HYDROLOGICAL FLOOD FREQUENCY ANALYSIS OF THE CHENAB RIVER BETWEEN QADIRABAD AND TRIMMU BARRAGES, PAKISTAN

Floods are considered among the most frequent and devastating natural disasters in Pakistan, particularly in the Indus Basin and its tributaries. Every year, especially during the late monsoon season, the Chenab River basin is prone to flood inundation, which has a devastating effect on human life and infrastructure. Pre-disaster estimation of flood magnitudes for various return periods is of vital importance to flood risk management and hydraulic infrastructure design for water sustainability. This study employed flood frequency analysis to estimate exceptional flood events by using yearly peak downstream discharge data gathered over 50 years (1975–2024) on two barrages of the Chenab River- Qadirabad and Trimmu. Five frequency distributions, including the Gumbel, Pearson Type 3, Log Pearson Type 3, Normal, and Log Normal, were fitted to the historical annual maximum discharge series for each site to estimate the corresponding flood magnitudes to return periods of 2, 5, 10, 25, 50, 75, 100, and 200 years. The Chi-square (χ²) test was used to assess the goodness-of-fit; 95% confidence intervals were computed to quantify estimation uncertainty. Modelled results showed that the magnitude consistently increases with the return period, with model differences being greater for more extreme events (≥50 years). In almost all cases, a Log Pearson Type III distribution provided the best balanced and reliable statistics of fit for all sites (lowest χ² values) that produced the highest discharge estimates for very rare floods. Confidence intervals widen significantly for longer return periods, a range of potential flood magnitudes expands, indicating an increase in uncertainty and anticipating less frequent occurrences. These results present the main importance of selecting an appropriate distribution pre-disaster assessment. The findings are helpful in floodplain management, flood control, climate-resilient infrastructure planning, and disaster preparedness across the Chenab River basin.