452. Tag ends, 2nd annual report Colorado River water forecast committee, Los Angeles, April 1946

UNIT iATION SERVICE

LL,

BOX

D OFFICIAL BUSINESS

Mr. Aelph 1. Parshall

Irrigation Investigations

c/o Colo. Agri. itxperinent Sta.

Fort jollins, Colorado

PAYMEN1 OF POSTAGE,P06STAGE,

foiri 1,60 r

A

T.r./ .11106":' 161;0'

(4)

of the

COLORADO RIVER WATER

FORECAST COMMITTEE

Los Angeles, California

April 19, 1946

sr

Fort Collins, Colorado

January 25, 1947

SOIL CONSRVATION SEVICE

DIVISION OF IRRIGATION

TRANSCRIPT OF MEETING

COLORADO RI= "AT FORECAST COMYITTEE

Held at Los Angeles, California, April 19, 1946

UNDER THE AUSPICES OF THE

Division of Irrigation

Soil Conservation Service

U.S .D

George D. Clyde, Chief

The iTeat Colorado River, drainin nearly 250;CUL square miles in the

combined areas in 'Tyomin:, Utah, Colorado, New ilexicc, Arizona, Nevada and California, results in a flow of water of much importance not only from the staidpoint of irri6ation but power and other uses as well. The utility of

the water of tlis stream in traversin its Course throw,h these states en-•

wives many problems of vital interest. In the up.er basin states, perhaps, the use of water for irrigation is the important and tl-,rouhout the lower reaches of the river power and municipal water supfilies are of breat concern. This varied use of the river .;ater involves the attention of e..„Lineers, soientists and others in the attempt to aproach an

understand-inc; of the variations of flow of this stream, )articularly the relation of snow cover on the watershed ancl.,:phe corres.00ndin: runoff,. Previous records

of the annual volume lisctar_, show that more than three-quarters of all the

water of the Colorado River came from the snoiT melt in the hih mountains and plateaus within the drainae basin.

The objective of the Colorado River 'Tater Forecast CoEmittee is primarily

that of studyin the relation of snow cover and the resultin runoff. This - .

conference, the second annua meetinL:, continued witL the discussion of methods and results of forecast in; as. was .the_main -.topic under consideration

at the first session of the CorTlittee, April 1Y1-5. Because of the intense interest shown in the principal subject of forecastin„_ at these annual con-ferences it is clearly evident that the problem is an important one, and

al-though proress is bein made in the understandin of the relations existinL, between the various factors envelved it can be generally concluded that the final conclusions are yet to be stated..

•

Irame

ROSTER OF ATTENDANCE 'Agency

Bertram S. Barnes Regional Engvr. 6th Region U. S. 'leather Bureau

Donald L. Baker Ruscardon Engineers'

Harry F. 731aney Division of Irrigation S.C.S., U.S.Dept. Agric. George H. Cecil Los Angeles Chamber of

Commerce

Bradley Cczzens Dept. of 'later & Power City of Los Angeles

C. C. Elder lietropolitan Water Dist. of Southern Californi-, P. H. Gilbert Jesse L. Honnold Southern California Edison Company U.S.Bureau of Reclamation

James E. .Jones . Dept. of Water & Power City of Los Angeles

1. A. Lang Southern California

George A. Lewis

A. A. Lott

John `,1. Luce

lloss 11. liat hews

1!red Paget

•

Edison Company

Dept. of Tat or & Power City of Los Angeles

Southern California Edison Company Los Angeles County Flecl Control District Dept. of Water c Power City of Los Angeles

Division of Hater

Resources, State of Calif.

Address

Los Angeles, Calif.

108, 7. 6th St.

Los Angeles 14,Calif. 1509 P.0.-Ct.Fouse Los Angeles, Calif. 1151 So. Broadway Los Angeles 15,0alif. 207 So. Broadway Los Anj,eles, Calif. 306 Het Third St. Los Angeles, Calif.

P. O. Box 351

Los Angeles 53,Calif. Denver 2, Colo.

207 Sc. Broadway Los Angeles, Calif. ,

P. O. Box 351

Los Angeles 53,Cdlif. 207 So. Broadway Los Angeles, Calif.

P. O. Box 351

Los Angeles

53,

Calif. 751 So. Figueroa St. Los Angeles

3,

Calif. 3409 Ferncroft Rd. Los Angeles 26, Calif. Sacramento

5,

Calif.

RCSTM

or

.ATTIMINCE

Name Agency

Ralph L. Parshall Division of Irrit;ation

U.S.Dept. of A.:;ric.

Christian K. Prior Dept. of Water Power

City of Los Angeles

7. P. Rowe ecnsultin€; En;4noer

J J. Snyder Coachella Va. by

County Water District

TiE.irlowe 17. Stafford U.S.Geolo;._;ical Survey

Henry L. Transtrom Dept. of 'later i• Power City of Los Angeles

C. P. Vetter U.S.Dureau of Reclardation

P. I. Voe1 Dept. of Water Power

City of Los Aneles

George 1. 'Ihitney Southern California

Edison Copany

Address

Fort Collins, Colo.

207 So. 3roaday Los Angeles, Calif.

736 C. Street

San Bernardino, Calif.

Coachella, Calif.

Los 2,nfe1es, Calif.

1L0 E. 4th Street Los Angeles, Calif.

TIoulder City, Nev.

207 So. 73roadway Los Aneles, Calif.

P, 0, Box 351

Los An,;eles,53, Calif.

The moetin was called to ordor by 1:r. Parshall, Committee

Chairman, at 9:45 A; .

•

,PROCEEDINGS OF THE C017:-ITT7E LOS ANGELES - APRIL 19, 1946

MORNING SESSION

Parshall: Gentlemen: This is the second annual meetinf: of this Committee to further discuss the common problem of forecasting the flow of the Colorado River. At our meeting just a year ago a number of

methods of predicting stream flow, as based on snow survey data and also precipitation records, were discussed. Of the several forecasts offered some were within reasonable agreement lehile others deviated rather widely as might be expected from the nature of the problem in

which we are concerned. At our first meeting we endeavored to follow a fixed pre-arranged program where a number of excellent papers were presented, all bearing on the general subject of snow and water.

The matter of fixing the date of this second meeting of the

Committee was somewhat delayed and therefore precluded the arrangement and preparation of a stated program for today9 s discussion. Since the main problem before the Committee is that of forecasting the flow of

the Colorado River into Lake Mead, plans were laid to make this the major subject for consideration. Many letters were sent out to all who were in attendance last year, together with contacts with others to join us today in the discussion of the various methods and results in

pre-dicting the filling of Luke Mead during the period of the spring and early summer flow in the river.

Because of the very fine representation here present, of the

several agencies interested in this common problem, it is confidently expected that todayls discussion will be quite worthwhile. The main

problem, gentlemen, for our attention is the discussion of methods of

forecasting runoff as results from snow melt and precipitation. IT° doubt some of you have based your studies and conclusions upon snow survey data, perhaps others have considered a combination of water

content of the snow and precipitation records as observed at special locations by the U. S. Weather Bureau while others may have approached

the problem on some other basis, such as previous runoff records of the river itself. It is anticipated that later in tie day, after we have reviewed the various methods of forecasting, we may like to post our forecasts for the coming runoff season. It is to be expected that our

figures will not *all be identical.

The time available for re-riewing the work for today is rather limited and your chairman is receptive to suggestions as to how best

. •

we can accomplish our assisnment.

Lewis: Hr. Chairman, it occurs to me that possibly some advantage AM.1••••••- WO. .0

would be gainod by dividing the group into subcommittees to discuss

the forecast problem relative to sub-basins. (Ho motion made.following this suggestion.) The magnitude of the Colorado River drainage area is such that no one or two men can handle it all in detail, 7hy not

segregate the different basins, stream areas, and for study purposes allot certain basins or streams to each committee and let thorn offer

their ideas of runoff from that particular area, of course not over-looking the fact of the forecast for tie entire basin" If the

findings prove to be of lesser importance the. ,results could be held for future reference., otherwise a report showing progress in the

solution of the forecast problem should be made a part of the trans-actions of our next annual meeting.

certain members of this group should be assined the problem of in-vesti:ating the forecasts on tributary streams, and brinr7 something

for discussion at the next meetin:: of the committee as a whole. Lewis:

_ I think i,!3 is a good idea to get a r:eneral picture of the _

entire drainaFe first.

'Parshall: Should it be my privile47e and honOr to serve as chairman

-* of this Committee next year I will endeavor to arrange for having reports on the forecast of the ujper tributaries of the Colorado.

Will tt now be agreeable if we call on some of the members present . ,

to discuss or us their methods of forecasting/

Paget: T should like to suggest that r. George 7.!hitney of the

Southern California Edison Company give a resume' of his rapid-fire

•

.fornu.4.a for predicting the annual runoff in the Colorado.

Whitney: Ty.renarks Will be rather'brief, When the snow courses on the Colorado. River.draina,ge were located they wer4 laid out for utility in order to get the best results a' short time, therefore our predictions are rather crude.

The fgures;I shall place on the blackboard cover the Colorado River and are based on the relationship between this year's water

Content and the 11-year averae Water content (Example. I) and between this year's water content and last year' water content (Exam0.0 II).

Colorado "iatershed Contribution of Total Runoff April 1, 1946 to :T:..rch 31, 1947

EX PL I

•

Estimate of Inflow into Lake Mead based on 1946

Snow Survey as percentage of. 11 year average water content Colorado

Colorado River above Grand Junction

(86-i,

of 11 year average)

Gunnison (45-/, of 11 year average) Dolores (401, of 11 year average) Green

Col. 1 Col. 2 Col.

₃

86

x

26.7

_

22.96

65

x

13.4 - = 8.71

40 x 4.3 = 1.72

Yampa).

Mite) (81.57, of 11 year average) 81.5 x . 13.9 11.33 Green (94T, of 11 year avera.ge) 94 x 11.5 10.81 Duchesne and others (assumed 94 x

_9.7

=

9.12

94% of 11 year

averae)

San Juan

San Juan (321. of 11 year average) 32 X 14.9 _{= 4.77} Percentage of the coming 12

nonths,

average inflow 69.427,

11-year averae inflow 12000,000 acre-feet (Apr.-liar.) Lee's Ferry taken as 89 percent into Lake Mead

Therefore 12,500,000 x 69.421, = 8,680,000 acre-feet (89/)

Estimate for 1946 at 100% would be 9,750,000 acre-feet for period April 1946 to Tarch 1947.

MCAIIPLE II

Estimate .of Inflow into Lake Tread based on 1946e

Snol-: _{Survey as percentage of last year (1945) water content}

Using the same methods as given above (Example I) for the per-centae of the 11 year average water content, the parcontar;e of last year's (1945) water content was applied to the percentage of con-tribution _{shown in Col. 2. Om this basis the veighted average} (Col. 3) was 68.31%.

1945-46 inflow 11,800,000 acre-feet (4r.-'nar.) Lee's Ferry taken as 89 percent into Lake :Teed

Therefore 11,900,000 x 68.311, = 8,060,000 acre-feet (89fl

Estimate for 1946 at 100% would be 9,056,000 acre-feet for period April 1946 to March 1947.

Average of two methods = 9,400,000 acre-feet for period ipri1 1946 to March 1947.

•

In these examples Col. 1 c,ives the percentage of snow cover from the Snow Survey Bulletin, Col. 2 gives the average contribution of

each wutershei expressed as a percentage of Leevs Ferry average

runoff, and Col.

3

gives the weighted average used in forecasting Lake Mead inflow.

For the Yampa and the 'Jhite rivers the best we can do is to take the average and show them together with a rating of 81.5. The Duchesne and

other streams all combined show a lack of sufficient data to warrant a definite conclusion, however, for an approximation a rating of 94 has been assumed.

Several years ago Bill Lang and I worked out the breakdown (Col. 2)

for each watershed as its proportion of the total contribution. On this basis, Lee's Ferry contributed 86.9 or

69

percent of the total inflow to Lake Yead.

'1e would be much ha;Tier if those living in the upper areas of the Colorado River -Ttershed could refine the snow survey data and

break down the figures ?. little closer. This would be a help and maybe result in the improvement of our predictions. In conclusion

I feel that after September 30th we can predict very closely what the final or actual annual runoff is going to be. Its the 4-month

period April-July that counts, unless a cloudburst occurs as in 1941. Parshall: Thank you, ir. 1hitney, for presenting to us your apparent clear cut method of forecasting the annual flow of the

Colorado. Have you any questions or discussion on Mr. ,Thitney's plan of forecasting? 1:r. Paget inquires about the matter of taking the total snow areas on the watershed and apply a factor of unification.

Each year we discuss this

interesting problem of

forecasting the

runoff in the Colorado. River

the more widespread

becomes the various

ways of aproach. Eventually

it may be expected

that closer

approxima-tions can be a ie as the period

of basic records

lengthens. Dr. Church,

Eeteorologist at the University

of Nevada, has repared

a summary

covering the Forecast of

the Colorado River flow

.t Bight Angel for

the coming April-July period,

1946. I have aslled

mrb

Honnold to present

Dr. Churches contribution. Honnold: In scanning

through Dr. Churchts paper

it becomes evident

that the northern streams north

of the watershpd are more

nearly normal

in water content of the snow

cover than those :4.n th'e

south.

As a basis he has tuken

the following:

Green

93.8 percent normal INT2.ter

content.

Colorado above Grand Junction

81,4 percent. ncrmal water

content.

Gunnison

64:6 percent normal water

content.

Dolores

39.6 percent normal water

content.

San Jun

32.4 percent normal water

content.

These various percentages

of normal for the Colorado

River above Grand

Junction and the prinaipal

tributaries are each given

an assigned

weight which results in

a weighted percentage

of normal water content

of snow of

68.7

for the entire

watershed. The weighted

percentage of

the normal precipitation

is found to be ?7.6.

As 100 percent normal

annual runoff, he has taken

13,500,000 acre-feet.

Since for 1946 the

water content of the snow

is only 69 percent of

normal he determines

for this year only 9,315,000

acre-feet as gross runoff.

From this is

deducted the diversions

for irrigation and other

consumptive uses in

the amount of 4,500,000

acre-feet or a balance

of 4,815;000 to be

available as storage

in Lake Mead. Dr. Churches

"Reno, Nevada April 16, 1946

Forecast of Color!7, do River near Bright Angel Creek

. April 1; 1946.• 1. Snow Cover Sub-basin Normal (in .water) (Uater Equivalent) 1946 Pct.of (in.mter) nonur.1 Weight assigned Total Tleights Green River 12.9 12.1 9.8 x 10 938 Yampa-White Rivers 17.2 14.0 81.4 X 16.5 = 1343.1 Colorado River above

Grand Junction 13.3 11.4 85.7 x 25 = 2.42.5

(;unnison River 16.4 10.6 64.6 x 15 = 969

Dolores 11-iver 11.1 4.4 39.6 x 7 7. 277.2

San Juan River 14.2 4.6 32.4 x 17

Total 90.5 6220.6

Weighted Percentage

68.7

. 2. ProciTit-Aion

Green River 4.23 4.44 105.0 x- 10 1050

Colorado River above

Grand Junction 1.99

1.53

76.9 x 25 = 1922.5

ban Juan River 5.01 3.13 62.5 x 17 = 1062.5

Total 52.0 4.035

Weighted Percentage

3.

Correction Factors

(1) Diversions, above Bright :Angel Creek• (Computable April 1 on basis of snow cover) Supply Pct. (Acre-feet) 100 13,500,000 69(196) 9,315,000 fit Diversions for Irrigation (Acre-foot) 4,500,000 4,500,000

77.6

Residue. Percentage • of normal (Acre-foot) 9,000,000 4,815,000

100

53.5

(2) Precipitation during Runoff (April) (Computed :May 1. Max. loss 20 percent)

- :Gain .can -be greater. Record.4ril.1-15 Station Green River .Normal (in.water) .1946 (in.water)

Green River (lyoming) 0.84 0.48

Colorado River.

Grand Junction 0.83 0474,

San Juan River

Durango

1.50

0490'

Precipitation to date normal

• 4 • Summary and Comments

(1) Snow Cover and Precipitation

The snow cover April 1 and precipitation (Oct.-ch.) in the Colorado -Basin are in clgAe .P:Grocmgnt, Snow 68.7 and Precipitation 77.6 percent of normal.

7 The -snow cover wid pvecdpitati..on diminish greatly southward from ndrnal in the.Green River Basin to one-third Of normal in the San Juan. The percentages are:

Sub-basins

•

Show Cover Precipitation

Green River

93.8

105.0

Yampa-I:lite Rivers 81.4

Colorado River. above Grand:

Junction.

_85.7

76.9 Gunnison River

64.6

Dolores River

_39.

San Iuan.River • 32.4 62.5 Weighted Pctge.

66.7

77.6' It

(2) Forecast .

Based on a 69%-q)er.cont snow cozr9r and a probable unrestricted use of 4,500,000 acre-feet for irrigation, only 4,615,000 acre-feet or

53.5

_{percent of normal should be available for storage in Lake Mead.}

-Since the diversion, _{.however will. lccur mainly on the Green and} Upper Colorado Rivers where the snow cover is nearer normal, the relative diversion loss at least on those streams should not be so great. The precipitation during runoff has so far been normal..

*There are many details yet to be worked out, 'particularly in diversions _{All computations have been based on data provided' by} Rulph L. Parshall, your chairman, who therefore shares this . report with me.

T. Ei Church, l'eteorologist

:Tevada Agricultural Experiment Station." Farshall _{Thank you, Jesse Honnold. Gentlemen, have you any} questions or ooments7

Paget: Yes, I should like to inquire if for a depletion of

4,500,000 acre,feet, as mentioned by Dr. Church, how would that

r•

figure compare with 7hitneyes for the 4-months flow? (Honnold posts

•

figures on blackboard and estimates that the total annual iiver4'flow may •

be divided on a basis of Co and 40 percent where the flood totals 60

• •

percent of the runoff and 40 percent for the rest of the year. On this assumption and using Dr. Churches figure

•

9,300,000 x

6(

)

- 4,500,000

4,C,00,000 9,300,000 x 40 as a round number 3,500 000

9,,300,000

Honnold: This figure would be in approximate agreement with 1•Thitneyes conclusions.

Other estimates ,yere posted on tho'board relative to the annual flaw

Period

April-June Aug.-April

Cozzens nrior Transtrom

Ac.-Ft.

6.48

3 - 3.6

Total annual from

April 1,t46 to :larch 31,t47 9,46 C0,7P.t •

6.6

3 - 3.6

A.-Ft.

6.2

-3

- 3.6

9.27

Cozzens: We aL)ply z, months' runoff instead of the total year.

The contribution being in the ratio of 71.4 to

97.77

where 71..- is a factor representing the total precipitation. On this basis the

ex-pected filling in Lake Iead this season will be 6,000,000 acre-feet. TranstrOm:* method 'I have used in approximating the annual

flow of the Colorado River is based on precipitation as correlated by records from the following stations: Tesa .7erde, Escalente,

Steamboat Springs and Crested Butte.

Barnes: In answer to the question of whether the Weather Bureauts

forecast for the Colorado is based partly on snow survey data: I am in-formed that it is based Upon precipitation gag,) records alone. The Bureau's policy is to depend upon observed precipitation, not because we do not recognize snow course data as a Proper basis for forecasting

runoff, but rather because we are especially concerned with precipita-tion data, its possibilities, and its use for the greatest benefit to the public. I do not know the exact procedure that was employed by our

7ansas City office in Makin this forecast but I understand that it

in-volves the statistical correlatlon of precipitation records from selected stations. expect to issue the Colorado River forecasts next year in a somewhat different form, They will be similar to the progressive

1e of the Weather Bureau recognize "the tnportance of Laintaining long, unbroken precipitation records and we, too, regret that some of

the older ones have teen interrupted by noving the observation .

sttions. This has been unavoidable in many cases because we cannot . r:aintain satisfactory records in places where We - cannot obtain

suitable observers, If you gentlemen will let us know which of our stations are important in your forecastin procedures, we shall make a

special effort to maintain those records. We shall also do. everything that we can to expedite the placing of the precipitation data from those stations in your hands.

Vetter: We have been working for the past 12 to 15:nonths on the

particular problem of fOrecasting the flow of the Colorado River into

Lake Mead. The forecast as of April 1st is i]de for the period inclusive. Our studies

of

this'problem•have involved various 7ethods, and we have generally eerie to the conclusion that using snow cover as of April 1st as a basis for prediction of runoff, leaves much to be desired. One line of attack, based on snow cover, was

breaking down the whole drainage area into its several co:.:onent watersheds, where each of these: were properly weighted. .This method did not give much encouragement and for the tine being we ‘have set

aside this study and nay later investigate further such relations involving the watei.

Conient

Of the snow measured

It

now appears that the weighting nethod is not wiry effective and for the present we are studying the problem from mother angle, where attention

Just now our most proriising line of study is of two parts:

first, where the forecast is 1)::.sed on prociA.tation records for certain stations scattered over the drainage area of the Colorado

River in Utah and Colorado and second, on about 50 snow courses using the 4pri1 1st water content data. The work carried on using •

snow cover has ben split up into about eleven differdnt combinations but tine did not permit me to subrAt for your consideration at this

, r

time a complete review of all our conclusions on snow surveys. I have

here a few duplicate copies of a brief outline prepared for considera-tion today showing the graph relaconsidera-tions of runoff, first on precipita-tion and second, on water content of the snow. These I will' .pasout to you in order that you nay better follow the methods we have 'found most

effective in solving the forecast problem of the Colorado River. The map of the entire basin of the river shows about 25 precipitation

stations and their elevations. Those with circled nur.:bers were con-sidered in the developuent of the forecast curve(1) as shown on the following page. Here is plotted the :;.pril-July runoff in units of

. , 1,000,000 acre-feet as the ordinate and the corresponding average

precipitation in inches, October through :-arch for the 13 'stations as the absoissa. The full line is drawn, y 2x - 4.2, and with the 0.9 probability, which is equivalent to 2.8 in acre-feet, the parallel

sloping dotted lines were drawn which cover in their spacing all

points except for the years 1921 and 1944. From last October '1st to parch 31st, this year, the average precipitation of these 13 stations is found to be 5.0 inches. It is now observed that this

•

amount indicates a runoff this comin6 April-July period of only

7

3,00,000 acre-feet. Our conclusion at this time is that we are goinG

to have a bad year, and it is possible that the runoff could be as low

as 134 which was only 2,247,000 acre-feet.

The plotting of the graph (2) is identical with that of .(1) except the average 7 -arch increase in the water content at 49 snow courses,

un-I •

weighted inches, are plotted as the abscissa. Here the slope of the

forecast line is different and has the equation y 1.2x -

5.5.

During rarch the average increase in the water content for these 49 snow courses

was 1.0 inch, which corresponds to a forecast runoff of 6,700,000

acre-feet. In comparison these two methods are reasonably close in agreement. The other pages have to do with correlation of group averages of

pre-cipitation and runoff, probability of predictions, and individual station correlation.

Last year Fr. Stanley apc:eared before you gentlemen and told you about the work he and his associates were doing with the present forecast problem. That work has been continued, and many new studies have been undertaken. /Its a result we have come to depend chiefly upon precipitation records for

our forecasts. We have accumulated from the Weather Bureau precipitation

records extending back for

33

years. It is generally felt among our

men that predictions based on 10 to 12 years of snow survey records is not satisfactory. It is my opinion that in the future snow cover will prove to be the base for forecasting runoff. It is felt that at least a 25-year record of snow survey data must be at hand to predict

Referrinc again to the forecast curves thich you have before you

may I add that barrinL; any other interference it .is found that it is the late snow that counts, that is, the melt appears to be more con-sistently tranlated into runoff. A hicher correlation seems evident

by simply usinu the larch increase than for other combinations of monthly precipitations. Studies have been made where the correlation of runoff was based on 29 precipitation stations and the relation of

runoff to precipitation for each individual station. The question was how valuable is that station in connection with the whole group. The maximum of the ten best stations cave us the best results in our

predictions. We, however, use the 13 best stations in the total group

because the minimum spread occurs at about the same point as the maximum. For the diagram (1) you will observe that the plotted

points are fairly well confined in a zone bounded by the two

probability lines, and for the time being; this scheme of forecasting may be the possible solution of the problem of runoff in the Colorado River.

I should like to mention the forecast made by the Kansas City

office of the Weather Bureau for the April-July runoff in the Colorado River into Lake read for 1945 of 6,600,000 acre-feet, (assume this

was based on snow cover data). Last year, 1945, the April-July runoff was G,100,000 acre-feet showinu the forecast about 20 percent under

the actual. The average flow of the river for this period, a mean of

several years, into Lake Mead, is close to 5,900,000 acre-foot. The Weather Bureau forecast is therefore about

75

percent of the normal.

That is about all I can contribute, gentlemen, I don't believe I

have anythinL: more to offer. It appears that we are goi, to have a bad year on the Colorado,- probably some 2,000,000 acre-feet less than

the past ten year average. This shortage is going to be somewhat serious, but on the lower river, below Lake read, the water supply will be far better than it was in 1934. It will not be until after next July that we will know exactly the answer to the problem now

being considered. e have prepared some storage figures for Lake Mead but I haven't them available. I fear the picture a year from now is not going to be a pleasant one. I shall not attempt to

de-scribe our snow measurement studies. I feel very strongly that snow survey data will be something we can work out in the future. There

are only about 10 years of snow records, and in the history of runoff this brief period is almost insignificant. I feel that at the present

time, if we base our conclusions on snow measurements only, we may find our forecasts much out of line. I am in favor of refining our

. .

methods of snow measurements and getting them organized in every way possible.

I want here to express my thanks to the Division of Irrigation of the Soil Conservation Service for their help. Just want to mention

one little angle, that of establishing snow courses on tht Bill •

7illiams watershed. We have a one-year record but unfortunately there has been no snow on the courses.

Parshall: r.ave you given any thought in the attempt to correlate

fall and summer flou to th_ problem of forecasting?

Vetter: Based on previous October. The precipitation for 1944

appears to be the driest year on record. Ile are trying to combine snow measurements with precipitation, Tay, June and July. Last July and .ligust there was a lot of rain over the watershed of the Colorado.

.Baker: ..:ould you conclude that your proposed method of forecasting is applicable to other streams?

Vetter: are particularly interested in vari9us streams but

efforts in, developing methods that Tit elsewhere apparently donct help much in finding the key for the Colorado River.

Parshall: Progress so far this morning has been profitable.

It is nearing the lunch hour and afterwardsTwe will want to continue with our discussion, I should like at this time to briefly mention

some of the forecast relations we have been able to develop at our

Fort Collins office, 4e are finding . that theassumed.stmple relation we

have been able to develop at our Fort Collins office.. .4e are finding that the assumed simple relationship between water content of the snow and the resulting runoff is not so evident as was once

thought. There are a few snow cchirses which appear to be especially

•

dependable as a basis of forecasting. The Tennessee Pass course, near Leadville, serves in predicting the summer flow in the

Colorado River at Glenwood Springs as well as .indicating the

flow in the Arkansas River at Salfda. The snow course at the -21,.st lortal of the Independence Pass Tunnel, on Lake Creek, a tributary to the .Arkansas is about equally good for foArecasting the runoff in the

z

LAKE MEAD 7200' 26. Gween River 6100'

w yomtNG

22 Vernal 5350' Ft Duchesne 4941' Duchesne 5528' 23 Price® 5507' 5. Castle Dale ®5500' 18 e Emery 6250' 24. Hanksville ® 4200' 14 oEscalante 5700' c‘: ‘,) i1 Watson ® 6200'

ii

Green River 4100' 0 4000 _5850' 0 <t CC 0 D _J Blanding® 6000' 10 4N JrkIN

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Grand Canyon

Gaging Station

20 0 20 40 60 80 100 MILES \

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_{0_,zazoi}

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PRECIPITATION STATIONS

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Num ers encircle • are stotions used in this study.

Ft Duchesne 0 4941' Duchesne 5528' 23. Price® 5507' r.k4 5. Castle Dale ®5500' • .t1 24. Hanksville® 42001 7200' 26. Green River 6100'

w yomING

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•

Arkansas at Salida. The Cameron Pass course at the headwaters of.tlw poudre River serves in forecasting the runoff for this river as well

as for the North Platte. Other snow course data when taken individually or in groups, does not appear to be sufficientlY consistent to establish a dependable forecast curve for some of the streams in our Colorado, Wyoming and New rexico areas. In a few instances wo have been able to put some of these outlaw streams into line by applyin.,

a

factor envolv'-ing the fall flo, of the particular stream. The significance of th.ls correct ion factor is not definitely knon but assume it might be

a-measure of the moisture content of the soil over the drainage

aroa:

• 7 •

This scheme, however, doesn 9 t work in evei:y case.

The general overall results in forecasting, covering about 10 years of experience has been, I would say, fairly

good.

Yet - for several

streams the results are rather wide in deviation and' for others quite out of bounds. Variable factors envolved which cannot be evaluated at the time of forecasting greatly influence the end result. This one bir. thing with us is the weather. To tell if there is goihg'to be

5 feet of new saow on the drainage during Aril and ray or 'none at all. The snow survey project is

a

highly co-operative undertaking envolving many federal and state agencies, together with irrigation, power and

• . • - •

other enterprises all interested in the common subject of water supply.

Throughout the Colorado River watershed in our state the Bureau of

Reclamation is our main supporting agency in assisting in the collection of the monthly snov survey data. In Wyoming

and

Neir Mexico the work is

largely supported through funds provided by the State Engineers of these states.

Vetter: About origanizations whereby these snow observations are

obtained. We have felt that the relationship is getting rather in-volved. I have been casting around to see if the relationship can be

simplified SO that we could combine our various agxeements with the different agencies into one working memorandum of understanding.

• Parshall: It is likely that as we proceed with the snoir survey work and determine the relative value of these records it will be

possible to develop an overall agreement with the Bureau of Reclamation

whereby the cost involved can be better proportioned among all con-cerned. Generally the expense of conducting the work is increasing, both for field or labor charges as well as for supplies and equipment. when the Sunshineldbuntain course was located in September 1935, near

a mine and mill then pperating„the expense of the snow surveys the

follow-ing winter was practically nil. , Later the minfollow-ing operations ceased and we had to engage the services of a surveyor out of Lake City,_{• •} two day trip at e5.00 per day. Our present expense on this particular course is 25.00 .for each of the 4 monthly surveys made. The war

is over but the cost of doing things still advances. Just le minute to mention that among our various methods qf. forecasting stream flow we are continuing with the photographic work in correlating the runoff

, in the Poudre as based on first-of-the-month pictures of the snow covered Hague Peak, which lies on the divide between the headwaters of the Big and Little Cache la Poudres. The agreement of percent of

coverage to runoff in the main stream is fairly good for April 1st conditions and slightly improved as, of My 1st.

•

'If there is nothing further for the moment- We wi.11.now adjourn for

lunch and recOnvone.at 1:30 P.F. You are adjourned.

AFT7RY0O1T SESSIO1T

1:30 4:15

p.r.

During the lunch hour the discussion continued among various groups. Parshall: Gentlemen, you will please come to order. In checking up on the 1945 forecasts we made for the Colorado River and a few of

the tributary streams I find some of these within reasonable limits and others rather wide in deviation. The detail tabulation of this

record is not at hand just now but will present these data later as a part of thc transactions of this meeting (see Appendix). Stream flow data are usually available some months later and for this reason com-parisons between our forecasts and actual flow can not be made

immediately at the close of the April-July period. In continuation of the general discussion of forecasting the runoff of the Colorado

River, I believe there are still others here present who would like to present their views on the subject of forecasting. r. Paget informs me that he has a direct straight forward method of solving all the ills

•'•

of this big problem and if agreeable, Fred, we should be pleased to hear

about your California method of forecasting.

Paget: The California method of forecasting is not mysterious and with us it works out quite satisfactorily, however, it might not fit Colorado conditions. (Draws sketch on blackboard, main stream and

tributaries with snow courses indicated on each respective watershed). After about three years of snow. survey records we attempted' forecasting

•

60 percent accurate. Later we were more successful, say 10 to 20

percent accurate. Je first develop a snow pack-runoff diagram by using the

April 1st average water content of the snow, for a selected group of , courses, this of course being plotted against the corresponding runoff

for the same year. The idea here is to -develop the relation between average water content and runoff. At first this average water content was arrived at by dividing the area into zones of elevation but later we found out it didn't natter so nov a straight average is used. As

anapproximation let it be assumed that "p0 inches of water content will give a 200,000 acre-foot runoff, April-July period, this being a natural or unimpared flaw. During April, precipitation .either as snow or

rain-fall, plays a very important part in the final figure and therefore precipitation correction is applied .and in many cases we find the

agreement between snow pack and runoff at the end of the., season to be

within about 10 percent.. Forecasts made on April 1st from a curve so developed work out reasonably well providing there is normal

pre-cipitation. in talking with LLr., Honnoid he says .precipitation

corrections for the.Qolorado,River,basin can't be Fade for April. alone but would have to take into.account May, June and July, ,It .would seem that a forecast on April lst.would have to assume-conditions.where the

,

-precipitation is norrp.1„ The effect of abnormal conditions can be de-termined as you go along from year to year. Uith tiis information

reservoir storage can be regulated for flood control early in the year with assurance of filling during the latter part of the season,

Par shall: Thank you Fred :-aget. I wish our Uolorado, I:yoming and New runoff .problems were as siMPle as that. - Has anyorie

questions or c ailment to offer at this time? •

Vett,er: The Coiordo being a major stream you actually have . ." .

more of a problem because Of the extent of the drainage'area, snow cover ."

quite far removed from Lake I...cad, and -the many tributaries, same of which contribute as much flood flow from rainfall as from sno,r cover.

•

I have .here a short discussion prepared by Fr. Stanlct,'dis-cussing the principles upon which the forecast diagraMs were based which I have just described to you. This memorandum iS follows:

• . • "the Office of River Control: of Bureau of P-_,clanatitin; 1Region III, at Boulder City, Fievada, has been investigating the -problem of

1ForecastingColorado Liver Flow,' for the past year. Details of work . accomPliShed are set, out in a - Paper which was presented at the lIestern,Snow Conference in Sacramento on F;A)ruary- 28, 1946, and is, to b. published in Transactions of the ...meriCan Gc.:ophybical

. • ,!• • . .

. For • the discussion. today, • I have prepared prints of a, few charts illustrating the .fundanentals of our forecaSt methods-. The first Chart ib a Map ,showing th(i Upper Colorado River Basin and the

locations ,of a.nuinbc.:r of . Precipitation stations. The stations. used in our forocastint;iare indicated on th,.-J map. It.ot shovm on the tap are .apprO.-4imateiy 50 snowfsarve-ry 'courses in the States of Color-ado, 7,tyaming, New Lexico . and ..rizona, the records fromvthichar used for a forecast independent of' the preciPitation data i'oreCast.

an&ther. chart are shown the diagrams frorl•whiCh our .April 1 forecasts are made. The upper diagr.am illustrates the relationship be,tween a,ccumulated precipitation for the period: ndtaber 'through

'.arch and the Subc,eedinE, runoff through. Juiy. It noted that the April 1 mean forecast' based on 'average accumulated pre-cipitation of 5.0 inches

is 5 .:9

millions of acre-feet, ,..,!ith'a

probability Of

9

chances in

10

*that the actual runoff will' be within

f •

“ _{Runoff against March increase in snow water content is plotted on} the lower diagram. The reason for using change in water content of

snow as the idependent variable rather then using the simple April 1 water content, is that a much higher correlation is obtained for the ten years of records by the former method. It will be noted that the mean forecast on the basis of these data is 6.7 m.a.f. with a forecast range essentially the same as for the precipitation data.

The forecast prepared in the Kansas City Office of the Weather Bureau is

6.6

m.a.f. for the period 2,pril-July,

Mr. Parshallts invitation to this meeting indicated that the chief topic of discussion would be expected condition of Lake Mead storage after the runoff season. There is no indication that storage in Lake Mead will approach the maximum of slightly more than 31

million acre-feet this year. Even if the runoff should be near the upper limit of the forecast range, storage would amount to only about 26 m.a.f. at the end of July. Should the runoff be near the mean of the forecast, total storage would amount to less than 24 m.a.f. at the end of the runoff season.

The last two charts of which you have prints, illustrate apart of the procedure in developing our forecast method based on pre-cipitation data. Efforts to obtain high correlation between precipitation and runoff by weighting subbasins, by weighting precipitation occurring in various months, and by many other trials, were unsuccessful. Finally, it was decided to examine

which ones might possibly be omitted to'improve the correlation. Results of this study are shown on the bottom of the third chart. It was then decided to find what was the highest correlation that might be obtained by combining these stations in the descending , order of their individual correlations. The result is shown at the top of the third chart. The highest correlation occurred with the first ten stations combined. Correlation for the first 13 stations was slightly lower than for the 10, and when more than 13 stations were used the correlation dropped consistently.

Our forecast on the basis of these data are given as a mean forecast, and the range within which the !actual runoff is expected to fall,

9

chances in 10. On the third chart is shown the results of the forecast by this method for each of the

33

years of record. It will be noted that the observed runoff fell outside, or nearly outside, the 9:10 line three times in the

33

years, or once in 10 years, which checks the computation."

Parshall: Thank you Carl Vetter for this splendid presentation

of the Colorado River forecast problem. You and your men appear to be on the right track.

I have

often wondered, Fred, how you can work so fast and do such a splendid job. ',fe publish our reports on the 10th of the month and have fine cooperation with the Weather Bureau. Sap of our pre-cipitt ion records are obtained by.telephone, part by.telgram from

more distant places and for the Denver and Cheyenne offices we make personal contacts. From these data we determine.the . devi- ti(2ns since las:t October first and also for the month covering the general

.precipitation over rather wide drainage areas in the several states

in which the snow surveys are made. So far We have been quite

successful in having these records

on

time. May I say that we fully appreciate that the Weather Bureau is not-always able to get reports

from all their tat ions before the 8th of the month which .is .approximr:tely our deadline date.

Barnes: There Pre times when

the

records from the field are delayed.

Paget: We send out postals and have the observers give us their figures at the time they send them in to the Weather Bureau. I phone San Francisco and get a list of; figures for some of my reports.

Parshall: The scheme we nil./ have is fairly satisfactory and I feel that should we have separate individual reports from many of the

isolated places we would in the end be no better off than, that of following our present system of getting tile desired information. It is more useful to get specific information from the field as.to unusual

snow conditions. Last year, we prepared a forecast of 525,000 acre-feet, North Platte at Saratoga. Conditions on the watershed, Hay 1st,

were above normal by about 4 inches and our forecapt statement was therefore strensthened in the Nay 1st report. The bad feature was the fact that during May over parts of the drainage area of this stream above Saratoga five feet 'of new snow was deposited. result of

this happening the actual '4ril-JUly runoff turned out to be 750,000

In this case we learned of this unusual condition about June 1st and much too late to correct our final farecast . Statenent Approximating' the runoff as early a April 1st is quite difficult and uncertain. At Fort Collins our annual precipitation r.verages about 1475 inches.

Of this we find on the average for More than 50 years' record that in larch we can expect 1 inch, 'April 2 inches and Tay

3

inches, or about 40 percent of the total in these three months. Wide'variations in the

precipitation occur with us. ..4)ri1 1900, there was 1056 inches; pril 1900 it was only .05 inch. Other months were equally-eratic.

Such variations =plicate our problem and if the 7eather bureau could come to our aid and tell us whether there is going to be 3 inches of

rainfall on the Poudre watershed next flay or none at all we couldthen do very well with our forecasts.

Barnes: Computations now take about three years.

Parshall: Years ago the ilorth Fork of the Poudre

had-a.sub-stantial runoff and of later years it is noticeably less. The trees on the watershed have grown in height and ametime 'wonder if there

isn't a very delicate balance between precipitation wind and variolls

Barnes: I do not believe that a noticeable ch,nGe in

precipita-tion would result from the Growth of forest trees.

Parsh11:. It is doubtful if we will ever be able to accurately forecast runoff in streams because of the rather wide variations of influencing factors that become effective subsequent to the statement of the prediction. Closer approximations may result after more

years of record and extended experience. I am quite interested in your method of forecasting, Fred, and hope that you are on the right track for a universal solution of the forecast problem.

In talking over the snow survey project with flt. McLaughlin, with special reference to the future of forecasting, he said:

"T:le want to tell the farmers how much water they can expect for the c5ning sec.sonts irrigation supply early enough so they • can plan their crop program."

Mth us most of the irrigation and water companies hold their manual meetings during January to elect officers for the ensuing years,

plan improvements and discuss other matters of business. One of the

chief topics discussed is the old question as to the outlook for the coming seasonts water supply. Letters, phone calls and messages came

to us asking our opinion. At this time the snow surveys have not yet boon made and only fraGmente.ry information is at hand as to the General snow

conditions in the mountains, T develop some scheme wherety we could approximate the trend of the expected water supply, attention has boon given to the problem of relating the fall flow to the summer runoff as an index of the coning soasonts water supply. These studies, so far,