Development of an integrated river bank erosion management framework in tidal plain

Abstract

From times immemorial, near bank floodplains have been the preferred locations for human settlement, agricultural development, growth-centers and socio-economic development. It is because of their proximity to rivers, guaranteeing rich soils, abundant water supplies and means of water-way transport. Unfortunately, some of the river banks erode and cause considerable loss of lives, livelihoods, property, adverse impacts on the economy and people’s safety. Therefore, living in the erosion vulnerable near bank floodplains is a challenge. In Bangladesh, generally bank protection works are considered when the eroding channel seriously intrudes into areas where substantial economic development has taken place and hence significant damage might occur. Usually after severe bank erosion a project would be quickly planned, designed and implemented. The erosion problem and its solution seeming self-evident without giving any thought to the impact of such solutions that would have on upstream and downstream areas. Thus, present erosion protection practices have largely been focused on reducing erosion vulnerability through protecting the river bank only on structural solutions. However, any complete framework for river bank erosion management that could be practiced in Bangladesh is yet to be developed. Although a few frameworks exist that cover one or two aspects of river bank protection work, these have been practiced in a piecemeal way in Bangladesh. But the full benefits of the project by protecting the bank were never achieved. Sometimes the structural measures adopted in these projects have been damaged partly or fully. Consequently, recognizing the importance of non-structural and structural measures, this research has been taken up to develop an integrated river bank erosion management (IRBEM) framework, which addresses all relevant aspects of river bank erosion management. In this context, it is needed to be understood not only in the scientific and technological methodologies but also in institutional management and skills with community involvement covering techno-socio-economic aspects. The relevant aspects of IRBEM are technological management, social management, risk management, environmental management, economic management and institutional management. Detail approach and methodology for individual aspects have been developed to recommend an IRBEM framework by integrating parameters of techno-socio-economic processes. By developing six individual schematic frames for each aspect, an integrated framework has been developed based on a set of linked parameters to address the techno-socio-economic impacts on river bank erosion management using multi-criteria analysis and sensitivity analysis of parameters. The six individual schematic frames considering all functional outcome stages have been developed based on their functional relationship between outputs of the particular aspect and inputs of other aspects. In addition, all schematic frames establish an interactive approach for pre-erosion and post-erosion management operations with erosion emergency management operations by introducing the monitoring and evaluation techniques. An integrated framework has been developed by linking common parameters of the six individual frames through sensitivity analysis and multi-criteria analysis. The functional form of local erosion management association (LEMA) has been addressed for ensuring the participation of the affected people. The erosion emergency operations with respect to IRBEM aspects including its time horizon have also been developed. The final IRBEM framework establishes five outcome stages: erosion assessment, risk assessment, mitigation measure, design and implementation. At least two or more aspects have been integrated to achieve the indicator of each outcome stage. In this framework, a procedure has also been developed for selecting the adaptive adequate erosion mitigation measures for two separate management operations: (a) pre-erosion and post-erosion, and (b) erosion emergency, where emergency work has been integrated with monitoring and evaluation. An implementation procedure of IRBEM framework has been developed for selecting the suitable adaptive erosion mitigation measures. IRBEM plays a key role in selecting the suitable mitigation measures on the basis of risk-safety, trade-off decisions and conflict resolutions. This framework has been tested in the ChanderChar erosion vulnerable area along the Nabaganga River. It is found that suitable erosion mitigation plan can be selected considering all aspects of river bank erosion management. Moreover, the challenges in operationalizing the IRBEM framework have also been identified that can be overcome following the procedure developed in the schematic frame of individual aspects. This new IRBEM framework can be further applied in other tidal plain locations. This can also be modified for application in non-tidal plain locations.