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Abstract

Due to the construction and operation of cascade reservoirs, the natural hydrological regimes have inevitably been altered and most fish spawning grounds have been destroyed, thus causing ecological impacts on riverine ecosystems and fish reproduction. An effective way to restore fish habitats and fulfill their spawning requirements is to generate an appropriate ecological flow regime guided by Natural-based solutions (NbS) that can help restore valuable functions provided by nature. With a focus on one major existing spawning ground for four major Chinese carps (FMCC) in the Hongshui River (HSR), China, this study first evaluated temporal variations of flow regimes and their ecological responses in multiple time scales by employing several eco-hydrological indicators. A fuzzy logic-based one- and two-dimensional-coupled fish habitat model was then built to estimate a suitable ecological flow to ensure the existence of continuous and connected habitats. Furthermore, an improved fluctuation identification algorithm was proposed to quantitatively identify naturally effective high-flow processes to trigger fish spawning behaviors following NbS guidance. Thus, suitable ecological flow regimes were established based on the notion of thresholds of flow discharge while meeting the requirements for water temperature during the spawning period of FMCC. The results recommended high-flow processes characterized with thresholds of flow indicators while mimicking natural flow regimes to be generated to stimulate FMCC spawning in different periods in HSR. The findings of this study provide actionable insights into the conservation of fish in dammed rivers and such NbS-oriented practices can create achievable strategies for reservoir operations.