Importance of Land use management on the Flood Management in the Chi River Basin, Thailand Kittiwet...

Importance of Land use management on the Flood Importance of Land use management on the Flood Management in the Chi River Basin, ThailandManagement in the Chi River Basin, Thailand

Kittiwet KuntiyawichaiKittiwet Kuntiyawichai

Bart Schultz

Stefan Uhlenbrook

F.X. Suryadi

Ann van Griensven

44thth International Symposium on Flood Defence International Symposium on Flood Defence

6 – 8 May 2008, Toronto, Canada

• Problem definition

• Objectives of the study

• Model setup

• Introduction

ContentsContents

• Conclusions & Recommendations

• Discussions

• SWAT & 1D/2D SOBEK simulations

IntroductionIntroduction

• Area = 49,47749,477 km2

• Main system: Chi River, Chi River, 765 km river length

•Population = 6.9 million6.9 million people

• Sub-basins: 2020

• Land use: 60%60% (30,000 km2) = agricultural land• Precipitation: 1,2001,200 mm/year

• Potential evaporation: 1,2901,290 mm/year


ObjectivesObjectives

Problem definitionProblem definition

Model setupModel setup

DiscussionsDiscussions

RecommendationsRecommendations

ConclusionsConclusions

Chi River Basin

Model simulationsModel simulations


Selection as a test area based on the availability of input data

results will be applied & provide benefit to the whole Chi River Basin at later stage

Study area: Study area: Yang River BasinYang River Basin










• Area = 4,1454,145 km2

• Land use: 8383%% (3,440 km2) = Agricultural land (Paddy field)

• Major flood events: 19781978 entire Chi River Basin

19801980 in the Yang River Basin

• Sub-basins: 55

Yang River BasinYang River Basin









Problem definitionProblem definitionLarge flood in 2001 Large flood in 2001 Precipitation = 315315 mm/3 days

Stagnant & urban flooding

‘‘How will the ongoing changes in land use, water management & flood How will the ongoing changes in land use, water management & flood protection influence floods & flooding, and what would be the protection influence floods & flooding, and what would be the implications for flood management?’implications for flood management?’









Objectives of the studyObjectives of the study

‘To identify both structural & non-structural measures in order to reduce flood impacts to settlements in the Yang River Basin’

Under Under different scenariosdifferent scenarios:

Storage improvement

Land use management changes










• Hydrologic model (SWAT)Hydrologic model (SWAT) calculate a tributary inflow at all the selected points on the river system.

• Hydraulic model (1D/2D SOBEK)Hydraulic model (1D/2D SOBEK) simulate the flow of water through a river channel network & create flood inundation

extents for the specified return periods.










Relationship between SWATSWAT & 1D/2D SOBEK,1D/2D SOBEK, & the physical aspects









Calibration resultsCalibration results

Calibration period: 1/6/2001-31/10/20011/6/2001-31/10/2001

SWAT simulationsSWAT simulationsIntroductionIntroduction








Calibration accuracy:

SWAT simulationsSWAT simulations

Table:Table: Calculated areal rainfallareal rainfall & peak peak dischargesdischarges for various return periods (ignoring flooding).

SWATSWAT 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 SWATSWAT.









1D SOBEK calibration results1D SOBEK calibration results

• Calibration period 1/6/2001-31/10/20011/6/2001-31/10/2001

• Calibration parameter Manning’s roughnessManning’s roughness

1D/2D SOBEK simulations1D/2D SOBEK simulationsIntroductionIntroduction








1D/2D SOBEK simulations1D/2D SOBEK simulations

Natural flood storageNatural flood storageTarget: arbitrarily set to limit a 100-year100-year incident event to a 10-year10-year target peak flow.










The modelled flood extentsThe modelled flood extents










Possible natural flood storagePossible natural flood storage

Basis: considering the simulated simulated 100-year flood level100-year flood level in relation to the topographic condition at the locations where the floodwater needed to be released to reduce

flood risk downstream.

11

22

33

Starting risk location










Possible natural flood storagePossible natural flood storage

Peak discharge reduced with the magnitude close to the 10-year event.

Comparison between the simulated 100-year discharge with/without flood retention for the same section of the downstream river channel.









DiscussionsDiscussions• The methodology used to investigate the flood management measures

Numerical modelling of inundation processes at the floodplains.

• SWATSWAT calculate the tributary inflow to the Yang River.

• Calibration results SWAT 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 SOBEK1D/2D SOBEK predict flooding behaviour within a river system for different flood magnitudes.

• 1D/2D SOBEK1D/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 storages3 flood storages ++ flood diversion channelflood 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 100-year peak discharge was reduced only about 3.5% with the magnitude

close to the 10-year target peak flow.










• Coupling of SWAT & 1D/2D SOBEKSWAT & 1D/2D SOBEK is being developed to enable a better modelling of the actual physical behaviour & processes.

• Storage improvement Storage improvement options have been formulated as proposed flood management scheme. A step towards land use & management land use & management scenarios.

• 1D/2D SOBEK1D/2D SOBEK is found capable of simulating flood events with/without flood mitigation measures & delivering reliable results. Moreover:

It can provide the maximum inundation level, which is predominant for determining the damage at downstream risk location.

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.










Future study will consider:Future study will consider:

• Areas that could not be used for storage Built-up area, i.e. urban, towns, villages (to minimize damage).

• Buffer zone to protect the built-up area from flooding.

• Full operation of flood detention basins, with many levels of floodwater sub-diversions, based on different floodwater levels.

• Examine the economic impacts for land within the assumed flood extent for flood storage by:

Categorize the land use types with respect to elevation

Define the cost for each land use type

Estimate an inundated area (incl. damage) per land use type









Thank youThank youThank you for your attentionThank you for your attention

Importance of Land use management on the Flood Management in the Chi River Basin, Thailand Kittiwet...

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