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ALASKA POWER AUTHORITY
SUS ITNA HYDROELECTR IC PROJECT
TASK 3 -HYDROLOGY
WATER QUALITY EFFECTS RESULTING FROM
IMPOUNDMENT OF THE SUSITNA RIVER
DECEMBER 1982
Prepared for:
ACRES AMERICAN INCORPORATED
1000 Liberty Bank Building
Main at Court
Buffalo,New York 14202
Telephone:(716)853-7525
Prepared by:
L.A.PETERSON &ASSOCIATES
118 Slater Drive
Fairbanks,Alaska 99701
Telephone:(907)456-6392
and
R&M CONSULTANTS,INC.
P.O.Box 6087
Anchorage,Alaska 99503
Telephone:(907)279-0483
ARLIS
Alaska Resources
".b..&InformatIon ServlcesLlrary..Anchorage,Al~ka
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ALASKA POWER AUTHORITY'
SUSITNA HYDROELECTRIC PROJECT
TASK 3 -HYDROLOGY
WATER QUALITY EFFECTS RESULTING FROM
IMPOUNDMENT OF THE SUSITNA RIVER
TABLE OF CONTENTS
ACKNOWLEDGMENTS.
1 -INTRODUCTION
2 -IMPOUNDMENT EFFECTS
Impoundments Processes and Interactions
2.1.1 -Processes
2.1.2 -Interactions
Sedimentation/Tu rbidity
Metals
Leaching
Heat Transfer/Evaporation
Dissolved Oxygen
Trophic Effects
2.7.1 -Introduction
2.7.2 -Results
2.7.3 -Population Equivalent
2.7.4 -Conclusion
2.7.5 -Summary
3 -DOWNSTREAM EFFECTS
3.1 -General
3.2 -Suspended Solids/Turbidity
3.3 -Heat Transfer
3.4 -Dissolved Oxygen
3.5 -Gas Supersaturation
4 -CONCLUSIONS
5 -REFERENCES
A TT ACHMENT A
1-1
2-1
2-1
2-1
2-3
2-5
2-6
2-7
2-7
2-9
2-11
2-11
2-12
2~17
2-18
2-18
3-1
3-1
3-1
3-2
3-3
3-3
4-1
5-1
ACKNOWLEDGMENTS
This report was prepared by Laurence A.Peterson and
Gary Nichols of L.A.Peterson &Associates,Inc.,under
subcontract to R&M Consultants,Inc.Literatu re searches were
provided by Linda Dwight.Additional references were supplied by
Stephen Bredthauer (R&M Consultants),Paul Woods (U.S.
Geological Survey),and Jeff Koenings (Alaska Department of Fish
and Game -FRED,Soldotna,Alaska).The report was reviewed
and edited by Stephen Bredthauer.Typing was done by
Kyin-Kyin Chen.
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1 -INTRODUCTION
The characterization of stream water quality is of vital importance
in making sound watershed management decisions.An assessment
of the physical and chemical quality of Susitna River water and the
potential impacts resulting from its impoundment are discussed in
this report.
If the Susitna Hydroelectric Project is developed,the Watana Dam
will be 860 feet high and will retain 9.6 million acre-feet of water
at full storage.The 'area of ,the reservoir at the maxium operating
level will be 38,000 acres.The Devil Canyon Reservoir will be
smaller,covering 7,800 acres at the maximum operating level,with
1.1 million acre-feet at full storage.The Devil Canyon Dam will
be 650 feet high.Either multi-level outlets or single outlets at a
depth no greater than 120 feet will be used.Consequently,
neither dam will have an outlet near the reservoi r bottom.
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2 -IMPOUNDMENT EFFECTS
The environmental conditions in an impoundment differ from those
in a flowing stream in many ways,including change in water
depth,increased detention time,and the possibility of
stratification,eutroph ication,increased evaporation,sedimentation,
and leaching.Each of these has an influence on the normal
physical,chemical,and biologic processes that cause changes in
water quality.Additional detention time allows natural processes
to proceed far beyond the extent feasible in a flowing stream.If
stratification exists,the bottom portion of the water (hypolimnion)
is trapped and does not contact aerated water or the atmosphere,
thereby having a matked effect on the natural processes that
occur in water,and leading to creation of poor-quality water.
Leaching also results in poor quality of the hypolimnion.
Eutrophication leads to algal blooms and nuisance conditions
throughout an impoundment,and evaporation concentrates the
dissolved fractions of minerals in water.
2.1 -Impoundment Processes and Interactions
The impoundment processes (stratification,eutrophication,
evaporation,sedimentation,leaching,and ice cover)are defined in
this section,and a summary of their interactions is presented.
The degree to which each of these processes is important in a
particular reservoir is variable,depending on geographical
location,climate,hydrologic regime,allocthonous nutrient inputs,
lake morphometry,biotic community activity,and inorganic
sediment inputs,as well as other parameters.
2.1.1 -Processes
Stratification.Stratification is a layeri ng of water because of
density differences,which can be caused by temperature or
sediment load.Stratification occu rs in the summer due to the
warming of the surface water by short and long-wave
radiation,by conduction,and by advection (Roesner,et al.
1971).Winter stratification can occu r in cold regions because
O°C water at the su rface is lighter than the warmer water
below (Kittrel,1965).Winter stratification is not as stable as
summer stratification,which is stable with cold,dense water
at the bottom and warmer,lighter water at the top,with very
little vertical mix-ing.The top layer of the reservoir (the
epilimnion)is of nearly uniform temperature,with the region
of changing temperature below the epilimnion called the
thermocline,and the bottom layer the hypolimnion (Symons,
1969).Only weak thermal stratification has been observed in
glacial lakes (R&M,1982b).Seasonal water temperature
fluctuations coupled with environmental factors such as wind
s18/a 2-1
velocity,direction and duration,and the geometry of the
reservoir basin create internal flow patterns that influence
water quality.Several distinct and independent currents may
exist simultaneously within a stratified reservoir.When river
water enters an impoundment it mixes and descends to a
depth at which the inflowing water has the same temperatu re
or density as the resident water.Depending on the
reservoir's temperature profile,inflowing water may travel
and remain as a surface-overflow current,an intermediate-
interflow current or a bottom-underflow current.Reservoirs
discharging water from the epilimnion encourage the
development of surface-type currents (Turkheim,1975).
Love (1961)noted·seasonal temperature gradient variations
and related them to seasonal salinity distribution and
circulation patterns in a reservoir he studied.At the time of
spring runoff,the temperature of inflowing water was about
the same as the surface of the reservoir and sediments settled
out rather quickly.Thus,in spring,inflow proceeds into
the reservoir as an overflow current.With the onset of
stratification,a vertical gradient of temperature and salinity
became established.Flow along the surface created cellular
circulation below the 150-foot level causing an upstream flow
along the bottom.In summer,inflow decreases in volume,
salinity increases,and river water proceeds as an interflow at
a depth of about 80 feet.In the fall,cool river temperatures
cause greater sin king of inflow water along the bottom until it
comes in contact with heavier layers,then spreads
horizontally.As reservoir surface waters become cooler than
deeper waters in the fall,vertical convection currents are
created,mixing reservoir waters until an isothermal state is
achieved (Smith and Justice,1976).
Eutrophication.Eutrophication is a term meaning en richment
of waters by nutrients,either man -induced or th rough
natural means (Mackenthun,1969).Phosphorus and nitrogen
are the fertilizing elements most responsible for lake
eutrophication.However,carbon and silica are important
nutrients in some systems.I ron and other trace elements
may also be important to a limited extent.
Evaporation.The major effect of evaporation on water quality
is the resulting hi9h~r concentration of dissolved substances
(Symons,1969;Love,1961).In Alaska,cool temperatures
and abundant water indicate that evaporation may not be
critical.Sublimation from ice and snow,however,may cause
significant water loss (Smith and Justice,1976).
Sedimentation.The quiescent conditions in impoundments
indicate that sedimentation will occur.The type of material
that will settle is dependent on upstream conditions.The
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rate of settling is a function of particle size,shape,and
density (Weiss et al.,1973).
Leaching.Leaching is the exchange of chemicals from an
impoundment bottom to the water mass.The process of
exchange is more rapid under reducing conditions than under
oxidizing conditions (Mortimer,1941,1942).
Ice Cover.An ice cover has one'di rect effect and some
indirect effects on impoundment water quality.The di rect
effect was noted by Mortimer (1941,1942),who discussed the
increased concentration of solutes just below the ice.As
water freezes,the dissolved .solids are exuded from the ice
and concentrated.The indirect effects include (1)the
prevention of atmospheric reaeration,(2)stratification,and
(3)a reduction in light penetration after snow covers the ice.
In addition,long periods of ice and snow cover will prevent
the addition of allocthonus nutrients to the reservoir (Ryder,
1978).
2.1.2 -Interactions
Each of the six processes defined above interact with one
another in impoundments.The cumulative effect of these
interactions on water quality is usually to further degrade it.
The process interactions described below are from Smith and
Justice (1976)unless otherwise indicated.
Stratification-Leaching.In a stratified reservoir,no vertical
mixing occurs between the epilimnion and the hypolimnion;
thus,no oxygen is transferred to the lower water.If
anaerobic conditions result,the redox potential will decrease,
and leaching rates will increase.
Stratification-Sedimentation.Stratification causes inflowing
water to enter at a depth with equal density,thereby
controlling the distance the sediment load has to fall before
being effectively removed from the incoming water.In some
cases,stratification determines whether or not the suspended
material will be removed at all.Also,loss of sediment
reduces the water density,which can affect stratification.
Stratification -Evaporation.Stratification increases evaporation
because the warm,less dense water remains near the surface.
On the other hand,surface cooling by evaporation and heat
loss can cause convective currents if the heat loss is greater
than the energy added by the sun's radiation.The
convective cu rrents keep the epilimnion isothermal and mixed.
s1a/a 2-3
Stratification-Eutrophication.Nutrient-rich hypolimnion water
is prevented from mixing with su rface water,thus controlling
algae growth if the concentration of the limiting nutrient is
controlled.
Eutrophication-Leaching.The dying and settling of algae
adds organic matter to the bottom.Upon degradation,the
organic matter depletes oxygen and releases chemicals.
Nutrients are released by the leaching of detritus material.
If the nutrients are transported to the surface,algae growth
may be stimu lated.
Eutrophication-Sedimentation.Dead algae settle to the
bottom.Settling of dead algae and of some precipitates
removes nutrients from the zone of algae growth.Increased
light penetration due to turbidity removal can stimulate algae
growth.
Eutrophication-Evaporation.Active algae growths at the
water surface cause an increase in evaporation rates.
Sedimentation-Leaching.Settling of inorganic material will
reduce leaching by covering or diluting organic deposits.If
the settled material is high in organic content,anoxic
conditions will increase,and thus leaching will be favored.
fce Cover-Evaporation.Water loss by evaporation will be
reduced if an ice cover exists,but sublimation will still occu r
and will remove some of the ice and snow cover.
Ice Cover-Eutrophication.The decreased light penetration
due to snow and ice cover will slow the growth of algae.
However,rapid algae growth has been observed under ice
cover.The intensity and distribution of solar radiation
penetrating an ice covered lake depends on the reflectance,
light-scattering and absorptive-optical properties of the ice
sheet and the water column.In addition,the geographical
location of the lake controls the duration and elevation of
solar radiation received during different seasons.Climatic
factors which are peculiar to individual water bodies also
influence the stratigraphy and duration of an ice cover
(Adams,1978).
Ice Cover-Stratification.Winter stratification is protected
from wind mixing by an ice cover.However,the frictional
effect of surface ice on inflowing water may influence
thermal-density water stratification and increase the rate of
sediment deposition as the colder inflowing water descends
and mixes with reservoir waters (Turkheim,1975).
s18/a 2-4
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Ice Cover-Leaching.Winter reaeration can only come from
advection of oxygen-rich water or through cracks in the ice
cover.If anaerobic conditions develop,leaching will
increase.The reduced eddy diffusion coefficient of water
under ice inhibits mixing,causing a slower spread of
nutrients released from bottom sediments and a shallower
anaerobic region.Chemical and biological reactions are also
inhibited in bottom sediments due to lower temperatu res.
However,the lack of atmospheric aeration in winter may lead
to severe water quality problems if chemical or biological
processes utilize all available dissolved oxygen.
Evaporation-Sedimentation.Loss
leaves the dissolved solids more
precipitation reactions to the solid
of reaction products.
2.2 -Sedimentation/Turbidity
of water by evaporation
concentrated,thus forcing
phase with possible settli ng
When a turbulent,sediment~laden stream such as the Susitna River
enters a reservoir,the quiescent conditions will allow much 0';:the
material to settle to the bottom.Weiss et al.(1973)Wright and
Soltero,(1973),Love (1961)and Churchill (1957),substantiate the
reduction of tu rbidity by the impoundment of a sediment-laden
river.
Turbidity caused by suspended sediments may have both beneficial
and detrimental effects in northern reservoi rs.High tu rbidity
.Ievels which prevent solar radiation penetration also restrict
photosynthetic activity to a relatively shallow zone just below the
air-water interface.As a consequence,nutrient rich lakes are
rendered unproductive if turbidity levels remain high throughout
the growing season (Ryder,1978).Suspended sediments also have
the capacity to bind nutrients and toxic pollutants,and remove
them from the water column as they settle to the bottom.
Furthermore,high turbidity levels limit flowing water aeration
capacities and aquatic fauna reproduction by inhibiting the
productivity of oxygen-producing organisms such as phytoplankton
and rooted aquatic plants (Turkheim,1975).Low turbidity levels,
on the other hand,may either encourage phytoplankton
productivity by increasing light penetration or kill photosynthetic
algae if they are intolerant of elevated light conditions (Smith and
Justice,1976).
Due to the fact the turbidity is caused mainly by inorganic
suspended solid loads,it can be used to trace the fate of river
water flowing into a reservoir (St.John et al.,1976).The depth
at which the inflowing water enters the reservoir will dictate the
distance that suspended sediments must fall before being removed
from the inflow.Temperatu re-density stratification will determine
s18/a 2-5
whether suspended solids·will be removed at all (Smith and
Justice,1976).When the inflowing stream is laden with suspended
sediments,the inflowing water may be heavier than resident water,
thus causing it to move as an under-current near the bottom of
the reservoir (Smith and Justice,1976).The following seasonal
turbidity pattern was noted in a glacial lake in Canada.Turbidity
increased in early spring,limiting light penetration near the
su rface.A turbid intermediate layer developed in June indicating
river water interflow.Turbidity remained low near the bottom
th roughout the summer but increased in September and October
due to re-suspension of bottom sediments (St.John et.aI.,1976).
Vertical mixing may be responsible for the re-suspension of bottom
sediments into the water column and a corresponding increase in
turbidity (Carmack and Gray,1982).
Color (Drachev,1962),particularate phosphorus (Wright and
Soltero,1973),dead microorganisms such as plankton and algae
(E;rickson and Reynolds 1969),and precipitated chemicals
(Mortimer;1941,1942)are removed in the sedimentation process.
According to reservoir sedimentation studies,70-97 percent of
sediment entering Watana Reservoir would settle,even shortly
after filling of the reservoir starts (R&M Consultants,1982b).
The Devil Canyon Reservoir would have a slightly lower trap
efficiency than Watana due to its smaller volume.However,most
sediment will be deposited in Watana,the upstream reservoir.
Turbidity levels and suspended solids concentrations downstream
from the reservoir will decrease sharply from natural levels during
the summer months due to the sediment trapping characteristics of
the reservoirs.The turbidity of water released during winter will
be substantially reduced from summer conditions,as suspended
sediment in near-surface waters should rapidly settle once the
reservoir ice cover forms and essentially quiescenf.conditions
occur.However,it is possible that glacial flour that entered the
reservoir during summer will pass through and out the reservoir
during winter.If this occurs,the turbidity of water released
during winter,although low,will be higher than pre-project
levels.
2.3 -Metals
A reduction of metal concentrations such as iron,manganese,and
trace elements occurs in reservoirs as these elements are
precipitated and settle to the bottom (Neal,1967).Oligotrophic
lakes having a low pH and containing low dissolved salt
concentrations generally contain higher concentrations of metals in
surface waters than oligotrophic lakes having a high pH and high
dissolved salt concentrations.The higher concentration of metals
is due to the absence of dissolved salts which react with and
precipitate metal ions.Since oligotrophic lakes are generally well
s18/a 2-6
aerated and low in productivity,there is little variation in metal
content with depth relative to mesotrophic and eutrophic lakes.In
eutrophic lakes,very high local concentrations of certain metals
are often present as a result of an acidic or reducing environment
near the bottom (Williams et al.,1976).
2.4 -Leaching
Anaerobic bottom conditions can harm aquatic life and cause the
reduction and release of undesirable chemicals into the water
(Fish,1959).The leaching process,which is more efficient under
anaerobic conditions,degrades bottom water quality by releasing
such chemicals as alkalinity,iron,manganese (Symons et al.,
1965),hydrogen sulfide,and nutrients (Turkheim,1975).Also,
leaching problems become more severe as the organic content in
the soils increase.The potential for leaching at the.Watana
Reservoir should decline over time as the inorganic glacial sediment
carried in by the river settles and blankets the reservoir bottom.
The products of leaching are not anticipated to be abundant
enough to affect more than a small layer of water near the
reservoir bottom..Also,leaching products will not degrade
downstream water quality over the long-term because water will be
released from the reservoir surface.A short-term increase in
dissolved solids,conductivity,and most of the major ions may be
evident immediately after closu re of the dam.The magnitude·of
increase cannot be quantified with available data,but it is
anticipated that the increase will not result in detrimental effects
to freshwater aquatic organics.Bol ke and Waddell (1975)report
that the highest concentration of all major ions,except magnesium,
occu rred immediately after closu re of the dam they were studyi ng.
They attributed the increase in concentration to the initial
inundation and leaching of rocks and soils in the reservoir area.
However,effects such as these are temporary and diminish as the
reservoir matures (Baxter and Glaude,1980).
2.5 -Heat Transfer/Evaporation
The four principle mechanisms of heat transfer in a reservoir
include evaporation,convection,r'ldiation loss,and solar radiation
gain.It is possible to predict what temperatu re changes will
occu r in an impou ndment before its construction,based on
estimates of these variables.The addition of heat to an
impoundment from solar radiation on large surface areas may
reduce dissolved oxygen and increase evaporation and microbial
activity unless the volume of warmed water is small in relation to
the total reservoir volume (Love,1961).
s18/a 2-7
The range and seasonal variation in temperature of the Susitna
River will change after impoundment.Boike and Waddell (1975)
noted in an impoundment study that the reservoir not only reduced
the magnitude of variation in temperatu re but also changed the
time period of the high and low temperature.This will also be the
case for the Susitna River~where pre-project temperatures
generally range from O°C to 13°C with the lows occurring in
October/November th rough March/April and the highs in July or
August.After closure of the dam gates,the temperature range
will be reduced and low temperatures will occur in November
th rough March.The period of highest temperatu re will be July
and August,as is the pre-project case.Reservoirs releasing
water from the surface are "heat exporter"reservoirs (Turkheim,
1975),and both Susitna River reservoirs fall into this category.
Post-project reservoi r temperatu res are discussed elsewhere by
Acres (1982).
Thermal stratification is likely to occur in both reservoirs during
summer and winter as a result of temperatu re density differences
within the water column,although stratification is often relatively
weak.Winter stratification would be less stable than summer
stratification because the maximum temperature difference would be
4°C,the temperature of water at its maximum density.It is
expected that vertical mixing will occur in the spring as a result
of the large input of water,wind effects,and surface-water
warming.During stratified conditions,vertical mixing is inhibited
or eliminated.Thus,the transport of oxygen from the surface,
where reaeration occurs,to the bottom,where biologic and
chemical processes use oxygen,is severely inhibited.
Due to an aggradation process whereby reservoir water levels are
increased in an upstream direction,a reservoir can increase the
amount of evaporation from a river (Turkheim,1975).However,
the amount of evaporation from the river will be a small percentage
of the total evaporation from the Watana and Devil _Canyon
reservoirs,and evaporation at these reservoirs will be minimal.
The average annual evaporation predicted for May through
September at Watana is 10.0 inches,and at Devil Canyon it is
11.1 inches.There is no evaporation during the period of ice
cover,November through May.The percentage of the reservoirs'
volume lost to evaporation during summer will be 0.3 percent at
Watana and 0.6 percent at Devil Canyon.Although evaporation
has been noted to cause an increase in dissolved sol ids
concentrations in reservoirs (Love,1961;Symons,1969),the
potential effect of a less-than 1 percent concentration increase is
not significant.Sublimation may also cause some water loss,
creating local effects,but this is not anticipated to be slgnificant
at the Watana or Devil Canyon impoundments.
In cold climates,reduced current velocities upstream from
reservoirs favor earlier freezeup and later breakup than in
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unregulated rivers (Baxter and Glaude,1980).Ice first forms in
quiescent waters such as a reservoir,whereas the faster flowing
reaches remain open initially.When reservoi rice accumulations at
the reservoir inlet have sufficiently raised the water level and
decreased the local water velocity,upstream rapids freeze and the
ice cover builds fu rther upstream.At breakup,ice jams may
occur at the reservoir inlet,causing higher water stages upstream
(Turkheim,1975).
2.6 -Dissolved Oxygen
Many changes in the chemical constituents of an impou ndment are
related to oxygen concentration s of the water (Mortimer,1941,
1942).Reservoirs decrease dissolved oxygen concentrations by
increasing depth,decreasing turbulence and increasing surface
temperatures,thus lowering oxygen saturation values (Smith and
Justice,1976).Slowing down of water transport by dams allows
more time for biochemical oxygen demand to consume the available
oxygen and also reduces the rate at which water is reaerated.If
gas exchange at the air-water interface cannot supply enough
oxygen to meet the respiratory demand,oxygen concentrations in
reservoir waters become very low (Ruggles and Watt,1975).When
phytoplan kton die or move out of the photosynthetic zone,oxygen
is consumed as a result of algal degradation and respi ration
processes.These processes usually take place in the hypolimnion
(Smith and Justice,1976).If anaerobic conditions develop,the
redox potential may decline,causing insoluble materials to be
reduced to soluble states (I ngols and Wilroy,1962).Smith and
,Justice (1976)note that carbonaceous biochemical oxygen demand
•and nitrification of ammonia caused anaerobic conditions in
reservoi rs.They fu rther noted two impou ndments wh ich contai ned
a zone of oxygen depletion just below the thermocline in addition
to one near the bottom.The oxygen demand in the upper zone
was attributed to 60-80 percent phytoplankton,15-20 percent
biochemical oxygen demand,and 1 -10 percent fish respiration.St.
John et aI.,(1976)report that decreases in summer dissolved
oxygenlevels in epilimnetic waters of Kamloops Lake,B.C.were a
response to higher temperatures and corres!-,onding decreases in
oxygen solubility.Conversely,oxygen concentrations above
saturation have been found at the surface of impoundments during
summer as a result of the photosynthetic activity of phytoplan kton
(Smith and Justice,1976).If surface waters become
supersaturated with oxygen,some will be lost to the atmosphere
(Symons et aI.,1965).Churchill (1957)reports that warm water
interflows remained near the surface of a reservoir where
pollutants were degraded aerobically,decreasing dissolved oxygen.
Such layers remain near the surface until fall when they enter the
hypolimnion just prior to overturn.In at least one instance,cold,
well-aerated water entered an impoundment as an underflow,
forcing warmer low-oxygen water to the surface.
s1S/a 2-9
Water level fl uctuations may cause [ow-oxygen problems at
hydroelectric dams.During dry years with low water levels,
lakeside vegetation may be prolific on exposed shores.When this
organic mass is inundated during periods of high water,it exerts
a high oxygen demand causing severe oxygen-related water quality
problems in the reservoir (I ngols,1959).High water levels may
also cause low groundwater-oxygen levels (Turkheim,1975).
In some cases a lake's trophic state can be related to areal oxygen
depletion rates St.John et al.(1976).Eutrophic lakes are
generally characterized by-areal depletion rates greater than
1.5 mg.02/cm2/month,which is sufficient to totally deplete
oxygen in the hypolimnion.The areal depletion rate is calculated
by obtaining the difference between the dissolved oxygen content
of two samples from a known depth in the hypolimnion taken on
two different occasions,and dividing the result by the time
interval.However,there are two reasons why it may be
misleading to relate the areal oxygen deficits to trophic states in
all lakes.First,lakes with depths greater than 50 meters,as well
as those which are narrow and steep sided,display high sediment
surface areas relative to hypolimnion-ceiling surface areas.
Dividing oxygen deficit values by the hypolimnion ceiling area
results in an areal depletion rate that is higher than would be
obtained if the sediment surface area were used.Second,the rate
of allocthonous organic matter input from the drainage basin into
the hypolimnion is unrelated to the production of organic matter in
-the epilimnion.Hence,decomposition of allocthonous materials in
the upper zones increases the areal depletion rate near the bottom.
Anothe.r technique used by St.John et !!.(1976)involved
measuring the volumetric oxygen depletion rate of a lake.This
was accomplished by dividing the difference between the average
dissolved oxygen concentrations in the hypolimnion determined on
two different occasions,by the time interval between them.The
average concentrations were calculated in tu rn by adding the
dissolved oxygen concentrations at 20 meter intervals in the
hypolimnion and dividing the sum by the total volume of the
measu red intervals.The volumetric depletion rate was expressed
in terms of milligrams per liter per day.It was noted,however,
that if the movement of the river plume mixes oxygenated water
with hypolimnetic water,the measu red net depletion rate will
considerably underestimate true absolute rates.
Oxygen demand in the Susitna River is typically low.Chemical
oxygen demand levels measured in 1980 and 19a1 at Vee Canyon
have averaged 16 mg/1.Consequently,dissolved oxygen levels
within the Susitna .impoundments are anticipated to remain
sufficiently high to support a diverse popu lation of aquatic
organisms.
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2.7 -Trophic Effects
2.7.1 -Introduction
The process of eutrophication is defined as the increase in
nutrient enrichment that causes increased productivity in
lakes.This enrichment is expressed in terms of nutrient
supply or load.Nutrient supply is the concentration of a
nutrient per unit volume of water received by a lake,
expressed in terms of mg/m3 .Nutrient load,on the other
hand,is the concentration of a nutrient per unit of Jake
surface area,expressed in terms of mg/m2 .
Lake trophic status is an expression of the eutrophication
process in a particular lake of a known mean depth,flushing
rate,and nutrient retention capacity.The major
characteristics used to quantify the trophic status of a water
body are nutrient concentration,chlorophyll "a"
concentration,and Secchi disc transparency.Phosphorus
concentrations measured at spring overturn best represent
the nutrient supply for plankton algae in the approaching
growing season.The critical level of dissolved inorganic
phosphorus is the level that,if exceeded,will produce
nuisance blooms of algae.Chlorophyll "aft concentration is
the best measure of algal biomass.Thus the spring
phosphorus concentration in epilimnetic (surface)waters is an
index of the trophic status of a lake.Trophic status can be
generally classified as:(1)oligotrophic 0-10 mg
phosphorus/m3 ,(2)mesotrophic 10-20 mg phosphorus/m3 ,
and (3)eutrophic greater than 20 mg phosphorus/m3 .
These conditions correspond to summer chlorophyll "a"
concentrations of 0-2 mg/m3 ,2-6 mg/m3 ,and greater than
6 mg/m3 ,respectively,in clear water lakes.Secchi disc
transparency is a convenient way of expressing the depth of
light penetration in relation to algal biomass in epilimnetic
waters.High Secchi disc transparencies reflect oligotrophic
conditions whereas low transparencies may reflect eutrophic
conditions.However,because Secchi disc transparencies also
reflect high levels of turbidity and suspended solids
concentrations in silt-laden waters,their use as trophic
status indicators is limited to clear water lakes.
The mean depth of a lake is a convenient index of a lake's
volume used to estimate the nutrient concentration from a
given nutrient supply.
2-11
The flushing rate expresses the rate at which water is
transported through a lake.This factor is important because
it determines the period of time that nutrients will be
available for use by algae.
Phosphorus retention is an expression of the fraction of
phosphorus not lost through the outlet or by settling.Thus,
the greater the retention factor,the greater the amount of
phosphorus retained for use by algae.
The eutrophication process in reservoirs is similar to that in
lakes.If water is released from a reservoir surface,the
reservoir is a "nutrient trap"(Turkheim,1975),much like a
lake.Both Susitna River reservoirs will release water from
at or near the su rface.Hence,they can be expected to
accumulate nutrients.However,the probability of eutrophic
conditions developing in these reservoi rs is not necessarily
high because they are nutrient traps.The trophic status of
the Watana and Devil Canyon reservoirs have been predicted
to be oligotrophic on the basis of spring phosphorus
concentrations derived from estimates of phosphorus supply,
mean depth,flushing rate,and phosphorus retention capacity
at each reservoir.
Chlorophyll "an data are unavailable from the Susitna River at
Vee Canyon.However,the high suspended sediment and
turbidity levels in the Susitna River indicate that
chlorophyll nan values will be low.In addition,Secchi disc
transparencies in the Susitna River will not accurately reflect
the level of algal biomass that will result from impoundment.
Consequently,the determination of chlorophyll "an
concentrations and Secchi disc transparencies resulting from
impoundment have been dis regarded in this study.
2.7.2 -Results
Results from the-application of a trophic status model in the
Susitna Hydroelectric Project are presented in this section.
Spring phosphorus concentrations,in combfnation with the
factors of mean depth,flushing rate,and phosphorus
retention capacity,indicate that both Watana and Devil
Canyon Reservoirs will be oligotrophic.A technical
discussion of the various aspects of two nutrient models is
presented in Attachment A.
Spring C:Si:N:P mass and atomic ratios were calculated for
the Susitna Project by assuming a worst case dissolved
orthophosphate value (0.01 mg/l)and by using values of total
carbon,dissolved silicon and inorganic carbon measu red in
June at Vee Canyon.The average 1980-81 June C:S:N:P
ratio at Vee Canyon was 1080:340:28:1 which corresponds to
2-12
--
.-.
an average atomic ratio of 3000:403:6?:1.Hence,from among
the nutrients considered to be important to algal growth,it is
apparent that phosphorus will be the limiting nutrient.
Successful use of the Dillon and Rigler (1975)equation
depends on the accurate determination of a phosphorus
retention coefficient for a particular water.body.The
reliability of determining a retention coefficient in
glacially-influenced lakes in Alaska has not been established.
Therefore,the use of this model is'questionable in relation to
the Susitna Project.Along these lines,St.John et al.
(1976)found that Kamloops Lake in British Columbia hada
measu red phosphorus retention capacity 760 times greater
than the predicted value using the Dillon and Rigler (1975)
retention coefficient equation.As a result,they suggest that
the use of this coefficient may lead to similar discrepancies in
other glacially-influenced lakes.The only known application
of a phosphorus model to glacially-influenced lakes in Alaska
involves the use of Vollenweider's (1976)equation.More
recently,Koenings and Kyle (1982)successfully utilized the
Vollenweider equation in calculating the annual total
phosphorus load to Crescent Lake in south-central Alaska.
In this instance,the measured in-lake total phosphorus
concentration at the time of spring overturn was used in
determining an annual loading value.Theoretically,the same
equation may be used to predict the spring phosphorus
concentration in a lake with a known annual loading value.
However,the reliability with which Vollenweider's model may
be applied to Alaska lakes may be complicated by the fact
that a high percentage of the total phosphorus load may be
non-reactive in lakes which are fed by silt-laden glacial
rivers.
As a result of the retention coefficient limitation in the Dillon
and Rigler (1975)model,and the successful use of
Vollenweider's model at Crescent Lake,the latter of the two
models was selected for use in the Susitna Project.At this
time there are no known limitations to the application of
Vollenweider's model in Alaska which are not common to both
models.
Application of the equation,
to the Susitna Hydroelectric Project was made using the
followi ng rationale.
-
L
[P]=
z p
x
1
1 +{II;
2-13
Natural Land Loading:According to Vollenweider (1976),the
spring concentration of total phosphorus in a lake is the
critical quantity used in evaluating a lake's trophic status.
On this basis,Koenings and Kyle (1982)utilized the measured
June phosphorus concentration in Crescent Lake to calculate
an annual areal phosphorus loading value.Using this same
logic,June phosphorus concentrations at Vee Canyon were
used to project spring areal loading values at Watana and
Devil Canyon.Loading values were in tu rn used in
predicting the June phosphorus concentration in both
reservoirs.In calculating spring areal phosphorus loads for
the Susitna Project,dissolved.orthophosphate is considered
the form of the total phosphorus pool which is available for
the use by microflora.The average 1980-1981 dissolved
orthophosphate concentration measured at Vee Canyon during
June was below the detectable limit (0.01 mg/I).However,
the "worst case"value of 0.01 mg/I was assumed because it
was felt that a value of zero was inappropriate for the
Susitna Project area.Upon conversion of this value,the
average June dissolved orthophosphate concentration becomes
10 mg/m3 .This concentration was multiplied by the average
annual flow at each damsite (7.0 x 109 m3 /yr at Watana and
8.0x 109 m3/yr at Devil Canyon)to derive the phosphorus
supply at each reservoir.Upon dividing the supply by the
surface area of each reservoir (153,786,000 m2 at Watana and
31,566,600 m2 at Devil Canyon),June areal phosphorus
loading from the land is obtained.The June natu ral land
load to the su rface at Watana is 456 mg/m 2 ,and at Devil
Canyon is 2533 mg/m2 ,if only one dam or the other is built.
The loading to Devil Canyon would be lower if Watana is in
place,because Watana will act as a nutrient trap.
Natural Precipitation Loading:The phosphorus
in precipitation was taken as 0.03 mg/I
phosphorus concentration reported in snow and
collected at Fairbanks,Alaska,by Peterson (1973).
concentration
the maximum
rain samples
Conversion of the area used to collect samples and the volume
of sample collected,and using the normal annual precipitation
at Talkeetna,indicates that natural precipitation loading will
be 22 mg/m2/yr.
2-14
Total Natu ral Loading:The total natu ral phosphorus load at
each reservoi r equals the sum of the natu rat land load and
the natu ral precipitation load.At Watana the total natu raj
load is 478 mg/m2 and at Devil Canyon it is 2555 mg/m2
(without Watana).Recalling the Vollenweider.(1976)critical
loading equation,the natural load below which results in
oligotrophic status is 1057 mg/m2 at Watana and 3763 mg/m2 at
Devil Canyon.Upon inspection,the su rface specific load
(Lp)is below the critical surface specific load (Lc)at both
reservoi rs.The calculated Lp/Lc ratio is 0.45 at Watana and
0.62 at Devil Canyon (when only one reservoir is in place).·
If both reservoirs are constructed,the surface specific load
at Devil Canyon may be reduced,resulting in a smaller Lp/Lc
ratio at this site.
Artificial Loading:This is assumed to be zero since there are
no man-induced sources of phosphorus in the study area.
Additional phosphorus loading to a reservoir will cause a
subsequent increase in the steady-state phosphorus
concentration,which may result in a change in water quality.
Therefore,artifical loading must be incorporated into the
phosphorus model if the capacity for residential dwelling or
summer cottage development is to be determined.
z,Mean Depth:The mean depth was calculated for both
reservoirs as the "full pool"volume divided by the reservoir
surface area.This is the same method used to determine
mean depths at Crescent Lake and Kamloops Lakes by
Koenings and Kyle (1982)and St.John et al.(1976),
respectively.The mean depth at Watana and Devil Canyon
will be 76 meters and 43 meters,respectively (R&M
Consu Itants,1982c).
p,Flushing Rate -The flushing rates at Watana and Devil
Canyon are 0.61 year and at 6.25 years,respectively (R&M
Consultants,1982b).
The above values indicates that both Susitlla River reservoirs
will be oligotrophic under existing conditions,as the spring
phosphorus concentration [P]will be 4.5 mg/m3 at Watana and
6.8 mg/m3 at Devil Canyon.The concentration at Devil
Canyon would be reduced if the Watana Reservoi r is in place
because Watana will act as a nutrient trap,thereby reducing
the natu ral land loading.
2-15
The above values of [P]plot in the same area as oligotrophic
water bodies (Figure 1)with similar phosphorus loading,mean
depth,and flushing rate values.levels below 10 mg/m3 are
indicative of oligotrophic conditions,10 to 20 mg/m3 are in
the mesotrophic range,and levels above 20 mg/m3 are
considered eutrophic (Vollenweider 1976).
Although both reservoirs initially will be oligotrophic,
artificial loading could shift the trophic status of one or both
reservoirs at some future time.Because of this concern,an
analysis of response time and artificial loading was made.
Response Time -The time required for a lake having an
initial loading rate (ll)to response to a change in loading to
a new level (l2)may be described by the half-life change in
concentration (Dillon and Rigler 1975).The half-life change
is the time requi red for a lake's phosphorus concentration to
move from the original steady-state concentration to the
advanced steady-state concentration.The half-life can be
estimated as:
t 1 =0.69
]"
p +10/-
z -Wlt
Where:tt =half-life time
p =flushing rate
z =mean depth
Watana will have a half-life time of 0.93 year and Devil
Canyon a half-life time of 0.11 year.However,Dillon and
Rigler.(1975)note that 3 to 5 times the half-life time can be
used as an indicator of a lake's response time to additional
phosphorus loading.Thus the time requi red to approach a
new steady-state phosphorus concentration following an
increase in loading will be 2.8 to 4.6 year in the Watana
impoundment and 0.3 to 0.6 year in the Devil Canyon
impou ndment.
2-16
-
..-I
2.7.3 -Population Equivalent
Results from 13 studies in North America and Europe
concl uded that the average per capita phosphorus supply
(excrement plus household waste)is 800,000 mg/yr from
domestic sources (Dillon and Rigler 1975).By dividing the
average per capita supply by the surface area of each
reservoir,the average per capita phosphorus load can be
obtained,which will be 0.005 mg/m 2/yr and 0.025 mg/m2/yr
at Watana and Devil Canyon,respectively.The maximum
permissible artificial loading resulting in o,ligotrophic status is
calculated as the difference between'the critical surface load
and the natural surface load at each reservoir.Thus,the
maximum permissible artificial loads are 579 mg/m2 /yr and
1208 mg/m2 /yr at Watana and Devil Canyon,respectively.'
The loading at Devil Canyon could be higher if Watana is in
place because Watana will trap nutrients.The permissible
number of permanent (year round)residents at each reservoir
is obtained by dividing the maximum permissible artificial load
at each reservoir by its corresponding average per capita
artificial phosphorus load.Assuming that all residents will be
permanent,Watana will accommodate a maximum of
115,800 individuals.Similarly Devil Canyon will accommodate
a maximum of 48,300 individuals if it is the only reservoir.
The maximum number of permanent dwelling unit equivalents
around each reservoir may be calculated by dividing the
number of permissible residents by the number of residents at
each dwelling unit.For example,if three individuals occupy
each dwelling unit for the entire year,the maximum
permissible number of permanent dwelling units will be 38,600
at Watana and 16,100 at Devil Canyon.In a situation where
dwelling units are (on the average)occupied for less that
365 days per year (i.e.summer cottages),the permissible
number of "seasonal"units may be calculated by multiplying
the number of permissible permanent units at each reservoir
by 365 days divided by the average number of days spent at
each unit per year.If both permanent and seasonal dwellings
are constructed,the total combined artificial phosphorus load
should not exceed the equivalent amount generated by 115,800
permanent residents at Watana or 48,300 permanent residents
at Devil Canyon,if oligotrophic conditions are to be
r laintai ned.
Artificial loading from a 3000 person construction camp would
amount to 15 mg/m2/yr at Watana and 75 mg/m2/yr at Devil
Canyon.These loading levels represent about 3 percent
(Watana)and 6 percent (Devil Canyon)of the -maximum
permissible artificial loading required to maintain oligotrophic
conditions .
2-17
2.7.4 -Conclusions
It has been determined that under natural conditions,both
the Watana Reservoir and the Devil Canyon Reservoir will be
oligotrophic.It was further determined that Watana and Devil
Canyon will maintain oligotrophic status if provided with a
maximum additional phosphorus supply equivalent to
115,800 permanent residents and 48,300 permanent residents,
respectively.Additional loading from a 3000-person
construction camp would amount to less than 3 percent of the
maximum permissible artificial phosphorus load at Watana and
6 percent of the maximum permissible artificial phosphorus
load at Devil Canyon.
2.7.5 -Summary
To summarize,reservoir trophic status is determined in part
by the relative amounts of carbon,silicon,nitrogen and
phosphorus present in a system as well as the quality and
quantity of light penetration.The C:Si:N:P ratio indicates
which nutrient limits algae productivity.The nutrient which
is least abundant will be limiting.On this basis,it was
concluded that phosphorus will be the limiting nutrient in the
Susitna impoundments.Vollenweider's (1976)model was
considered to be the most reliable in determining phosphorus
concentrations at the Watana and Oevil Canyon·impoundments.
However,because the validity of this model is based on
phosphorus data from temperate clear water lakes,predicting
trophic status of silt-laden water bodies with reduced light
conditions and high inorganic phosphorus levels may
overestimate actual trophic status.The spring phosphorus
concentration in phosphorus limited lakes is considered the
best estimate of a lake's trophic status.Sio-available
phosphorus is the fraction of the total phosphorus pool which
controls algae growth in a particular lake.The measured
dissolved orthophosphate concentration at Vee Canyon was
considered to be the bio-available fraction in the Susitna
River.Accordingly,the average June dissolved
orthophosphate concentration was multiplied by the average
annual flow at each reservoir to calculate spring phosphorus
supplies from the land.These values were in turn combined
with phosphorus values from precipitation and divided by the
surface area of each impoundment.The resultant spring
phosphorus loading values at Watana and Devil Canyon were
below the maximum loading levels required for the maintenance
of oligotrophic conditions.Likewise,upon incorporating
spring loading values into Vollenweider's (1976)phosphorus
model,the volumetric spring phosphorus concentration at both
reservoirs fell into the same range as oligotrophic lakes with
similar mean depths,flushing rates,and phosphorus loading
values.
2-18
The aforementioned
several assumptions
existing information.
tropliic 'status predictions·depend upon
that cannot be quantified on the basis of
These assumptions include:
(1)the C:Si:N:P ratio does not fluctuate to the extent that
a nutrient other than phosphorus becomes limiting,
(2)no appreciable amount of bio-available phosphorus is
released from the soil upon filling of the reservoirs,
(3)pho~phorus loading levels are constant th roughout the
peak algal growth period,
(4)June phosphorus concentrations measured at Vee Canyon.
correspond to the time of peak algal productivity.
(5)phosphorus species other than dissolved orthophosphate
are not converted to a bio-available form,
(6)flushing rates and phosphorus sedimentation rates are
constant,
(7)phosphorus losses occu r only th rough sedimentation and
the outlet,and,
(8)the net loss of phosphorus to sediments is proportional
to the amount of phosphorus in each reservoir.
Artificial phosphorus loading represents any additional input
from domestic or industrial sou rces.The difference between
critical loading and natural loading is defined as the maximum
allowable artificial load.The maximum artificial phosphorus
load at the Watana impoundment is equivalent to
115,800 permanent residents and at Devil Canyon it is
equivalent to 48,300 permanent residents.These estimates
are conservative in that the effect of low light penetration
has been neglected in thei r calculation.In addition,artificial
phosphorus loading may be reduced if septic filter bed or
other treatment systems a re employed at each dwelli ng,
thereby increasing the number of permissible residents.
2-19
MESOTROPHIC
-
-L..»......
N
~1000f
Q.
CI
E-
(!)
z
Ci«o
...J
(f)1001-
=>a::o:x:
Q.
(J)o
:t:a..
EUTROPHI C
,/
""""-----
""""""",,"0
,,"DEVIL CANYON
"/
"/
""",;
./'"oWATANA
./
'"./
""""""
-
-
-
.
OLIGOTROPHIC
I0 L....-_.L--..J-...L....I....L-I....Ll..J.1L...-._L..-.-1-.J--l-l...J...I...LI''L...-._J.--..J-...L....I--I-u...LJ'1__L-....L.-..J....L....J..Ju.&.J
0.1 I 10 100 1000
MEAN DEPTH Z -HYDRAULIC FLUSHING RATE I P (m/yr)
SUSITNA PROJECT DATA APPLI ED TO VOLLENWEIDER (t976)
PREPARED BY'
R&M CONSULTANTS,INC.
PREPARED FOR'
PHOSPHORUS LOADING a MEAN DEPTH •
HYDRAULIC FLUSHING RATE RELATIONSHIP 1PI
FIGURE I.no
~-
3 -DOWNSTREAM EFFECTS
3.1 -General
Construction of hydroelectric dams and thei r reservoi rs has a
profound effect on the river regime of downstream reaches.The
effects are summarized here;more detailed discussion is presented
in "River Morphology Studies"(R&M Consultants,1982b).Since
the rate of reservoir water outflow is controlled,the downstream
reach is no longer subject to the fluctuations of a normal river
regime,with the consequence that the'flow becomes more
seasonally uniform throughout the year (Kellerhals and Gill,1973;
Tu rkheim,1975).The,minimum flow rate is significantly
increased,and peak flows are decreased.The decrease in spring
flood magnitude,especially during the initial impoundment,may
result in negative effects on the downstream environment.It is
reasonable to expect that the interference with natural Susitna
River flows will cause a change in stream levels and ban k storage
levels for some distance downstream from the dams.
3.2 -Suspended Solids/Turbidity
Low tu rbidity waters immediately below a reservoi rare accompanied
by an increased sediment transport potential and erosion potential
as well as a high nutrient level.These phenomena may result in
considerable streambed material removal,to the extent which the
affected channel is scou red to bedrock or becomes armored.
Consequently,downstream waters immediately below a dam often
become unsuitable for the breeding of upstream species sucl;l as
arctic char,'grayling,inconnu,lake chub,and long nose suckers
(Turkheim,1975)0 Bed material below the Susitna dams is large
enough that scour is not expected at the regulated flow levels
(R&M Consultants,1982b).
Farther downstream from a dam,sediments eroded from stream
banks and channels are re-deposited.Heavy silting of gravel
interstices result in decreased intergravel water flow and oxygen
content.RiverfJow regulation associated with hydroelectric dams
eliminates spring freshets which normally cleanse the downstream
channel substrate of such silt deposits.Thus,changes in natural
turbidity and sedimentation processes due to impoundment may
have a detrimental impact on fish spawning habitat many miles
downstream from a hydroelectric dam,even when reservoir
discharges are low in turbidity and suspended solid loads
(Turkheim,1975)0
Operation of the Watana Reservoir will sharply reduce summer
suspended solids concentrations and turbidity levels downstream
from the reservoir.The velocity of water entering the
impoundment will be reduced,which will allow all but the finest
s1S/b 3-1
particles to settle.The turbidity and suspended solids levels of
water released du ring winter will be lower than summer conditions
because of quiescent conditions occurring under an ice-cover.
However,glacial flour that entered the reservoir during summer
may pass through and out the reservoir during·winter,resulting
in turbidity levels which,although low,may be higher than
pre-project levels.Addition of the Devil Canyon Dam will have
little additional effect on downstream tu rbidity levels because any
particles carried through the Watana Reservoir will also pass
through the Devil Canyon Reservoir.
The range and seasonal variation in temperatu re of the Susitna
River will change after impoundment.The magnitude of
temperature variation will change from the pre-project range of
O°C to 13°C to a range having slightly warmer temperatures in
winter and slightly colder temperatures in.summer.Under existing
conditions,the lows occur in October/November through
March/April and the highs appear in July or August.After
impoundment,low temperatures will occur in November through
March,but high temperatures will still occur in July or August.
3.3 -Heat Transfer
When water is released from the epilimnion of a deep reservoir,
there is likely to be a warming effect on the stream below the dam
(Turkheim,1975;Baxter and Glaude,1980).There may also be
an increase in the amount of organic detritus originating from
plankton in the reservoir.Furthermore,this type of release will
encourage the accumulation of poor quality bottom water in the
reservoir until the time of fall overturn when water becomes mixed
(Baxter and Glaude,1980).
Comparatively little work has been done in Alaska pertaining to the
effects that impoundment-related temperature changes have on
stream biota.However,there is evidence indicating that
impoundment-related water temperature changes alter resident fish
distribution and abundance,fish.food productivity,and organism
development rates downstream from dams (Baxter and Glaude,
1980).The timing and extent of temperature changes is of
importance since the breeding seasons and life cycles of most
stream organisms are integrated with annual temperature changes.
Water temperature changes may also alter the pattern of
anadromous fish migration below a dam (Tu rkheim,1975).
Baxter and Glaude (1980)report that certain insect species which
are important fish food sources are particularly sensitive to
changes in the downstream thermal regime because their
metamorphosis is induced by temperature changes.If these
changes do not occur or occur at the wrong time,their life cycles
will be disrupted.Fu rthermore,change in seasonal temperatu re
s18/b 3-2
patterns may change the timing of anadromous fish spawning to
their detriment (Baxter and Glaude,1980).
In reservoirs at high latitudes,large-scale downstream river ICIngs
have been known to occur when winter flows are greatly reduced
for the purpose of hydroelectric peaking.These icings are thick
accumu lations of bottom-fast ice resulting from low flow,extreme
cold and the constriction of bedrock or permafrost below the
channel bed (Turkheim,1975).Downstream channel icings may
significantly increase erosion with consequent increase in sediment
loads downstream (Baxter and Glaude,1980).Furthermore,flow
regulation may delay spring breakup downstream if breakup is
otherwise accelerated by a rapid increase in discharge (Turkheim,
1975).
The range and seasonal variation in temperature of the Susitna
River will change after impoundment.The magnitude of
temperatu re va riation will change from the pre-project range of
DoC to 13°C to a range having slightly warmer temperatures in
winter and slightly colder temper·atures in summer.Under existing
conditions,the lows occu r in October/November th rough
March/April and the highs appear in July or August.After
impoundment,low temperatures will occur in November through
March,but high temperatures will still occur in July or August.
3.4 -Dissolved Oxygen
Water released from near the su rface of an impoundment generally
provides a higher dissolved oxygen content in downstream waters
than waters released from the deeper levels (Love,1961).
Turkheim (1975)notes that open water downstream from an
impoundment created by water discharge through a dam,produces
a significant increase in winter dissolved oxygen concentrations.
Dissolved oxygen concentrations below the reservoi rs will be
relatively high.Tu rbulence created by spillage over the dams and
transit through the power tunnels will aerate water to or slightly
above satu ration levels.
3.5 -Gas Supersaturation
Turkheim (1975)reports that nitrogen supersaturation of water
below a dam is possible in certain seasons,extending an unknown
distance downstream.This is certainly a possibility below both
Susitna dams.Data'from the Columbia River indicate that at least
75 kilometers may be required before nitrogen equilibrium
conditions are re-established below an impoundment (Geen,1975).
The work of Beiningen and Ebel (1970)revealed that downstream
supersatu ration levels only dropped from 135%to 114%over a
s1S/b 3-3
distance of 120 kilometers below a dam they were studying.It is
expected that equilibrium conditions are achieved more rapidly the
more turbulent the water is downstream (Geen,1975).The
ultimate impact of nitrogen supersatu ration is its effect on fish.
Supersaturation has a serious impact on adult and young salmon
below a reservoir (Geen,1975).If dissolved gases reach levels of
supersaturation,lethal gas embolisms in fish may result for miles
downstream of an impoundment (Tu rkheim,1975).The death of
Atlantic salmon by "gas-bubble"disease was di rectly attributable
to nitrogen supersatu ration below a dam in Canada (Ruggles and
Watt,1975).Potential nitrogen supersaturation problems will be
solved structurally at the Susitna dams through the use of
Howell-Bunger valves,.eliminating plunging spills up to the
1 :50 year flood.Portage Creek,just below Devil Canyon,is
essentially the upstream limit for spawning salmon under natu ral
conditions,although some salmon may negotiate Devil Canyon
Rapids at low flow.With Watana only,power releases will travel
through several sets of rapids as well as Devil Canyon before
reaching Portage Creek.It is reasonable to expect that,will the
natural plunging and turbulence of the canyon,post-project
nitrogen supersaturation levels with Watana only will be the same
as the pre-project levels at the dOWllstream end of Devil Canyon.
However,nitrogen 'supersaturation caused by spills from Devil
Canyon Dam during an extreme event will not have as much
opportu n ity to attain natu ral levels.
-
s18/b 3-4
,~
--1
4 -CONCLUSIONS
Impoundment of the Susitna River will affect water quality in the
reservoir area(s)and downstream from the reservoir(s).The
major changes will result from impoundment of the flowing river,
and minor changes will occur below the impoundment(s).The
above assessment of the effects of impounding the Susitna River is
summarized herein.
(1)The reservoirs will be oligotrophic.The oligotrophic status
can be maintained at both reservoirs if they are provided
with less than a maximum additional phosphorus supply
equivalent to that produced by 115,800 year-round residents
at Watana and 48,300 yea·r-round residents at Devil Canyon
(if only one dam is built).The Devil Canyon Reservoir could
support a large population if Watana is in place because
Watana will trap nutrients,reducing the natu ral supply to
Devil Canyon.Additional loadi ng from a 3000-person
construction camp would amount to less than 3 percent of the
maximum permissible artificial phosphorus load at Watana and
6 percent of the maximum permissible artificial load at Devil
Canyon.
(2)A short-term increase in di ssolved solids,conductivity,and
most of the major ions may be evident immediately after
closure of the dam(s).Inundation and leaching of rocks and
soil in the impoundment area promote this situation.The
magnitude of increase cannot be quantified with available
data,but it is anticipated that the increase will not result in
detrimental effects to freshwater aquatic organisms.The
leaching effects will diminish for two reasons as the
reservoir(s)matures.First,the most soluble elements will
dissolve into the water rather quickly and the rate of leachate
production will decrease with time.Second,much of the
inorganic sediment carried by the Susitna River will settle in
the Watana Reservoir.The formation of an inorganic sediment
blanket on the reservoir bed will retard leaching.
(3)About 70-97 percent of the suspended solids load in the river
is expected to settle in Watana Reservoir.Consequently,the
reservoi r and downstream area will be significantly less tu rbid
than the pre-project condition du ri ng summer.Glacial flou r
entering the reservoir during summer may still be passing
th rough du ring winter.Consequently,winter tu rbidity
values,although low,may be higher in the reservoi rand
downstream area than under pre-project conditions,where
turbidity is essentially zero.
(4)The percentage of the reservoirs'volume lost to evaporation
during summer will be less than 1 percent at both reservoirs.
s18/c 4-1
The potential effect of a less-than 1 percent concentration
increase in dissolved solids is not significant.
(5)The range and seasonal variation in temperature of the river
""ill change after impoundment.There will be a reduction in
the magnitude of temperature variation and some shift in the
time period of low temperatures.
(6)Many metals'concentrations will be reduced in Watana
Reservoi r as these elements will be precipitated and wi II settle
to the bottom.
(7)The reservoi res)will maintain relatively high oxygen levels
and low algal productivity.Productivity will be limited by
low light conditions.Turbidity in the summer and an ice
cover in the winter (especially if snow covers the ice)will
reduce the depth of the photic zone.Dissolved oxygen
should remain high because the existing oxygen demand is
low.
s18/c 4-2
5 -REFERENCES
Adams,W.A.,1978.Effects of ice cover on the solar radiation
regime in Canadian Lakes.Vehr.Internat.Verein.Limnol.,
Vol.20,pp.141-149.
Baxter,R.M.,and P.Glaude,1980.Environmental effects of
dams and impoundments in Canada:experience and prospects.
Bulletin 205,Canadian Bulletin of Fisheries and Aquatic
Sciences,Dept.of Fisheries and Oceans,Ottawa,Canada,
34 pp.
Beiningen,K.T.,and W.J.Ebel,1970.Effect of John Day Dam
on di.ssolved nitrogen concentrations and salmon in the
Columbia River,1968.Trans.Am.Fish.Soc.99,pp.664-
671.
Boike,E.L.,and K.M.Waddell,1975.Chemical quality and
temperature in Flaming Gorge Reservoir,Wyoming and Utah,
and the effect of the reservoi r on the Green River.U.S.
Geological Su rvey,Water-Supply Paper 2039-A,814 pp.
Carmack,E.C.,and C.B.J.Gray,1982.Patterns of circulation
and nutrient supply in a medium residence-time reservoir,
Kottenay Lake,British Columbia.Canadian Water Resou rces
Journal,Vol.7,No.1,12 pp.
Churchill,M.A.,1957.Effects of storage impoundments on water
quality.Journal of Sanitary Engineering Division,A.S.C.E.,
SAl,paper 1171,pp.1-48.
Dillon,P.J.,and F.H.Rigler,1975.A simple method for
predicting the capacity of a lake for development based on
lake trophic status.Jou rnal Fish.Res.Canada,Vol.32,
No.9,pp.1519-1531.
Drachev,S.M.,1962.The oxygen regime and the processes of
self-purification in reservoirs with retarded discharge.In:
B.A.Southgate (ed.),Advances in Water Pollution Research,
Pergamon Press,New York.
EriCkson,P.A.,and J.T.Reynolds,1969.The ecology of a
reservoir.Natural History,Vol.83,No.11,pp.48-53.
Fish,F.F.,1959.Effect of impoundment on downstream water
quality.JAWWA,Vol.51,pp.47-50.
Geen,G.H.,1975.Ecological consequences of the proposed Moran
Dam on the Fraser River.Journal Fish Res.Board Canada,
Vol.32,No.1,pp.126-135.
s18/e 5-1
._-------
Ingols,R.S.,1959.Effect of impoundment on downstream water
quality,Catawba River,S.C.JAWWA,Vol.51,pp.42-46.
_----:;::--_--:'and R.D.Wilroy,1962.Observations on magnanese in
Georgia waters.JAWWA,Vol.54,pp.203-207.
Kellerhalls,R.,·and D.Gill,1973.Observed and potential
downstream effects of large storage projects in northern
Canada.In:Proc.,11th International Congress on Large
Dams,Madrid,Spain,pp.731-754.
Kittrel,F.W.,1965.Thermal stratification
Symposium on Stream Flow Regulation
U.S.Department of Health,Education
D.C.,279 pp.
in reservoirs.In:
for Quality Control,
and Welfare,Wash.
Koenings,J.P.,and G.B.Kyle,1982.Limnology and fisheries
investigations at Crescent Lake (1979-1982),Part I:Crescent
Lake limnology data summary.Alaska Department of Fish and
Game,F.R.E.D.Division,Soldotna,Alaska,54 pp.
Love,K.S.,1961.Relationship of impoundment to water quality.
JAWWA,Vol.53,'pp.559-568.
Mackenthun,K.M.;1969.The practice of water pollution biology.
U.S.Department of the Interior,Fed.Water Poll.Control
Admin.,Div.of TechniCal Support,281 pp.
Mortimer,C.H.,'1941.The exchange of dissolved substances
between mud and water in lakes,Parts 1 and 2.Journal of
Ecology,Vol.29,pp.280-329.
I 1942.The exchange of dissolved s.ubstances between----;--mud and water in lakes,Parts 3 and 4.Journal of Ecology,
Vol.30,pp.147-201.
Neal,J.K.,1967.Reservoir eutrophication and dystrophication
following impoundment.In:Reservoir Fish Resources
.Symposium,Georgia University,Athens,pp.322-332.
Peterson,L.A.,1973.An investigation of selected physical and
chemical characteristics of two subarctic streams.M.S.
Thesis,University of Alaska,Fairbanks,185 pp.
R&M Consultants,Inc.,1982a.Reservoir sedimentation studies.
Susitna Hydroelectric Project,Alaska Power Authority,
Anchorage,Alaska,January.
R&M Consultants,Inc.,1982b.
Susifna Hydroelectric Project,
Anchorage,Alaska,January.
River morphology studies.
Alaska Power Authority,
s18/e 5-2
,~
R&M Consultants,Inc.,1982c.Personal communication to Larry
Peterson,L.A.Peterson &Associates,Fairbanks,Alaska.
Roesner,L.A.,W.R.Norton,and G.T.Orlob,1971.International
symposium on mathematical models in hydrology,Warsaw,
Poland,19 pp.
Ruggles,C.P.,and W.D.Watt,1975.Ecological changes due to
hydroelectric development on the St.John River.Journ.
Fish.Res.Board Canada,Vol.32,No.1,pp.161-171.
Ryder,R.A.,1978.
reservoi rs a
(ed.) ,Ecology
Blackwell Science
Fish yield assessment of large lakes and
prelude to management.In:S.D.Gerking
of Freshwater Fish Production,Chap.16,
Publ.,Oxford,U.K.,pp.403-423.
Smith,D.W.,and S.R.Justice,1976.Clearing Alaskan water
supply impoundments:literatu re review.Report IWR-67-A,
Institute of Water Resources,University of Alaska,
Fairbanks,96 pp.
St.John,B.E.,E.C.Carmack,R.J.Daley,C.B.J.
C.H.Pharo,1976.The limnology of Kamloops
Dept.of Environment,Inland Waters Directorate,
Yukon Region,Vancouver,B.C.
Gray,and
Lake,B.C.
Pacific and
Symons,J.M.,1969.Water quality behavior in reservoirs.U.S.
Public Health Service,Bureau of Water Hygiene,Cincinnati,
Ohio,200 pp.
_--;--,,-_'S.R.Weibel,and G.G.
influences on water quality.
pp.51-75.
Robeck,1965.Impoundment
JAWWA,Vol.57,No.1,
Tu rkheim,R.A.,1975.Biophysical impacts of a rctic hydroelectric
developments.In:J.C.Day (ed.),impacts on hyd roelectric
projects and associated developments on a rctic renewable
resources and the Inuit,University of Western Ontario,
Onta rio,Canada,199 pp.
Vollenweider,R.A.,1976.Advances in defining critical loading
levels for phosphorus in lake eutrophication.Mem.I st.Ital.
Idrobiol.,33,pp.53-83.
Weiss,C.M.,D.E.Francisco,and D.R.Lenat,1973.
Pre-impoundment studies,Howard Mills Project.Department
of Environmental Sciences and Engineering and the University
of North Carolina Wastewater Research Center,Chapel Hill,
North Carolina,190 pp.
s18/e 5-3
Williams,S.K.,D.B.Aulenbach,and N.L.Clesceri,1976.
Sou rces and distribution of trace metals in aquatic
environments.In:A.J.Rubin (ed.),Aqueous-Environmental
Chemistry of Metals.Ann Arbor Science Publishers,An n
Arbor,Michigan,pp.77-127.
Wright,J.C.,and R.A.Soltero,1973.
Reservoir and the Bighorn River.
Washington,D.C.,105 pp.
Limnology of Yellowtail
Re-73-002,U.S.EPA,
s18/e 5-4
..-
I
-
ATTACHMENT A
METHODOLOGY FOR THE PREDICTION OF
THE POTENTIAL FOR EUTROPHICATION
Two widely recognized models for the prediction of trophic status
in phosphorus limited lakes are presented in this attachment.In
addition,the applicability of each model in Alaskan waters is
discussed.
The relative quantities of carbon,silicon,nitrogen,and
phosphorus (i.e.C:Si:N:P ratio)in a lake or reservoir indicates
which of these nutrients controls the eutrophication process.A
particular C:Si:N:P ratio that exists at any given time in a lake
may be subject to change,depending upon the rate at which
available forms of these nutrients from both internal and external
sources are supplied to a water body,as well as the rate of their
utilization or transformation to available forms.Among these
nutrients,phosphorus and nitrogen most often limit the growth of
algae in aquatic systems.Since algae production occurs rapidly
over a short period of time,it is the bio-available fraction of these
nutrients present,rather than the quantities of total nitrogen or
phosphorus,that determine the limiting nutrient.The form of
phosphorus that is bio-available in natural fresh water consists of
the dissolved orthophosphate fraction,and the bio-avai lable form
of nitrogen consists of the inorganic fraction.An inorganic
nitrogen to dissolved orthophosphate mass ratio between 5:1-10:1,
corresponding to an atomic ratio of between 11:1-22:1,is the
critical range above which phosphorus is limiting and below which
nitrogen is limiting (Rast and Lee,1978).
Phosphorus is usually the least abundant nutrient controlling algal
growth in lakes ..Phosphorus loading --the amount of phosphorus
added to a lake per unit area per unit time --is recognized as the
best measure of the degree of eutrophication that may be predicted
in a phosphorus limited lake.Two models for predicting the
spring total phosphorus concentration in a lake appear below.
The phosphorus imported to a lake in runoff,when combined with
input directly to the lake's surface through precipitation and dry
fallout,gives a measu re of the natural total phosphorus load.The
total natural phosphorus load can be combined with the total
artifical phosphorus load,the mean depth of the lake,the lake's
water budget expressed as the flushing rate,and the phosphorus
retention coefficient of the lake,to predict spring total phosphorus
concentration in the lake.The predicted spring total phosphorus
concentration can then be used to predict trophic status,which is
di rectly related to summer ch lorophll "a"concentration,and sec(;hi
disc transparency.Dillon and Rigler (1975)present an equation
to predict the total,steady-state phosphorus concentration which
is expressed by:
L (l-R)
[P]=
z p
-
Where:[P]
s18/f
=steady-state phosphorus concentration
A-2
Ii"'"
I
L =total loading (natural and artifical)
F'Z =
P =
1-R =
mean depth of the lake (lake morphometry)
flushing rate (water budget of the lake)
retention coefficient (the fraction of the loading
that is nqt lost via the outflow)
According to the equation,the total concentration of phosphorus
may be predicted for a lake.The correlation coeffici.ent between
measured and predicted phosphorus concentrations for eleven lakes
in southern Ontario (r =0.90)indicates that lake phosphorus
concentrations can be accu rately predicted in at least some la kes
(Dillon and Rigler,1974).However,because the equation for
determining the retention coefficient was developed for a
homogeneous set of lakes,its application may be iimited to lakes in
similar geographical areas.
Subsequently r a model was developed by Vollenweider (1976)which
is considered to be an improvement over the Dillon and Rigler
model.In this model r the retention coefficient is replaced by a
factor which incorporates the flushing rate ( 1 / 1 +ifr7P ).
Theoretica Ily,either of these models may be used to predict the
trophic status of a reservoir following the impoundment of a stream
or river,based on the assumptions that:(1)phosphorus will be
the factor controlling phytoplan kton productivity,(2)the influx of
phosphorus is constant,(3)phosphorus losses occu r th rough
sedimentation and the outlet,and (4)the net loss of phosphorus
to sediments is proportional to the amount of phosphorus in the
reservoir (Utturmark and Hutchins,1978).Also,phosphorus
concentrations tend to increase with the age of a reservoi r (Smith
and Justice,1976),and peak algae biomass and productivity levels
may occur under spr)ng ice rather than in summer (LaPerriere et
~,1978),making both models inapplicable.
When values for loading and flushing rate are estimates (as
opposed to direct measurements)then it is likely that the
uncertainty of these estimates will be quite large (Reckhow;1979).
The uncertainty of natural phosphorus loading figures can in
themselves result in a 100 percent error in the calculation of the
natural phosphorus budget in a reservoir,while other factors are
only approximations.Nevertheless,these estimates are valuable
because of thei r simpl icity and quantitative natu ref provided that
caution is taken in interpreting the results (Dillon and Rigler,
1975).
s18ff A-3
Loading
Total phosphorus loading is calculated by totalling the phosphorus
load from the land (runoff),the phosphorus load from
precipitation,and the artiHcal phosphorus load (from human
development).Total phosphorus load from the land is equal to the
total area of each watershed or drainage basin contributing runoff
to the lake multiplied by the phosphorus export coefficient.This
coefficient is the phosphorus exported from each m2 of land in the
watershed per year,and is calculated by combining the measured
amount of phosphorus carried by each stream in the watershed
with the total discha rge for a given period of time.Dillon and
Kirchner (1975)measured·the total phosphorus export for 34
southern Ontario watersheds.The total phosphorus export for all
watersheds was tabulated along with additional information on the
geology,land use,and population density of each watershed.
Upon inspection of these data,it was apparent that the watersheds
could be grouped according to whether they were forested or
consisted of pasture as well as forest,and according to whether
they were on igneous or sedimentary formations.The range and
mean phosphorus export values (mg/m2 /yr)obtained for each
two-way (land use-geology)classification were:
t
l
l
l
Land Use
Forest
Range
Mean
Forest &Pasture
Range
Mean
Igneous
2.5 -7.7
4.8
8.1 -16.0
11.7
Sedimentary
6.7 -14.5
10.7
20.5 -37.0
28.8
L
L
Changing land use from "forest"to "forest and pastu re"in
watersheds on igneous rock apparently more than doubles the
phosphorus export.Similarly,the export from a sedimentary
forested watershed is about double that from an igneous forest
watershed.The advantage of using export coefficients is that the
total phosphorus load to a lake can be estimated without extensive
field investigations.However,an export coefficient must be
selected which was determined for a land use similar to the area
under consideration.In areas where no export coe,fficient has
been establ ished,the total phosphorus load to a water body may
A-4
L
-
;~,
i I
be determined by combining the measured amount of phosphorus
carried by each·contributing stream (mg/m 3 /yr)with the total
stream discharge (m 3 /yr).In effect,this is the method by which
Dillon and Kirchner (1975)initially determined export coefficients
for 34 southern Ontario watersheds.Until such regional
coefficients are determined for Alaska land uses,the latter of the
two methods probably offers a higher degree of total phosphorus
export reliability.
The total phosphorus load from the lahd is combined with the total
phosphorus load from precipitation to calculate the total
phosphorus load.Vollenweider (1976)established a method for
determining the maximum phosphorus load to a lake which will
result in oligotrophic status.This method is expressed by:
Lc =10 [zp (1 +Jlip ) ]
Where:Lc =critical areal phosphorus load (mg/m 2 /yr)
Z =me~n depth
p =Jlushing rate
,....
....
The fraction of the phosphorus load which is biologically available
may be significantly different than the total measured phosphorus
load.Accordingly,the steady-state concentration of total
phosphorus in a lake may be different than the concentration of
phosphorus which is available to the growth of lake algae.For
example,Kamloops Lake is an oligotrophic lake in British Columbia
with a very high phosphorus load (22,800 mg/m2 /yr)and mean
depth of 75 m (St.John et aI.,1976).Without differentiating
between the various forms-of phosphorus,the predicted
phosphorus concentration in the lake was above what is considered
to be oligotrophic.When the appropriate corrections were made
for availaLle phosphorus forms,and the lake's flushing rate was
taken into account,the steady-state phosphorus concentration fell
well within the oligotrophic category.It was determined that 80
percent of the total phosphorus in Kamloops Lake occurred as
particulate phosphorus,of which 80 percent W::lS -biologically
unavailable over a wide range of particle sizes in the water
column.The dissolved fraction was not analyzed for its
orthophosphate content,which is considered the most important
algae nutrient in lakes (St.John et~,1976).
The recent investigation of a glacially influenced lake in Alaska
(Koenings and Kyle,1982)indicates that 50 percent of the total
phosphorus concentration in the lake was biologically inactive,
owing to the fact that the greatest percentage of the lake's total
phosphorus occu rred in the inorganic particulate form.In
A-5
addition,non-particulate (soluble)inorganic phosphorus was to a
great extent converted to particulate phosphorus in the epilimnion
in mid-summer.It was concluded that the nutrient dynamics in
glacially influenced lakes which have high silt inputs are different
than those of clear water lakes.
Mean Depth
The mean depth of a lake or a measure of the lake's morphometry
is required in using the predictive model for phosphorus
concentrations.
Flushing Rate:The flushing rate is the reciprocal of the detention
time of a unit volume of water within a lake and is the equivalent
of the lake's annual water budget expressed as the total outflow
volume per year divided by the lake volume.
Estimation of a reservoi r's water budget from precipitation and
evaporation data may be quite inaccurate,especially for small lakes
and small drainage areas.Actual measurement rather than
estimation of the water budget undoubtedly provides much more
accurate results,and should be undertaken where possible (Dillon
and Rigler,1975).
Flushing rate is significant in that it holds down'algal production
in lakes which may otherwise be highly productive.In lakes with
high flushing rates,biologically available phosphorus accumulates
much slower than in lakes with relatively low flushing rates.In
lakes containing a high percentage of suspended phosphorus,the
flushing rate may not reflect the rate at which total phosphorus is
removed.I nstead it may be an expression of the percentage of
dissolved phosphorus removed from the system,if particulate
phosphorus settles to the bottom before it can be removed (St.
John et~,1976).
Flushing rate is an important variable since it regulates both the
degree and regime of phosphorus loading.'In re~ervoirs,the
flushing rate is controlled by the amount of water allowed to
escape relative to the reservoir volume (Ryder,1978).
Calculations of flushing rate may be complicated by the varying
hydrologic regime of a reservoir.For example,St.John et al.
(1976)report that flushing rates may vary 20-fold over oneyear,
and at times inflowing'water may pass directly through a lake,
thus increasing the flushing rate even further.
Retention Coefficient:The retention of phosphorus in a reservoir
is dependent.upon factors suc,h ..as the dissolved oxygen
concentration and the pH at the sediment-water interface,and
s18/f A-6
.I!"'"
I
r
..-
I
~
I
upon major cations that combine with phosphorus and transport or
retain it in sediments.Thus,the phosphorus retention coefficient
is actually a simplification of the phosphorus retention process
(Reckhow,1979).For instance,phosphorus contained in reservoir
sediments may be released and redistributed under reducing
conditions during fall overturn (Hutchison,1957).Successful use
of this coefficient is dependent on an accurate estimate of the
phosphorus retention in the lake in question.A large discrepancy
between predicted phosphorus retention (0.1 percent)and
measu red phosphorus retention (76 percent)was found by
St.John et al.('1976)in Kamloops Lake.This discrepancy was
attributedto a situation where most of the phosphorus load was in
the form of inorganic particulate phosphorus,which is converted
to dissolved phosphorus at a much slower rate (if at all)than
particulate organic phosphorus.Phosphorus retention in a lake is
a function of sedimentation--specifically,the amount of phosphorus
that is retained by sedimentation.This amount is difficult to
calculate.However,a model was by Kirschner and Dillon (1975)
developed for lakes in southern Ontario relating the areal water
load (qs)to phosphorus retention as expressed by:
Rp =1 -[0.426 exp (0.271 qs)+0.574 exp (-0.00949 qs)]
Areal loading (qs)in mlyr is the surface overflow rate and is
calculated as the lake outflow volume divided by the lake surface
area.Values for phosphorus retention in 15 Ontario lakes,using
the measurement model and the values derived from the theoretical
model,were in close agreement (r =0.94)."The fact that the
retention coefficient of phosphorus is more closely related to the
areal water load (qs)than the volumetric water load (i.e.water
renewal time)is not readily explainable,but in light of the above
advantages we feel that this model warrants acceptance on purely
empirical grounds"(Kirschner and Dillon,1975).
An alternative method of estimating phosphorus retention
(-:::-----c1,---=-,....--)
1 +lip
was derived·by Vollenweider (1976)which is an expression of the
relationship between phosphorous residence time and the residence
time of water in a lake.This equation was used in calculating
phosphorus concentrations in 60 heterogenous northern temperate
lakes and plotted against chlorophyll "a"concentrations in the
same la kes.The resultant correlation coefficient (0.868)verified
the "unquestionable"relationship between Vollenweider's model and
algae production among lakes in the north temperate zone
(Vollenweider,1976).
s18/f A-7
ATTACHMENT A
REFERENCES
Dillon,P.J.,and W.V.Kirchner,1975.The effects of geology
and land use on the export of phosphorus from watersheds.
Water Research,Vol.9,pp.135-148.
Dillon,P.J.,and F.H.Rigler,1974.A test of a simple nutrient
budget model predicting the phosphorus concentration in lake
water.Journal Fish.Res.Board Canada,Vol.31,No.11,
pp.1771-1778.
,1975.A simple method for predicting the capacity of a-----:,...-,..--::lake for development based on lake trophic status.Journal
Fish.Res.Board Canada,Vol.32,No.9,pp.1519-1531.
-,
Hutchinson,G.E.,1957.
Geog raphy ,Physics
1015 pp.
A
and
Treatise on
Chemistry,
Limnology,
Wiley,New
Vol.1,
York.
Kirchner,W.B.,and P.J.Dillon,1975.An empirical method of
estimating the retention of phosphorus in lakes.Water
Resources Research,Vol.11,No.1,pp.182-183.
Koenings,J.P.,and G.B.Kyle,1982.Limnology and fisheries
investigatLons at Crescent Lake (1979-1982),Part I:Crescent
Lake limnology data summary.Alaska Dept.of Fish and
Game,F.R.E.D.Div.,Soldotna,Alaska,54 pp.
LaPerriere,J.D.,T.
chemistry of a
EPA-G00/78-008,
Oregon,129 pp.
Tilsworth,and L.A.Casper,1978.Nutrient
large,deep lake in subarctic Alaska.
U.S.EPA,Env.Res.Lab,Corvallis,
Rast,W.,and F.Lee,1978.Summary analysis of the North
American (U.S.portion)OECD eutrophication project:
nutrient loading,lake response relationships and trophic
state indices.Env.Research Lab.,Office of Research and
Development,U.S.EPA,Corvallis,Oregon,455 pp.
Reckhow,K.H.,1979.Quantitative techniques for the .assessment
of lake quality.Dept.of Resou rces Development,Michigan
State University,prepared for U.S.EPA,Office of Water
Planning and Standards,146 pp.
Ryder,R.A.,1978.Fish yield assessment of large lakes and
reservoirs a prelude to management.In:S.D.Gerking
(ed.)Ecology of Freshwater Fish Production,Chap.1G,
Blackwell Science Publ.,Oxford,U.K.,pp.403-423.
s18ff A-8
Smith,D.W.and S.R.Justics,1976.Clearing Alaskan water
supply impoundments:literature review.Report IWR-67-A,
Institute of Water Resources,University of Alaska,
.Fairbanks,96 pp,
St.John,
C.H.
Dept.
Yukon
B.C.,E.C.Carmack,R.J.Daley,C.B.J.
Pharo,1976.The limnology of Kamloops
of Environment,Inland Waters Directorate,
Region ,Vancouver,B.C.
Gray,and
Lake,B.C.
Pacific and
Uttormark,P.D.,and M.L.Hutchins,1978.I nput/output models
as decision criteria for lake restoration.Technical completion
report,Project C-7232,U.S.Dept.of the Interior,Office of
Water Research and Technology,62 pp.
Vollenweider,R.A.,1976.Advances in defining critical loading
levels for phosphorus in Jake eutrophication,Mem.1st.Ital.
ldrobiol.,33,pp.53-83.
s18/f A-9
---_._-------------------------