ABSTRACT
Bangladesh is vulnerable for tropical cyclone due to geographical position, wide and shallow continental shelf and the funnelling shape of the coasts. With the advancement of cyclone warning systems, shelters, and awareness in people regarding tropical storm reduced loss of life, but the amount of property has risen quite significantly. But recorded evidence shows that Ghorkumarpur, a small coastal village at Shamnagar Upazila has surprisingly survived the strong thrust of cyclonic wind not only during Sidr, Aila and Amphan but also at previous storms with its thatched houses, whereas neighbouring villages were washed away. The dynamics of cyclonic wind gust and obstacle aerodynamics at roughness layer has a correlation with wind pressure within settlement form. The gust of wind speed, threshold of comfort, discomfort and danger at settlement level depends on settlement porosity factor at interfacial layer. Settlement form and features plays a vital role to decrease or increase frictional force within boundary layer which determines destruction or minimization of the damage and discomfort caused by cyclonic wind. Observation from filed survey and in-situ measurements at Ghorkumarpur village indicates several physical parameters of the village land use morphology has helped the survived settlement to act like a bluff body during cyclonic storm and minimized the damage from cyclonic wind by increasing frictional force within the settlement boundary layer. Literature review supports different settlement morphology parameters at interfacial has a possibility to form defensive landscape against extreme wind events. Existing ranges of these parameters has been measured during field survey at Ghorkumarpur, village. For a better understanding of cyclonic wind movement through settlement porosity, selected sample among survived settlements form of the village is modelled and simulated within cyclonic wind turbulence using CFD techniques. Findings from CFD simulation shows that wind speed around the survived homesteads, during category 5 cyclone remains below danger level (20 m/s). Results indicates a defensive landscape morphology has been created at Ghorkumarpur village which has an impact in reduction of vulnerability due to cyclonic wind. The present case study aims to investigate the parametric ranges behind forming defensive landscape morphology against cyclonic wind at rural settlement level.
