During severe summer droughts, the Danube River flow rate can drop drastically below normal historical averages (~2,000 m³/s to <900 m³/s). The Paks Nuclear Power Plant relies on gravity/pumps drawing surface cooling water from the river. When river stage falls below 84.20 meters Baltic elevation, intake pumps risk air entrainment, vortexing, and insufficient suction head for reactor condenser heat extraction.
To prevent mandatory reactor throttling or emergency power reduction during extreme low water stages, Hungarian water authority engineers implemented an emergency hydrodynamic technique: sinking two ballasted steel barges into designated cross-sections of the Danube downstream/adjacent to the intake canal.
The sunken barges function as a broad-crested submerged weir, creating a backwater profile ($\Delta h$) that locally raises upstream water levels right at the intake mouth without completely damming navigation or exceeding riverbed structural stress bounds.
Where C_s represents the submergence reduction factor based on tailwater ratio $H_2 / H_1$, b is the effective unblocked river width, and Δh is the engineered backwater level rise upstream.