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BEFORE THE IDAHO PUBLIC UTILITIES COMMISSION
IN THE MATTER OF THE
APPLICATION OF IDAHO POWER
COMPANY TO DEFER EXPENSES
ASSOCIATED WITH ITS CLOUD
SEEDING PROGRAM FOR INCLUSION
IN THE COMPANY PCA ON AN
ONGO ING BAS IS. CASE NO. IPC-05-
IDAHO POWER COMPANY
DIRECT TESTIMONY
GARY RILEY
October 2005
Please state your name and business address.
My name is Gary Riley and my business address
is 1221 West Idaho Street, Boise, Idaho.
By whom are you employed and in what
capaci ty?
I am employed by Idaho Power Company as
Senior Meteorologist in the Water Management department.
Please describe your educational background.
I attended the USAF Weather Observers School
in 1965 and the Weather Forecasters School in 1970-71,
graduating from both with honors.I received a Bachelor of
Science Degree from Longwood College (now Longwood
University) in 1981, graduating Summa Cum Laude with a major
in physics and a minor in mathematics.I received a Mas ter
of Science degree in Atmospheric Science from the State
University of New York at Albany in 1984.
Please describe your work experience wi
Idaho Power Company.
I was hired by Idaho Power Company in June
2002 to implement and run the Company s cloud seeding
project on the Payette River Basin and to provide weather
forecasting support tailored to the Company s needs and
interests.
The cloud seeding proj ect is designed to augment the
wintertime snowpack in the Payette River Basin and thereby
RILEY, DI
Idaho Power Company
increase spring and summer runoff through the Company
Hells Canyon Complex.The project became operational in
late January of 2003, with the first seeding on February
2003.Operations ended for the season on April 15, 2003 and
resumed between November 1, 2003 and April 21, 2004.The
third season of seeding was operational between November
2 004 and Apr i 1 21, 2 005 .
Please describe your experience in the field
of weather modification.
Prior to joining Idaho Power, I was Vice
President and Chief Scientist for Atmospherics Incorporated
in Fresno, CA.Founded in the mid 1960s, Atmospherics is
one of the oldest and most respected weather modification
companies in the world.I first began working for
Atmospherics in December 1991, and while there I supported,
operated, and/or managed weather modification projects in
California, Nevada, Colorado, and Texas.Internationally,
projects were conducted in Spain, India, Indonesia, and
Costa Rica.
From 1987 through early 1991, I was employed by
Intera Technologies of Calgary, Alberta, Canada as a Senior
Meteorologist and I was the Assistant Manager of the Greek
National Hail Suppression Project.
What is the purpose of your testimony in this
proceeding?
RILEY, DI
Idaho Power Company
I will describe the scientific basis
supporting the effectiveness of cloud seeding.I will also
describe the mechanics of how Idaho Power accomplishes its
cloud seeding program and the steps the Company has taken to
measure the effectiveness of its cloud seeding program.
Based on the testing and measurement steps
the Company has taken to date, do you have an opinion as to
whether the Company s cloud seeding program will be cost-
effective on a long-term basis?
Yes.Based on Idaho Power s experience to
date and the sophisticated testing and measurement analysis
described in my testimony, I conclude that the Company
cloud seeding program presents posi ti ve benefi ts to the
Company and its customers and would be cost-effective on a
long-term basis.
Please briefly describe the theory behind
cloud seeding as it applies to Idaho Power s proj ect to
augment snowfall.
The natural precipitation processes
fundamentally inefficient in the maj ori ty of cases.That is
to say that more water is available for precipi tation than
actually falls as precipi tation.The air in a storm system
usually contains plenty of water, but it does not contain
enough of the types of particles capable of acting as ice
nuclei.These particles start the process of converting the
RILEY, DI
I daho Power Company
available water into ice and finally, into snowfall.Cloud
seeding to augment wintertime snowfall works by partially
reducing the deficit by introducing more of these particles
into the storm system.
What factors are necessary for cloud seeding
to be effective and provide the benefit of additional
snowfall?
To be effective, three fundamental and
necessary condi tions need to exist in the airmass passing
over the target area - in our case, the Payette River Basin.
First, the air must already be producing, or be
about to produce, precipitation (this is snow enhancement,
not snow making) Such a winter storm can produce a
thermodynamic environment favorable for activation and
transport of the seeding material into the part of the storm
where the- precipitation forms.
Second, the air must contain an appreciable amount
of supercooled liquid water.Supercooled liquid water is
simply water suspended in the air at temperatures below
freezing, that is below 32 OF or 0 oC.Pure water can exist
in the liquid state to temperatures as cold as -40 oc (or
- they are the same at that temperature)This liquid water
is converted, first to ice, and then to snow, by contact
wi th a nucleating particle by processes called contact and
condensation nucleation.
RILEY, DI
Idaho Power Company
Third, and as is usually the case, there must be an
insufficient numb~r of naturally occurring ice nucleating
particles to efficiently convert the available supercooled
liquid water first into ice crystals and ultimately, into
snowfall.These particles typically consist of dust,
pollens, salts, and clays that have been picked up and
transported into the cloud by the wind.
Given an environment where snow is falling
and surplus supercooled liquid water exists, but there are
insufficient ice nucleating particles, what can be done to
produce addi tional snowfall?
When there is more supercooled liquid water
present than can be converted to ice by the available ice
nucleating particles, the introduction of addi tional
nucleating particles can convert some of the surplus
moisture into ice crystals.These subsequently grow into
snowflakes and fall to the ground.
What does Idaho Power Company utilize as ice
nucleating material?
The primary seeding material used by Idaho
Power Company is silver iodide.It has been known since the
later part of the 1940s that silver iodide acts as a very
effective ice-nucleating particle at temperatures between
about -4 oC and -15 oC.One gram of the material creates
from 1010 to 1015 ice nuclei, depending on the temperature and
RILEY, DI
Idaho Power Company
composi tion of the seeding agent.Our network of ground-
based genera tors each release 20 grams per hour.Depending
on the configuration and other constraints, the proj ect
aircraft can release from 151 to as much as 1500 grams per
hour.
Are you able to target where the addi tional
snow will fall?
To place this addi tional snowfall in the
proper place, the target area, requires a clear
understanding of how, and how fast, the process works.For
effective cloud seeding, accurate information about the
temperature and moisture structure and about the wind flow
into and across the target area is needed.The seeding
material must be released so that there is the correct
amount of time available for it to be transported into the
portion of the storm having the proper temperature and
humidi ty structure and where the factors mentioned earlier
exist.
How long does it take to form snow once the
silver iodide has been introduced into the storm?
The typical timeframe required for the
addi tional particles to be transported into a sui table
environment, induce freezing and grow into snowflakes is on
the order of twenty to forty minutes, but it can be as long
as 100 minutes.The amount of time required can be
RILEY, DI
Idaho Power Company
controlled to some extent by adjusting the formula of the
seeding material.For the material IPCo uses, the silver
iodide needs to be introduced into the storm system in a
wind regime that will carry it into a zone of favorable
temperatures and moisture and transport it into and across
the target area in a time "window" of fifteen to forty
minu tes .
How do you know tha t the snow on the ground
is the result of cloud seeding efforts rather than snow that
would have been present without cloud seeding?
Cloud seeding projects have, until recently,
relied on statistical analysis of Target - Control, or
seeded area vs. non-seeded area, data sets.Because the
yield from any particular cloud seeding season lies well
within the natural range of variability of precipitation, it
can take many years to obtain statistically significant
resul ts and determine a reliable measure of success or
failure.For that reason, many scientists and statisticians
were reluctant to accept the results indicative of success.
Nevertheless, this procedure is still commonly used.
In the last ten to fifteen years however,
significant advances have been made in both our
understanding of the physics involved and in our ability to
confirm and evaluate results through trace chemistry
investigations.
RILEY, DI
Idaho Power Company
Because the materials used for cloud seeding are
known, as is the time of their release, analysis of the
snowpack itself provides information about where the seeding
material fell, how much of the material went towards
addi tional snowfall, and how much was simply scavenged, or
swept out of the air, by precipitation already occurring.
The presence of enhanced si 1 ver in the target area
snowpack indicates accurate targeting, but it says nothing
abou t whether it was deposi ted in the form of addi tional
snow or scavenged.Releasing an inert, non-nucleating
tracer simul taneously wi th the active seeding agent makes it
possible to determine if the source was addi tional
precipi tation or scavenglng.That information, when
combined wi th densi ty variations wi thin the snow samples,
allows quantification of the amount of addi tional snow
falling on the area.
Did Idaho Power Company take steps to measure
the effect of its cloud seeding program using this new,
sophisticated approach?
Yes.Idaho Power contracted Desert Research
Institute (DRI), an extension of the Community College
Nevada, to perform an analysis of snowpack samples from the
Payette River Basin the past two winters.The tracer used
was indium sesquioxide (In )' whose particles are similar
in size and dispersion characteristics to the nucleating
RILEY, DI
Idaho Power Company
silver iodide (AgI)However, unlike the active material,
the tracer is non-nucleating and is removed from the air
only by scavenging.Therefore, any change in the ratio of
silver to indium from what it was at the point and time of
release gives a measure of how many of the silver particles
went into making additional snow and how many were
scavenged.
Did Idaho Power measure the success of its
cloud seeding efforts in the winter of 2002-2003?
Yes.The original proj ect plan did not
include an evaluation of benefi t for the first season.The
combination of start-up operations and a short operational
season, only 2 ~ months, severely limi ted the amount of data
available.However, two direct, and one indirect, analyses
were conducted, and all produced similar results.All three
of the analyses were independent.No Idaho Power Company
personnel involved in seeding decisions took part in the
evaluation.
Please describe the two direct analyses of
the cloud seeding effort during the winter of 2002 - 2003.
The first was by an Idaho Power employee not
otherwise involved in the project.The second evaluation
was done by an independent consultant (RHS Consulting of
Reno, NV)A tradi tional Target - Control analysis,
consisting of a linear regression of precipitation at sites
RILEY, DI
Idaho Power Company
inside and outside of the target area indicated a 17%
increase in precipitation during the 2 ~ month period
between February 1 and April 15, 2003.That translates to
2 .4 inches of addi tional water when averaged over the
Payette River Basin.Given a target area of approximately
938 square miles, that works out to 120,000 acre-ft of
wa ter
The precipitation data was also provided to RHS
Consulting who determined that the project would likely have
produced a 9% increase had it been operational for the
entire winter.Using the quali ty controlled data available
now that number rises to 11%
Please describe the indirect evaluation of
the cloud seeding effort during the winter of 2003 - 2003.
An indirect evaluation was provided by North
American Weather Consultants of Sandy, UT.North American
operates a snow enhancement project on the adjacent Boise
River Basin for the Boise Project Board of Control.Their
initial analysis of the Boise Basin 2002 - 2003 season data
indicated a "no effect" result until it was realized that
the "non-seeded" Control si tes being used for the Boise
project were seeded Target sites for Idaho Powers ' Payette
proj ect After developing a new set of unseeded Control
sites, North American arrived at a 13% increase for the
Boise proj ect, and by inference, for Idaho Power s proj ect
RILEY, DI
Idaho Power Company
as well.
Did Idaho Power measure the success of its
cloud seeding efforts in the winter of 2003 - 2004?
Yes.Similar to the analysis done on the
2002 - 2003 season, a Target - Control analysis indicated a
6% increase in precipitation in the Payette River Basin for
tha t season.This reduced yield - 6%, down from 17% - was
expected because it was a dryer than normal year and the
inclusion of the trace chemistry analysis mentioned earlier
placed several constraints on operations.Still, even wi
only 80% of normal precipi tation, the yield represents an
addi tional 85,000 acre-ft of water.
Snow samples collected by DRI and analyzed in their
ultra-clean laboratory in Reno showed very high levels of
silver present and very little indium.Further, comparison
of the depth at which the silver was found with data from
nearby SNOTEL si tes shows it to be consistent wi th seeded
events.Degradation of the snowpack prior to sample
collection prevented the laboratory from quantifying the
yield in augmented precipitation, but the 2002 - 2003 data
indicate scavenging was not a significant factor and Idaho
Power has an effective project.
That conclusion is substantiated by the results of
measurements made by an aircraft especially modified for
airborne cloud physics data collection.Measurements were
RILEY, DI
Idaho Power Company
made prior to, during, and after a seeding flight on March
26, 2005.The data indicate water production from the
aircraft alone to have been in excess of 600 acre feet per
hour.
What were the results of the cloud seeding
program undertaken during the winter of 2004 - 2005?
This last season s SNOTEL data indicate a 26%
increase in precipi ta tion for the Payette River basin.
While a percentage increase of that magnitude is possible,
the number seems very high and should be viewed in the
context of an ongoing effort to obtain a statistically
significant evaluation of the cloud seeding proj ect.
However, the resul ts from the second year of trace chemistry
evaluation performed during the 2004-2005 season are very
posi ti ve and similar to those of the preceding years and
they are consistent wi th resul ts obtained by other
successful programs.
Samples collected by both DRI and RHS Consul ting
found positive evidence of an effective project.Using
newly developed procedures and sampling equipment, DRI was
able to correlate the silver, indium, and cesium in the snow
with density gradients, allowing a quantitative estimate of
augmentation.This makes it possible to distinguish between
the seeding material released by the ground-based and
airborne equipment and mathematically determine how much
RILEY, DI
Idaho Power Company
addi tional snow fell on the sampling si te.The data provide
clear evidence of an effective program.
Can you provide examples from this analysis
to help the Commission understand how the silver and indium
relate to each other and how they relate to seeded snowfall?
Yes.As an example, I would like to offer
Exhibit These figures were provided by Dr. Ross Edwards
of DRI.The first shows the concentrations of silver and
indium detected in a snow sample from the east side of the
Payet te River Basin target area.The sample was collected
on Mount Zumwalt at an elevation of 8,225 feet.Note the
different scales for silver (left side) and indium (right
side) Three seeding events are depicted and the silver to
indium ratios show that for every silver iodide particle
scavenged, between 6 and 19 other silver iodide particles
contributed to addi tional snowfall.
The second figure graphically shows enhanced levels
of both cesium and silver in a sample collected in December
of 2004.Recall that ground-based units release only silver
iodide while the airborne generators released a solution
that included the cesium tag.Superimposing these diagrams
(third figure,prepared by IPCo for purposes of
demonstration) allows one to distinguish between silver
released by the aircraft and that released at ground level.
The fourth figure shows how the presence of enhanced
RILEY, DI
Idaho Power Company
silver content that coincide with a layer of anomalous
density can be evaluated for the amount of augmented snow in
the sample.In the example shown, there is a 13% increase
due to seeding.DRI found augmentation values ranging from
13 to 34%, wi th a mean of 22%.Consequently, this is a
conservative example.DRI concluded that the overall
augmentation in the target area for this past season was
between 7 and 9 % .
Finally, the fifth figure shows where the samples
were taken and gives an indication of how the degree of
silver content departs from what would be expected in
pristine snow.As noted by Dr. Edwards, this provides
evidence of effective targeting of the watershed.
. Is DRI preparing a final report containing
the analysis that supports your testimony?
Yes.The report is in the final stages of
completion and will be filed with the Commi~sion as
Exhibi t 4 to my tes timony as soon as it is received from
DRI.
Were the results of your measurement of cloud
seeding success consistent with those for other projects and
enti ties?
The yields I have indicated, 6 to 17%,Yes.
are wi thin the range of expectations from wintertime
orographic cloud seeding contained in statements from the
RILEY, DI
Idaho Power Company
World Meteorological Organization, the American
Meteorological Society, the American Society of Civil
Engineers, the Weather Modification Association, and even
the Idaho Department of Water Resources.All of these
indicate cloud seeding to augment wintertime snowpack can
produce increases of from 5 to 20% when done correctly.
Both RHS Consul ting and DRI have said the resul ts of their
trace chemistry evaluations are consistent wi th and similar
to those from investigations of this type in California and
Nevada and elsewhere.Two of the comparable proj ects in
California are operated by power companies (Pacific Gas and
Electric and Southern California Edison) for the same
purpose as Idaho Power s program.The resul ts of trace
chemistry evaluations of the Lake Almanor project run by
Pacific Gas and Electric and those from Southern California
Edison s proj ect on the San Joaquin River have appeared in
peer reviewed publications of the American Meteorology
Society and the North American Hydroelectric Industry.
Can you provide one of these articles that is
written in non-technical language that is easier to
understand by someone not familiar with weather and cloud
seeding?
Yes.I have here a copy of an article by
Brian McGurty reporting on the resul ts of the study on the
San Joaquin River project that appeared in Hydro Review.
RILEY, DI
Idaho Power Company
think the Commission will find it very readable, and I offer
it as Exhibit
Given a quantification of additional snow
resulting from the Company s cloud seeding efforts, have you
quantified how the addi tional snow translated into
additional stream flows at the Company s hydro facilities
over the pas t three winters?
Yes.The process is complex and requires a
review of what was done in each of the three individual
years to fully describe the process.First, the preliminary
data from the 2002 - 2003 Target - Control evaluation was
fed into the CHEOPS hydrological model to determine the
generation potential of the augmented water when it passed
through the Hells Canyon Complex.That allowed the
determination of the benefit gained from the augmented water
to be evaluated under several scenarios of seeding
effectiveness and varying losses of the augmented water
prior to reaching the Hells Canyon Complex.The mode
indicated increased generation capaci ties ranging from
approximately 14,000 MWh if only 25% of the additional water
reached the power plants to as much as 56,000 MWh if all of
the water passed through the complex These numbers would
be expected to increase if the model was re-run wi th the
quali ty controlled numbers available now.
The preliminary SNOTEL data from the 2003 - 2004
RILEY, DI
Idaho Power Company
season was entered into the .National Weather Service River
Forecast System Model, and the inflow into the reservoirs on
the Payette River was calculated for Seed and No-seed
scenarlOS.The computer simulation determined that an
additional 67,700 acre-ft of water flowed through the
payet te drainage in the seeded scenario.Tha t is in very
good agreement wi th the 68, 000 acre- ft determined from the
Target - Control regression that was also based on the
pre 1 iminary da ta .The difference is easily accounted for,
in that the model takes losses to soil moisture and
evaporation into effect and these factors are not included
in the simpler regression analysis.Also, software
limitations caused the input data to be cut off near the end
of March.Consequently, precipitation after that was not
included.
Did you quantify the financial benefit of the
additional stream flow at the Company s hydro facilities?
Yes.Along wi th the calculation of
additional generation capacity, the CHEOPS data for the 2002
- 2003 season places the dollar value of the water at $ 1.
million if only 50% of the augmented water reaches Hells
Canyon Complex.However, the payet te River Basin was chosen
for the cloud seeding proj ect in part, because the river
reservoirs have a high probabili ty of refill.Hence, the
actual value would be closer to the 100% expectation with a
RILEY, DI 1 7
Idaho Power Company
value of $2.1 million.
Using the yield from the quali ty controlled Target -
Control data, 120,000 acre-ft of water, and the in-house
rule that for every hour one acre foot of water passes
through Hells Canyon Complex, 0.5 MW can be generated, the
value can be readily estimated.Taking the average high
($32 .13 /MWh), the average low ($29.47 /MWh), and the average
average ($30.47/MWh) price of power for the period May
through August 2003 gives a comparable value between $1.
and 1.93 million.For example, using the average price:
120,000 acre-ft times 0.5 MWh/ acre-ft times $30.47 /MWh
indicates the water to be worth $1.83 million for hydropower
generation alone.This number does not consider any
monetary value of ancillary benefits to the region in the
form of improved water conditions for fish and wildlife,
recreation and navigation, irrigation, or additional
drinking water, although these benefits also exist.
With the above-described results in hand, the value
of the 2003 - 2004 yield was estimated by taking the yield,
85,000 acre-ft, and using the approach identified above.
The generation potential from last season would be $1.
million at an average price of $41.76/MWh.(85, 000 acre-
times 0.5 MWh/acre-ft times $41.76/MWh = $1.77 million.
That value is obtained by using the average of the On Peak
and Off Peak Mid-C prices for the period from 1 May through
RILEY, DI
Idaho Power Company
31 August 2004.The value is closer to $ 1.95 million if
the higher Border prices are used.
Similarly, using the 7 to 9% yield determined by DRI
for the 2004 - 2005 season and applying this same procedure
at an average price of $36.71: the yield for 2004-2005 is
between 85,000 and 105,000 acre-ft of water, or between
43,000 and 53,000 MWh of additional production.That would
be worth $1.5 to 1.9 million.
Both of the . computer simulations reveal one
additional benefit from cloud seeding.The flow in the
payet te River
shifted later
longer.This
is not only increased, the peak flow is
into the year and higher flows are maintained
means that more water will be available to the
Hells Canyon Complex as heavier summertime loads begin to
become a significant factor for operations.
Can you provide an example of the computer
model output that illustrates this later peak in streamflow
and the enhanced flow duration?
Yes.Exhibi t 3 was prepared using the model
output and shows the peak flow is shifted from late May into
June and that higher flow levels are maintained into early
July.Note that the figure does not include data for all of
July and August.
Over the past three years, how have the
financial benefits of cloud seeding compared to the costs of
RILEY, DI
Idaho Power Company
cloud seeding?
The answer to this question will depend to
some extent on the accounting period chosen.Because most
of the activity associated with the project is based on the
water year (October through the following September) rather
than the calendar year, the accounting period was defined as
July 1 through June 30.
The proj ect expenses between July 1, 2002 and June
30, 2003 were:
Capi tal:23,723 and
0 & M:$ 802,348
$ 826,071.Total:
The project yield, based on the average results
already discussed was $1.83 million.That gives a benefit
to cost ratio of 2.2 to
For the twelve month period of July 1, 2003 through
June 30, 2004, the project incurred significant additional
expenses in association with the trace chemistry evaluation.
These included not only the direct costs of the evaluation
in payments to DRI, but the added burden of building and
maintaining seven addi tional ground-based generator uni ts
release the tracer.Consequently, the expenses during this
timeframe were:
Capi tal:237 ,067 and
0 & M:$1,066,408
RILEY, DI
Idaho Power Company
Total:$1,303,475.
Using the Mid-C power costs and the estimated yield
value, $ 1.78 million stated earlier, the benefit to cost
ratio for the 2003 - 2004 season, even with the high costs
and reduced efficiency associated with the trace chemistry
evaluation, is 1.: 1.
Finally, the total expenditure for the twelve months
from July 1, 2004 through June 30, 2005 was $1,008,487.
Wi th the yield of augmented snow and power production worth
$1.54 to 1.91 million as presented above, the benefit cost
ratio is between 1.5 and 1.: 1.
What is the cumulative benefit to cost ratio
for the Idaho Power cloud seeding program?
For the Idaho Power cloud seeding project to
date, considering the cumulative outlay of $3.14 million and
the cumulative return of $5.43 million, the current benefit
to cost ratio is 1.: to 1, even wi th the high costs of the
trace chemistry evaluation.
Does this conclude your testimony?
Yes, it does.
RILEY, DI
Idaho Power Company
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BEFORE THE
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LICI LJ;\ Ii U 1-" t3
UTILITIES COt1J1rSSfON
IDAHO PUBLIC UTiliTIES COMMISSION
CASE NO. IPC-O5-
IDAHO POWER COMPANY
EXHIBIT NO.
G. RILEY
Exhibit 1.
Site MZ Silver and Indium
Ag/ln =19 Ag/ln =11
Ag/ln =6
II"-
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Snow Depth (em)Indium
Silver
Figure 1.1. This diagram shows the concentrations of silver and indium detected in a snow
sample from the east side of the Payette River Basin target area. The sample was collected on Mount
Zumwalt at an elevation of 8 225 feet during March 2004. Note the different scales for silver (left side) and
Indium (right side); the scales differ by a factor of 12. Three seeding events are depicted and the silver to
indium ratios show that for every silver iodide particle scavenged, between 6 and 19 other silver iodide
particles contributed to additional snow. The figure was prepared by Dr. Ross Edwards of Desert Research
Institute, Reno, NY.
EXHIBIT NO. .
CASE NO. IPC-05-
G. RilEY, IPC
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Figure 3-2. From the Desert Research mstitute s 2005 preliminary report: Payette River Basin
Targeting Maps. Red circles represent Snow silver masses integrated over a given time period.
EXHIBIT NO.
CASE NO. IPC-O5-
G. RILEY, IPC
Page 5 of 5
'-' \;.. \~." ,,-- ..".- ,~ ; ,..
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IDAHO PUBLIC UTILITIES COMMISSION
CASE NO.IPC-O5-
IDAHO POWER COMPANY
EXHIBIT NO.
G. RILEY
Exhibit 2
Exhibit 2 is a copy of an article appearing in the April 1999 issue of
Hydro -Review entitled Turning Silver into Gold: Measuring the Benefits of Cloud
Seeding The article has been peer reviewed, and was written by Brian McGurty.
Mr. McGurty is Chief Hydrographer and Technical Specialist/Scientist for
Southern California Edison. In that capacity, he oversees that company s year round
cloud seeding program to augment water supplies for hydropower generation on the San
Joaquin River in the central Sierra Nevada of California.
This project, along with five others sponsored by Pacific Gas and Electric and
the Los Angeles Department of Water and Power, are all in place to augment water for
hydropower generation. Other projects exist for both hydropower generation and for
public water supplies. Some of the California projects have been acti ve for 50 years or
longer.
The Exhibit consists of seven (7) pages, including this one.
EXHIBIT NO.
CASE NO. IPC-05-
G. RILEY , IPC
Page 1 of 7
Reprinted from
IS1A
HYDRO.
REVIEW
The Magazine of the
North American Hydroelectric Industry
Volume Number 2, April 1999
Turning Silver into Gold:
Measuring the Benefits of Cloud Seeding
By Brian M. McGurty
C9Copyright HC! Publications , 1999.410 Archibald Street, Kansas City, MO 64111.816-931-131\
EXHIBIT NO. ~
CASE NO. IPC-05-
G. RILEY, IPC
Page 2 of
W: J::.: ~" 6~ E ~
EXHIBIT NO.
CASE NO. IPC-05-
G. RILEY, IPC
Page 3 of 7M; Q; 1.).( I, F' I: C 'P' 1 Q' ~,:
Turning Silver to Gold:
Measuring the Benefits of Cloud Seeding
Although it is a widely used technology, cloud seeding still is
regarded with 'skepticism by many who are unfamilia r with its
application. A recent research program in California is helping
the practice gain the respect it deserves.
By Brian M. McGurty
eteorologists estimate that
about six times more water
passes over the U.S. each year
as vapor and cloud droplets than runs
down all of its streams and rivers com-
bined. Only a small portion of the avail-
able water in the clouds actually falls to
the ground as precipitation. In a water-
starved , populous region such as Cali-
fornia, any improvement in the effi-
ciency of the precipitation process
would yield widespread benefits. These
benefits would include an increase in
clean, renewable electricity from hydro-
power; increased reservoir storage for
recreation; increased water supplies for
domestic and agricultural consumption;
groundwater recharge; and various envi-
ronmental enhancements for fish,
wildlife, and botanical resources.
Many California water managers
seeking to extract additional water from
Brian McGurty is chief hydrographer
and technical specialist/scientist in the
hydropower generation division
Southern California Edison. He has
been responsible for Edison s cloud
seeding program for more than ten
years.
~1fii~~~j_~~
2 HYDRO REVIEW / APRIL 199')
the atmosphere, use cloud seeding to
enhance mountain snowpacks. Num-
erous comparisons of seeded and un-
seeded watersheds, dating back to the
1950s, have indicated that the technique
does produce a significant increase in
watershed runoff. A 1997 study by
Atmospherics, Inc., of Fresno, Califor-
nia, highlighted the economic impor-
tance of even moderate increases in
runoff. 1 Using data from ten cloud seed-
ing programs and site-specific watershed
and hydro project , information, the
study s author showed that a reported 2
to 9 percent increase in supplemental
runoff from the seeding programs had an
annual value of between $25 million and
$115 million. This value resul ted from
increased hydroelectric generation and
increased water supply for agricultural
municipal, and environmental uses.
In 1992 , Southern California Edison
commissioned the Desert Research Insti-
tute of Reno, Nevada, and Atmospherics
Inc. to conduct a five-year field and lab-
oratory research program to verify and
document the effects of cloud seeding
over Edison s 1 000-MW Big Creek
project. The study, the most comprehen-
sive research of its kind yet conducted
corroborated previous indirect estimates
of gains in snowpack caused by cloud
seeding. It also indicated that, from the
perspective of benefit-cost ratio, the pro-
gram is remarkably successful.
Gaging Success through
Comparisons
In the past, Edison and others have in-
directly inferred the success of cloud
seeding efforts through "target versus
control" statistical comparisons of
streamflow data snow survey data
rain gages , and radar data in seeded
and un seeded watersheds. For example
since the 1950s comparisons of runoff
in the San Joaquin River (seeded by
Edison) to the nearby Merced River(not seeded) have consistently sug-
gested that Edison s cloud seeding pro-
gram increases the water supply of the
San Joaquin River by about 9 percent
on average. Other industry estimates of
the increase in other watersheds, based'
on the same analytical methods, range
from about 5 to 15 percent.
Unfortunately, the large range of nat-
ural variability associated with these
methods can limit the statistical signifi-
cance of the results. In addition, tradi-
tional streamflow measurements often
are only accurate to within about 10 per-
cent and are particularly uncertain in
wet years, and an unknown amount of
water is lost to evaporation and percola-
tion. Also, it is becoming increasingly
difficult to obtain "control" data because
virtually every available watershed is
either directly or indirectly seeded.
Unlike many previous indirect esti-
mates of seeding s effects, the Big
Creek research was based on field and
laboratory studies of seeded snow. The
research team was able to use physical
and chemical methods to make direct
measurements of the snowpack affected
by seeding and to compare the water
content of the seeded snowpack to nat-
ural snow.
Understanding Cloud Seeding
Water vapor is continuously present to
some degree throughout the atmosphere.
If some mechanism, such as an advanc-
ing front,. causes air to cool sufficiently,
the water in the air is condensed from
vapor to cloud droplets that form around
microscopic particles called cloud con-
densation nuclei. On average, about one
million cloud droplets are needed to
produce a single raindrop, and a typic",l
cloud condensation nucleus is only
about one-one-hundredth the size of a
cloud droplet.
Among the various condensation par-
ticles present in the atmosphere, a few
have just the right size and shape to
become ice nuclei. The water vapor
phase is converted to a solid precipita-
tion phase when cloud droplets freeze
around ice nuclei and become ice crys-
tals. However, the vast majority of the
available water in the clouds remains in
a vapor and cloud droplet phase. This
creates an opportunity to artificiallyassist the precipitation process
adding more ice-forming nuclei (such as
silver iodide) to the atmosphere.
In addition to providing additional
nuclei, cloud seeding increases updrafts
in the cloud through a secondary latent
heat of fusion effect. This makes the
cloud larger, more buoyant, and able to
process a greater amount of water over a
longer period of time. Radar images of
seeded clouds indicate increased cloud
top height, increased precipitation area
and longer precipitation times than in
adjacent un seeded clouds.
From the Laboratory to the Watershed
In 1946, Dr. Vincent Schaefer of the
General Electric Research Laboratory in
Schenectady, New York, was conduct-
ing experiments on supercooled clouds
in a refrigerated "cold box." Anxious to
quickly cool the box to the temperature
needed for his experiments, he placed
some pieces of dry ice in the box. Much
to his surprise, in the presence of the
extremely cold dry ice , aerosol particles
began to act as condensation nuclei, and
the vapor around the nuclei froze into
crystals. Some ice crystals grew large
enough to fall and coat the inside of the
box, fortuitously pointing to a new wayto artificially glaciate super-cooled
clouds. Dr. Schaefer then repeated the
effect in the free atmosphere by dispens-
ing crushed dry ice from an airplane. In
this way he was able to create snow
crystals in a cloud, verifying the earlier
cold box laboratory experiments and
calculations.
Once the ice-forming properties of
dry ice were demonstrated, researchers
recognized that other solid substances
with crystalline structures similar to that
of ice could function much the same. In
1947, Drs. Bernard Vonnegut and Irving
Langmuir (also of the G.E. Lab) found
that the atoms in silver iodide in a
hexagonal crystaL form assume
arrangement identical to the positioning
of the oxygen atoms in ice. Silver iodide
crystals act as ideal ice nuclei at temper-
. atures below -5 degrees Centigrade.
After Vonnegut s findings, enthusi-
asm ran so high among the experi-
menters that they initially talked about
the possibility of modifying the weather
over the entire D.S. using only a small
amount of silver iodide. By 1950, about
10 percent of the land surface of theS. was being seeded by farmers,
ranchers , utilities , lumber companies
irrigation districts, and municipalities.
In the past , as many as 20 programs
have been in operation at the same time
in California alone. In an average year
there are 13 seeding programs in Cali-
fornia, targeting vi rtually every major
watershed in the state.
Edison s Cloud Seeding Program
For nearly 50 years, Edison has seeded
the clouds over its Big Creek hydroelec-
tric project in order to increase the water
supply to the reservoirs of the project.
The Big Creek program is the oldest
continuously operated cloud-seeding
program in the world. The hydroelectric
project, located on the San Joaquin
River in central California, includes six
major reservoirs with a combined stor-
age capacity of over 500,000 acre-feet
and nine hydroelectric powerhouses
with a total generation capacity of
approximately 1 000 MW. The water-
shed above the Big Creek hydroelectric
facilities consists of about 1 600 square
miles of rugged mountainous terrain
with elevations ranging from less than
000 feet to over 13 000 feet.
Edison s program is currently run by
Atmospherics, Inc. The program is
staffed by experienced pilots , meteorol-
ogist-forecasters, and various support
personnel. Major equipment includes a
computerized ground-based radar sur-
veillance system with digitized outputs
specially equipped turbocharged twin
engine aircraft, a network of aircraft
and ground-based silver iodide dispens-
ing systems, a computerized satellite
weather data acquisition system, a com-
bined dual-channel radio and satellite
communication system, and a computer-
ized targeting model. The personnel
and equipment are available 24 hours
per day, seven days a week, year-round.
Edison s use of both ground and air-
borne dispense mechanisms is unique;
other programs typically use only one of
the two methods.
Seventeen fixed-location manual and
remote-controlled ice nuclei generators
are located on the ground throughout t'
watershed. Mobile dispensing syst'
include the aircraft-mounted nucle
: .
erators and a mobile ground-bas'
erator. The fixed ground gene'strategically placed throu
watershed at elevations
800 feet to nearly 10
seeding of cloud syster
en-
(s are
IU t the
ill about
.;et to allow
Goving from
Southern California Edison operates a cloud seeding program to enhance snowpacks in theSierra Nevada headwaters of the San Joaquin River. There is much evidence that the programdoes produce an increase in runoff, with benefits for hydroelectric generation, agriculture, anddomestic water supplies.
EXHIBIT NO.
CASE NO. lPC-05-HYDRO REVIEW / APRIL 1999
G. RILEY, IPC
P::\n~ .1 nf 7
southerly to northwesterly directions,
The locations of the fixed ground gen-
erators are based on a variety of factors,
including the effects of low-level bound-
ary layer windflows over complex terrain.
Activation of the generators is based upon
a theoretical 17-minute interval from ice
nucleation to crystal fall-out along a path
perpendicular to the prevailing wind
direction. The generators produce silver
iodide smoke particles by burning a 2
percent solution of silver iodide in ace-
tone, injected into a propane flame,
Through the years there has been sub-
stantial indirect evidence that the seed-
ing program enhances the snowpack and
results in increased water supply to the
project reservoirs. However, until recen-
tly the technology to make direct mea-
surements of seeding s contribution to
the snow pack did not exist.
Sampling, Testing Seeded Snow
The Big Creek research team was able
to take advantage of several recently-
developed techniques, which included:
- State-of-the-art vertical snow profil-
ing to measure the concentration of sil-
ver (the seeding agent) in the snowpack;
Innovative trace (source-receptor)
chemistry tagging techniques;
Measurement of supercooled liquid
water using dual channel microwave
radiometers;
- Upper air sounding measurements;
Mountaintop icing and other meteor-
ological measurements; and
- New seeding solution formulations
for improved ice nucleating perfor-
mance.
Cesium and indium, inert trace chem-
icals , were used as source-receptor tags
on the seeding agent, silver iodide.
Cesium was used with the ground gen-
erators and indium with the aircraft gen-
erators. This was the first research effort
in which trace chemistry was used to
determine the relative contributions of
seeding using both ground-based and
airborne sources,
After seeding with the tagged nuclei
the investigators sampled the snow in
vertical profiles to detect the presence of
silver iodide and the tracer chemicals,
Eleven sites were sampled following
storm events from January to April 1994,
The snow profiles were set up to
determine the chemical and water con-
tent of the snowpack as a function of
depth and time. Precipitation data were
concurrently collected to establish the
timing of the snow profile samples,
To collect the samples, the investiga-
EXHIBIT NO.
CASE NO, IPC-05-
G, RILEY, IPC
Page 5 of 7
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'5l. -~4..:'
'",:"'"# :..~..:.. ;.:.~.:,.~'..'., ~"'~.:j.:';'.
:'t:.
Figure 1: These micro-photographic images of ice crystals before, during, and after a pulseof cloud seeding show the effects of introducing silver iodide nuclei to the cloud. The silver
iodide promotes the formation of the smaller, more densely packed crystals shown in themiddle periods of the time sequence. (From Volume 29 of the Journal of Weather Modifica-
tion-see Note 5)
tors pushed the vertical snow profiler
downward into the snowpack , then dug
a pit next to the profiler so that partition
plates could be inserted into the profiler.
Each partitioned layer, 2 centimeters
high and with a 200-square-centimeter
cross section, became one sample for
chemical and water content analysis
yielding well over 600 samples. The
samples were rapidly carried by heli-
copter to a staging area and transported
in a refrigerated truck to the lab. After
each sampling visit , the investigators
moved a snow board and a snow pole
onto the surface of the snow to establish
the level at which the next round of
sampling would begin.
Accurate detection of the tracersdepended on careful handling of the
samples during and after extraction.Prior to use, each profiler was cleaned
with detergent, rinsed with distilled
deionized water, and then sealed
polyethylene bags. The samples were
collected with gloves and baggies to
prevent contamination and were kept
frozen to prevent adsorption by the con-
tainer walls while in route to the lab.
In the laboratory, the project team used
flameless atomic absorption spectropho-
tometer techniques to detect the tracers in
the snow samples, Metal concentrations
were determined from the absorption
peak height measurements by compari-
Table 1: Concentrations of Silver Iodide (Agl) at Sample Sites in 1994
Seeding
Target
Area
Sampling
Location
Percent of
All Samples ConcentrationElevation Number of Containing Agl of Agi(feet) Samples Above Background (ppt)
Primary 10,400 117.
22.
66.
21.6
13.
100 121.
29.
60.
14,
14,
11.5
12.4
Pioneer Basin
Rosemarie
Meadow
Colby Meadow
Mammoth Pass
Dutch Lake
Edison Lake
Florence Lake
Mean
000
700
500
100
800
200
Secondary Strawberry Mine
Huntington Lake
Cow Meadow
Shaver Lake
Mean
800
000
200
370
HYDRO REVIEW / APRIL 1999 4
Table 2: Calculated Increase in Precipitation Due to Cloud Seeding, in 1994
Density Calculated Increase inSamplingRatioPrecipitation
Location (Seeded/Unseeded)Percent Inches
Pioneer Basin 1.22 21.
Rosemarie
Meadow 1.29
Colby Meadow 22.
Mammoth Pass 1.09
Dutch lake 1.02 1.22
Florence lake
Mean 09'
Strawberry Mine
Huntington lake 1.47
Cow Meadow 1.05 1.46
Shaver lake
Mean
Seeding
Target Area
Primary
Secondary
son with a second degree polynomial
regression fitted to standard peak height
data for the tracers and silver iodide.
Modified analysis of variance techniques
were used to determine the sample
errors, which included component contri-
butions from both standard calibration
and from individual sample runs.
Measuring the Presence of
Seeded Silver
The 11 sample sites included seven
inside the primary target area for seed-
ing and four representing a secondary
target area. Table 1 lists the results of
vertical snow profiling for the presence
of silver at each of the 11 sites.
In the primary target area, seeded sil-
ver was detected above the background
level of 6 parts per trillion (ppt) in more
than 70 percent of the samples. The
measured concentrations of 13.
121.0 ppt, 2.3 to 20 times the back-
ground level , indicated very effective
seeding results. By comparison, in other
programs silver has been found in only
10 to 20 percent of the samples and at
concentrations of only 10 to 40 ppt.3 As
expected and h9ped, both the frequency
and concentration of silver detected in
the samples were greater in the primary
target area than in the secondary area. In
addition, seeding from ground genera-
tors was most effective for target sites
such as Pioneer Basin , that are located
in canyons where stable southwesterly
flow is frequently channeled. It was
least effective for sites, such as Rose-
marie Meadow, that are sheltered
ridges from the predominant southwest-
erly flow.
Detecting the Source of Seeded Silver
The project team used two of the sam-
5 HYDRO REVIEW / APRIL 1999
pIing sites, Pioneer Basin and Rose-
marie Meadow, to study the sources of
the seeded silver in detail. The useof different tracers for the aircraft
and ground-based seeding solutions-
cesium for the ground generators and
indium for the aircraft-made this
analysis possible. Although Pioneer
Basin and Rosemarie Meadow are at
similarly high elevations, Pioneer Basin
is exposed to southwesterly windflows
while Rosemarie Meadow is not.
At Pioneer Basin , both tracers were
present in the snowpack , but indium
showed the lowest frequency and con-
centration, indicating that the majority
of the silver at Pioneer Basin originated
from ground-based generators. Based on
loading estimates and the composition
of the ground-based tracer solution, 72
percent of the silver detected at Pioneer
Basin was released from the ground
generators. In contrast, no cesium was
detected at Rosemarie Meadow, indicat-
ing that all of the silver detected at that
site originated from the aircraft. These
results showed the value of trace chem-
istry as a way to differentiate between
seeded snow from different sources, and
thus to study the relationship between
the prevailing windflow patterns at a
site and seeding effectiveness;
Analyzing the Density
Seeded Snow
lee particles produced by seeding are
smaller than those that would occur
naturally. Therefore, measurements of
snow density can be used to infer
whether the snow crystals were formed
naturally or by seeding with silver
iodide. In particular, when seeding is
conducted from the ground, a substan-
tial portion of the seeded ice crystals
EXHIBIT NO.
CASE NO. IPC-05-
G. RILEY, IPC
Page 6 of 7
would be expected to be smaller than
natural snow crystals, which form and
fall from greater heights and colder tem-
peratures. Additionally, crystals falling
from a seeding plume would be ex-
pected to be more uniform than natural
crystals and primarily of needle, col-
umn, and plate forms.
, Researchers working in the Wasatch
Mountains of Utah in 1993 and 1994
documented ice crystal images before
during, and after a pulsed seeding
experiment.4 (See Figure 1.) During the
seeding portion of the experiment, the
ice crystals increased in number and
uniformity compared to the unseeded
crystals, which were much more vari-
able in size and habit. In addition, dur-
ing the seeding pulse ice crystal concen-
tration, ice nuclei concentration, and
precipitable water increased, and the
percent of ice crystals of larger size
dropped significantly. These experimen-
tal measurements suggest a conceptual
model , which is that seeding would pro-
duce an increase in snow pack density
due to the increased packing of smaller
denser seeded crystals among the larger
natural crystals.
From this conceptual model , seed/
no-seed density ratios can be compared
to silver concentrations. Previous ex-
periments, in which the relative fre-
quency distributions of silver were
related to snow density, have docu-
mented that higher-density snow is cor-
related with higher concentrations of
seeded silver. Therefore , an equation
can be developed that relates the esti-
mated increase in precipitation due to
seeding to the total amount of precipita-
tion containing silver (above the back-
ground level) and the average seed/no-
seed sample density ratio. The Big
Creek investigators applied such an
equation to snow samples taken in
March and April 1994 at the 11 sample
sites, with results as shown in Table 2.
Snow samples unaffected by seeding
would be expected to have density
ratios, on average, around 1.0. The data
in Tables 1 and 2 show that, as more sil-
ver is contained in a sample , the density
ratio rises higher above the threshold of
0. This increase indicates that the
seeding process is directly associated
with changes in sample density.
Adding Up the Benefits
The Big Creek researchers, using direct
measurements of snowpack density, cal-
culated that the seeding program pro-
duced a minimum increase in precip-
it~ltion of more than 8 percent in the
primary target area during the months
studied. This figure corroborates Edi-
son s previous indirect statistical calcu-
lations and observations for the Big
Creek project.
Edison estimates that the additional
volume of water produced from cloud
seeding in 1994 alone (a dry year),
even accounting for little or no benefit
of cloud seeding in the secondary tar-
get area, has a value of over $10 mil-
lion in additional hydroelectric genera-
tion. The associated benefit:cost ratio
for hydro generation alone is more than
30 to 1. Adding nearly $20 million for
the total value of the additional water
supply, including domestic and agricul-
tural uses, gives a total benefit:cost
ratio of more than 60 to 1. The equiva-
lent value of cloud seeding in average
or wet years would be expected to be
even greater.
Although considered preliminary,
these results have important and encour-
aging implications for Edison s cloudseeding program.
Brian McGurty may be contacted at
Southern California Edison, 300 North
Lone Hill Avenue, San Dimas, CA
91773; (909) 394-8718.
Notes:
I Henderson, TJ., "New Assessment of the
Economic Impacts from Ten Winter
Snowpack Augmentation Projects,
Journal of Weather Modification Vol-
ume 29, pages 42-1997.
General Electric Co.
, "
First Man-Made
Snow " State University of New York,
GE Research & Development Center
1978.
3Stone, R.H., SCE Hydro Resources Man-
agement Project: Phase 1: Data Collec-
tion and Preliminary Analysis, Prelimi-
nary Report for Southern California
Edison Co., Contract No. C4l03905
Atmospheric Sciences Center, Desert
Research Institute, Reno, Nevada, 1997.
Super, A.B., "Two Case Studies Showing
Physical Effects of Both AgI and Liq-
uid Propane Seeding on Utah's Wasatch
Plateau Proceedings 13th Conference
on Planned and Inadvertent Weather
Modification, Atlanta, Georgia, Ameri-
can Meteorological Society, 1996.
sSuper, Arlin B., and Edmond W. Hol-
royd III
, "
Some Physical Eyidence of
AgI and Liquid Propane Seeding
Effects on Utah's Wasatch Platetiu
(Figure 7), Journal of Weather Modifi-
cation Vol. 29, 1997, pages 8-32.
References:
Dennis, A.Weather Modification by
Cloud Seeding. Academic Press, 1980.
Griffith. Donald A.
, "
Planting the ' Seeds
for Increased Water Availability for
Hydro Hydro Review Volume 12, No.
, August, 1993.
Henderson, T.
, "
A Summary of Cloud
Seeding Activities Conducted Over the
San Joaquin River During the Period
October 1996 to 30 September 1997
Report for Southern California Edison
Co., Contract No. P2095902, Atmos-
pherics Inc., Fresno, California, 1997.
Riley, G.T. and Henderson, T.J.
, "
Find-
ings from the Atmospherics Incorpo-
rated Component of the Southern Cali-
fornia Edison Hydro Resources Man-
agement Research Program, 1993-
Report to Southern California Edison
Company,' Atmospherics , Inc., Fresno
California, 1995.
EXHIBIT NO.
CASE NO. IPC-05-
G. RILEY, IPC
Page 7 of 7
HYDRO REVIEW / APRIL 1999
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EXHIBIT NO.
G. RILEY
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Exhibit 3
NWSRFS Model - Observed Flows and Simulated Flows with Reduced SWE
Payette River at Payette, ID
9000
----
8000
7000
6000
3000
2000
1000
3/10 3/30 4/19 5/9 5/29 6/18 7/8
Observed Natural Flows -Simulated Flows, Reduced SWE Augmented Fish Water
Hydrograph produced from the National Weather Service River Forecast
System Model output showing the effect on flow in the Payette River with and without
snow augmentation by cloud seeding. Note that not only is the total flow increased, but
also that the peak flow occurs later and higher flows are maintained longer into the year
in the seeded case,
EXHIBIT NO.
CASE NO. IPC-O5-
G. RILEY, IPC
Page 1 of 1