A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Environment, Resources and Development

Thesis (M.Eng.) - Asian Institute of Technology, 1979

This study was an initial study conducted in Iloilo, Philippines during the 1978 wet season. The area describes a representative condition of a small watershed covered with trees and upland crops that supplies runoff, both surface and subsurface flow. It is further limited to a lowland rice grown under rainfed conditions, wherein the land receives water inputs directly from rainfall and runoff. For a scarce resource like water, there is a compelling need for effective allocation of whatever water that becomes available to the farm. This could be done by the water balance approach wherein all of the components of flow within a porous medium can be evaluated and integrated in detail. From this study the results are that: (a) in a topo sequence of paddies, paddy to paddy flow down the slope could be an additional source of water supply for the low lying areas; (b) elevation reduced significantly the yield of rice crop (IR 36 variety for that matter) and that the crop was more vulnerable to late stresses than the early ones; (c) elevation has a significant effect to the field water requirement of the crop (higher in elevated plots than on lower plots); (d) a moisture level stress index was developed to estimate the number of stress days that could effectively reduced crop yield. The stress days determined were fitted to a regression model together with other factors. For the farmer managed plots the same regression equation was used while for the cropping pattern plots, lower plots require higher stress index than the elevated plots to significantly lower the yield.