Final report on a model study of the Kremasta Dam spillway: Kremasta hydroelectric project, Acheloos River Development, Greece

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HYDRAULIC MODEL STUDY OF THE

KREMASTA DAM SPILLWAY

KREMASTA HYDROELECTRIC PROJECT ACHELOOS RIVER DEVELOPMENT

GREECE

ADDENDUM I

FLIP BUCKET RELOCATION

Colorado State University Research Foundation Civil Engineering Section

Hydraulics Laboratory Fort Collins, Colorado

AUG 16

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_{HYDRAULIC MODEL STUDY}

M

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FILE

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OF THE

KREMASTA DAM SPILL\VAY

-K·REM.ASTA HYDROELECTRIC PROJECT

AC HE LOOS RIVER DEVELOP~;IENT

GREECE

ADDEr-.TDUM I

FLIP BUCKE f RELOCATION

Colorado State University Research Foundation

Civil Engineering Section

Hydraulics Laboratory

Fort Collins, Colorado

September 1962 CER62SSK19a

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KINGDOM OF GREECE PUBLIC POWER CORPORATION

A THENS. GREECE

FINAL REPORT ON A MODEL STUDY

OF THE

KREMASTA DAM SPILLWAY

KREMASTA HYDROELECTRIC PROJECT ACHELOOS RIVER·DEVELOPMENT

GREECE

ADDENDU1vl I

FLIP BUCKET RELOCATION

Prepared for

Engineering Consultants Inc. Denver. Colorado

by S. S. Ka.r&..ki Hydraulics Laboratory Colorado State University

Colorado State University Research Foundation

CivH

Engineering Section

List of Figures Introduction . • • Flip Bucket CONTENTS

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l l 1 Slope Protection • • . . • . . . • • • . • • • 4 River Bed Erosion and Power Plant Tail

Figure

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FlGU.RES

63(a) through (j) Flow conditions from flip bucket in

revised location

64 Recommended flip bucket geometry

65 Water su~face profiles and pressure heads in flip bucket

66 Slope protection, preliminary design

67 Preliminary slope protection below

fiip bucket

68(a) through (c) Flow over preliminary paved protection

Q = various ems

69 Flip bucket jet clears paving edge and cliff

70 Slope protection, recommended design

71 Recommended paved slope protection

72

73

7

4

75

Vertical section to left wall at the

down-stream end of paving

Recommended paving, Q. = 100 ems

.Recomrnended p3.ving. Q = 150 ems

Stage discharge rating cu:.'ves at

model gaging station

-i-z

5 6 1 8 3 9 11 10

10

12 12 13

Figure

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,-•

FIGURES-Continued

76(a) and (b) Scour pattern '\vith 3/8-inch gravel

Q s 1000 ems. power plant Q = 400 ems 14 77(a) and (b) Scour pattern with 3/8-inch gravel

Q = 2000 ems. power plant Q = 400 ems 15

78(a) and (b) Scour pattern with 3/8-inch gravel

Spillway Q = 3000 ems, power plant

Q = 400 cm~ 16

79 Step Hydrograph 17

80(a) Scour pattern with hydrograph of Figure 79 18

80(b) Power plant tailwater level 18

80(c) Power plant tailwater level

No power plant discl13.rgc 19

81 River stage studies 20

82(a) through (c) Scour patterns with 3/·1-inch gravel 21

83(a) through (c) Scour patterns with bed roe'· at

elevation 139. O m .21

84 Power plant tail water levels,

bed rock at elevation 139. 0 22

-ii-INTRODUCTION

Subsequent to the publication of "Hydraulic Model Study of the

Kremasts Dam Spillway" in 'larch, 1962, additional foundation investigations revealed the advisability of relocating the spillway flip bucket. It was pro-posed that the chute spillway be shortened a horizontal distance of 25 meters with no change in slope so that the floor oi the flip bucket would be at eleva-tion 195.21 meters and the flip bucket would terminate at station 0+580.56

meters.

The general model of the Krem.asta Dam spillway which had been

constructed in the hydraulics laboratory at Colorado State University was altered to meet the above conditions. Additional model tests were performed

to

check the flip bucket performance in the revised location. Specifically, the objectives of the study were to:

1. Determine the jct impact area of the flip bucket in the revised location and modify the flip bucket if necessary.

2. Determine the effect of the jet impact on the river bed and on the water level in the power plant tail race.

3. Determine the slope protection necessary at the flip bucket

to

prevent erosion of the hillside.

Flip Bucket -- The chute spillway of the general model was

shortened a horizontal distance of 23 meters with no change in the spillway

slope so that flip bucket terminated at station O + 580, 56 meters and the bucket floor was at elevation 195, 21 meters.

The recommended flip bucket described in "Hydraulic :Model Study

of the Kremasta Dam Spillway" was tested in the revised location on the model

-

.

discharges greater than approximately 200 cms1 the flip bucket performed

satisfactorily. The resulting flow conditions are shown in Figures 63(a) through (j) . Figure 63(a) Figure 6 3( c) -2-t

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,-. ' ,:~ . • '1 -(/ I t. ;,,' I Figure 63( d)

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Figure 63(e) --.

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Figure 63(h) Figure 6 3(J)

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Discharges less than 200 _. ems impacted on the hillside before

,

cascading into the river below. The recommended measures

to prevent

erosion are discussed in the section on slope protection.

Due to a slightly lower velocity or flow through the flip bucket in the revised location and the resulting greater flow depth, the left wall height of the recommended flip bucket has been increased. A higher flow line along the left was -also caused by interception of the standing wave at a different point from the original flip bucket location. The pertinent dimensions of the recommended flip bucket are shovvn in Figure 6·1.

Dynamic pressure heads were measured at selected points in

the model flip bucket at a prototype discharge of 3000 ems. The pressure point locations and measured pressure heads are shown in Figure 65. No negative pressures were recorded. Figure 65 also shows the water surface profile along the right wall of the flip bucket for discharges of 1000, 2000. and 3000 ems.

Slope Protection -- At spillway discharges less than approxi-mately 200 ems. the jet emerging from the model flip bucket irr:.pacted on

the hillside before falling to the river below. Because spill'way discharges

of this magnitude will occur frequently in the prototype. some preventative

pleasures should be taken to protect the hillside impact area from erosion.

The preventive measures consisted of slope protection by paving with

retaining walls.

The first method investigated, as proposed by Engineering

Consultants Inc .• consisted of a paved area bounded by the flip bucket, two

curved training walls and the cliff edge as shown in Figures 66 and 67. The flow at the right was contained by a wall tapering in height from 2. 0 meters at the flip bucket to 4. 5 meters at the edge of the cliff. A freeboard of

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TRUE SHAPES OF PLANES

B- B SECTIONS Sta. 577.9 4 8.05 m .E e

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~ Sta. 60~.50 e

~~~~d=i2.22m

PLAN OF FLIP BUCKET

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2 .... __

--PROFILE OF FLIP BUCKET

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4 r, " d')2! 1. R ::, 1 - . 1 I PIEZOMETER LOCATIONS

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"-WATER SURFACE PROFILE ALONG RIGHT WALL OF FLIP BUCl<ET

FLOW DEPTH ABOVE FLIP

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BUCKET FLOOR IN METERS

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1000 2000 . 3000

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CMS CMS 0 2.55 4.25 6,.33 I 2.30 3.76 5.84 · ') _{2.78 4.38 6.21}

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3 3.03 4.75 6.94

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3000

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RIGHT WALL PROFILE

PRESSURE HEADS IN FLIP BUCKET IN METERS OF WATER PROTOTYPE

PROTO-

_{PIEZOMETER NUMBERS}

TYPE Q CMS I 2 3 4 5 6 7 8 9

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10 II 12 13 14 15 16 17 18 19 20 21 22 23 -1000 2000 _{I I} 3000 35.432.6 26.t 31.0 41.2 33.3 10.1 27.1 26.€ 2.9.5 f46.3 - 3.3 9.6 2.6

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33.3 12.1 26.C 33.8 340 15.6 11.8

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Flip Bucket _ _ _ _ _ S_p1_·11_wa1_ Centerline

Flip Bucket Floor Elevation= 195. 21 m.

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Upstream Troinin<J Woll U) lO 0 co lO

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Area Downstream Woll

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... PLAN SCALE: 1:300

CONTOUR INTERVAL: 5 METERS ON NATURAL GROUND

I METER ON PAVED SURFACE

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Figure 67 Preliminary slope protection below flip bucket.

Figure 68(b) Flow over prelimi -na.ry paved protection.

Q = 100 ems.

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-8-Figure 68(a) Flow over

pre-r

liminary paved protection

at Q = 50

e

m

s.

Figure 68{c} Flow over

pre-liminary paved protection.

Q = 150 ems.

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1. O meter is afforded by this. wall hdght. A fillet at the base of the wall

was provided. Although this fillet is not required for hydraulic reasons

it

might be used to structurally stabilize the w~ll. The left wall was

4.0 meters in height which contained discharges up to 50 ems, but w:is

not adequate for higher discharges. Discharges above 50 ems , bul less

than 200 ems impacted on the hillside dovrnstream of the wall. Figures 68(a) through G8(c) illustrate the flow conditions for discharges of 50 •

100, and 150

ems.

The jet for discharges above approximately ZOO ems

cleared the cliff edge as shown by Figure 69.

Figure 69 Flip bucket jet clears paving edge and cliif.

-9-Downstream walls of various heights and alignments were tested to

determine a.'1 economical and effective solution to the problem. The

recommended slope protection consists of a large paved area bounded by

the upstream curved wall described above~ the flip bucket. the cliff edge,

and a straight vertical wall 2. 0 meters in height extending along the left

edge of the paving from the flip bucket to the cliff edge as shown in Figures

70 and 71. In order to prevent overtopping near the downstream end of the

left wall without increasing the wall height,

it

is recommended that a curved deflector be constructed 16 meters long, along the downstream length of the wall as shown in Figure 72.

Figure 71 Recommended paved

slope protection.

-10-T

R= 0.5 m.

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2.0m.

_____

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_, Figure 72 Vertical section of left wall at tl e downstream end of paving.

I ... ... Flow

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0 0 C\J Spillwo Centerline

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Flip Bucket Floor Elevation= 195.21m.

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Upstream Training Woll

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PLAN SCALE: 1: 300

CONTOUR INTERVAL: 5 METERS ON NATURAL GROUND

I METER ON PAVED SURFACE

FIGURE 70 SLOPE PROTECTION, RECOMMENDED DESIGN

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Figure 7 3 R ,ecommended paving

Q = 100 ems , (

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Figure 74 Recommended paving

Q = 150 ems

Figures 7 3 and 7-4 show model flow conditions over the paving with discharges

of 100 and 150 ems rcsp.ectively.

River Bed Erosion and Power Plant Tail V./ater Levels

The stage-discharge curves at the location of the model gaging

station are reproduced as Figure 75 which coincides 1.vith Figure 53 of the

parent report.

To provide a range of possible c.:)nditicns of the river bed in the

prototype, as was done in the parent study, the model tests included two

dif-ferent bed material sizc6 and the elevation of the ''bed rock11

was studied at

two levels ( 115. 0 meters and 139. 0 meters). Description of the model

river bed materials can be found on page 30 of the original report.

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Figure 75 STAGE DISCHARGE RATING CURVES AT MODEL GAGING STATION

The development of scour in the river bed with the 3/8~inch

gravel and spillway discharge of 1000 ems is shown in Figure ?6{a). The

tailwater levels at the power plant are shown in Figure 76(b) with

pro-gressive stages of scour beginning with the existing river bed level at

ele-vation 140. 6 m. The white lines in the photograph are contour lines. The

:minimum elevation in the scour hole was 128. Om. Test results for dis

-charges of 2000 and 3000 ems are shown in Figures 77 and 78 respectively.

The power plant wall was not overtopped in any of the tests.

Scour development after a flow cycle, the hydrograph of which is shown in Figure 79. is shown in Figure 30(a). The scour area was more

ex-tensive and a greater amount of river bed material was transported down

-stream. Variatio. of tail water levels with discharge are shown in Figure 80{b).

The maximum tailwater level was 153. 1 m providing 2. 9 meters cf freeboa.rd

to the top of the wall. On the recession cycle of the hydrograph the power

plant was shut down and tailwater levels were measured with only the

spill-way flows. The result is shown in Figure eO(c).

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151 ~ 150 z _J w > w _i 149 a:: w r-<! 3 148 0

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Figure 76(a) Scour pattern with 3/8-inch gravel

Q =. 1000 ems

Power Plant Q = ,.~00 ems

Model time = 23 min.

Maximum scour= Elevation 128. 0 m

.

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RIVER LEVEL AT MODEL GAGING STATION

---

\POWER PLANT

TAILWATER LEVEL

-<--MAXIMUM SCOUR

DEVELOPMENT

2 3 4 5

TIME IN HOURS PROTOTYPE

Figure 76(b)

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(/) er w I--w ~ z _J w > w _J er w I--<l: 3';

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154 153 152 ~ - - - · - --- - - -

-Figure 77(a) Scour pattern with 3/8-in. gravel

Q = 2000 ems

Power plant Q = 400 ems Model time = 30 min.

Maximum scour El. = 130 m

RIVER LEVEL AT

MODEL GAGING STATION

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\ POWER _{PLANT TAIL WATER LEVEL}

151 0 2 3 4 5 TIME IN HOURS 6 7 PROTOTYPE Figure 77(b) -15 -8 9 -10

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Figure 78(a) Scour pattern with 3/8-in. gravd

Spillway Q = 3000 ems

Power plant Q = 400 ems

Model time = 40 min.

Maximum scour El. = 124 m

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177 METERS

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FLIP BUCf<ET .FLOW Figure 78(b) -16-RIVER LEVEL AT GAGING STATION 155. 7

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Figure 80{a) Scour pattern with hydrograph of Fig-ure 79.

156

g?

154

TOP OF POWER PLANT WALL:"\_

w ~ 152 ~ 150 z _Jl48 w

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146 . _J cr144 w f- 142 <t

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140 0 A '1/' 500 Figure 80{b)

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---RIVER L E V E V ---- 1----GAGING STATION _{i _ _ - -}.__

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PLANT TAILWATEF-< LEVEL , 1000 1500 2000 2500 3000 DISCHARGE IN CMS POvVER PLANT Q = 400 -CMS

Po,Her plant tailwater level. -18

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If.€ CJ> 154 0:: ~ 152 w :ii: 150 z 148 _J ~ 146

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TOP OF POWER PLANT WALL

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l.---RIVER _{LEVEL A ~} GAGING STATION _,,,

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°lpoWER PLANT / TAILWATER LEVEL /

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~ 140 0 500 !000 15CO 2CvC 25C C 3COC Figure 80( c) DISCHARGE IN CMS

Power plant tailwater level. No power plant discharge

Because of the gravel bar formed downstream of the scour area., the tailwater levels at discharges less than 2000 ems were higher than at

corresponding discharges during the ascending cycle of the hydrograph.

T?ere was sufficient freeboard to the top of the power plant wall at all discharges.

To determine at what river stage the power plant wall would be overtopped, tests were run at several discharges with imposed hi~h-river levels to cause overtopping. The tests were made with maxin1um dis

-charges through four turbine units. Results are shown in Figure 81. There was at least 5. 5 meters of allowance in depth between the calculated stage and that which would cause overtopping.

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154 ~ w 152 ~ z 150 ...1 148 w > 146 ~ er: 144 w

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142 ~ 1400 -

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"L -RIVER LEV AT WHICH

POWER PLANT WALl.::1

'WAS OVERTOPPED ~

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L--" ~ -_,/ _{'¥-_CALCULATED RIVER}

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STAGE AT MODEL

-/ '>AGING STATION

V

~ ; 500 1000 1500 2000 2500 3000 DISC~ARGE IN CMS

Figure 81 River stage studies

The results of tests with 3/ ~-inch gravel L'1 the n~odel river

bed arc shown in Figures 82(a) through (c) for discharges of 1000~ 2000.

and 3000 ems. The power plant tailwater levels were the same as tests

with the 3/8-inch gravel bed.

Tests results with river bed rocks located at elevation 139. 0 m

are shown in Figures 83(a) through (c) for discharges comparable to

Figure 82. Measured tailwater levels at the power plant are sho · n in

Figure 84. The tailwater at the power plant ,vas lower for corresponding

discharges during tests with the bed rock at elevation 139. Om than during

tests with the bed rock at elevation 115. O m. This was because of the draw -down effect of the flip bucket jet. No apparent tailwater problem will arise

if bed rock is near the present river bottom.

-20-)

Figure 82(a.)

~-' / _/

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Figure 82( c)

Scour patterns with

3/

4-inch gravel

Q = 1000 ems

Scour patterns with

3/4-inch ·gravel Q = 3000 ems Figure 82(b) -, ' I Figure 83{a}

-21-Scour patterns with

3/4-inch gravel

Q = 2000 ems

j

Scour patterns with

bed rock at elevation

139. 0 m

Q = 1000 ems

.

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ry

V • r-· Figure 83(b) 160 158 (f) ~ 156 1--~ 154 2 152 ..J 150 w ~ 148 ..J 146 er ~144 <t ~ 142 140 0 ., . I -~ ,>-,,.

--

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- ~~~ / . I 1 "

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..JCOUl' patt<:!rl.1S with

bed rock at

cl~V'.:i-tion 139. O ·m

Figur·e 83(c) Scou, p~-itte.rns with

bed 1·oc': at

eleva-tion 130. 0 m

Q • 2000 ems Q

=

3000 crns

I I I I

TOP, OF PO,WER PLANT WALL~

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_,,.,.-RIVER LEVEL AT MODEL _.,--,

GAGING STATION POWER PLANT .• TAILWATER . / ' ~~UNITS_-~00 ~MS __

v

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. / POWER PLANT TAILWATER

-NO FLOW THROUGH TURBINES

500 1000 1500 2000 2500 3000

DISCHARGE IN CMS

FIGURE 84 POWER PLANT TAILWATER LEVELS

BED ROCK AT ELEV. 139.0