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

1. 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

2. Contents • Introduction • Problem definition • Objectives of the study • Model setup • SWAT & 1D/2D SOBEK simulations • Discussions • Conclusions & Recommendations

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. Model setup Introduction Relationship between SWAT & 1D/2D SOBEK, & the physical aspects Problem definition Objectives Model setup Model simulations Discussions Conclusions Recommendations

10. Introduction SWAT simulations Problem definition Calibration results Objectives Model setup Model simulations Discussions Conclusions Calibrationperiod: 1/6/2001-31/10/2001 Calibration accuracy: Recommendations

11. 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

12. 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

13. 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

14. Introduction 1D/2D SOBEK simulations Problem definition The modelled flood extents Objectives Model setup Model simulations Discussions Conclusions Recommendations

15. 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

16. 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

17. 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

18. 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

19. 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

20. Thank you Thank you for your attention