<Notes>A Subdivision of the Chao Phraya Delta in Thailand Based on Hydrographical Conditions: Water Condition in Deltaic Lowland Rice Fields(I)

Abstract

Based on hydrographical conditions for rice cultivation, the lowland rice area in the deltaic region of the Chao Phraya river basin in Thailand was subdivided into five zones. The zones were comprised of (1) Main Area of the Old Delta, (2) Chains of Depressions, (3) Retarding Basin of the Delta, (4) Poldered Flat Delta, and (5) Knotty River Area of the Coastal Zone (Fig. 8). Hydrographical conditions were described for each zone. Hydrographical elements taken for the subdivision of the region were; method of rice cultivation, eg. transplanted or broadcast, as an indicator of general water condition in the fields (Fig. 1), date of transplanting as an indicator of the water conditions at the early stage of rice growing (Fig. 2), period of inundation (Fig. 3), depth of the maximum inundation (Fig. 4), date of the maximum inundation (Fig. 5), rate of increase of the water table (Fig. 6), and drainability (Fig. 7).