Wind Analysis for Wave Prediction in Haor Areas

Abstract

The Study area covers the haor areas of Bangladesh which lies in the North eastern part of Bangladesh and includes the districts of Sylhet, Moulavibazar, Sunamganj, Habiganj, Netrokona, Kishoreganj and Brahmanbaria. There are four meteorological stations in the areas for wind observation. These are (i) Sylhet Meteorological Station, (ii) Srimangal, Moulavibazar Meteorological station, (iii) Mymensingh Metrological Station and (iv) Comilla Metrological Station. For this study the historical wind speed data from 1948 to 2008 of these meteorological stations have been collected from Bangladesh Meteorological Department (BMD) at Agargaon, Dhaka. Collected 3-hour duration wind speed data were scrutinized and computerized as an annual maximum value for statistical analysis. Monthly maximum wind speed data were also scrutinized as an annual maximum value for comparison with 3 hr. duration annual maximum values. Statistical analysis of the comprehensive wind data were made by (i) “Extreme Value Type-I”(EV-1/Gumbel) distribution method, (ii) Normal Distribution method, (iii) Log normal Distribution and (iii) Log Pearson Type –III distribution method for 25, 50 & 100 years return period. Confidence Limit (95%) of these methods for 100 years return period has been calculated. Probability plots and best fit curves drawn by normal distribution, log normal distribution and Extreme value type-I distribution methods at different locations have been considered for graphical calculation/presentation and comparison with analytical analysis. Results obtained from extreme value type-I distribution method in all locations approximately yield average value in comparison to other methods and wind speed value obtained from analytical and Graphical system by Extreme value type-1 distribution appear to be more or less similar. In this study it has also been found that probability plotting and best fit check by Extreme value type-I distribution method; the plotted data and theoretical line matched well. Therefore wind speed value obtained by Extreme value type-I(Gumbel) distribution method has been considered for final results and the haor areas are classified into 5 groups. An overland wind speed table and a zonal map have been prepared according to this classification. To make the wind transformation from overland to water surface zone five adjustment factors have been considered. The study revealed that 1-hour average wind speeds vary between 30.14 m/sec and 28.28 m/sec while the wind speed factor varied between 46.85 m/sec. and 43.31 m/sec for 100 years return period. This study also observed that in haor areas wind is strong during March to November. During this period wind blows from the South-East and East direction in Sylhet and Srimangal area. In Mymensingh and Comilla area wind blows from the South and South-East direction.