330 - The Adaptive Approach for Riverbank Erosion Management in Bangladesh

Bangladesh is home to some of the world’s largest, most dynamic rivers. Due to a combination of highly erodible riverbanks and extensive floods, riverbank erosion is ubiquitous within the country. The high morphological variability limits predictions of location and magnitude of riverbank erosion to only one year in advance. Due to this environment of extreme uncertainty, an adaptive approach is mandatory for long-term successful riverbank erosion management. The adaptive approach has been developed in Bangladesh in conjunction with the rise of geobag revetments since 2006. It minimizes risks by ensuring flexible responses to the recurring, unpredictable river processes and de-connecting new construction and maintenance. There are eight chief elements to the adaptive approach: (i) predicting the river behavior to facilitate the planning process; (ii) allocating funds for flexibly multi-year financing of works along river reaches, 50 to 100 km in length; (iii) accounting for site specific geotechnical conditions, including the placement of riverbank protection on more recently deposited sediments; (iv) constructing works as per actual eroding length and riverbed levels; (v) preparing as-built drawing for asset management systems; (vi) systematic monitoring and evaluation of works at least over the first ten years after construction; (vii) strengthening works as required by extending the works to greater depth to address newly scoured slopes, eventually reaching the design scour level; and (viii) maintaining the works for long-term sustainability during the envisaged service life. The adaptive approach is a pragmatic way to build riverbank protection in unpredictable sand bed rivers to the design scour level while minimizing the total initial investment cost.