NAME =  Sombat CHUENCHOOKLIN  
ORGANIZATION =  Naresuan University  
ADDRESS =  Faculty of Engineering, Naresuan University, Phitsanulok 65000  
COUNTRY =  Thailand  
PHONE =  66-5526-1000 ext 4003-6, 4055  
FAX =  66-5526-1062  
E-MAIL =  sombatc@nu.ac.th  
POSTER_ONLY =  no  
THEME =  T5  
DATE =  31-Jul-04-12:58:12  
ABSID = T5SC31Jul04125812 
TITLE = RUNOFFS AND PHREATIC SURFACES BEHAVIOURS OVER LARGE FLOODPLAIN AND LOWLAND PADDY FIELD 
AUTHOR_1 = Sombat CHUENCHOOKLIN 
INSTITUTION_1 = Graduate School, Khon Kaen University,Khon Kaen, Thailand 
PRESENTER = AUTHOR_1 
AUTHOR_2 = Tsutomu ICHIKAWA 
INSTITUTION_2 = Prof. Dr., Department of Civil Engineering, Kyushu Tokai University, Kumamoto, Japan 
AUTHOR_3 = Sanguan PATAMATAMKUL 
INSTITUTION_3 = Assoc. Prof. Dr., Department of Civil Engineering, Khon Kaen University, Khon Kaen, Thailand 
ABSTRACT = ABSTRACT

Research of the exchange between surface and subsurface flows included some interactions over large floodplain and lowland paddy field within recharge zone has been studying. A case study in Phichit’s Floodplain within lowland paddy field and location in the Lower Yom River’s Basin, Phoprathabchang District, Phichit Province, Thailand was selected to this research since year 2001. Field measurements included infiltration capacities, percolation rates according to flood depths and phreatic surface changes have been observed within the same period. The trend analysis and some numerical techniques were applied for those relationships presented by curves fitting and generating the surface of both runoff and phreatic levels, respectively. The results show that the relationships between the change of water tables and heads or fluxes were fitted with R^2 approximately 0.90. Those comparisons either during the period of the rising limb hydrographs or the period of recession limb hydrographs especially during larger floods in 2002 and fewer floods in 2003 were presented. Moreover, subsurface flow was studied using the technique of hydrograph separation method by mean of baseflow hydrograph and compared to the change of phreatic levels. They yielded good result with R^2 equally of 0.70 to 0.90. However, the trend of baseflow hydrograph is going downward which might be due to the effect of over groundwater withdrawal for supplying paddy fields during drought period.

Keywords: Surface-subsurface flow interaction, Infiltration, Phreatic surfaces, Floodplain