Abstract:
The wetlands of Bangladesh are precious gifts of nature. Wetland includes haors, baors, bills, jeels, lakes, depressed land etc. Among them haor is the most prominent and resourceful wetland which occupies North-Eastern part of Bangladesh known as Sylhet basin. There are a total of 373 no’s of haor in the Sylhet basin which covers almost 7 districts of Bangladesh. Sunamganj district consists of 95 haors and most of them are deeply flooded in the monsoon period in every year. According to Sunamganj district digital elevation model, the elevations of haors bathymetry are lower than the normal plain lands. Maximum people living in these haor areas are directly or indirectly beneficiary from these wetlands.
The inundation of wetland (haor) of Sunamganj district depends on the rainfall in the upstream catchment which lies within and outside of the country. Also the river discharge and water level within the district plays an important role in the inundation pattern. It has been found that the overall pattern of inundation in different times of the year and also in different years has not been documented in earlier studies.
Therefore, a study has been conducted to assess the spatio-temporal changes and water feature extraction of Sunamganj district for the period from 1973 to 2017 by using the multi-temporal Landsat 5-TM, 7-ETM+, 8-OLI/TIRS images. Hydrological analysis has also been carried out from the year 1983 to 2016 which has indicated the relationship of the inundated area with the parameters like water level, discharge and rainfall. There are different satellite-derived indexes including Normalized Difference Water Index (NDWI), Modified NDWI (MNDWI), Normalized Difference Moisture Index (NDMI), Water Ratio Index (WRI), and Automated Water Extraction Index (AWEI) for the extraction of surface water from Landsat data. Based on previous studies, the NDWI has been found to be superior than other indexes and therefore it was used to analyze the spatio-temporal changes of Sunamganj district’s wetland area.
From the study it is seen that because of low land, the left side of Sunamganj district has been flooded earlier than the right side. During the monsoon time around 62.54-77.42% of the district’s area become as haor area. Also in the dry season 1.2-5% area is under water. So there is a huge change in water area each year which effects the hydrological, morphological and anthropological conditions. The impact of hydrological changes based on the statistical significances has been provided an understanding about the inundation pattern of the study area.
