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

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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. 4 th International Symposium on Flood Defence 6 – 8 May 2008, Toronto, Canada. Contents. Introduction.

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

Kittiwet Kuntiyawichai

Bart Schultz

Stefan Uhlenbrook

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

Chi River Basin

Introduction

Introduction

Problem definition

Objectives

Model setup

• Area = 49,477 km2

Model simulations

• Population = 6.9 million people

Discussions

• Main system: Chi River, 765 km river length
• Sub-basins: 20

Conclusions

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

Recommendations

• 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

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

Recommendations

Yang River Basin

Introduction

Introduction

Problem definition

Objectives

Model setup

Model simulations

• Area = 4,145km2

Discussions

• Sub-basins: 5

Conclusions

• Land use: 83%(3,440 km2) = Agricultural land (Paddy field)
• Major flood events: 1978entire Chi River Basin
• 1980in the Yang River Basin

Recommendations

Stagnant & urban flooding

Problem definition

Introduction

Large flood in 2001 Precipitation = 315 mm/3 days

Problem definition

Objectives

Model setup

Model simulations

Discussions

Conclusions

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

Recommendations

Introduction

Objectives of the study

Problem definition

Objectives

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

Model setup

Model simulations

Under different scenarios:

Storage improvement

 Land use management changes

Discussions

Conclusions

Recommendations

Introduction

Model setup

Problem definition

Objectives

Model setup

Model simulations

Discussions

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

Conclusions

• Hydraulic model (1D/2D SOBEK)simulate the flow of water through a river channel network & create flood inundation extents for the specified return periods.

Recommendations

Model setup

Introduction

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

Problem definition

Objectives

Model setup

Model simulations

Discussions

Conclusions

Recommendations

Introduction

SWAT simulations

Problem definition

Calibration results

Objectives

Model setup

Model simulations

Discussions

Conclusions

Calibrationperiod: 1/6/2001-31/10/2001

Calibration accuracy:

Recommendations

Introduction

SWAT simulations

Problem definition

SWATcalculate a tributary inflow on the Yang River for different return periods.

Objectives

Observed rainfall for each station (4 stations)  converted into areal rainfall (Thiessen method) & used as input to SWAT.

Model setup

Model simulations

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

Discussions

Conclusions

Recommendations

Introduction

1D/2D SOBEK simulations

Problem definition

1D SOBEK calibration results

Objectives

Model setup

Model simulations

Discussions

Conclusions

• Calibrationperiod 1/6/2001-31/10/2001
• Calibration parameter Manning’s roughness

Recommendations

Introduction

1D/2D SOBEK simulations

Problem definition

Natural flood storage

Target: arbitrarily set to limit a 100-year incident event to a 10-year target peak flow.

Objectives

Model setup

Model simulations

Discussions

Conclusions

Recommendations

Introduction

1D/2D SOBEK simulations

Problem definition

The modelled flood extents

Objectives

Model setup

Model simulations

Discussions

Conclusions

Recommendations

1

2

3

Starting risk location

1D/2D SOBEK simulations

Introduction

Problem definition

Possible natural flood storage

Objectives

Model setup

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.

Model simulations

Discussions

Conclusions

Recommendations

Introduction

1D/2D SOBEK simulations

Problem definition

Possible natural flood storage

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

Objectives

Model setup

Model simulations

Discussions

Conclusions

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

Recommendations

Discussions

Introduction

• 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 100-year peak discharge was reduced only about 3.5% with the magnitude close to the 10-year target peak flow.

Problem definition

Objectives

Model setup

Model simulations

Discussions

Conclusions

Recommendations

Introduction

Conclusions

Problem definition

• 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.
• 1D/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.

Objectives

Model setup

Model simulations

Discussions

Conclusions

Recommendations

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).
• 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

Model setup

Model simulations

Discussions

Conclusions

Recommendations

Thank you