New insights on the surface hydrological connectivity of water depth thresholds in a flood-pulse-influenced floodplain system (Poyang Lake, China)

Knowledge of hydrological connectivity and its threshold behaviors plays an important role in sustaining and managing floodplains; however, threshold behaviors at a system scale have not received adequate attention. This study used a geostatistical connectivity method in combination with hydrodynamic modeling experiments to provide new insights on the surface hydrological connectivity of water depth thresholds in a flood-pulse-influenced floodplain system (Poyang Lake, China). The results reveal that hydrological connectivity is more sensitive to changes in water depth during dry, rising, and receding water phases than in the flooding phase under different depth thresholds. Geographically, the connectivity patterns show that large water bodies are mainly distributed in the main lake and floodplain river channels; extensive floodplain areas are dynamically connected to the main lake, indicating that the lake's floodplain is a sensitive area of the flood pulse system. From a systemic perspective, the surface water connectivity exhibits abrupt changes under the depth threshold of around 50 cm, demonstrating a rapid system response to the threshold value. In the floodplains of Poyang Lake, surface topography and flood pulse dynamics play a combined role in affecting hydrological connectivity, especially low and intermediate connectivity. The filling-spilling process generally extends from the lower-lying main lake and floodplain rivers to the upper-lying floodplains of the lake. The current work quantifies the influences of depth thresholds on surface hydrological connectivity to pave the way for performing a joint assessment of hydrological connectivity and ecological responses based on developing comprehensive modellings in threshold-affected floodplains. Graphic abstract