Hydrological Analysis and Statistical Modelling of Swat River Basin for Flood Risk Assessment

The climatic variations and anthropogenic activities in the river catchments worldwide are causing severe weather events and flooding. The narrowing down of natural floodplains/ channels, land-use changes, deforestation and mushroom urbanisation with unplanned infrastructure development are aggravating causes of severe storms and floods, especially in developing countries. Hydrological studies, flood modelling and statistical flood frequency analysis are considered imperative to assess the hazards/ risks of flooding and their mitigation measures. Estimating predicted storms/ floods for different return periods can give a reasonable idea about the frequency of storm events. This study analysed the Swat river basin to determine the predicted return periods with expected storm/ flood in its catchment and Swat river. The weather and rainfall in the Swat river basin remain unpredictable. Historically, it has seen peak precipitation of 150mm – 274mm and a super flood of 10050 m3/sec in 2010, more than its 200 years return period. Flood frequency and statistical analysis using Log Pearson 3 (LP3), Generalized Extreme Value (GEV) and Gumbel Maximum (Gumb-Max) on Easy Fit software and Log Pearson 3 equations have predicted weather instability in the Swat basin with the prediction of super flood like 2010 happening in 40 years return period. Construction of Swat expressway on elevated embankment will disturb the natural drainage pattern and likely result in inundation in flood plains due to inadequate capacity of cross drainage structures to withstand the spontaneous flash flooding. However, these have been designed on 100 years return period. However, probability density and hazard functions show a lesser probability of any mega hazard; therefore, cross drainage structures and crisscrossing channels in the river catchments may be planned on a minimum 100 years return period as an economic/ reasonable safe limit. Still, additional structural/ non-structural measures should augment these for efficient flood-fighting like plantation and maintenance of drainage structures, construction of small dams/ reservoirs for swift water management in case of a flash flood and placement of rescue/ relief resources at accessible points as per flood zoning.