Embankment dam spillways and energy dissipators

Transcription

1 Embankment dam spillways and energy dissipators by Prof. Hubert CHANSON The University of Queensland, School of Civil Engineering, Brisbane QLD 4072, Glashutte dam, 22 Aug Australia, Clermont MEL weir in 1993

2 Spillway Designs for Embankment Overtopping System and Earth Dams Introduction Embankment failure & breach development Minimum Energy Loss weirs Embankment overflow stepped spillways Precast concrete blocks Gabions & Reno mattresses Design considerations CHANSON, H. (2014). "Embankment Dam Spillways and Energy Dissipators." in "Labyrinth and Piano Key Weirs II - PKW 2013." Proceedings of 2nd International Workshop on Labyrinth and Piano Key Weirs - PKW 2013, Nov., Paris-Chatou, France, CRC Press, pp (ISBN ).

3 Introduction Sorpe dam, Germany Embankment = earthfill structures Applications Dams River training / Flood protection Coastal protections Tsunami barrier Storm surge barrier Natural lakes & Landslide dams Man-made flooding (during wars) Kyoto, Japan New Orleans, USA in 2005 (Hurricane Katrina)

4 Embankments Earthfill structures Levees, Dykes Erodible systems when overtopped

5 Dale Dyke dam (UK) Construction: 1863 Failure: 11 March 1864 (piping, poor construction) 150 lives lost

6 South Fork dam (USA) Construction: Failure: 31 May 1889 (spillway capacity & construction) 2,209 lives lost

7 Lake Ha! Ha! (Canada) Failure: July 1996 (spillway capacity)

8 Opuha dam (NZ) Construction: Failure: 5 February 1997 (outlet capacity) Opuha Dam Failure on 5 February 1997

9 Glashutte dam (Germany) Construction: 1953 Failure: 12 August 2002 (spillway capacity)

10 Downstream flooding and damage Images courtesy of Dr Bornschein

11 Embankment failure & breach development Embankment failure = dam break but. Relatively slow failure process Teton dam (USA, 100 m high) 12 h to drain reservoir (1976) Zeyzoun dam (Syria) breach opening = 3 ½ h (2002) Glashutte dam (Germany) 4 hours overtopping + breach opening = 30 min (2002) Zeyzoun Dam Failure on 4 June 2002

12 Embankment breach development & inlet shape Sequence of 8 shots within 20 s Non-cohesive embankment overtopping model

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14 Natural scour = similarity with MEL inlet (McKAY 1970, CHANSON 2003 JHE) Saaiplaas tailings failure in 1993 Island of Capri canal Merriespruit tailings dam failure in 1994 (Courtesy of Pr A. FOURIE)

15 Analogy with Minimum Energy Loss (MEL) culvert inlet MEL culvert at Redcliffe (Australia) CHANSON, H. (2004). "Overtopping Breaching of Noncohesive Homogeneous Embankments. Discussion." Journal of Hydraulic Engineering, ASCE, Vol. 130, No. 4, pp CHANSON, H. (2005). "The 1786 Earthquake-Triggered Landslide Dam and Subsequent Dam-Break Flood on the Dadu River, Southwestern China. Comment." Geomorphology, Vol. 71, pp

16 Overflow protection systems Reinforced grass Macro-roughness elements Minimum Energy Loss weir & spillway Concrete stepped spillway Precast concrete blocks Gabion (& Reno mattress) structures Irago peninsula, Japan Choctaw 8A auxiliary spillway (USA) in 2002 Brushes Clough dam, UK in 1993 Brazil Crotty dam, Australia, 1991

17 Overtopping protection - Minimum Energy Loss weirs Developments in 1950s in Queensland (Australia) by late Prof Gordon McKay ( ) Developed to pass large flood flows with minimum afflux in tropical catchments with very-flat bed slope Chinchilla MEL weir (1973), Q = 850 m 3 /s, zero afflux

18 Basic design features Smooth flow contraction towards the crest Critical flow conditions at crest Converging chute walls Energy dissipation in channel centreline A A Bank top Earthfill Concrete slab Section AA Chinchilla MEL weir (1973), Q des = 850 m 3 /s, zero afflux, ICOLD register listed View from downstream (400 m 3 /s) U/s water level D/s water level

19 Clermont weir (1962/63), Q des = 850 m 3 /s

20 MEL spillway inlet designs Swanbank power house (1965) Lake Kurwongbah (850 m 3 /s, ) MEL inlet design allowed extra m of water storage Lake Kurwongbah, Q = 850 m 3 /s Swanbank

21 Prototype experience Operation for more than 60 years (incl. Q > design flow) Soundness of design + Little maintenance There is no better proof of design soundness than successful prototype experience Key issue: expert design (Hydraulics expert & Physical modelling) Major structures 1- Sandy Creek MEL weir (Clermont) 1962/63, 850 m 3 /s, zero afflux 2- Chinchilla MEL weir 1973, 860 m 3 /s, zero afflux large dam with international exposure (ICOLD) 3- Lake Kurwongbah (850 m 3 /s, ) MEL inlet design allowed extra m of water storage CHANSON, H. (2003). "Minimum Energy Loss Structures in Australia : Historical Development and Experience." Proc. 12th Nat. Eng. Heritage Conf., IEAust., Toowoomba Qld, Australia, N. Sheridan Ed., pp (ISBN X).

22 Embankment overflow concrete stepped spillways Developments during 1990s Numerous applications Secondary & primary spillways Choctaw 8A auxiliary spillway in 2002 Salado Creek Dam Site 15R

23 Tongue river dam (USA, 1997) RCC stepped spillway for a detention basin in west Las Vegas (USACE) Ashton dam embankment overflow (USA, ) : h = 0.6 m, l = 0.9 m, Q max = 690 m 3 /s (PMF)

24 Melton dam (Australia, 1916/1990s) Q ~ 2,800 m 3 /s (secondary spillway) Opuha dam (NZ, ) H = 50 m

25 Construction Concrete layers (RCC/rollcrete suitability) Protection layer (in some cases) Drainage layer beneath steps Supplemented by drainage holes Overflow hydraulics Adequate discharge capacity Skimming flow regime (Design flow) Downstream dissipator

26 Embankment with precast concrete block stepped spillways Russian design under the leadership of P.I. GORDIENKO Overlapping precast concrete bocks Klinbeldin Primary spillway applications Kolymia (or Kolyma) (Courtesy of Prof. Yuri PRAVDIVETS) Sosnovsky dam (Photograph by Prof. Yuri PRAVDIVETS) Farm dam, H = 11 m. q w = 3.3 m 2 /s, S o = B = 12 m

27 Brushes Clough dam spillway (UK, ) - wedge shaped concrete blocks (120 kg each) - Chute slope : 18.4, h = 0.19 m - Inclined downward steps (-5.6 ) - Trapezoidal cross-section (2-m bottom width, 1V:2H sideslope) - Design flow : 3.66 m 3 /s, H dam = 26 m - Field tests in 1993

28 Prototype experiences Solid record (q w up to 60 m 2 /s) Bolshevik farm dam (1980), H = 11.5 m. q w = 3.3 m 2 /s, S o = , B = 12 m High construction standards required Importance of drainage layer Flexibility of spillway channel bed Hydraulics considerations Volymia experimental earth dam (H=20 m) in the Magadan region (Siberia) * Skimming flow operation * Straight prismatic cross-sectional channel * Downstream stilling structure

29 Gabion & Reno mattress protection Porous material no uplift pressure interactions between seepage & overflow Flexible stepped construction differential settlement Stacked vs lined placement Gabion stepped chute Duralie, NSW (Australia) Robina, QLD (Australia) Limited lifetime (5-10 y) gabion resistance to damage by sediments and debris

30 Design considerations Overflow protection (all systems) Construction Stability of earthfill structure is essential Good construction quality & Simple sound design Drainage of embankment during overflow Hydraulic Engineering Discharge capacity estimate Downstream dissipation structure Down-to-earth considerations Human interferences Vandalism (Brushes Clough; Africa) Prototype experiences: no better proof of design soundness than successful prototype operation No need to re-invent the wheel

31 Summary and Conclusion Embankments & Earthfill structures Erodible systems when overtopped Overtopping protection systems Minimum Energy Loss weirs & spillways Concrete stepped spillways Precast concrete blocks Gabion stepped spillways Macro-roughness elements Design and Construction must be sound No better proof of design soundness than successful prototype operation Learn from successful designs!!!

32 Look forward seeing you at the 5 th International Symposium on Hydraulic Structures 25-27June 2014 Full Paper submission deadline: 2 December 2013

33 THANK YOU