a effect of benthic organism not considered.
a Main cause of entrainment is oscillating wave action.
o Report does not include settling,flocculation,and mechanical
degradation in calculations of sediment transport in a lake.
Lerman,A.,Devendra Lal,and Michael F.Dacey,1974,"Stoke's Settling and
Chemical Reactivity of Suspended Particles in Natural Waters,"R.Gibbs,ed.,
Suspended Solids in Water,Plenum Press,New York,Pages 17-44.
Organization for Economic Cooperation and Development,1979,Joint Activity on
Multi-Purpose Hydraulic Projects:The Planning of the Vuotos Reservoir,
National Board of Waters,Finland.
0strem,G.!T.Ziegler,S.R.Ekmkan,H.C.Olsen,J.Andersson,and B.Lunden,
1971,Studies of Sediment Transport at Norwegian Glacier Streams,Stockholm
University,Department of Physical Geography,Report 12,133 pp.
Ragotzkie,R.A.,1974,
Superior,"Proceedings
Pages 456-461.
"Vertical Motions Along the North Shore of Lake
from the 17th Conference on Great Lakes Research,
C
!
Slow net upward motion has been documented in Lake Superior.Vertical
motion extending from as deep as 190 meters to near surface levels with
vertical velocities up to 30 meters per day have been observed during the
period of thermal stratification.
",""
I:"""
!;
,-
Ritchie,J.C.,Frank Schiebe,and J.Roger McHenry,1976,"Estimating
Suspended Sediment Loads from Measurements of Reflected Solar Radiation,"
H.L.Gotterman,ed.,Proceedings of the 1st Symposium on Interaction between
Sediments and Freshwater,Amsterdam,1976.
Data from temperate region lake has shown that a quantitative relationship
exists between surface suspended sediments and reflected solar
radiation.Most significant in the wave lengths between 700-800 mm.
Concentration of surface suspended sediment can be used to estimate total
suspended sediment concentration in a vertical water column.
Scott,Kevin,M.,1982,"Erosion and Sedimentation in the Kenai River,
Alaska,"Geological Survey Prof.Paper 1235,3lJ pp.
o Sediment concentration generally lower primarily due·to storage in
lakes.
o Give sediment concentration for Kenai River at Soldotna and
Kenai River at Cooper Landing.
No turbidity measurements reported.
No turbidity-sediment concentration correlation presented.
Shuter,N.,K.Stortz,G.Oman,M.Sydor,1978,"Turbidity Dispersion in Lake
Superior Through Use of Landsat Data,IT Journal of Great Lakes Research,
4(3-4):359-360.
Sly,P.G.,1978,"Sedimentary Processes in Lakes,"Abraham Lerman,ed.,Lakes:
Chemistry,Geology and Physics,Springer-Verlag Press,New York,Pages 65-
89.
)~
o Review and discussion of various factors influencing sedimentary
processes in lakes including,but not limited to,lake morphology,
characteristics of inflowing sediment,and climatic settling.
Stortz,K.,R.Clapper,and M.Sydor,1976,"Turbidity Sources in Lake
Superior,"Journal of Great Lakes Research,2(2):393-401.
o Strong correlation found between average turbidity and average
suspended load of red clay in turbidity plumes.
o Major source of turbidity due to shoreline erosion by wind driven
waves during ice free season.
o Most of scattered light observed arises from fines less than 3p (=25%
of bank material).
I
I
I
I.
o For maximum sediment concentration observed in plume =20 mg/l
T(NTU)18.5 based on correlation
S =1.3 x T -4.0
o Sediment resuspension in winter with partial ice cover
=10 6 metric tons
o During severe storms:range =5 x 10 5 metric tons of eroded
material/storm.
Suggest 50%of lake turbidity comes from these storms.
Sturm,M.,1979,"Origin and Composition of Elastic Varves,"Ch.Schluchter,
ed.,Mora·ines and Varves-Origin,Genesis and Classification,A.A.Balkema,
Rotterdam,Pages 281-285.~
Sturm,M.,,"Depositional and Erosional Sedimentary Features in a
Turbidity Current Controlled Basin (Lake Brienz),t1 IXth International Congress
on Sedimentology,5(2):385-390.
Sturm,M.,and A.Matter,1972,"The Electro-Osmotic Guillotine,A New Device
for Core Cutting,"Journal of Sedimentary Petr61ogy,42(4):987-989.
--
.,..,.
rp-
"l.i
1
'1"""
, Il.~
r~
!L:
Sundborg,Ake,1980,"Symposium Theme No.IV:Reservoir Sedimentation,"
Proceedings of the International Symposium on River Sedimentation,Beijing,
China,March 24-29,1980,Pages 1325-1333.
Sundborg,Ake,1981,"Environmental Problems of Reservoir Development with
Special Regard to Conditions in Sweden,"Proceedings of the International
Symposium of Reservoir Ecology and Management,Quebec,June 1981,Pages 63-
72.
Thomas,R.L.,1968,A Note on the Relationship of Grain Size,Clay Content,
Quartz and Organic Carbon in Some Lake Erie and Lake Ontario Sediments
Wunderlich,Walter .0.,,"The Dynamics of Density-Stratified Reservoirs,
Gordon E.Hall,ed.,Reservoir Fisheries and Limnology,Special Publication
No.8,Pages 219-231.
Data from Tennessee Valley Authority field investigations are used to
illustrate dynamic reservoir processes and their influence on water
quality.Water movement into,within,and out of,the reservoir in the
presence of density stratification are described.