Floods and society : Going beyond borders : Understanding the dynamics of the southwest coastal region (Satkhira-Khulna-Bagerhat) of Bangladesh as a coupled human-water system

Bangladesh is a large delta and most of the people live in the floodplains. Flooding is a normal phenomenon along the floodplains and it plays a vital role on the social processes of that area. To refuge from flooding people are undertaking flood control measures and changing land use pattern for a sustainable society. But in a long run, these human activities have an impact on hydrology and vise-versa.This interaction and associated feedback between the hydrology and human society is still poorly understood and largely unexplored, especially here in Bangladesh. This study presents the interaction between the human and water system in southwest coastal region of Bangladesh. The southwest coastal region is developed in the Ganges tidal floodplain and an enormous number of large and small tidal rivers are crisscrossed along this area. Social responses with the changes of hydrology and factors influencing these changes are intended to explore in this study.Data about the hydrology, water system and demography of the southwest coastal region were collected through respective government and non government institutions and different relevant reports. To understand about the social responses and their characteristics with the changes in water system and climate changes were obtained through interviewing 100 households mainly with the farmers and fishers randomly selected in Polder 33 of Dacope upazila under Khulna district. This information was further cross-checked through focus group discussions (FDGs) with different livelihood groups (farmer, fishers and women) in that polder.The rivers of the southwest coastal region are dominated by regular tidal phenomenon and these rivers are very much sensitive to any kind of interventions. The Gorai River is the only corridor for fresh water supply to this region which is also depends on the flow of the Ganges River. But fresh water supply to this region has been decreased drastically and it is almost nil in the dry season since 1975 after the construction of the Farakka barrage on the Ganges River by India. Due to the shortage of upstream fresh water supply the salinity of this area has been increased and it is accelerated by the sea level rise. The saline front is forwarding towards the upstream in every year.To restrict the tidal flooding, saline water intrusion and increase agricultural productions many polders were constructed in southwest coastal region in the 1960s and 1970s. These polders restrict the tidal water to spread over the adjacent floodplain areas which caused amplification of tides and decrease tidal prism considerably. As a result, along with salinity intrusion, rapid sedimentation is occurring on the river beds by flocculation process which enhances decrease of rivers depths in that area. And again tidal water levels variation is increasing which enhancing the chances of overtopping the tidal surges inside the polders. On the other hand, due to climate changes, in the recent decades extreme cyclonic events have been increased which are producing higher storm surges and causing flooding in the polders. These extreme events caused huge sufferings to the people of the southwest coastal region of Bangladesh by damaging human lives and destroyed many buildings, homesteads, agricultural products. The recovery from these losses is very much difficult for many people and for some cases it is impossible. Thus many people have been migrated to urban areas or other places to survive themselves. Here in this area, migration is dominating by the hydrological and biophysical processes rather than social, political and environmental reasons. It is evident that hydrological processes influencing the social processes of that area and again, human are undertaking safety measures which interns causing change in hydrological patterns. It becomes a never ending cycle between hydrology and social processes. Further studies on other areas of Bangladesh could further enhance the knowledge on interaction between hydrology and social processes