Your SlideShare is downloading. ×
Ce154   lecture 3 reservoirs, spillways, & energy dissipators
Upcoming SlideShare
Loading in...5
×

Thanks for flagging this SlideShare!

Oops! An error has occurred.

×
Saving this for later? Get the SlideShare app to save on your phone or tablet. Read anywhere, anytime – even offline.
Text the download link to your phone
Standard text messaging rates apply

Ce154 lecture 3 reservoirs, spillways, & energy dissipators

428

Published on

Published in: Technology, Business
0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total Views
428
On Slideshare
0
From Embeds
0
Number of Embeds
0
Actions
Shares
0
Downloads
82
Comments
0
Likes
0
Embeds 0
No embeds

Report content
Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
No notes for slide
  • 60 ft diameter outlet tunnel
  • Transcript

    • 1. Reservoirs, Spillways, & Energy Dissipators CE154 – Hydraulic Design Lecture 3 Fall 2009 1CE154
    • 2. Fall 2009 2 Lecture 3 – Reservoir, Spillway, Etc. • Purposes of a Dam - Irrigation - Flood control - Water supply - Hydropower - Navigation - Recreation • Pertinent structures – dam, spillway, intake, outlet, powerhouse CE154
    • 3. Fall 2009 3 Hoover Dam – downstream face CE154
    • 4. Fall 2009 4 Hoover Dam – Lake Mead CE154
    • 5. Fall 2009 5 Hoover Dam – Spillway Crest CE154
    • 6. Fall 2009 6 Hoover dam – Outflow Channel CE154
    • 7. Fall 2009 7 Hoover Dam – Outlet Tunnel CE154
    • 8. Fall 2009 8 Hoover Dam – Spillway CE154
    • 9. Fall 2009 9 Dam Building Project • Planning - Reconnaissance Study - Feasibility Study - Environmental Document (CEQA in California) • Design - Preliminary (Conceptual) Design - Detailed Design - Construction Documents (plans & specifications) • Construction • Startup and testing • Operation CE154
    • 10. Fall 2009 10 Necessary Data • Location and site map • Hydrologic data • Climatic data • Geological data • Water demand data • Dam site data (foundation, material, tailwater) CE154
    • 11. Dam Components • Dam - dam structure and embankment • Outlet structure - inlet tower or inlet structure, tunnels, channels and outlet structure • Spillway - service spillway - auxiliary spillway - emergency spillway Fall 2009 11CE154
    • 12. Spillway Design Data • Inflow Design Flood (IDF) hydrograph - developed from probable maximum precipitation or storms of certain occurrence frequency - life loss ⇒ use PMP - if failure is tolerated, engineering judgment ⇒ cost-benefit analysis ⇒ use certain return-period flood Fall 2009 12CE154
    • 13. Spillway Design Data (cont’d) • Reservoir storage curve - storage volume vs. elevation - developed from topographic maps - requires reservoir operation rules for modeling • Spillway discharge rating curve Fall 2009 13CE154
    • 14. Reservoir Capacity Curve Fall 2009 14CE154
    • 15. Spillway Discharge Rating Fall 2009 15CE154
    • 16. Spillway Design Procedure • Route the flood through the reservoir to determine the required spillway size ∆S = (Qi – Qo) ∆t Qi determined from IDF hydrograph Qo determined from outflow rating curve ∆S determined from storage rating curve - trial and error process Fall 2009 16CE154
    • 17. Spillway Capacity vs. Surcharge Fall 2009 17CE154
    • 18. Spillway Cost Analysis Fall 2009 18CE154
    • 19. Spillway Design Procedure (cont’d) • Select spillway type and control structure - service, auxiliary and emergency spillways to operate at increasingly higher reservoir levels - whether to include control structure or equipment – a question of regulated or unregulated discharge Fall 2009 19CE154
    • 20. Spillway Design Procedure (cont’d) • Perform hydraulic design of spillway structures - Control structure - Discharge channel - Terminal structure - Entrance and outlet channels Fall 2009 20CE154
    • 21. Types of Spillway • Overflow type – integral part of the dam -Straight drop spillway, H<25’, vibration -Ogee spillway, low height • Channel type – isolated from the dam -Side channel spillway, for long crest -Chute spillway – earth or rock fill dam - Drop inlet or morning glory spillway -Culvert spillway Fall 2009 21CE154
    • 22. Sabo Dam, Japan – Drop Chute Fall 2009 22CE154
    • 23. New Cronton Dam NY – Stepped Chute Spillway Fall 2009 23CE154
    • 24. Sippel Weir, Australia – Drop Spillway Fall 2009 24CE154
    • 25. Four Mile Dam, Australia – Ogee Spillway Fall 2009 25CE154
    • 26. Upper South Dam, Australia – Ogee Spillway Fall 2009 26CE154
    • 27. Winnipeg Floodway - Ogee Fall 2009 27CE154
    • 28. Hoover Dam – Gated Side Channel Spillway Fall 2009 28CE154
    • 29. Valentine Mill Dam - Labyrinth Fall 2009 29CE154
    • 30. Ute Dam – Labyrinth Spillway Fall 2009 30CE154
    • 31. Matthews Canyon Dam - Chute Fall 2009 31CE154
    • 32. Itaipu Dam, Uruguay – Chute Spillway Fall 2009 32CE154
    • 33. Itaipu Dam – flip bucket Fall 2009 33CE154
    • 34. Pleasant Hill Lake – Drop Inlet (Morning Glory) Spillway Fall 2009 34CE154
    • 35. Monticello Dam – Morning Glory Fall 2009 35CE154
    • 36. Monticello Dam – Outlet - bikers heaven Fall 2009 36CE154
    • 37. Grand Coulee Dam, Washington – Outlet pipe gate valve chamber Fall 2009 37CE154
    • 38. Control structure – Radial Gate Fall 2009 38CE154
    • 39. Free Overfall Spillway • Control - Sharp crested - Broad crested - many other shapes and forms • Caution - Adequate ventilation under the nappe - Inadequate ventilation – vacuum – nappe drawdown – rapture – oscillation – erratic discharge Fall 2009 39CE154
    • 40. Overflow Spillway • Uncontrolled Ogee Crest - Shaped to follow the lower nappe of a horizontal jet issuing from a sharp crested weir - At design head, the pressure remains atmospheric on the ogee crest - At lower head, pressure on the crest is positive, causing backwater effect to reduce the discharge - At higher head, the opposite happensFall 2009 40CE154
    • 41. Overflow Spillway Fall 2009 41CE154
    • 42. Overflow Spillway Geometry • Upstream Crest – earlier practice used 2 circular curves that produced a discontinuity at the sharp crested weir to cause flow separation, rapid development of boundary layer, more air entrainment, and higher side walls - new design – see US Corps of Engineers’ Hydraulic Design Criteria III-2/1 Fall 2009 42CE154
    • 43. Overflow Spillway overcrestheadenergydesign crestoverheadenergytotal spillwayofwidtheffectiveL esubmergencdownstreamPfC CLQ H H H H H o e o e e = = = = = ),,,( 2/3 θ Fall 2009 43CE154
    • 44. Overflow Spillway • Effective width of spillway defined below, where L = effective width of crest L’ = net width of crest N = number of piers Kp = pier contraction coefficient, p. 368 Ka = abutment contraction coefficient, pp. 368-369 HKKL eap NL )(2 ' +−= Fall 2009 44CE154
    • 45. Overflow Spillway • Discharge coefficient C C = f( P, He/Ho, θ, downstream submergence) • Why is C increasing with He/Ho? He>Ho → pcrest<patmospheric → C>Co • Designing using Ho=0.75He will increase C by 4% and reduce crest length by 4% Fall 2009 45CE154
    • 46. Overflow Spillway • Why is C increasing with P? - P=0, broad crested weir, C=3.087 - P increasing, approach flow velocity decreases, and flow starts to contract toward the crest, C increasing - P increasing still, C attains asymptotically a maximum Fall 2009 46CE154
    • 47. C vs. P/Ho Fall 2009 47CE154
    • 48. C vs. He/Ho Fall 2009 48CE154
    • 49. C. vs. θ Fall 2009 49CE154
    • 50. Downstream Apron Effect on C Fall 2009 50CE154
    • 51. Tailwater Effect on C Fall 2009 51CE154
    • 52. Overflow Spillway Example • Ho = 16’ • P = 5’ • Design an overflow spillway that’s not impacted by downstream apron • To have no effect from the d/s apron, (hd+d)/Ho = 1.7 from Figure 9-27 hd+d = 1.7×16 = 27.2’ P/Ho = 5/16 = 0.31 Co = 3.69 from Figure 9-23 Fall 2009 52CE154
    • 53. Example (cont’d) • q = 3.69×163/2 = 236 cfs/ft • hd = velocity head on the apron • hd+d = d+(236/d)2 /2g = 27.2 d = 6.5 ft hd = 20.7 ft • Allowing 10% reduction in Co, hd+d/He = 1.2 hd+d = 1.2×16 = 19.2 Saving in excavation = 27.2 – 19.2 = 8 ft Economic considerations for apronFall 2009 53CE154
    • 54. Energy Dissipators • Hydraulic Jump type – induce a hydraulic jump at the end of spillway to dissipate energy • Bureau of Reclamation did extensive experimental studies to determine structure size and arrangements – empirical charts and data as design basis Fall 2009 54CE154
    • 55. Hydraulic Jump energy dissipator • Froude number Fr = V/(gy)1/2 • Fr > 1 – supercritical flow Fr < 1 – subcritical flow • Transition from supercritical to subcritical on a mild slope – hydraulic jumpFall 2009 55CE154
    • 56. Hydraulic Jump Fall 2009 56CE154
    • 57. Hydraulic Jump yy11 VV11 VV22 yy22 LLjj Fall 2009 57CE154
    • 58. Hydraulic Jump • Jump in horizontal rectangular channel y2/y1 = ½ ((1+8Fr1 2 )1/2 -1) - see figure y1/y2 = ½ ((1+8Fr2 2 )1/2 -1) • Loss of energy ∆E = E1 – E2 = (y2 – y1)3 / (4y1y2) • Length of jump Lj ≅ 6y2 Fall 2009 58CE154
    • 59. Hydraulic Jump • Design guidelines - Provide a basin to contain the jump - Stabilize the jump in the basin: tailwater control - Minimize the length of the basin • to increase performance of the basin - Add chute blocks, baffle piers and end sills to increase energy loss – Bureau of Reclamation types of stilling basin Fall 2009 59CE154
    • 60. Type IV Stilling Basin – 2.5<Fr<4.5 Fall 2009 60CE154
    • 61. Stilling Basin – 2.5<Fr<4.5 Fall 2009 61CE154
    • 62. Stilling Basin – 2.5<Fr<4.5 Fall 2009 62CE154
    • 63. Type IV Stilling Basin – 2.5<Fr<4.5 • Energy loss in this Froude number range is less than 50% • To increase energy loss and shorten the basin length, an alternative design may be used to drop the basin level and increase tailwater depth Fall 2009 63CE154
    • 64. Stilling Basin – Fr>4.5 • When Fr > 4.5, but V < 60 ft/sec, use Type III basin • Type III – chute blocks, baffle blocks and end sill • Reason for requiring V<60 fps – to avoid cavitation damage to the concrete surface and limit impact force to the blocks Fall 2009 64CE154
    • 65. Type III Stilling Basin – Fr>4.5 Fall 2009 65CE154
    • 66. Type III Stilling Basin – Fr>4.5 Fall 2009 66CE154
    • 67. Type III Stilling Basin – Fr>4.5 • Calculate impact force on baffle blocks: F = 2 γ A (d1 + hv1) where F = force in lbs γ = unit weight of water in lb/ft3 A = area of upstream face of blocks in ft2 (d1+hv1) = specific energy of flow entering the basin in ft. Fall 2009 67CE154
    • 68. Type II Stilling Basin – Fr>4.5 • When Fr > 4.5 and V > 60 ft/sec, use Type II stilling basin • Because baffle blocks are not used, maintain a tailwater depth 5% higher than required as safety factor to stabilize the jump Fall 2009 68CE154
    • 69. Type II Stilling Basin – Fr>4.5 Fall 2009 69CE154
    • 70. Type II Stilling Basin – Fr>4.5 Fall 2009 70CE154
    • 71. Example • A rectangular concrete channel 20 ft wide, on a 2.5% slope, is discharging 400 cfs into a stilling basin. The basin, also 20 ft wide, has a water depth of 8 ft determined from the downstream channel condition. Design the stilling basin (determine width and type of structure). Fall 2009 CE154 71
    • 72. Example 1. Use Manning’s equation to determine the normal flow condition in the upstream channel. V = 1.486R2/3 S1/2 /n Q = 1.486 R2/3 S1/2 A/n A = 20y R = A/P = 20y/(2y+20) = 10y/(y+10) Q= 400 = 1.486(10y/(y+10))2/3 S1/2 20y/n Fall 2009 CE154 72
    • 73. Example • Solve the equation by trial and error y = 1.11 ft check ⇒ A=22.2 ft2, P=22.2, R=1.0 1.486R2/3S1/2/n = 18.07 V=Q/A = 400/22.2 = 18.02 • Fr1 = V/(gy)1/2 = 3.01 ⇒ a type IV basin may be appropriate, but first let’s check the tailwater level Fall 2009 CE154 73
    • 74. Example 2. For a simple hydraulic jump basin, y2/y1 = ½ ((1+8Fr1 2 )1/2 -1) Now that y1=1.11, Fr1=3.01 ⇒ y2 = 4.2 ft This is the required water depth to cause the jump to occur. We have a depth of 8 ft now, much higher than the required depth. This will push the jump to the upstream 3. A simple basin with an end sill may work well.Fall 2009 CE154 74
    • 75. Example • Length of basin Use chart on Slide #62, for Fr1 = 3.0, L/y2 = 5.25 L = 42 ft. • Height of end sill Use design on Slide #60, Height = 1.25Y1 = 1.4 ft • Transition to the tailwater depth or optimization of basin depth needs to be worked outFall 2009 CE154 75

    ×