Quantification of eroded and deposited riverbanks and monitoring river's channel using RS and GIS

摘要

The Padma and the Jamuna are the two of three major rivers those flow within few meters of height in Bangladesh. These rivers are very important in context of water navigation, irrigation, fishing and fresh water for down stream. On the other side, those are the rivers of erosion of riverbanks and deposition of sandbanks. The main objective of this study is to estimate the eroded and deposited banks of the Padma and the Jamuna and to visualize movement of their channels from 1977 to 2000. Three dates of Landsat images were acquired in 1977 (MSS), 1989 (TM) and 2000 (ETM+) over the study area. Processing of Landsat images was performed by PCI Geomatics and ArcGIS 9.2 was used for quantification of eroded and deposited land covers. Subset the data was performed as preprocessing of image. Seven types of land covers of level I were decided for imagery classification where settlement areas were separated using mask. Supervised classification method was applied using 200 pixels for each class as test set other than training area for accuracy assessment where average accuracies of 85.64%, 89.14% and 90.07% were achieved in 1977 (MSS), 1989 (TM) and 2000 (ETM+) respectively. ArcGIS 9.2 was used to transfer the classified images to GIS layer for quantification. Eroded and deposited areas of the Padma and the Jamuna between the years were calculated by superimposition and pair-wise comparison of river layers in 1977–89 and 1989–2000. From 1977 to 1989 and 1989 to 2000, estimated average erosion was 5436 and 2954 hectares/year and deposition was 773 and 1954 hectares/year correspondingly. In 1977, 1989 and 2000, estimated rivers area in the study area were 2789, 3348, 3458 sq km. During this period, there was more erosion than deposition which indicates that rivers were getting wider. The confluence point of the Padma and the Jamuna was migrated toward southeast and their channels were moved by erosion and deposition following their direction. General trend of - channel movement of the Padma was toward south but for the Jamuna, it was quite irregular.