Generating a flood level probability map for Bangladesh

Abstract

Flooding in Bangladesh has considerable economic and sociological impacts. For this reason a map showing consistent and easily accessible flood level information would benefit the development of flood management programs which involve flood warning, flood zoning, flood proofing, and flood protection. Flood levels in Bangladesh are affected by many factors, which give rise to considerable joint probability problems when estimating extreme events. An approach which overcomes these difficulties is to generate contours of flood levels for particular exceedance probabilities using the time series of historical annual maximum water level data. This has been performed across Bangladesh and has resulted in the preparation of a flood level probability map. Water level data have been analyzed from 266 stations, and a total of 131 out of the 266 stations examined were found to be stationary and independent. The average length of the data samples was 29 years. Stations that had less than 15 years of data were not included in the analysis. Six different probability distributions were fitted against the annual maximum water level data at selected stations for comparison purposes. The results indicated that the Generalized ExtremeV alue distributionw as the best among the six distributionsA. s a result the Generalized Extreme Value distribution has been adopted to develop the flood level probability map. At most of the gauging sites the Generalized Extreme Value distribution indicated the presence of an upper bound in the extreme flood levels.