Safety of Safety of Dams and Dams and

Barrier Barrier LakesLakesAlessandro Palmieri,

World Bank Lead Dam Specialist

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Outline Outline

Key issues in assessing damage Key issues in assessing damage Addressing barrier lakesAddressing barrier lakesCase study example/lessons Case study example/lessons learned learned Longer term implications for safety Longer term implications for safety managementmanagement

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Key issues in assessing damage Key issues in assessing damage

PostPost--earthquake inspection earthquake inspection procedures should be specified in the procedures should be specified in the "Standing Operation Procedures"Standing Operation Procedures““ of of each dam;each dam;in particular in the in particular in the ““Emergency Emergency Preparedness PlansPreparedness Plans”” ((EPPEPP).).Water level in reservoir is the first Water level in reservoir is the first vital information to obtain.vital information to obtain.

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Large dams seem to be in reasonably Large dams seem to be in reasonably safe conditions, but what about other safe conditions, but what about other

water retaining structures?water retaining structures?Two major concerns:Two major concerns:

1.1. Past experiences (e.g. Bhuj earthquake) have Past experiences (e.g. Bhuj earthquake) have shown that shown that ‘‘rural damsrural dams’’ of small to medium of small to medium size are the most vulnerable.size are the most vulnerable.

2.2. Problems exist with river blockages due to Problems exist with river blockages due to landslides.landslides.

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Embankment dam failures caused by the 2001 Bhuj earthquake (7.6REmbankment dam failures caused by the 2001 Bhuj earthquake (7.6RM; M; e.d. 10 to 23 km) in Gujarat (courtesy Prof. S. K. Jain)e.d. 10 to 23 km) in Gujarat (courtesy Prof. S. K. Jain)

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Addressing barrier lakesAddressing barrier lakes

They normally last days or weeks.They normally last days or weeks.Life span depends mainly on: Life span depends mainly on:

Water and sediment flow,Water and sediment flow,Size and shape of dam,Size and shape of dam,Materials forming the dam,Materials forming the dam,Rate of seepage through the dam.Rate of seepage through the dam.

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Landslide DamsLandslide DamsMost used stabilization Most used stabilization method has been method has been construction of protected construction of protected spillway;spillway;Also drainage by means of Also drainage by means of siphons, pumping, tunnels siphons, pumping, tunnels outlets and diversions.outlets and diversions.In a few cases, blasting to In a few cases, blasting to open new stream channelsopen new stream channels

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Case study example/lessons Case study example/lessons learned learned

Landslide dams normally fail after days or months due to overtopLandslide dams normally fail after days or months due to overtopping or ping or internal erosion, with a few exceptions internal erosion, with a few exceptions ……..

Lake Sarez, Tajikistan

600m high dam,

13 bm3 lake

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Monitoring TrainingEarly Warning System

Long TermSolutions

Consequences Occurrence

Lake Sarez Risk Mitigation Project

Risk = consequences x probability

Components A AB C

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RiskRiskreductionreduction

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Longer term implications for Longer term implications for safety managementsafety management

1.1. Small and medium size, mainly rural, dams are Small and medium size, mainly rural, dams are at higher risk; they need rehabilitation at higher risk; they need rehabilitation measures commensurate to level of risk, mainly measures commensurate to level of risk, mainly population at risk. population at risk.

2.2. Add Risk Management dimension to existing Add Risk Management dimension to existing regulations, in particular Emergency regulations, in particular Emergency Preparedness Plans (EPPs).Preparedness Plans (EPPs).

3.3. Monitoring barrier lakes formation and Monitoring barrier lakes formation and evolution for plannning adaptive risk mitigation evolution for plannning adaptive risk mitigation measures; measures; ‘‘longer livinglonger living’’ lakes need to have lakes need to have EPPs.EPPs.