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 downstream.

1.      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?

2.      As water is withdrawn from Lake Almanor, the thremocline perimeter decreases.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.

3.      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.

4.      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 thermocline 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.   

5.      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 curtain?

6.      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? 

7. 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?

8. 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 Prattville curtain?

9. 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?

10. 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 temperature curtain?

11. 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?

12. 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?

13. 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 intercepting sunlight?

14. 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 water?

15. 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?

16. 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?

17. 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? 

18. 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?

19. 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?

20. 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?

21. How might wind, waves and ice impact the Prattville temperature curtain?

22. 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?

23. 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?

24. 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?