Design Of Stepped Spillway 24u58

A Stepped Spillway Preceded by a Supercritical Flow Channel H Harold ld Huff H ff – Hydraulic H d li Engineer E i Sacramento District Corps of Engineers June 14, 2011

US Army Corps of Engineers

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General Location - Folsom Dam

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Location of Folsom Dam

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Folsom Dam Dam Safety • Only 65% PMF Capacity

Flood Protection • D/S Levee Capacity – 160 000 cfs 160,000 f • Lower Outlets 25,000 cfs

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Folsom Dam JFP Main Dam

Control Structure Spillway Chute A Approach h Channel

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Folsom Dam JFP Spillway Chute

Stilling Basin

Stepped Chute

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Background  CORPS CONSTRUCTED DAM IN 1950’S  DAM TURNED OVER RECLAMATION ((HYDROPOWER AND WATER SUPPLY))  RECENTY HISTORY – CORPS AUTHORIZED TO INCREASE FLOOD REDUCTION CAPABILITY OF DAM; USBR FOR DAM SAFETY PROJECT

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T FEDERAL PROJECT  CORPS MODS TO MAIN DAM PROJECT TOO COSTLY  USBR FUSE PLUG SPILLWAY INCL LONG EXCAVATED CHUTE BETWEEN DAM EMBANKMENT AND FOLSOM PRISON  CORPS BEST ALT FOR MODS PROJ – AUX SPWY WITH SUBMERGED GATE; SAME ALIGNMENT AS FUSE PLUG BUILDING STRONG®

DESIGN CONSIDERATIONS  PMF Q = 320K CFS; FC DESIGN Q = 135K CFS THRU AUX SPWY  LIMITED SPACE FOR AUXILIARY SPWY 6 – 34’ HIGH BY 23’ WIDE SPWY; SUBMERGED (BY 100’ +) TAINTER GATES IN CONTROL STRUCTURE ; CHUTE WIDTH = 169’; HIGH UNIT Q  q = 800 (DES) AND 1900 (PMF) CFS/FT

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DESIGN CONSIDERATIONS  2100’ LONG CONCRETE LINED, RECTANGULAR CHUTE; SLOPE OF 2% BASED ON ROCK LINE RESULTED IN VERY HIGH VELOCITIES  V = 67’ FPS FOR 135k CFS & 80 ‘/SEC FOR 320k CFS @ DOWNSTREAM END OF CHUTE

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Stepped Spillway in Supercritical Spillway Chute Design Flow (135,000 cfs)

Maximum Flow (320,000 cfs)

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800 cfs/ft f /ft 78 ft/sec - Max 3.7 - Froude # 10.8 ft - Depth

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1,900 1 900 cfs/ft 84 ft/sec - Max 2 8 - Froude # 2.8 23.2 ft - Depth

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DESIGN CONSIDERATIONS  STEPPED CHUTE U/S OF A STILLING BASIN SELECTED INSTEAD OF MORE CONVENTIONAL PARABOLIC DROP / STILLING BASIN BASED ON COMPARATIVE COSTS.  OVERALL INVERT PROFILE WAS BASED ON A PARABOLIC DROP EQ.  STEP HEIGHTS VARY FROM ABOUT 0.8’ AT U/S END TO 3’ (MOST ARE 3’) BUILDING STRONG®

Stepped Spillway in Supercritical Spillway Chute S=0.02 Y=0.02*X+0.000472406*X

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1V:2.483555158H

Stilling Basin

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DESIGN CONCERNS       

ENERGY DISSIPATION INTERACTION OF STEPS AND BASIN CAVITATION POTENTIAL ABRASION OF STEPS NEED FOR ADDED AERATION DURABILITY / MAINTENANCE LOADINGS FOR STRUCTURAL DESIGN BUILDING STRONG®

MODELS HELP ADDRESS CONCERNS     

SAFL 1:26 SCALE PHYSICAL MODEL USBR 1:48 SCALE PHYSICAL MODEL USBR LAPC CAVITATION MODELING USBR CFD (FLOW-3D) ALDEN LABS CHECK OF CFD RESULTS

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SAFL 1:26 SCALE MODEL

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SAFL 1:26 SCALE MODEL

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SAFL 1:26 SCALE MODEL

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SAFL 1:26 SCALE MODEL

Q = 22,000 22 000 cfs 20

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Stepped Spillway – 135K CFS

Q = 135,000 cfs 21

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SAFL 1:26 MODEL Q = 322,000 cfs

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VELOCITY DATA LOCATIONS Profile of Stepped Spillway 340

Velocityy Profile @ Step 0

320 300

Elevation, feet

280

Velocity Profile @ Step 32

260 240

Velocity Profile @ Step 61

220 200 180 160 140 120 31+00

32+00

33+00

34+00

35+00

36+00

37+00

38+00

39+00

40+00

Station, feet 23

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135,000 , CFS VELOCITIES 12

10 Step 0_5 Step 0_4 Step 0_3 Step 0_2

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Step 0_1

Depth (ft)

St 32_5 Step 32 5 Step 32_4 Step 32_3

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Step 32_2 Step 32_1 Step 61_5 Step 61_4 Step 61_3

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Step 61_2 Step 61_1

2

0 35

45

55

65

75

85

95

105

115

Velocity (ft/sec)

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320 000 CFS VELOCITIES 320,000 25 Step 0_5 Step 0_4 0 4 Step 0_3 Step 0_2

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Step 0_1 Step 32_5

Depth (ft)

Step 32_4 Step 32_3

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Step 32_2 Step 32_1 Step 61_5 Step 61_4 St 61_3 Step 61 3

10

Step 61_2 Step 61_1

5

0 40

50

60

70

80

90

100

110

120

130

140

Velocity (ft/sec)

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SAFL ENERGY LOSS

22,508

Total Energy Loss 93%

Stepped Spillway Energy Loss -

89,969

86%

-

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113,049

83%

-

-

139 049 139,049

80%

55%

25%

158,249

78%

-

-

301,710

67%

34%

33%

Discharge

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Stilling illi Basin i Energy Loss -

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ENERGY LOSS CONFIRMATIONS     

ANALYTICAL COMPUTATIONS USBR CFD MODEL USBR 1 1:48 48 SCALE PHYSICAL MODEL CFD MODEL AT ALDEN LABS ANALYTICAL COMPS ABOUT 10% LOWER THAN OTHERS  MODELS WERE CLOSE. BUILDING STRONG®

USBR CFD MODELING Design Flow (135,000 cfs) Step 1 Velocity (ft/s)

Step 1 Pressure (psi)

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USBR CFD MODELING Design Flow (135,000 cfs) Step 35 Velocity (ft/s)

Step 35 Pressure (psi)

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USBR CFD MODELING Design Flow (135,000 cfs) Step 67 Velocity (ft/s)

Step 67 Pressure (psi)

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LAPC @ USBR LAB

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Test section for atmospheric work on laboratory floor.

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PIV – data (large steps-slope 0.4)

Step 4 – velocity magnitude

Step 14 – velocity magnitude

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Incipient Cavitation  = 0.68 0 68

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Cavitation Index  = 0.44 0 44

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MODELING ADDRESSED  ENERGY DISSIPATION  INTERACTION OF STEPS AND BASIN  CAVITATION POTENTIAL

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MODELING NOT FULLY ADDRESSED  ABRASION-DURABILITY-MAINTENANCE ABRASION DURABILITY MAINTENANCE  NEED FOR ADDED AERATION  LOADINGS FOR STRUCTURAL DESIGN

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