The enormous energy carried by discharged water poses a serious threat to the Piano Key Weir (PKW) and its downstream hydraulic structures. However, previous research on energy dissipation in PKWs has mainly focused downstream effects, and the research methods have been largely limited to physical model experiments. To deeply investigate the discharge capacity and hydraulic characteristics of PKW, this study established a PKW model with universally applicable geometric parameters. By combining physical model experiments and numerical simulations, the flow pattern of the PKW, the discharge at the overflow edges, and the variation in the energy dissipation were revealed for different water heads. The results showed that the discharge of the side wall constitutes the majority of the total discharge at low water heads, resulting in a relatively high overall discharge efficiency. As the water head increases, the proportion of discharge from the inlet and outlet keys increases, while the proportion from the side wall decreases. This change results in less discharge from the side wall and a consequent reduction in the overall discharge efficiency. The PKW exhibits superior energy dissipation efficiency under low water heads. However, this efficiency exhibits an inverse relationship with an increasing water head. The overall energy dissipation efficiency can reach 40% to 70%. Additionally, the collision of the water flows inside the outlet chamber and the mixing of the overflow jet play a primary role in energy dissipation. The findings of this study have significant implications for hydraulic engineering construction and PKW operational safety.

Seasonal hydrological fluctuations can substantially reshape river–lake networks, but changes in water extent, network morphology, and structural connectivity may not occur synchronously. This study investigated wet–dry seasonal variations in the Poyang Lake Basin using Landsat imagery from eight representative years between 1990 and 2025. Surface water was extracted using a consistent NDWI threshold, and 30 m DEM-derived channel information was used to correct interrupted, duplicated, and spurious river centerlines before Horton–Strahler ordering and graph-theoretic analysis. Mean water area increased from 3407.14 km² in the dry season to 6872.87 km² in the wet season, while mean river-network density increased from 0.0348 to 0.0461 km/km². The maximum Strahler order increased from III in the dry season to IV in the wet season. River-network complexity increased from a dry-season mean of 12.85 to 58.38 in the wet season, and the river-network development coefficient increased from 3.28 to 13.59, indicating a substantially more developed tributary and hierarchical structure under wet-season conditions. In contrast, the mean α, β, and γ indices increased by only 9.8%, 4.6%, and 4.3%, respectively, and dry-season values exceeded wet-season values in some years. From 1990 to 2025, wet-season water area increased by 11.11%, whereas river-network length decreased by 2.77%. These results demonstrate that seasonal changes in water extent, river-network morphology, and structural connectivity are asynchronous, highlighting the need to distinguish these complementary dimensions when evaluating large river-connected lake systems.