Hydropower is a mature and cost-competitive renewable energy source and plays a central role in the European electricity system by providing flexibility, reserves, and grid stability. However, expanding hydropower generation capacity and operational capabilities is increasingly constrained by environmental regulations, competing water uses, and limited opportunities for new infrastructure development. This study explores the feasibility of deploying hydrokinetic turbines within tailrace channels downstream of hydropower dams as an infrastructure-efficient opportunity to incrementally expand energy production at existing facilities or enable generation at Non-Powered Dams (NPDs), while leveraging regulated flow releases and existing assets. Hydrokinetic turbines harness the kinetic energy of water currents, using the same physical mechanism as wind turbines, and can complement conventional hydropower without requiring additional storage or major civil works.Tailrace channels offer favourable conditions for hydrokinetic applications due to their fast-moving currents, predictable operating regimes, proximity to grid interconnections, and limited incremental environmental footprint. However, energy extraction introduces additional flow resistance that may induce a backwater effect in subcritical flows, potentially reducing the available hydraulic head at the upstream powerhouse and offsetting net energy gains. To quantify this tradeoff, we propose a simple one-dimensional momentum balance approach to estimate the induced water-level increase as a function of tailrace hydraulics, turbine operating conditions, and channel blockage. The model is non-dimensional and geometry-agnostic, enabling rapid screening across a wide range of sites, and is validated against laboratory and field-scale measurements.By coupling this formulation with traditional backwater calculations, we show how turbine siting distance can be optimized to maximize net power production while remaining within tailrace boundaries. This approach enables a system-level evaluation of hydrokinetic integration that explicitly balances marginal hydropower losses against hydrokinetic gains. Results suggest that tailrace hydrokinetic deployment can provide incremental generation and operational flexibility using existing assets, supporting grid resilience and renewable integration without requiring major modifications to hydropower plant operation or additional storage infrastructure.