Prattville Temperature Issues
August 25, 2004
The following statements are a compilation of comments
made at various public meetings in Chester and Chico, comments and concerns
raised by Ron Decoto in a letter to FERC dated June 14, 2003 and recent
comments by Bill Dennison in regard to the September 2, 2004 2101LG
meeting. The statements do not reflect
all comments made on the subject of temperature reduction. The statements are biological or physical in
nature only and with one exception do not reflect any comments made concerning
cost or economic impacts.
A common thread running
through statements concerning the temperature curtain evaluation is that the
statements nearly universally are defined in terms of the maximum predicted
change in a physical attribute. For example,
it has been predicted that in certain situations the depth to the Lake Almanor
thermocline will increase by 10 feet.
It is then assumed that the 10-foot change will occur every year. What is vitally necessary for the full
understanding of the potential changes that might take place is to define those
changes in terms of water year type and summer meteorology. By placing impact within the contest of
climate we will be able to see how frequently an impact of a given magnitude is
expected to occur and whether the predicted impact is within the range of
variability currently experienced.
Questions are in no
particular order of importance but generally start at Lake Almanor and move
Cultural resource surveys have been conducted on the portion
of Lake Almanor exposed during low lake levels. There is a possibility that sites are located beneath the lake in
the vicinity of the Prattville Intake.
Local tribes have knowledge of sites now inundated by Lake Almanor. Photos of construction of the Prattville
Intake would be beneficial in identifying probable sites. Surveys, if undertaken, could take place
under water. How will local tribes be
assured that removal of levee material and associated construction of the
temperature curtain will not impact sites?
As water is withdrawn from Lake Almanor, the thremocline
perimeter decreases. The change in
perimeter is dependent on lake elevation at the beginning of summer, rate of
water withdrawal, and summer meteorological conditions. Based on the 33 years of synthesized reservoir
operations, what is the total reduction in perimeter under various combinations
of water year type, and cool, average, and above average summer meteorological
conditions with and without the Prattville curtain? Since water year type is not necessarily a good predictor of
reservoir elevation at the beginning of the summer, use initial elevation if
that gives more predictable results.
Under current conditions, water withdrawn from Lake Almanor by
the Prattville Inlet is composed of both warm and cold water. Construction of the Prattville temperature
curtain will result in withdrawal of cold water only in wet and normal
years. In Dry and Critically Dry years
little cold water is available for withdrawal.
Surface water temperatures are predicted to change up to one-half degree
Centigrade with installation of the temperature curtain. Based on the 33 years of synthesized
reservoir operations, what is the expected change in surface temperature under
various combinations of water year type, and cool, average, and above average
summer meteorological conditions with the Prattville curtain? Compare the predicted surface temperatures
to existing conditions for the 33 years of record.
Under current conditions the depth to the
thermocline in Lake
Almanor during the summer is controlled somewhat by the non-selective nature of
the Prattville Intake. Construction of
the temperature curtain at Prattville will result in selection of cold water at
the expense of warm water. The depth to
the thermocline is expected to increase under certain combinations of summer
temperature and water year type. Based on the 33 years of synthesized reservoir
operations, what is the expected increase in the depth to the
various combinations of water year type, and cool, average, and above average
summer meteorological conditions with and without the Prattville curtain? Since water year type is not necessarily a
good predictor of reservoir elevation at the beginning of the summer, use
initial elevation if that gives more predictable results.
During the summer salmonids prefer a layer of water located
just above the thermocline that meets temperature preferences and also contains
adequate dissolved oxygen for survival.
As water is withdrawn from Lake Almanor, the volume of water occupied by
salmonids shrinks necessitating movement by salmonids if they are to remain in
preferred water temperature and dissolved oxygen conditions. Where do salmonids go to take refuge from
high water temperatures and low dissolved oxygen levels during stressful
conditions caused by low lake level or unusually warm air temperatures? Based on 33 years of reservoir operations,
how are these places of refuge impacted with and without the Prattville
Observations have shown that salmonids will move to the
vicinity of springs located in Lake Almanor to take refuge from high summer
water temperatures. Based on the 33
years of synthesized reservoir operations how might access to the cold water
discharging from the springs be impacted under various water year types and
cool, average, and above average summer meteorological conditions with and
without the Prattville temperature curtain?
Under existing conditions what proportion of salmonids are found in
areas other that immediately surrounding springs?
- Warm water preferring fish occupy the upper
layers of Lake Almanor during the summer.
In some water year types and meteorological conditions the depth to
the thermocline will increase as cold water is withdrawn at the Prattville
Intake with installation of the Prattville temperature curtain. In such years, will warm water
preferring fish be favored in terms of individual growth or numbers?
- Currently lake Almanor is occupied by both warm
and coldwater fish each occupying preferred habitat conditions. Water year type and meteorological
condition variability would appear
to favor one or the other at times.
By utilizing the 33 years of synthesized operations, is it likely
that warm water fish abundance would change with construction of the
- During the summer, water in Lake Almanor is
heated from above by solar radiation and convection and cooled from the
bottom by the lakebed causing temperature stratification in the lake. The temperature stratification is also
equivalent to stratification by density as well with the warmer and less
dense water lying on top of the cooler, and more dense water. The Prattville temperature curtain if
deployed would extract cool water from below the
thermocline. Would withdrawal of cold water initiate
currents within the coldwater pool that would result in unequal
distribution of cold water or is the coldwater pool of equal consistency
throughout the reservoir?
- During the summer surface inflow, and to some
extent depending on location and the elevation of Lake Almanor, is cooler
than the receiving water. As the
cool water descends through the warmer lake water, drag is exerted on the
adjacent warm water entraining some of that water in a downward
motion. The warm water is replaced
to some extent by upwelling cold water.
What changes in biological activity and water chemistry would be
expected at these inflow points with operation of the Prattville
- During low inflow years, Lake Almanor does not
fill to the extent it does in wet years.
As water is drawn into the Prattville intake in low elevation
years, the proportion of warm versus cold water increases since the
thermocline elevation will be quite close to the inlet elevation. In Dry and Critically Dry years what is
the difference in volume of cold water removed with and without the
Prattville temperature curtain?
Would differences be better illustrated if withdrawal was described
in calories rather than volume of water?
- The Chester arm of Lake Almanor is quite shallow
compared to the Hamilton Branch arm.
The bottom of the reservoir in the Chester area was once a rather
extensive meadow with a gentle slope.
Residents have commented that aquatic plants have been a problem in
the past. If the Prattville
temperature curtain is constructed the perimeter of the lake will not
change since the quantity and timing of water withdrawal from the lake
will be the same with or without the Prattville curtain. The surface temperature of the lake and
depth to the thermocline will increase under some conditions. Will aquatic plant volume or area
increase with operation of the temperature curtain due to the presence of
warmer water in contact with the reservoir bottom under certain
conditions? Which combinations of
water year type and summer meteorological conditions will result in
additional aquatic plant growth?
What is the maximum rooting depth of aquatic plants commonly found
in Lake Almanor?
- Will the withdrawal of cold water and the
increase in depth to the thermocline in some years result in increased
algae production in Lake Almanor?
Would additional algae reduce the depth to the thremocline by
- The dissolved oxygen content of cold water
withdrawn from Lake Almanor will be quite low. When released into Butt Valley Reservoir at the Butt Valley
Powerhouse, the cooler, dissolved oxygen deficient water is likely to not
mix readily with Butt Valley Reservoir water. What is the impact of the release of oxygen deficient
coldwater on the Butt Valley Reservoir fishery and what mitigating
measures could be taken to increase the dissolved oxygen content of the
- As coldwater from Lake Almanor passes through
Butt Valley Reservoir warming takes place negating a portion of the
coldwater benefit. Temperature
modeling has demonstrated that it is possible to recapture a portion of
temperature gain by construction of a temperature curtain at the Caribou 1
and 2 intakes as well as the tailrace of Butt Valley Powerhouse. The recapture is greatest with two
curtains in Butt Valley Reservoir.
What is the estimated cost of constructing curtains at Butt Valley
Powerhouse and near the Caribou 1 and 2 intakes? Black and Veatch has provided the estimated cost of
constructing the Prattville temperature curtain. What is the estimated annual cost of maintaining the
curtains? Will replacement be
necessary during the term of the license?
- The Prattville temperature curtain if constructed
would occupy approximately 14 of the 27,000 acres or five one-hundredths
of one percent (1 in 1,929) of the surface area of Lake Almanor. On an expansive scale the curtain is
insignificant. The curtain may
have aesthetic impacts if seen from nearby residences. Would the curtain be visible from
nearby residences? Would the
curtain add to the visual impact of the existing intake structures and
associated PG&E on-shore facilities?
Are their mitigating measures that would reduce the visual presence
of the curtain structure?
- Currently large numbers of Japanese pond smelt
pass through the Prattville tunnel and Butt Valley powerhouse to emerge as
chum for brown trout. With
construction of the temperature curtain, the pond smelt will no longer be
drawn into the tunnel. What is the
effect of reduction of chum to Butt Valley Reservoir and the increase in
numbers of pond smelt remaining in Lake Almanor? If the Prattville temperature curtain is constructed in a
manner to allow opening of the curtain, would Japanese pond smelt be drawn
into the Prattville Intake?
- A fixed curtain installed at Prattville will
withdraw cold water year-long. Is
there a combination of timing and selective withdrawal that minimizes the
additional depth to the thermocline experienced with the fixed curtain?
- Would additional warm water under certain
combinations of water year type and summer meteorological conditions
impact existing programs designed to improve fish habitat in Lake
Almanor? Is the impact positive or
negative? If negative, what is the
expected frequency of negative impact years?
- What water quality, aquatic habitat and fish
monitoring will take place in order to quantify changes in Lake Almanor
and Butt Valley Reservoir due to withdrawal of cold water. Is it possible to modify the existing
aquatic and water quality program or will new monitoring be necessary?
- How might wind, waves and ice impact the
Prattville temperature curtain?
- If it is assumed that the temperature curtain
with levee removal takes place in Lake Almanor and temperature curtains
are constructed at Butt Valley Powerhouse and at the Caribou inlets and
mitigation of dissolved oxygen deficiencies occurs:
What are the anticipated
reductions in water temperature at Butt Valley Powerhouse?
What is the anticipated
warming of water temperature as it passes through Butt Valley Reservoir?
What warming occurs in
the Belden Forebay?
What is the anticipated
warming of water temperature in the Belden reach?
What is the “best and
worst case scenario” for the expected August temperature in the Rock Creek and
Cresta reaches during Wet, Normal, Dry, and Critically Dry water year types?
- Modeling of the effectiveness of the Prattville
temperature curtain in reducing downstream stream temperature has
demonstrated that any combination of curtains in Lake Almanor and Butt
Valley Reservoir will reduce downstream water temperature under some but
not all situations. Based on the
33 years of synthesized reservoir operations, what is the expected
reduction in stream temperature under various combinations of water year
type, and cool, average, and above average summer meteorological
conditions in the Rock Creek and Cresta reaches?
- Reductions in stream temperature in the Rock
Creek and Cresta reaches will not occur in all water years. It appears that reductions in
temperature will occur in Wet and Normal years with Dry and Critically Dry
years receiving little if any temperature reduction. Since the area climate tends to exhibit
precipitation extremes, Dry and Critically Dry years frequently
occur. What physical and
biological parameters will be used to monitor aquatic environment response
to installation of temperature curtains?
How will improvements in aquatic health be quantified?