A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering

Thesis (M.Eng.) - Asian Institute of Technology, 1989

This study was an attempt to estimate from insufficient hydrometric information the low flow characteristics of a river and apply in the estimation of irrigation potential during dry season. The Tank Mode l was used to generate long term streamflow data from which the average low flow discharges for n-consecutive days were extracted. To describe graphically the recurrence intervals between events less than the specified magnitude and durations, frequency curves using the Weibull. probability distribution function was fitted to the extracted data samples. In its application an estimate of the seasonal irrigation water need is a requisite. Fairly simple and project specific criteria were developed and applied in the intercomparison and selection of the appropriate index or indices. The Libungan River basin in the Philippines was used as the case study. The results indicated the applicability of low flow indices in the planning and operation, particularly in the determination of command area during dry season for run-of-the-river type irrigation projects where water is the limiting factor. In terms of hectarage, it gave estimates lower than those derived from the conventional methods. Judging from the method developed, the estimate obtained was considered more reliable for it was based on an improved level of understanding of the extreme-low characteristics of the river.