Presentation on theme: "By Mr. Sombat Chuenchooklin Application of geographic information systems for flood extent determination in floodplain : a case study in the Yom River."— Presentation transcript:
By Mr. Sombat Chuenchooklin Application of geographic information systems for flood extent determination in floodplain : a case study in the Yom River Basin in Phichit Province Working group: CGIST at Lower- Northern Regional Office, Phitsanulok E-mail: firstname.lastname@example.org Department of Civil Engineering, Faculty of Engineering, Naresuan University, Phitsanulok 65000 Thailand
Introduction Determination of flood extent in floodplain is difficult due to flat topography and there are many obstructs. By using hydrologic & hydraulic principles incorporated to physical characteristics, flood can be estimated. Those basins characteristics can be found as existing database presented by GIS. Those data included some attributed data which has been digitized from aerial map i.e. roads, streams, water sources, wetlands, contour-lines, land-uses, soil series, rainfall-gauges, and local administration boundary as well as location of villages.
Objectives of the study To use of some existing data and data generation using GIS techniques to generate some basically parameters in the Hydrological Model based on limit data. To compute flood volume and inundated extent in the floodplain area in ungauged basin for a given period using appropriate techniques in hydrologic & hydraulic models.
Steps to estimate flood extensive in river floodplain Input data Process Output -GIS, topographic map & basically data -Basin characteristics, streams, slope -Soil & vegetative cover, land-use -Cross-sectional profile of floodplain & main streams -Rainfall data from rain gauges in basin -Meteorological data, max-min temperature, etc. -Draw sub-basin characteristics & contours -Generate rainfall isohyets, ET using ArcView GIS -Compute surface runoff, traveling time from each sub- basin to floodplain using appropriate hydrology techniques i.e. synthetic unit hydrograph using Gamma function -Calculate over-bank flow from river to floodplain using river hydraulic analysis model (HEC, 2001) -Estimate inundated volume & extent boundary Flood volume & extensive map Materials & Methods
Kaengsuaten dam site Maeyom weir Maesong Maethang Thaphae Existing Project Road Strea m Irrigable area SUKHOTHAI PRAE PHITSANULOK PHICHIT KAMPAENG PHET NAKHONSAWAN Nan Wang Ping Chaophya Central Plain Rices Bowl Yom Pasak Sakaekrang Enlarger of the Yom Basin Study area & Chaophya R. Basin Thajean Maeklong Bangprakong Study area
Existing database in the Yom R. & its catchments –Area of 1,705 sq.km. in Kampaengphet & Phichit. –Flat sloping land lay from west to east & north to south ranging from 0.0001 to 0.0005. –There are 7 sub-basins divided with average size of 41.18 sq.km, average stream length of 7.893 km. –Most side-flow runoff comes from the west via Kampaengphet to the Yom R. in in Samngam, Phopratabchang, Buengnarang & Phothale in Phichit. –Floodplain of the Yom with normally 1-3 m. deep by flood in September-October. –Most of vegetative cover over the basin is rice. –Sugarcane is popular growing in upland area.
Flooded photograph interpreted from satellite was used for contour-lines construction (adapted from JICA, 1999) Study area Contours construction based on flood recorded
3-D landslope, streams & floodplain of the Yom using GIS Hydrological studying
7 Sub-basins as runoff studying, using ArcView GIS Hydrological studying
A B E C D Crop nameJanFebMarAprMayJunJulAugSepOctNovDec A. HYV rice in lowland floodplain B. HYV-rice in middle zone C. Plants in upland zone1 D. Plants in upland zone2 E. Plants in upland zone3 1 1 2 Flood 1 2 3 1 Vegetables Mungbean corn sugarcane Cropping pattern in Phopratabchang as water utilization in the water budget model Flooded zone HYV-rice Hydrological studying
Side-flows 1-hr synthesized unit hydrograph using Nash- model & Gamma function Basin characteristics based on US. Army Crop of Engineers method applied with Nash U.H. whereas tp is time to peak discharge, S is channel slope, L and Lc are stream length measure at the longest point and from the centroid of basin, and Ct, Cp, a1, a2 are coefficients getting from linear regression, (Linsley et al., 1988; Jira, 2003). a), b) Runoff hydrograph synthesized Hydrological studying
Daily rainfall from various rain-gauges in the basin. Daily river flow from RIDs gagging stations at upstream & downstream of the study area in the Yom R. in 2001 Hydrological studying
Spatially annual rainfall in study area in 2001 using ArcView GIS Hydrological studying
Result of floodplain charac Elevation-Volume-Area Hydrologic & Hydraulics studying Result: local streamflow hydrographs
Total mean annual rainfall in 2001 = 1,146.3 mm Rainy days = 99, mean daily rainfall = 11.4 mm Max. temp.=32.6, min. temp.=23.6, Humidity=75.5%, Sunshine duration=6.9 hr/d, Evap.=4.28 mm/d Runoff coefficient in rational formula = 0.337 Total Side-flows volume=742.35 MCM or 14.9% of annual flow at Y17 (Samngam) =4,984 MCM Return period of max. flood depth in the river measured at Y17 and analysis based on Gumbel distribution: in year 1995 the return period (Tr) =38yr and max. water level at +38.14 m(MSL), while in 2001 the Tr=5 yr +37.57m, and in 2002 with Tr=50yr (+38.24m) Flooded area of 234.231 sq.km occurred in year 2001. Hydrologic & Hydraulics studying
Simulated result of flood extent on 26 September using HEC-RAS (HEC-2001) Distribution of flood flow along the Yom R. Hydraulics studying
Flood photograph from RADARSAT was used to verify flood extent & flood flow direction on 20 September (GISTDA, 2002)
Flood flow pattern of the Yom R. in Phopratabchang Hydraulics studying
Conclusion & Recommendation Daily flood storage and inundated area in the study site can be estimated corresponding local inflows, overflow from bankfull of river, existing database from generated contours & basin characteristics using GIS techniques and hydrologic models. Most of flood came by overtopping from river bank due to sub- catchments are smaller size than overall river basin area. Flood risk map can be processed corresponding GIS, hydrological statistics, and hydrodynamic model, which can be developed and extend to local administration offices and farmer in order to change or shift cropping pattern in floodplain and avoiding flood. Infiltration & percolation as losses from surface runoff & flood downward to underground can be considered as flood reduction by temporarily storing into groundwater zone. Many sandpits in the basin can be used to reduce flood by infiltration processed which needs to further research. Thank! to whom supported useful resources i.e. RID, TMD, ESRI, GISTDA, HEC, and ones in ref. (…..).