Shf Jan09 Pjo Sogreah Evacuateurs 3 English

7/30/2019 Shf Jan09 Pjo Sogreah Evacuateurs 3 English

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Colloque CFBR-SHF Janvier 2009Evacuateurs de surface

Surface spillways

Pierre JEHANNOSOGREAH/ARTELIA, Grenoble France


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Subject of the presentation

Experience on some existing projects,

limites of standardized/normalized design,

Some elements of design of spillways,

presentation of some perculiar solutions.


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General remarks on spillways and spillway deisgn

Types of spillways

Types of dissipating strutures

Standard conception and their limits

Problems posed by low and medium head spillways

problems posed by scourable scale models

Problems posed by stilling basins

Limits of scale models

Limits et promises of mathematical models *

Some indications of improved design

(*) to be developed


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Energy dissipation

Stilling basins (Jupia /Brsil, Nam Leuk /Laos)

concrete apron (Vouglans /France, Orange River /RSA)

plunge pool (Kariba /Zimbabwe, Katse/Lesotho)

Dissipation on natural bed rock (Song Loulou/Cameroun, El Breck/Tunisie)

Problems posed by spillways (low & medium heads)

heads too low to move away the impact of water sheet

which leads to stilling basins *) et associated problems: high cost,cavitation, drainage, under-pressures, material circulation (erosion),uncertainties on downstream Z(Q) relationship.

(*) if dissipation on natural bed rock is not contemplated


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Examplesdifferent types ofspillways and dissipation

structures


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Scourable scale models

Limits:

When the model is stopped, the movable material fills in partially the

plung pool underestimation of scour, Case of broken rock: the equilibrium slope is less than prototype

slope,

Reprsentation:

Use of transparent surface (Turwel, Katse), Painted layers at different depths (Katse),

Use of cohesive material, in order to represent steep slope after scour(Agoyan)


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Some indications/ideas for a improved design

Stilling basins: modified blocks, modified end sill (Sidi Aich/Tunisia,Upper Atbara/ Sudan)

Shorter stilling basins with reinforced downnstream protection, Splitters type colonel Robert ,

Special Teeths and buckets (along the chute or at the end of thespillway),

Spilling over a very large width in order to limit specific discharge

( Comoe/Burkina Faso ) Generalisation of impact basin (USBR VI, SAF) for high heads and

discharges.


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Plung pool: Notion of dissipation rate

project Q (m3/s) q (m3 /m/s) Head (m) P/V (Kw /m3 )

P.K. Leroux 13 000 62 71 # 30

Cambambe 9 500 150 60 # 56

Maguga 7 000 35 85 # 31

Ertan 23 900 - 165 21

Xingo 16 000 - 83.5 22

Kariba 8710 - 88.7 9

Sidi Saad 5400 - 50 9.3

Katse 6040 - 142 20


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Stilling basins USBR VI: max:14.5 kW/m3

According to P. Mason (*): 10 30 kW:m3 (plunge pool); 60 kW/m3 (impactbasins)

Hydraulic jumps: 7 kW/m3 17 kW/m3 (heads: 10 to 50 m), pratically

indpendant of specific discharge.

note: Scour depths calculated by classical formulae give a depth very closeto jump depths.

(*): A guide to energy dissipaters, HRW, March 2004


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Some examples ofsurface spillways


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Stilling basins with dispersion bucket


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Advantages:

Rduction of 12% stilling basin volume,

Scouring 2 time less, Pressure fluctuations reduced by 50%,

No more return currents downstream the basins,

Certain aeration.

Is contemplated if the head is > 4 times the critical head.


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Chute equiped with modifiedsplitters:

Katse dam (Lesotho)


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Alternative studied on scale model 2 & 3

Q=6080 m3 /s

Dam heigth: 185 m

head: 160 m

Adopted alternative: n3

(scouring reduced by 8 m)

C C S


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C ll CFBR SHF J i 2009


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USBR III basin modified

Er Mel (Tunisia)

(Q=1600 m3/s, head: 20 m)



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Er Mel dam: baffle Blocks: outlets ofdrainage

Pressure profil along a change of direction



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Renforced stilling basinMequinenza dam (Spania)

(Q=11 000 m3 /s, head: 55 m)

Colloque CFBR SHF Janvier 2009


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Plunge pool + pre-excavation+ dispersion teeths

Sficifa dam (Tunisia)

(Q= 1200 m3/s, head: 23 m)



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Elavation Partial view from downstream



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Side spillway equiped with a aeratedbucket and pre-excaved pool

Kouris (Cyprus)

(Q=1600 m3/s, head: 90 m)

Colloque CFBR-SHF Janvier 2009


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Large weir and pre-excaved pool

Tucurui dam (Brazil)(Q= 110 000 m3/s, Q25= 52400

m3

/s, dam head: 80 m)



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Colloque CFBR SHF Janvier 2009Evacuateurs de surface



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Shf Jan09 Pjo Sogreah Evacuateurs 3 English