Theme C1: Flood management in arid regions ICOLD Workshop - 20 May 2016 Theme C1:Theme C1: Flood management in arid regionsFlood management in arid regions ICOLD Workshop - 20 May 2016 THE LONG TERM SAFETY OF DAMS AND SPILLWAYS Presented by - Bryan Leyland, New Zealand

Theme C1: Flood management in arid regions ICOLD Workshop - 20 May 2016 What should the design life be? The 5 oldest dams still in use: Lake Homs, Syria 7 m 1300 BC 3300 yrs Proserpina, Spain 22 m 100 AD 1900 yrs Kaerumataike, Japan 17 m 150 AD 1850 yrs Cornalvo, Spain 24 m 200 AD 1800 yrs Kallani, India 5.4 m 250 AD 1750 yrs Design life? – 150 years? 500 years? 1000 years? 5000 years? 2

Theme C1: Flood management in arid regions ICOLD Workshop - 20 May 2016 Kariba at 55 Major problems foundations AAR stilling basin spillway gates If it failed millions would be at risk 3

Theme C1: Flood management in arid regions ICOLD Workshop - 20 May 2016 Eroded plunge pool 4

Theme C1: Flood management in arid regions ICOLD Workshop - 20 May 2016 Mosul dam in Iraq 5 One million people along the Tigris could be at risk from a 20 m high wall of water if the dam collapses

Theme C1: Flood management in arid regions ICOLD Workshop - 20 May 2016 Concrete faced rockfill dam 6 Heavily dependent on the integrity of the concrete facing

Theme C1: Flood management in arid regions ICOLD Workshop - 20 May 2016 Sayano Shusenskaya accident 6400 MW Concrete arch- gravity dam 242 m high Crest length 1074 m Power station was flooded 7

Theme C1: Flood management in arid regions ICOLD Workshop - 20 May The accident happened at 8:13:25 local time 75 lives were lost Single gantry crane lifts all 11 spillway gates Supply to the single gantry crane was lost Emergency arrangements were made in time

Theme C1: Flood management in arid regions ICOLD Workshop - 20 May 2016 If the Dam had failed.. Within a few hours, more than 1 million people could have drowned and 13,000 MW of generating capacity would have been lost This could have been hydropower’s Chernobyl... Has the lesson been learned? 9

Theme C1: Flood management in arid regions ICOLD Workshop - 20 May 2016 Dam failures 90 recorded dam failures have killed at least 200,000 people Since 2010, 15 failures have killed 98 people Radiation caused deaths at Chernobyl were less than 60 and were zero at Fukushima billions have been spent on safety improvements and many reactors have been shut down at a huge cost How much has been spent on upgrading dam safety in the same period? How much should be spent? 10

Theme C1: Flood management in arid regions ICOLD Workshop - 20 May 2016 Documentation and monitoring The long life of dams makes it vitally important that documentation is comprehensive, accurate, and regularly updated Copies of documentation should be archived on and off site. Monitoring of dam movements, pore water pressures, seepage and the like must be done regularly and properly documented Spillway gates must be inspected and exercised regularly If they rely on power to operate, then any emergency generators must be tested regularly at full load testing that they will start does not prove that they can operate for hours at full power! 11

Theme C1: Flood management in arid regions ICOLD Workshop - 20 May 2016 In summary Dams can last several thousand years many dams are designed for no more than 150 years in general, large dams cannot be decommissioned Large dams require constant surveillance and maintenance for as long as they last how can we make sure that this will happen? Dam designers and owners must make every effort to ensure that they will be safe and easily maintained for hundreds - or thousands - of years 12

Theme C1: Flood management in arid regions ICOLD Workshop - 20 May 2016 The safety of dams and spillways Design considerations for new dams select the safest suitable dam option if two sites are available, select the upstream site select the safest practical spillway option Upgrading the safety of existing dams enhanced monitoring and careful record keeping re-evaluate extreme floods review the safety of the whole spillway gate system gates, lifting gear, power supply, control system 13

Theme C1: Flood management in arid regions ICOLD Workshop - 20 May 2016 Spillway options for new dams Overspill - no risk of failure -ogee weir -labyrinth weir -fuse gates Float operated gates - very low risk Flap gates - power not needed to open gates - low risk -conventional -Obermeyer Radial gates - power needed for opening - high risk -range of lifting systems - some better than others 14

Theme C1: Flood management in arid regions ICOLD Workshop - 20 May 2016 Overspill 15

Theme C1: Flood management in arid regions ICOLD Workshop - 20 May 2016 Float operated gates No external power or controls required Extremely reliable Seldom used! 16

Theme C1: Flood management in arid regions ICOLD Workshop - 20 May 2016 TOPS pivoting gate 17

Theme C1: Flood management in arid regions ICOLD Workshop - 20 May 2016 Flap gates 18 Can be lowered in the absence of a power supply Superseded by the pivoting gate?

Theme C1: Flood management in arid regions ICOLD Workshop - 20 May 2016 Radial/Sector/Tainter gate An external power supply is needed to open the gate The hydraulic cylinder is long and expensive If a hose fails the gate cannot be opened 19

Theme C1: Flood management in arid regions ICOLD Workshop - 20 May 2016 Gates that need power to open A single event must not disable the gate It must have: Reliable redundant power supply If diesel generators are used healthy battery tank full of clean fuel effective cooling system Secure control system Open automatically if operators are absent Protection against hacking 20

Theme C1: Flood management in arid regions ICOLD Workshop - 20 May 2016 Diesel problems Starting relies on a battery Must have clean fuel Needs an effective cooling system Solution hydraulic starting air cooling fuel treatment 21

Theme C1: Flood management in arid regions ICOLD Workshop - 20 May 2016 Duplicated lifting system Each gate has two sets of rams that extend to open the gate The backup set does not need an outside supply or operator intervention 22

Theme C1: Flood management in arid regions ICOLD Workshop - 20 May 2016 Duplicate lifting gear 23

Theme C1: Flood management in arid regions ICOLD Workshop - 20 May 2016 Failure modes 24 X X X X X

Theme C1: Flood management in arid regions ICOLD Workshop - 20 May 2016 Existing dams Review the extreme flood Almost always, the design flood is revised upwards as more information becomes available In New Zealand, a 500 year flood turned into an 80 year flood! Contemplate installing an emergency spillway to pass floods beyond the spillway capacity to reduce the chance of gate failure overtopping the dam statistically, the biggest risk is a moderate flood and all gates failing 25

Theme C1: Flood management in arid regions ICOLD Workshop - 20 May 2016 Upgrading spillways on existing dams Reliability can be increased by: replacing existing gates with pivoting gates replacing mechanical lifting gear with hydraulic increasing the reliability of the power and control systems installing duplicate lifting rams and hydraulic power supply Storage capacity can be increased by: installing tipping blocks, fuse gates or labyrinth weirs installing pivoting gates installing radial gates Flood discharge capacity can be increased by adding an emergency spillway with tipping blocks or fuse gates 26

Theme C1: Flood management in arid regions ICOLD Workshop - 20 May 2016 Conclusion Dams and gated spillways must last a long time can never be safe enough In many cases, a substantial improvement in gate safety can be achieved by: increasing the reliability of the emergency diesels hydraulic starting/air cooling/fuel monitoring and treatment replacing obsolete gates and lifting systems by changing to: tipping blocks/tilting gates/radial gates replacing obsolete and unreliable mechanical lifting systems with hydraulic upgrading control systems to provide automatic opening for dangerously high water levels and to resist hacking 27