Measuring dam induced alteration in water richness and eco-hydrological deficit in flood plain wetland

Along with wetland loss, the damming effect on hydrological modification in wetland is another less debated and challenging topic, which needs to have urgent attention. The present work intended to investigate the damming effect on the water richness and eco-hydrological condition of the floodplain wetland and its consequent ecological responses in Punarbhaba River Basin of India and Bangladesh. Satellite images derived hydro-period, water presence frequency (WPF), and water depth were generated for developing water richness model in pre (up to 1992) and post dam conditions (1993-2019). The range of variability (RVA) was modelled using time series satellite images based water index or normalized difference water index (NDWI). Based on RVA model, the hydrological failure rate was developed. Depth of water was used for preparing the flow duration curve (FDC) to estimate the eco-hydro-deficit and surplus condition in wetland at spatial scale for pre and post-dam periods. Satellite image based trophic state index models for pre and post dam conditions were constructed to investigate the ecological response of dam on floodplain wetlands. Results of water richness model showed that wetlands area under high wetland water richness zone decreased from 71.83% to 7.65% in the post-dam conditions. Results of hydrological failure rate showed that high failure rate captured 45% of total wetland area in the post-dam period. Results of eco-hydro-deficit exhibited that eco-hydro-deficit areas increased from 11.22% to 52.19% and 35.03%-52.67% respectively in post-dam conditions indicating growing ecological stress. The TSI models showed that most parts of the wetlands were converted from oligotrophic to meso-eutrophic state signifying the qualitative degradation of water and potential ecosystem health. The area under high TSI was observed in the wetland area having eco-hydro-deficit and high hydrological failure rate zones. These characteristics of wetland areas were found at the fringe of wetlands and fragmented smaller wetland units. The study concluded that damming over the Punarbhaba River adversely affected the water security of the floodplain wetlands in terms of modifying the hydrological richness, ecological condition of the wetland habitat, and ecological systems. The findings of the present study could provide a comprehensive research on the monitoring of surface water crisis in the wetlands, which will be the basic foundation to formulate water resource management plans for conservation, management and restoration of wetlands.