Flood Control Challenges for Large Hydroelectric Reservoirs
1. FLOOD CONTROL CHALLENGES FOR LARGE
EXAMPLE FROM NAM THEUN-NAM KADING BASIN IN LAO PDR
Peter R.B. Ward, Timo A. Räsänen, Peter-John Meynell, Tarek Ketelsen, Khamfeuane Sioudom
and Jeremy Carew-Reid
CHALLENGE PROGRAM ON WATER & FOOD IN THE MEKONG: Optimizing the management of hydropower cascades at the catchment level (MK3)
2. Flood Control for Large Reservoirs:
Design and Operation
• Climate and Expected Large Flood Events
• Storage for Flood Pulse Modulation
• Spillway Flow Capacity and Operation
• Mechanical Reliability and Servicing
8. Ubol Ratana Dam, Thailand
• 1966 Dam commissioned, primarily for storage for agriculture
• 1978 Disaster narrowly averted when a flood overtopped the core of the
dam by 24 cm. Average daily peak inflow more than triple the designed
maximum spillway capacity.
• Original design flood estimate was insufficient.
• EGAT began formal dam safety practices, such as comprehensive dam
safety reviews, emergency preparedness
• 1986-7 Dam was raised by 3.1 m, and spillway capacity was increased by
40%. Additional work cost $15 million, an outlay of 70% on top of the
9. Nam Theun River Basin: overview
• Difficult climate: periodic extremely heavy rain events associated
with tropical cyclone weather: typhoons and tropical storms. Global
climate change promises more extreme future weather.
• Short number of years for hydrological data set for the basin: design
• Three projects in operation, and others proposed
• Dams are not owned by one entity, communications question
• Nam Theun 2 flow scheduling and reservoir operation is done from
12. Table 1. Main characteristics of Theun-Hinboun, Nam Theun 2 and Nam Gnouang
hydropower projects. Data from Then-Hinboun are before the (2012) expansion project
Theun-Hinboun Nam Theun 2* Nam Gnouan
Dam height [m] 27 39 67
Active storage [mcm] 15 3530 2260
Flood buffer [mcm] 1410 470
Reservoir drawdown [m] 5 12.5 35
Surface area at FSL [km2] 6.3 450 107
Average discharge [m3/s] 220 (460 before NT2) 240 95
Catchment area [km2] 8937 4013 2942
Installed capacity [MW] 210 to be enlarged 1090 60
Head [m] 230 348 47
Turbine discharge [m3/s] 110 330 144
Annual production [GWh] 1356 (1645 after NG) 5936 294
Spillway type 2 radial gates 5 radial gates (1374 5 radial gates
3 3 3
(1160m /s/gate); 1 flap m /s/gate ); 2 flap gates (3144 m /s/gate)
gate (50m /s); 4 sand (192m /s/gate)
Spillway capacity [m3/s] 12500 6870 15700
* Data are for Nakai Dam on Nam Theun River. Reservoir is also contained by an (earth)
saddle dam, on the south side.
16. Nam Theun: Water balance
• We used simple model for NT2 reservoir, with computed
inflows based on flow data before and during the 2002
extreme flood event, to check on reservoir water surface
heights. Peak inflow on 22nd Sept was 12,000 m3/s.
• We wanted to see what would happen during a “Normal”
procedure, and a “Too little too late” procedure for
operating the spillway gates.
• We assumed that at the start of the extreme runoff event
the reservoir was full to the FSL, and that there was still
available the (large) flood buffer storage above this level.
18. Nam Theun:
simulated reservoir storage
NT2 reservoir water surface during typhoon induced major runoff event
All gates at Nakai dam working, and timely response
19. Nam Theun:
simulated reservoir storage
Too-little-too-late operation. One spillway gate not functioning, and delayed
maximum opening of other gates. Dangerously high water level in reservoir.
20. Nam Theun: conclusions
• We concluded that a great deal of care and a very
tight requirement for timely response is needed
at NT2 dam, even for management of a flood
event (10 year event?) that is not extreme.
• Not clear how future exceptional flood events will
be managed successfully.
• Need for a variety of
21. Nam Theun: Recommendations
1. Adherence to a well conceived rule curve for reservoir surface
levels in the flood season, with periodic updating of the rule curve
to reflect improved knowledge of the basin, and long term shifts
from climate change
2. Ready access to long term and short term weather predictions,
particularly for heavy rain expected from typhoon events.
3. Responsiveness to daily and hourly developments during major
4. Periodic comprehensive dam safety reviews, by an independent
team that should include engineering experts, with backgrounds
in hydrology, geotechnology, mechanical engineering and
22. Nam Theun: Recommendations
Suggestions are made for
• the establishment of a strengthened capacity for the
NT-NK River Basin Committee Secretariat
• emergency communications capability between
stakeholders, e.g. dam operators and downstream
• periodic, long-term requirements for engineering
assessment concerning safe operations at the dams.
23. • Ongoing research work on climate periodicities in
the Mekong region is encouraging, as it promises
to offer ways of achieving advance notice of the
likelihood of an extreme weather season.
• Links between the WNPM, ENSO and PDO events
is being established, and this understanding will
provide extremely helpful with advanced warning
24. Flood Control for Large Reservoirs: Design and Operation
Thank you for your attention
Thank you for your attention
26. Columbia River Treaty
• 11 years of discussions post 1948.
• Ratified in 1964 for 60 year period. 10 year prior notification before
• Basic idea was to construct and operate four projects (3 in Canada)
that would achieve hydropower generation and flood control.
• Several downstream projects in the US benefit from the upstream
Treaty projects with the ongoing benefit of generating more HP
• Treaty covers Canadian entitlement “one half of the estimated
increase in US downstream power benefits”
27. Srinagarind Dam, Thailand
• Periodic extremely heavy rain events, determined by monsoon
conditions, and weather associated with tropical cyclone activity
• Short data set available when design was undertaken (early 1970s).
• Design flood selected, and spillway size with operating procedures
determined. Construction was delayed, and dam finally completed
• 18 years later, review of hydrological conditions, spillway capacity
shown to be less than desirable.
• Decision made to operate the reservoir with a different set of RULE
CURVES, for dam safety reasons.