Evaluation of the hydrological risk during the construction phase of Kavsakbendi Dam and HEPP

Transcription

1 Evaluation of the hydrological risk during the construction phase of Dr.-Ing. Ronald Haselsteiner Björnsen Consulting Engineers, Germany (formerly: EnerjiSA) Stavanger, Norway June 2015 MSc. Koray Z. Özbek, PhD. Taylan U. Evcimen Koza Construction Trade Co., Turkey (formerly, EnerjiSA)

2 Outline Introduction Kavsakbendi Dam and Characteristics Approach, Data and Statistics Results of Analysis Realization 2

3 Outline Introduction Kavsakbendi Dam and Characteristics Approach, Data and Statistics Results of Analysis Realization 3

4 Introduction Joint-Venture 15 hydropower projects in the period between 2007 to 2015 under development Ceyhan Seyhan Status

5 Outline Introduction Kavsakbendi Dam and Characteristics Approach, Data and Statistics Results of Analysis Realization 5

6 Introduction Map & Characteristics Cofferdam Type: Concrete Dam H = 31 m Diversion Tunnels 2 x Ø 8,0 m Q D = 1,500 m³/s Main Dam Type: CFRD H = 80 m Headrace tunnel Ø 8,0 m Q D = 260 m³/s Main Powerhouse P = 177 MW 3 x Francise turbines 6

7 Introduction Map & Characteristics 7

8 Kavsakbendi Dam and Characteristics Main components 8

9 Introduction - Challenge Headrace tunnel Andirap landslide Rock slide slope Foundation conditions clay, & gypsum & karst Diversion tunnels 9

10 Outline Introduction Kavsakbendi Dam and Characteristics Approach, Data and Statistics Results of Analysis Realization 10

11 Approach, Data and Statistics Approach Motivation & Hydrolgocial Risks No impoundment strategy/concept High risk dam project: rock slopes, Andirap landslide, foundation conditions, fault zone Unknown hydrological risks during impoundment Evaluation of monthly hydrological risks Definition of 7 scenarios and constellations Preparation of impoundment strategy/concept 11

12 Approach, Data and Statistics Hydraulic capacity curves for S0 to S6 Bottom outlet Spillway 2 x Diversion Tunnels Q D = 1,500 m³/s 1 x Diversion 12

13 Approach, Data and Statistics Data Hydrological scheme Flood season 13

14 Approach, Data and Statistics Time series flood occurence Period % from Nov to Jan 70 % from Mar to Apr 10 % May and Feb 14

15 Approach, Data and Statistics Flood statistiscs - Pearson III and Gumbel HQ T = MHQ + k T σ HQ T MHQ k T σ [m³/s] [m³/s] [-] [m³/s] Flood discharge with T [a] Average flood discharge Statistical parameter Standard variation HQ 1 = MHQ 0.5 σ HQ 1 [m³/s] Annual flood with p = 100 % 15

16 Outline Introduction Kavsakbendi Dam and Characteristics Approach, Data and Statistics Results of Analysis Realization 16

17 Results of Analysis S0 Construction phase Q D = 1,500 m³/s at 286 masl 2 diversion tunnels Normal construction phase Cofferdam crest level (p = 1 % in March) Pre cofferdam level (p = 18 % in March) Pre-cofferdam Cofferdam 17

18 Results of Analysis S1 Original concept Bottom outlet works at 288 masl Only bottom outlet Extreme harmful waterlevels (p = 100 % from Dec to Jun) Unacceptable risk for completion construction phase Change of existing concept!!! 18

19 Results of Analysis S2 One diversion tunnel available Cofferdam level at 286 masl Unacceptable risks in Dec+Jan and Mar+Apr (p = 10-20%) Closure of one diversion tunnel from May to Nov (Feb neglected) Only one diversion tunnel Pre-cofferdam 1st stage cofferdam Cofferdam Spillway sill Dam crest 19

20 Results of Analysis S3 Diversion tunnel + bottom outlet Bottom outlet affects only higher water levels Diversion tunnel + bottom outlet No effect of BO on construction phase when dam is not completed Bottom outlet plays minor role for impoundment stage due to its small hydraulic capacity Reduced risk 20

21 Results of Analysis S4 One diversion tunnel, BO and spillway Spillway controls water levels at masl 1 div. tunnel + bottom outlet + spillway The risk of overtopping tends to be zero! As soon as spillway is ready impoundment may be initiated Spillway completion was scheduled after dam completion No overtopping! 21

22 Results of Analysis S5 BO+SP+HAT without diversion tunnels Control of high water levels Overtopping of cofferdam due to high elevation of BO and HT (p = 100 %) bottom outlet + spillway + headr. tunnel Spillway sill One diversion tunnel required during construction and impoundment phase No overtopping! 22

23 Results of Analysis S6 One diversion tunnel + spillway No overtopping of dam crest 1 diversion tunnel + spillway Controlled risk also during rainy season Application of a control gate at one of the diversion tunnels Dry season Rainy season Dry season Spillway ready for impoundment No overtopping! 23

24 Results of Analysis Consequences New temporary control gate in the second diversion tunnel Both diversion tunnels required for controlling the flood periods during ongoing construction Impoundment phase scheduled after April/May and before November Preparation of a detailed impoundment strategy Drawdown option during and after impoundment essential Vertical shaft of control gate 2nd diversion tunnel closed 24

25 Results of Analysis Impoundment strategy Roller gate Roller gate+ spillway Drainage pipe Pumping/refilling 4 phases A to D 25

26 Results of Analysis Impoundment rates r i vs. reservoir elevation Control of effective reservoir inflow by roller gate Continuous impoundment at stages 1+2 Staggered impoundment at stages l/s 4.5 m³/s 15 m³/s 6.5 m³/s 26

27 Outline Introduction Kavsakbendi Dam and Characteristics Approach, Data and Statistics Results of Analysis Realization 27

28 Realization Refitting of DT 2 with control gate Diversion tunnel (DT) 1+2 open Construction of vertical shaft Closure of DT 2 Adaptation of existing tunnel gate chamber Completion of roller gate before March 2013 Opening of DT 1 Diversion Tunnel 1 open Diversion Tunnel 2 closed Controlled impoundment Gate chamber Vertical shaft 28

29 Realization After impoundment, operation upstream upstream downstream 29

30 Evaluation of the hydrological risk during the construction phase of Thank you!