Environmental and regulatory constraints are increasingly posing challenges to the optimal operation of hydro-electric facilities. Hydrogen energy storage (HES) is well-suited to address these challenges. Using excess or low-cost hydroelectric power during off-peak hours to produce hydrogen can help reduce water spills and unlock opportunities for energy arbitrage. Moreover, the oxygen byproduct of electrolysis can be used to improve the dissolved oxygen (DO) levels in tailrace water. This paper presents an innovative framework for modeling and as-sessing the integrated hydroelectric-hydrogen system, considering subsystem constraints and coupling, benefits in spill water reduction and DO mitigation, as well as Comprehensive case studies were conducted to assess the techno-economic performance of the integrated system in different deployment scenarios.