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

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

3. Introduction 49,477 Area = 49,477 km 2 Chi River, Main system: Chi River, 765 km river length 6.9 millionPopulation = 6.9 million people 20 Sub-basins: 20 60% Land use: 60% (30,000 km 2 ) = agricultural land 1,200 Precipitation: 1,200 mm/year 1,290 Potential evaporation: 1,290 mm/year Introduction Objectives Problem definition Model setup Discussions Recommendations Conclusions Chi River Basin Model simulations

4. Introduction  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: Yang River Basin Introduction Objectives Problem definition Model setup Discussions Recommendations Conclusions Model simulations

5. Introduction 4,145 Area = 4,145 km 2 83% Land use: 83% (3,440 km 2 ) = Agricultural land (Paddy field) 1978 Major flood events: 1978 entire Chi River Basin 1980 1980 in the Yang River Basin 5 Sub-basins: 5 Yang River Basin Introduction Objectives Problem definition Model setup Discussions Recommendations Conclusions Model simulations

6. Problem definition Large flood in 2001  315 Large flood in 2001  Precipitation = 315 mm/3 days 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 Problem definition Model setup Discussions Recommendations Conclusions Model simulations

7. Objectives of the study ‘To identify both structural & non-structural measures in order to reduce flood impacts to settlements in the Yang River Basin’ Under different scenarios Under different scenarios:   Storage improvement   Land use management changes Introduction Objectives Problem definition Model setup Discussions Recommendations Conclusions Model simulations

8. Model setup 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. Introduction Objectives Problem definition Model setup Discussions Recommendations Conclusions Model simulations

9. Model setup SWAT1D/2D SOBEK, Relationship between SWAT & 1D/2D SOBEK, & the physical aspects Introduction Objectives Problem definition Model setup Discussions Recommendations Conclusions Model simulations

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

11. SWAT simulations Table:areal rainfallpeak discharges Table: Calculated areal rainfall & peak discharges for various return periods (ignoring flooding). SWAT  SWAT  calculate a tributary inflow on the Yang River for different return periods.  SWAT Observed rainfall for each station (4 stations)  converted into areal rainfall (Thiessen method) & used as input to SWAT. Introduction Objectives Problem definition Model setup Discussions Recommendations Conclusions Model simulations

12. 1D SOBEK calibration results  1/6/2001-31/10/2001 Calibration period  1/6/2001-31/10/2001  Manning’s roughness Calibration parameter  Manning’s roughness 1D/2D SOBEK simulations Introduction Objectives Problem definition Model setup Discussions Recommendations Conclusions Model simulations

13. 1D/2D SOBEK simulations Natural flood storage 100-year10-year Target: arbitrarily set to limit a 100-year incident event to a 10-year target peak flow. Introduction Objectives Problem definition Model setup Discussions Recommendations Conclusions Model simulations

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

15. 1D/2D SOBEK simulations Possible natural flood storage simulated 100-year flood level 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. 1 2 3 Starting risk location Introduction Objectives Problem definition Model setup Discussions Recommendations Conclusions Model simulations

16. 1D/2D SOBEK simulations Possible 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. Introduction Objectives Problem definition Model setup Discussions Recommendations Conclusions Model simulations

17. Discussions  The methodology used to investigate the flood management measures  Numerical modelling of inundation processes at the floodplains. SWAT  SWAT  calculate the tributary inflow to the Yang River.  SWAT 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  1D/2D SOBEK  predict flooding behaviour within a river system for different flood magnitudes. 1D/2D SOBEK  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  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. Introduction Objectives Problem definition Model setup Discussions Recommendations Conclusions Model simulations

18. Conclusions SWAT & 1D/2D SOBEK Coupling of SWAT & 1D/2D SOBEK is being developed to enable a better modelling of the actual physical behaviour & processes. Storage improvement land use & management Storage improvement options have been formulated as proposed flood management scheme. A step towards land use & management scenarios. 1D/2D SOBEK 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. Introduction Objectives Problem definition Model setup Discussions Recommendations Conclusions Model simulations

19. Recommendations 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 Introduction Objectives Problem definition Model setup Discussions Recommendations Conclusions Model simulations

20. Thank you Thank you for your attention