Towards a cyclone resilient settlement form for coastal areas of Bangladesh

Abstract

Bangladesh is vulnerable for tropical cyclone due to geographical position, wide and shallow continental shelf and the funneling shape of the coasts. With the advancement of cyclone warning systems, shelters and awareness in people regarding tropical storm reduced the number of loss of life, but the amount of property loss is having a sharp rise. In the last 170 years Bangladesh has faced 151 tropical storms and every time most of its rural coast line got washed away and then rebuilt again as a part of rehabilitation. According to NOAA, anthropogenic warning by the end of 21st century global warming will cause an increase in and then storm occurrencend of 21st century global warming will cause an iGhorkumarpur a small coastal village at Shamnagar Upazila has surprisingly survived the strong thrust of cyclonic wind not only during Sidr and Aila but also at previous storms with its thatched houses, whereas neighboring villages were washed away. This research focuses on physical and environmental characteristics of the village morphology as observed through survey and in-situ measurements. It is believed that the findings will provide direction in design of cyclone resilient coastal settlement form. Randomly selected sample survived settlement form from the village was modeled and simulated cyclonic wind turbulence using CFD techniques to study wind movement through settlement porosity. Also, 3D fractal dimension of a sample survived settlement zone form and ideal example indicated in literature review was calculated and compared to find out required ranges of porosity in a settlement form to survive against cyclonic wind. Results indicate that certain parameters like ratio between minimum street segment length and building height, ratio between minimum alleyways width and building height, placement of trees along the street and coastline, terrain elevation of settlement, alleyways length to alleyway the street and coastline, terrain elevation of settlement, all placement of courtyard, ratio of length and width of housing unit, elevation of plinth level, typology and placement of trees around a homestead and coastline, reduces vulnerability to cyclonic wind speed below danger level (20 m/s) around the homesteads. Adopting appropriate ratios for the above-mentioned parameters at existing coastal settlements or when designing new coastal settlement could potentially save properties of million dollars during cyclonic storm.

Key words: cyclone, settlement form, wind speed, defensive landscape, settlement porosity