Reservoirs, Spillways, & Energy Dissipators

1. Reservoirs, Spillways, & Energy Dissipators CE154 – Hydraulic Design Lecture 3 CE154

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. Hoover Dam – downstream face CE154

4. Hoover Dam – Lake Mead CE154

5. Hoover Dam – Spillway Crest CE154

6. Hoover dam – Outflow Channel CE154

7. Hoover Dam – Outlet Tunnel CE154

8. Hoover Dam – Spillway CE154

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. 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 CE154

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 CE154

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 CE154

14. Reservoir Capacity Curve CE154

15. Spillway Discharge Rating CE154

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 CE154

17. Spillway Capacity vs. Surcharge CE154

18. Spillway Cost Analysis CE154

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 CE154

20. Spillway Design Procedure (cont’d) • Perform hydraulic design of spillway structures- Control structure- Discharge channel- Terminal structure- Entrance and outlet channels CE154

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 CE154

22. Sabo Dam, Japan – Drop Chute CE154

23. New Cronton Dam NY – Stepped Chute Spillway CE154

24. Sippel Weir, Australia – Drop Spillway CE154

25. Four Mile Dam, Australia – Ogee Spillway CE154

26. Upper South Dam, Australia – Ogee Spillway CE154

27. Winnipeg Floodway - Ogee CE154

28. Hoover Dam – Gated Side Channel Spillway CE154

29. Valentine Mill Dam - Labyrinth CE154

30. Ute Dam – Labyrinth Spillway CE154

31. Matthews Canyon Dam - Chute CE154

32. Itaipu Dam, Uruguay – Chute Spillway CE154

33. Itaipu Dam – flip bucket CE154

34. Pleasant Hill Lake – Drop Inlet (Morning Glory) Spillway CE154

35. Monticello Dam – Morning Glory CE154

36. Monticello Dam – Outlet - bikers heaven CE154

37. Grand Coulee Dam, Washington – Outlet pipe gate valve chamber CE154

38. Control structure – Radial Gate CE154

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 CE154

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 happens CE154

41. Overflow Spillway CE154

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 CE154

43. Overflow Spillway CE154

44. Overflow Spillway • Effective width of spillway defined below, whereL = effective width of crestL’ = net width of crestN = number of piersKp = pier contraction coefficient, p. 368Ka = abutment contraction coefficient, pp. 368-369 CE154

45. Overflow Spillway • Discharge coefficient CC = f( P, He/Ho, , 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% CE154

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 CE154

47. C vs. P/Ho CE154

48. C vs. He/Ho CE154

49. C. vs.  CE154

50. Downstream Apron Effect on C CE154