PROBABILITY MODELING OF LOW FLOWS AT DIFFERENT SITES OF INDUS BASIN IN PAKISTAN USING L-MOMENTS AND TL-MOMENTS

Abstract

At-site Frequency Analysis (ASFA) of low flow was carried out for nine sites of
Indus basin in Pakistan. In the present study, 10-day annual low flow series were analyzed by robust
estimation methods such as Method of L-moment (ML) and TL-moment (MTL) to identify best fit
probability distributions for each site. Best distribution for each site was identified using different
goodness-of-fit Tests (GFT). No single probability distribution was declared as the best-fit distribution
for all sites included in the plan. The GFT results indicated GPA was the most appropriate distribution
for most of the sites followed by GLO and GEV distributions. On comparison, it was found that for
most of the sites ML was best estimation method and for others MTL. For ASFA, the quantiles of best
fit distribution were also estimated. It was found that estimated low flows based on fitted distribution
were in close agreement with observed flows.