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F!t[ COP·Y B!JfU.:,:W OF RECLAMATION

J-!YJRAULIC LABOPATORY

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UNITED ST],TES DEPAR'ThrnNr OF TBE INTERIOR

BURE!--1U OF RECL.:,H; TION

HYDR,1ULIC L.'.,BOR,;TORY REPORT NO. 109

HYDRt,ULIC MODEL �TtmIE� JF GRANBY D,�M SPIILW;,y ·

COLOR'.,.DC - BIG THOMTSON F?.GJECT

By

R. R. Pomeroy

Denver, Colorado

March 31. 1942

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UNITED STATES DEPARTMENT OF THE INTERIOR

BU.RE.AG OF RECLAMATION

Branch of Design and Construction Engineering and Geological Control

and Research Division

Laboratory Keport No. 109 Hydraulic Laboratory Compiled by: R. R. Pomeroy

Denver, Colorado March 31, 1942

Subject: Hydraulic Model �tudies of Granby Dam �pillway -Colorado-Big Thompson Project.

IN TRODlJCTION

Granby Dam is located �bout four miles northeast of the town of

Granby, Grand County, Colorado (figure 1). The darn is to be a com­

bination earth and rockfill structure having e height of 223 feet above

river level. It will intercept the flows of the Colorado River, Willow

Creek, Meadow Creek, and Strawberry Creek to form a. reservoir with an

estimhted capacity of 482,860 acre-feet at the maximum water surface,

elevation 8275. Water from this reservoir will be pumped into �hadow

Mountain Lake and thus made available for delivery through the Contin­

ental Divide Tunnel to the Egstern slope.

The outlet works and spillway, with capacities of 500 second-feet

and 12,000 second-feet respectively, are locared on the left abutment

of the dam. The spillway channel is spirally curved downstream from

the gate structure, and the channel floor is superelevated. The channel

floor intersects the natural slope of ti1e mountainside at a point ap­

proximately J65 feet downstream from the spillway crest, from which

point ��e discharge is allowed to flow down the mountainside to the

river bed 200 feet below.

PROBLEMS FOR MODEL STUDY

A comprehensive study of the spillway performance was the primary

objective in building the model. The outlet tunnel was installed only

to observe the effect of tne spillway flow on the tunnel exit. The

study of the spillway was to stress three principal points:

(1) Determination of the adequacy of the entrance

and tie feasibility of a satisfactory substitute for the

costly warp in the original design.

(2) Determination of the influence of the spiralled curve and superelevated floor of the spillway channel on the flow action.

(3) Determination of the path ta.ken by the flow issu­ing from the downstream end of the spillway channel and of the possibility that the material disturbed by this flow mi€ht be deposited in a location impairing the opera­tion of the outlet tunnel.

CONSTRUCTION OF MODEL

The model of the Granby Dam spillway was constructed to a scale of 1 to 24 and consisted of a head box, outlet tunnel, entran·ce and channel of the spillway, and a tail box (figure 2). The head box was made of wood with light sheet-metal liniil@• A cast-iron pipe was used for the outlet tunnel with a iate valve located near the midpoint of the tunnel as the medium for controlling the amount of flow. The spill­way entrance and channel were constructed of concrete, the gate structure of redwood and sheet metal. The teil box was constructed in the same manner as toe head b9x and included a hinged wooden and canvas gate for regulating the tailwater elevation. Water columns attached to piezom­

eter openings in the h·�ad and tall box were utilized to measure the

depth of water ente:-ing the gate structure and the heitht of the ta.H­wa.tar. The bedrock and topography of the spillwey area represented in the model was formed of a mixture of concrete, small rocks, and sand.

ENTRANCE TO SPil,LWAY:

Model teats on the original design indic�ted that the entrance would perform satisfactorily without aey change (figure J). It was

realized, however, t..1-iat the warp, necessitating a large area of paved surface, would be costly and difficult to construct; therefore"it was desirable to develop a design which would eliminate this feature, if such a design would not seriously impair the performance of the entrance.

The approach to the gate structure has as 1 ta left boundary a l/.2zl slope. In the first of the attempts to develop a new entrance design, a slope of tnis same magnitude was substituted for the warp on the right side of the approach, a sharp break being formed by the inter­

section of this slope and an extension of the 3:1 slope of the upstream

face of the dam (figure 4). It was this sharp break, extending from the floor of the approach channel to an elevation above that of the maximum water surface, which appeared to be responsible for the undesirable flow conditions obtained in the design. Excessive turbu­lence caused by the inability of the flow to accomplish such a rapid change in direction at relatively high velocities was apparent.

Numerous designs were also tested in which flatter slopes were substituted for the 1/2:l slope. These substitutions of flatter slopes were considered to be possible solutions because they placed tne sharp corner formed by the intersection of the two slopes at a greater dis­tance from the gate structure and made the drop from the 311 slope of the dam face to the floor of the entrance less abrupt. None of the variations tested reduced the unsatisfactory flow conditions to an extent deemed necessary for an adequate design.

The final design differed in that an intermediate slope was used between the l/2il and 3:1 slopes, thus reducing the abruptness of

transition from one to the other (figures 5 and 15). It also allowed the highest point on the sharp break to be lowered to approximately ele­vation 8265.0, an elevation which is below the water surface of all flows above 4000 second-feet. Thus, under the conditions most conducive to high velocities.and subsequent turbulence, the effect of the break was at least partially damped because of its origin within the body of liquid and not on the surface. More gradual increases in velocities aleo resulted from the less abrupt drop to the floor of the entrance and the less abrupt decrease in the cross sectional area of the approach.

Extensive tests to determine the discharge and coefficient curves , .. "of this entrance (figure 6), revealed that the discharge for any water

surface elevation was as great for tnis design as it had been for the first design. A comparison was also made of the coefficients of dis­charre for this entrance with ��ose determined from previous model tests wherein the entrance approach conditions, position of gates, and shape of crest differed materially. as a medium in making such a comparison, the coefficient of discharge, calculated from the formula Q = 2/3

I �12. CL/2g- (h1

3 2 - h/ ) , was plotted against h1/d, the ratio of the head above the gate seat to the gate opening ( fifure 7) •

The resulting curve, covering a wide range in gate openings,

shows that the coefficients for all the entrances, including Granby,

c�n be considered equal for corresponding values of h1/d, provided

that the ratio of h1 to dis not less than 2.250 in other words,

it is only for values of h1/d below i.�5 that the coefficient is ap­

preciably influenced by the approach conditions. The depth of approach

is one of the prime factors causing differences in the Vl:i.lue of the co­

efficient, another being the crest shape.

All the model tests indicated that the performance of this design

would compare favorably with that of the original, which was adequate in every respect. The reduction of turbulence to a minimum, the satis­

factory entrance coefficients, and ��e saving in cost and ease of

cons�:ruction to be accomplished by the elimination of warped surfaces,

made tnis desirn the logical choice •

.A comparison of the rlgh t approach of' the entrance on the final

design prototype drawing ( figure 16) with .that on the model drawing

(f1r.ure 15) shows a dtfference in the len€th of the 1/2:l slope of

approximately 2.5 feet prototype. The· increase in length on the proto­type design was made in order that the sl6pe of the plane surface join-

ing the J:l and 1/2:l slopes would become 2:1, thus simplifying con­

struction. The change was considered so slight as to make further model

tests unnecessary.

SPILLWAY CHANNEL

The channel of ��e spillway on Cranby Dum is unusual in that it

is curved in plan so th�t t!1ere is an angle of approximately �4 degrees

between the extension of the center-line of the gate structure and the center-line of the channel at its downstream end (figure 2)o The origi­

nal design provided that this ctiange in direction of flow would be ac­

complished as gradually as possible by spiraling the curve, and it

also superelevated the floor within the liini ts of the curve in order to

prevent the piling of the flow on one siJe of the channel.

The channel, as originally designed, functioned properly, and no

changes were made in either the curve or the superelevation. It was,

however, decided to line the floor and the sides to a height of 15 feet

with concrete in order to improve flow conditions and increase the

4

velocity of flow at the downstream end. Thie increase in velocity seemed desirable because of the effect it would have on the path of

flow after leaving the spillway.

EROSION AT DJWNSTREAM END OF SPILLWAY

It was fully realized before any model tests had been made that

there would be considerable erosion ct1.used by the spillway discharge

in reachinc the bed of the river. The questions of the extent of' this

erosion and where the disturbed material would be deposited had to be

answered by model tests. The location of the deposit was important in

tha. t it might have a det_rimen tal effect on the operation of the outlet

if it were too near the downstream end of the tunnel.

Under the c:Jnditions existing within the area in question, the

four most important factors influencing location and amount of erosion

and the location of the deposition of eroded material would be (a) the

quantity and velocity of the flow causinf the erosion, (b) the direction

of the general slope of the bed rock and top soil surfaces, (c) the a­

mount of top soil present in the eroded area, and (d) the general

characteristics of the erodible material. Of these factors, only the

last is virtually impossible to slmilate on a model, and it is this

last consideration which becomes increasingly important es the anele of repose of the top soil and the slope of' the medium supporting it increase.

The overburden on Granby dam site consists of slide rock, glacial

outwash gravels, river sand and gravels, and slope wash, the latter com­

posed of a mixture of soil, sandy clay and rock fragments wnich rante

in size from pebbles up to l�rge boulders. The slope wash is 5 to 10 ·

feet deep on the µpper slopes and thickens to as much as 45 feet on the

lower slopes. That ��e impact of the water would be great enough to

sweep away this hifhly compacted soil and rock as quickly as the sand and

rock used in the model, is unlikely. The erosion pattern might eventually

become the same on the protov pe as on the model, but the difference in

the relative time necessary for 1 t to assume that shape would have an ef­

fect on the extent and location of the final depositions. Because of this

limitation, the model was not expected to indicate the exact rate and a­

mount of erosion which would occur, but only an approximation of the direction the flow would eventually assume and whether or not dePosition

of eroded material would occur in a location likely to interfere with the

operation of the outlet.

5

t'

Care was used in trying to make the surface elvations of the bed­

rock and topsoil accurate on the model, but difficulty was encountered in the case of the bedrock, because of lack of information as to con­

tours and outcrops. Very few test pits had been dug in the area immedi­

ately below the downstre&m end of the spillway, and th� extent and loca­

tion of outcrops were not adequately defined. The bedrock was placed in

accordance with the available data, but its possible inaccuracy was

recognized.

In testinf, the outlet was operated at the maximum discharge of 500

second-feet and only the leakage from the gates was allowed to flow

through the spillway. Tnis condition was maintained for some time, and resulted in the erosion pattern shown in figure 8. The spillway gates

were then slowly opened until the maximum discharge of 12,000 second-feet w�s flowint through the spillway ( figure 9). After operating the

model under this condition of �aximum discharge for one-half hour, spill­

way �ates were closed and the erosion and deposition observed (figure 10) .

�e path ta.ken by very low discharges through the spillway was such that most of the resultant deposition partially blocked the outlet exit. As the discharge increased and the velocity of the water became

sufficient to resist the tendency to follow a path followine, the direction of the general slope of the surfaces of the top soil and bedrock, the

line of flow gradually became straighter. This action did notv however,

remove the material already deposited in front of the outlet exit by the smaller flow.

The problem then was one- of evolving a method by which the smaller discharees could be forced to follow a path whereby the resultant deposi­tion would occur in some less objectionable location. The most obvious

method was that of excavating a pilot channel which, eliminating the

necessity for the water to cut its own channel, �ould allow £Uiding the

discha.rfe to a place where the erodible material carried by it could be

deposited without harm. This scheme was successful, but the excavation

necessary to create such a channel on the prototype would be additional

expense. The other method considered as a means of attacking the problem in­

volved two chanfes at the downstream end of the lined spillway. The length of the spillway was increased by ten feet, at the downstream end p

6

and a lip with an ave-rage height correspondinl to three feet on the

proto type structure was placed across the end of the lined section .

The cre st of this lip varied in elevation, the lowe st point occurring

at the point of intersec tion with the left spillwey- wall . It was

thought that these two changes would e stablish a channel for tne flow

of water as far as pos�ible from the outlet exit , because the leakage

from the gate s , the means by which this channel would be sttt.rted, would

tend to flow over the lowest elevation on the cre st of the lip and would

be thrown outward by the lip and �dded spillway length in such a manner

that the distance it would travel before tending to curve toward the out­

let. exit would be increased o

There was no indication that the lip helped in any was to attain

this obj ective , so it was removed. The 10-foot le?l€ th added to the spill­

way was retained, however, as it seemed to have some beneficial effect in

directine. the hi@her d i s cha�ges in the path desired . Since the model tests indicated ttlat the conditions below the spill­

way depended on the authenticity of the bedrock and overburden contours, a request was made that more feolog ical information concerning the site

be furnished . Several test pits were dug in the area in question. 'l'he contours of the bedrock as defined by information from these teat pits

s.nd rock outcrops as shown on a geolo[ic map were incorporated in the model to make it more nearly simulate the protQtype. The chanfe had a tendency to decrease the slope of the surface toward the outlet , and it seemed probable that the location of deposition would not be as unfavor­

able. Tests comparable to those on the orif inal arrangement were made.

The gates were slowly raised unt il a maximum discharge of 12 ,000 second­

feet was flowing throurh the spillway , th i s now being maintained fo:r:· one­

half hour . The results ( figures 11 , 12 , and 13) showed the expected

improvement . 1'he channel cut by the low nows in finding a path down the

slope emerged much further from the outlet exit; and , while eroded mate­

rial was still deposited in that vicinity , an adequate channel was cut

throuih it hy the comb ined flow from the outlet and part of the flow from

the spillway . I t was also a matter of conjecture as to how the final erosion pat-

tern would be changed if the gates were opened rapidly instead of slowly .

The eroded material was replaced and the maximum flow of 12 ,000 second-

7

feet was discharged through the spillway by suddenly ope ning the fate s .

A comparison o f the diffe renc e i n erosion patterns made by rapid open­

ing and slow opening is shown in firure 14.

The pos s ih il i ty that th e e ro sion p3.ttern as obtained in the model

tests is not ne c e ssarily a true reiJreeentation of thut wtli ch \\'ill occur

on the prototype s truc ture must be em_phe.sized a.gain . I t i s prob11ble ,

however, that the model erosion pattern repre sents u worse condition thun

the fJ.nal p>.it'Lern on the pro b typd . 3ecause of tae chtiracte r i stics of

th e top soil mute ril:l.l at the dctm site , a.::; compared to those of the lo8sely

compttcted material used on the mod�l , i t is ne. tural to assume that the

pro cess of eroaion will he much slower· on the prototype structure than

model test re sul ts wo uld indi C !i te . :Such 11 retarding effec t on the ero­

sion proeess would g ive the dis charge from the outlet more opportunity

to sluice an adequate channel tnrou[h t..'1e depositions from the spillway

are a , and the r i sk of such a channel beint, cloned by more deposition

would be considerably les sened . } or thi s reason , the results of the

model eros ion tests are bel ieved to indicate that the danger of seriously

harnperinf the outlet disch11rge i s small.

CONCLUSIONS

( a) A spillway en trance tran�ition consisting of a series of plane

surfaces gave satisfactory re ::;ults for all re servoir elevations . I t was

used tq replace tne warp sh,)wn in the original ciesit- n be cause of its ad­

vantage s of sm1:1ller ini tia.l cost and ease of construction ( .fit;ure 15) .

( b ) The performance o f the spillwuy channel a s orir,inally de::Jigned

was sati sfac tory . Linint,_ the channel with concrete improved the flow

condi tions and increased the veloc i ty of flow. Such an increase in

velocity w ill be instrumental in s traigh tening the flow path downstream

from the channel . A height of 15 fee t was sugt e sted as be in£ suffi cient

for tne l ining of the wal l s .

( c ) An addi tion o f 10 foot made to the leneth o f the spillway at

the downstream end was benefic ial in directing the higher di8charges in

tne pa.th desired immediately below the epillway channel .

( d ) Although the model ero s ion pattern may n0t b e an exac t repre­

sentation of that wn ich will occur on tne pro totype stru c ture , it is a

8

qualitative indication of tn e proto ty pe conditions to be expecteq.

Wbe n the model re aiults are j udged in this manne r , it appean1 probable

tnat the ero�ion rn1d consequent depo s ition will n o t interfer·e seriously

Vi i th operation o f 1:,he outlet .

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I i I I ' I I I I I I I I J_ I i I I I I I I ' ' I I I I I I ' I I I I I I

I I I I I 1+t .j __ , _ I I ' I I - - - -·t-· ----i-

! I I I I I I I I I I ' I I -- I l r--1 ' ' -- ' I=:.. · - 0 -- :.d �--h-� . ' .

·,- . ' , . ... .,.,/ ··-- ' ' ' : '

- / a , ., -�- ' I ' --� p / � 1-=!=-.-I: -l.--.1 .•. - ,-. . - -1--t->- � I f+ ' ' ' ' ' d ; ' ' ' I '

. L- I 1- - - . - f- L·=F t-: r rt ft l t i I I ii ..• ! . \-- · ·(.I. L -

-i-- ' I 11 ---- � l i r · - ' - --·r-i-, I i I I i I I I I I I I I I I I I I I I I I I I I I I I I

1 . 5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 h ,/d

6.0 7,0 8.0 9,0 1 0

i

N OTE : The coeff i cient of d i scharge was calculated from the formula

Q = 2/3 CL V2g ( h;-'2 - h:12) .

C O E F F I C I E N T O F D I S C H A R G E

R A D I A L G A T E S

4 - 2 - 42 R. R. P.

• Stewart Mountain Dom S c a le J : SO , Bu ! I Loke Dom .5 c ale 1 : 30 • Wheeler .Qom S c a le 1 : 3 6 • Coddoo Dom Scale I : 3� • R. E . Horton's Experiments • Granby Dom S c a fe I :48

' I

X- D - 4 4 1

20

DOVINSTREAM END OF SPILLWAY AND OUTLE:r WORKS.

EROSION CAUSED BY M.AXn.ruM FLOW THROUGH OUTLEJ' AND LEAKAGE THROUGH SPILLWAY GATES.

ORIGINAL DESIGN

FIGURE 8

SECOND SI'EP IN EROSION CAUSED BY GRADUALLY OPENING SPIIJ.,\'/AY GATES. MAXIMUM FLOW 'rllROUGH ourLEr.

EROSION CAUSED BY MAXIMUM FLOW THROUGH SPIILWAY OF 12 , 000 SECOND-FEET, MAXIMUM FLOW THROUGH ourLEr .

ORIGINAL DESIGN

FIGURE 9

FIGURE 10

EROSION CAUSED BY MAXIMUM FLOW THROUGH SPILLWAY AND OUTLEI'.

ORIGINAL DESIGN

DOWNSTREAM END OF SPILLWAY AND OUTLE:r WORKS.

EROSION CAUSED BY MAXIMUM FWW THROUGH OUTLEI' AND LEAKAGE THROUGH

SPILLWAY GATES.

ORIGIN.AL DESIGN WITH CORRECI'ED TOPOGRAPHY

FIGURE 11

FIGURE 12

SECOND srEP IN EROSION CAUSED BY GRADUALLY OPENING SPILLWAY GATES. MAXThUJM FLOW THROUGH OUTLEI' .

THIRD srEP IN EROSION CAUSED BY GRADUALLY OPENING SPILLWAY GATES. MAXD.fu"'A FLOW TEROUGH OU'I'LEl' .

ORIGINAL DESIGN WITH CORREGrED TOPOGRAPHY

EROSION CAJJSED BY MAXIMUM FLOW THROUGH SPILLWAY OF 12 , 000 SECOND-FEET. llAXD(tM FLOW THROUGH OUTLEI',

l . :

EROSION CAUSED BY GRADUALLY OPENING SPILLWAY GATES TO MAXIMUM DISCF.ARGE.

ORIGINAL DESIGN WITH CORRECI'ED TOPOGRAPHY

FIGURE 13

..

EROSION CAUSED BY MAXIMUM FLOW THROUGH SPILLWAY WEEN GATES ARE OPENED RAPIDLY. MAXJMUM FLOW THROUGH OUTLEI' •

EROSION CAUSED BY MAXIMUM FLOW THROUGH SPILLWAY WHEN GATES ARE OPENED SLOWLY. MAXIMUM FLOW THROUGH OUl'LEI' .

ORIGINAL DESIGN WITH CORRECTED TOPOGRAPHY

FIGURE 14

•

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/.. ' ',

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c�: I

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El. 8262. Bf ' ' I

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-� _ -.-:- __ _________/_ ___ -_�_G_a_f e sfr u c t u ce ___ _

f PLAN

I II - 4 - - - >--4-

VIEW OF RIGHT HA LF OF APPROA CH

5 !?_ I I

/6

v • •

�- - · (£ Ge de sfruc fure

9 11 · · S - . 16

- · ·Er. 8285. 0

. . : · "' ' . · . · . "

c, # . - ; •

: . . . .

SECTION THRU APPROACH

G R A N B Y D A M

MODEL EN TRANCE A PPROACH - FINA L DES IGN

/ :48 M O D EL OF SPILLWA Y

F I G U R E 15

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\ O B O \ Sta z,90 00 . 'i.' spillway " �r � Cr o � � _ Sta 10•15. 00, ax is of 001 1 1, ;... __.......o ">·

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s1o I ? Z.S 50 15 1yo . � ,iii � . �

_._ c:: ·· a -<1�:" · ....... " . I V')

� ,,� / ',, - ,) 5 C A L E. Of FE.E.T

'R1prap on upstream -- - - · face of dam 0 51 8

� � � 0 rouno' surface on <t: <:) g � � g � g M � O Vi � ,E lti - 0 � �

� '!' � v:> � � 't + J, - -- - --=---=--=..---...-_-_.r_____ - - - -A ssumed rock surface on <£ rt N E: t; � � : � 0 ,," .; - - -- -�·.::_.. � CO c:, O CJ; cu ..... ,._ _ _ .._ ,, ....., � � a 0.0) y � l{) � --- �< ..... � :i � � \ I'll,, \"IJ,,o ' ,I! �� "' - • t I .... ... N ; ,, • Max W5. EI. BZ75.00 -:;:"---- - · --===·.=c-..c.. · - - _, , - , - =-· __ .-Remforcemen near face on y "' � _1 1J.�" _; Future /minq _ _ ..... __ :�,;::;,.,-- .._�==-,;=,,-..=-1::!-m'. . �- · ·£/. 8265. 30 � u.J:"''; ,n

$ ..

..... ........ .... ....

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<£ Sp1/!1va

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..... ......... uround surface

......... .......... ..... -;,- , A ssumed .-' ' -....

rock surface - - , · '- ...._

-....

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Bottom of supere ·e

channel

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a s a 6 •25;

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El 8l89. 0

onr.b/e slope .v \\/ 5. U 82 75.()0

------� Cu·· of

f

wall

S E C T I O N

� 10:o·--

G - G

£1. 82lJS.0 i'_ I

--:,.-;:- - E.I. 8Z51.0- ---, , · 't. Slope • o.o3 :' .. --' -, · · -s - o. o;: ___,..,,_._;;._......,�TV--ro;=vn�r<:r---'<----.J....!1""�fr'-=��"Nir:i,,.,=:�ift��-�- m "r w - - - - -- - .XL -�'

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.,....of'_. ·'><:_!-�·--rO 'Min .. ' .,

,��--- . , Ground �., ',:_:: -I surface

, · . '-., ...... , � ...

�� ..,; i. j' \ '·<.>' ! A ' ' ' 3 �-- -�i : 8 : � ·· £y..covated , Grout holes ----r ;"' ::i � '°! 5 E. c TIO N A - A su bgrade ·· � �vi V) J i : J - ., - '��

.-· <£ Spillway I

-.;i Cl "-I .___ ' M.',, ' � \hCO r,"')

......: --: � :::.; l.J V") c..: Ground surface

--�::..::-.:::::..:,. I ,,--Assumed rock surface _:,, i � ·· 't. Sprllwa

...:::: .... ;

Reinforcement ':<· 17! o··>< , El l3Z85'c,}':..:::. �-near face only - -- -- ·• : t · · -..::- . f : t . , • . . ( ' \ . ,.,-_ � . . . .

I -,�

float - well _ __ _ \··\ , · ZZ'J"·· intake pipe -- --

_,, 7:';.: / " '

< ----- ' ' ! __,., "A , ' ,;, _____ .,;. .. v _. :/ r,,_y>-<, \,. ' _/ / "1 . \ �-� :- . �\;�qp,/4'.l"

(;;out hofe5 as/

/ .,-, -/- '- jiT __ _ __

T_ -l

I

direc}td in field-<. • • . • . ..

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I I I I I I S E. C T/ O N B -B

�

-- - Contraction joints

.... ' .... ' ' ' r<--17.0 1->- ...... ...... :_: ...... ..

i ...... ............ ... £1. 8285.00 · · · ·- - :·}

'

4 · Min :;f:,--- Top of qafe . . 0 . . , .,� £1. 8ns oo ..., rain 1n ·- 1. �1--�---

po;ous concrete -_:.;. ·-:- '(�11'-_=_=_=_= -�-.t.jl

1{ A nchor bars - t . @ 5 ' ± crs - - : _;.

Req1on behind side wall to be � , r , thoroughly 9routed before excava- : , - ' Jl.ri;,� ;�� t1on below £1. 8285.00 1s started- ,

Porous concrete 9 ·a 1'. , 6 "mi

S E. C T/ O N C - C

0 �

I S E C TI O N F-F

��- .... ,,L. -f

',, ',, 5 £ C T/ O N £ · £.

-- Top of dam DBZ85 00

- · Region to be thor­ouqhly grouted before excavation below fop of lining ,s started·- - - - - - · ·

' ' ' ' ' ", ... ...

1-<.- - - ·

,,. - 'i. 5piJJwar ' ',

'............ ..r . 39 � 3" --- ��,;

· Ground surface

iissumed rock surface , · ·El 8285 o : \ . .:' ·-- . . -<- ,

4 "Drain tn porous concrete ­

-� . /

� - ,; ., _/iZ-Av �-- ·

9"Mm;

·arioble slope .. -f; · t at Sta. 3 t 75

' : Variable 1vidtn,

,· Jam surfac� j_

,_ �·->-....._ ---......... I.;_ ·,t- / ".):-:-_, Region to be l�"'- . .,. thoroughly grouted . - 4 .,.,tn.

4"Droin in gravel·'' �tf0Anchor bars @ 7 '± crs

· 6 " Jram in gravel

S E C TION D · D

N � !'.!

8215 ... � "' 8270 O "-� · sz.;.s w . "' > .., w r< .., "' &H»O

a2ss ��-�-�-��-� 0 Z. 4 , 8 10 ll 015CH ARG[ • T HOUSAND SEC. FT .

S P I LLWAY DISCHARGE. CURVE.

U N I T E D S TA T E S

DEPARTMENT OF THE IN TERIO"

8U,.EAU OF "ECLA.MAT I ON COI.O"AOO 8/G Tl<OMP9aN P"OJECT • COLO.

G R A N B Y D A M S PI LL W A Y

PLAN A NO SECTIONS

DRAWN • . J/1 L • • • 5V8MIT1l0 /�

V ff'� .. TRACC..D Wf!1,S - H.R.S RCCOMMt..ND!D �C....-4�---- -- - -CHCCK£D L,'1,3, _ A�PROVLD. }:!�_ ��-�---

DCNVl"lfµL01iADO JiJN�