Presentation - International Flood Initiative

Presentation - International Flood Initiative

Importance of Land use management on the Flood
Management in the Chi River Basin, Thailand
Kittiwet Kuntiyawichai
Bart Schultz
Stefan Uhlenbrook
F.X. Suryadi
Ann van Griensven
4th International Symposium on Flood Defence
6 – 8 May 2008, Toronto, Canada
Contents
• Introduction
• Problem definition
• Objectives of the study
• Model setup
• SWAT & 1D/2D SOBEK simulations
• Discussions
• Conclusions & Recommendations
Introduction
Introduction
Problem definition
Objectives
Chi River Basin
Model setup
• Area = 49,477 km2
Model simulations
•Population = 6.9 million people
Discussions
Conclusions
• Main system: Chi River, 765 km river length
• Sub-basins: 20
• Land use: 60% (30,000 km2) = agricultural land
Recommendations
• Precipitation: 1,200 mm/year
• Potential evaporation: 1,290 mm/year
Introduction
Introduction
Problem definition
Study area: Yang River Basin
Objectives
Model setup
Model simulations
Discussions
Conclusions
Selection as a test area  based on the availability of input data
Recommendations
 results will be applied & provide benefit
to the whole Chi River Basin at later stage
Introduction
Introduction
Problem definition
Objectives
Model setup
Yang River Basin
Model simulations
Discussions
• Area = 4,145 km2
• Sub-basins: 5
Conclusions
Recommendations
• Land use: 83% (3,440 km2) = Agricultural land (Paddy field)
• Major flood events: 1978 entire Chi River Basin
1980 in the Yang River Basin
Introduction
Problem definition
Large flood in 2001  Precipitation = 315 mm/3 days
Problem definition
Objectives
Model setup
Model simulations
Discussions
Conclusions
Recommendations
Stagnant & urban flooding
‘How will the ongoing changes in land use, water management & flood
protection influence floods & flooding, and what would be the
implications for flood management?’
Introduction
Objectives of the study
Problem definition
Objectives
Model setup
Model simulations
Discussions
‘To identify both structural & non-structural measures
in order to reduce flood impacts to settlements in the
Yang River Basin’
Under different scenarios:
 Storage improvement
 Land use management changes
Conclusions
Recommendations
Introduction
Model setup
Problem definition
Objectives
Model setup
Model simulations
Discussions
Conclusions
Recommendations
• Hydrologic model (SWAT)  calculate a tributary inflow at all
the selected points on the river system.
• Hydraulic model (1D/2D SOBEK)  simulate the flow of
water through a river channel network & create flood inundation
extents for the specified return periods.
Introduction
Problem definition
Objectives
Model setup
Model simulations
Discussions
Conclusions
Recommendations
Model setup
Relationship between SWAT & 1D/2D SOBEK, & the physical aspects
Introduction
SWAT simulations
Problem definition
Calibration results
Objectives
Model setup
Model simulations
Discussions
Conclusions
 Calibration period: 1/6/2001-31/10/2001
 Calibration accuracy:
Recommendations
Introduction
SWAT simulations
Problem definition
Objectives
Model setup
Model simulations
Discussions
Conclusions
Recommendations
SWAT  calculate a tributary inflow on
the Yang River for different return periods.
Observed rainfall for each station
(4 stations)  converted into areal rainfall
(Thiessen method) & used as input to
SWAT.
Table: Calculated areal rainfall & peak
discharges for various return periods
(ignoring flooding).
Introduction
1D/2D SOBEK simulations
Problem definition
1D SOBEK calibration results
Objectives
Model setup
Model simulations
Discussions
Conclusions
Recommendations
• Calibration period
 1/6/2001-31/10/2001
• Calibration parameter  Manning’s roughness
Introduction
1D/2D SOBEK simulations
Problem definition
Natural flood storage
Objectives
Model setup
Model simulations
Discussions
Conclusions
Recommendations
Target: arbitrarily set to limit a 100-year incident event to a 10-year
target peak flow.
Introduction
1D/2D SOBEK simulations
Problem definition
The modelled flood extents
Objectives
Model setup
Model simulations
Discussions
Conclusions
Recommendations
Introduction
1D/2D SOBEK simulations
Problem definition
Possible natural flood storage
Objectives
1
Model setup
Model simulations
Discussions
Conclusions
Recommendations
Basis: considering the simulated
100-year flood level in relation to
the topographic condition at the
locations where the floodwater
needed to be released to reduce
flood risk downstream.
2
3
Starting risk
location
Introduction
1D/2D SOBEK simulations
Problem definition
Possible natural flood storage
Objectives
Comparison between the simulated 100-year discharge with/without
flood retention for the same section of the downstream river channel.
Model setup
Model simulations
Discussions
Conclusions
Peak discharge reduced with the magnitude close to the 10-year event.
Recommendations
Introduction
Problem definition
Objectives
Model setup
Model simulations
Discussions
Conclusions
Recommendations
Discussions
• The methodology used to investigate the flood management measures 
Numerical modelling of inundation processes at the floodplains.
• SWAT  calculate the tributary inflow to the Yang River.
• Calibration results  SWAT is able to simulate the discharge
reasonably. However, further calibration efforts for longer period & model
validation are required to obtain more accurate/reliable results.
• 1D/2D SOBEK  predict flooding behaviour within a river system for
different flood magnitudes.
• 1D/2D SOBEK simulation outputs  it seems viable to provide enough
flood storage to limit 100-year event to 10-year target peak flow by using
the natural floodplain.
• 3 flood storages +
flood diversion channel were identified by
considering the calculated 100-year flood level in relation to the
topographic condition upstream of the risk location  The simulated 100year peak discharge was reduced only about 3.5% with the magnitude
close to the 10-year target peak flow.
Introduction
Conclusions
Problem definition
Objectives
Model setup
• Coupling of SWAT & 1D/2D SOBEK is being developed to enable a
better modelling of the actual physical behaviour & processes.
• Storage improvement options have been formulated as proposed flood
management scheme. A step towards land use & management scenarios.
Model simulations
Discussions
• 1D/2D SOBEK is found capable of simulating flood events
with/without flood mitigation measures & delivering reliable results.
Moreover:
Conclusions
 It can provide the maximum inundation level, which is predominant
for determining the damage at downstream risk location.
Recommendations
 A sustainable method of flood risk management can also be
established at later stage, which will be a useful component additionally
to conventional flood defences in the Chi River Basin.
Introduction
Recommendations
Problem definition
Future study will consider:
Objectives
• Areas that could not be used for storage  Built-up area, i.e. urban,
towns, villages (to minimize damage).
Model setup
• Buffer zone to protect the built-up area from flooding.
Model simulations
• Full operation of flood detention basins, with many levels of
floodwater sub-diversions, based on different floodwater levels.
Discussions
Conclusions
• Examine the economic impacts for land within the assumed flood
extent for flood storage by:
 Categorize the land use types with respect to elevation
Recommendations
 Define the cost for each land use type
 Estimate an inundated area (incl. damage) per land use type
Thank you
Thank you for your attention