Ljiljana Spasic-Gril -EDS Panel of Experts Almaty, November 6 – 7, 2012

1

Why are the Design Criteria important? To apply consistent criteria/safety standards to existing

works which will become a part of the final project.

To demonstrate that current international guidelines (i.e. ICOLD) for design and construction of high dams are followed

The Design Criteria have been prepared by the TEAS Consultant and reviewed by the EDS Panel of Experts’ (PoE)

This presentation summarises the Design Criteria and incorporates PoE comments & recommendations

2

Scope of the Design Criteria The document covers the following aspects: Design Parameters – Section 2

Design Criteria for the Dam – Section 3

Design Criteria for Hydraulic Works – Section 4 Design Criteria for Underground Works – Section 5

Scheme Operating Criteria – Section 6

Sedimentation Management –Section 7

Downstream Right Side Zone of the Valley – Section 8

3

Scope of the Design Criteria, cont’d

PoE considers that the Design Criteria should be further expanded to cover the Mechanical and Electrical aspects

The Design Criteria are applicable to existing works, and if necessary, existing works must be adjusted or reinforced to meet the Design Criteria

4

General Layout

5

Footprint of the Dam

6

Design Parameters – Section 2 Dam Hazard classification (ICOLD Bulletins 72 and 82) will be

based on the dam height, volume, population at risk and potential economic losses.

Design Floods during operation: 1 in 10,000y flood, and Probable Maximum Flood (data, derivation, impact of global

warming, Glacial Lake Outburst Floods (GLOFs)

Flood management during construction: The flood evacuation system should be such that at any step of

construction, the reservoir level remains lower than the dam elevation less the adapted dry freeboard.

Geological & geotechnical parameters: will be derived based on previous and current ground investigation findings

7

Design Parameters – Section 2, cont’d

Seismic Design Parameters: seismic accelerations associated with OBE and MCE earthquakes will be selected for the seismic design.

Sedimentation: the data will be taken from the Hydro Project Institute (HPI) 2009 reports, based on Nurek’s data. If necessary, some additional survey will be undertaken; also susceptibility of the sediments to liquefy during a seismic event will be assessed

8

Design Criteria for the Dam – Section 3

• Freeboard determination.

• Management of hydrological risk requires that construction of the dam continues without suspension. A contingency plan will be developed to mitigate hydrological risk in case that would not be possible.

• Embankment design: 1. Stability of the slopes under static and seismic conditions: will

be assessed using 2D analysis and will meet required minimum factors of safety (FoS), according to USBR

2. Assessment of displacements during a seismic loading in case FoS for this condition is <1.

3. Anti-seepage measures will be implemented, especially with regards to the salt wedge and into the right abutment of the dam

4. Settlements of the dam will be calculated and compared with the available freeboard

9

Design Criteria for the Dam – Section 3 cont’d

• Design of filters: this will be done in accordance with the

international criteria for filters [USBR, 1994].

• Special Design features to accommodate regional seismicity.

• Criteria for faults crossing: within 50m of an active fault, thickness of any layer in the direction of the fault movement shall be at least 1.5 times the expected fault displacement;

• Salt wedge: in addition to treatment of the upper, weathered part of the wedge, the following measures will be defined:

• installation of a monitoring system to follow-up performance of the treatment works during reservoir filling and operation;

• definition of a contingency plan which identifies remedial measures to be implemented in case the monitoring system triggers pre-defined indicators.

10

Design Criteria for Hydraulic Works – Section 4 The main hydraulic facilities envisaged for the project are:

Diversion tunnels; Headrace tunnels; Tailrace tunnels; Spillways

The capacity of the water conveyance works shall be consistent

with the required reservoir drawdown rate Phase II design will be based on hydraulic calculations and

experience of similar works.

Detailed design of major hydraulic structures will require studies on hydraulic models to confirm the adequacy of the design, and determine detailed characteristics and special requirements.

11

Design Criteria for Underground Works – Section 5

• Most of the Underground Works have already been excavated and fully or partly lined/supported in accordance to FSU design criteria.

• Existing works are being assessed for their appropriateness in Phase I of the study.

• In Phase II, a Comparative Analysis of Alternative Schemes will be undertaken for the remaining underground works, yet to be executed.

• In Phase II, a pseudo-static analysis will be undertaken for seismic design of caverns and tunnels.

• At detailed design level, the most complex structures and connections will have to be subject to a dynamic analysis.

12

Scheme Operating Criteria – Section 6 A Cascade Operations Model is currently being prepared by

the TEAS Consultant, in consultation with the ESIA Consultant (Poyry). The model will incorporate:

Rate of filling and emptying of the reservoir - this will take into account:

observations made for the Nurek Dam, hazards of landslides being triggered along the reservoir rim, downstream water demand

Emergency drawdown requirements Requirements for energy production

Rogun dam will be provided with facilities which will discharge the PMF flood.

However, due to design criteria used during FSU, other dams on the Vaksh River were not provided with facilities which could safely pass the PMF flood. This issue is being carefully reviewed by the Consultant.

13

Sedimentation Management – Section 7 Mitigation measures to address the long term sediment impacts are

being considered to demonstrate that dam safety can be assured in the very long term.

The reservoir’s operating rules will have a large influence on the way

deposition takes place in the reservoir. Attention has therefore to be paid in the operation simulations to the variation of reservoir elevation throughout the year, particularly during the flood season.

The sediment management will also impact the arrangement of the

spilling facilities and the selection of the type of spillways as well as surface protection requirements.

Studies will use information on Nurek sediment deposit pattern. If necessary, additional survey and investigations will be carried out.

14

Stability of the Downstream Right Side Zone of the Valley – Section 8

The morphology of the area is a result of complex tectonics, with a wide plateau at the elevation of about 1700 masl, characterized by a big number of depressions and sinks. The downhill area forms a steep slope down to the river;

The area is currently under investigation; it had not been investigated in the past.

Main scope of the investigations is to assess long term stability of the area where important hydraulic works are planned (diversion, tailrace and spillway tunnels).

If necessary, mitigation measure will be provided, depending on the findings of site investigation.

15

Plateau on the downstream Right Side Zone of the Valley, seen from d/s

16