Abstract: Fish habitat suitability models are critical to assessing riverine ecological health. Previous studies on the habitat simulations of the Yellow River carp－an ecological indicator species－rely largely on two-dimensional or three-dimensional hydrodynamic modeling. However, most of these approaches are limited to short river reaches of tens of kilometers due to high computational demands and challenges in acquiring high-resolution topographic data, focusing on the influence of water depth and flow velocity in rivers. This study develops a one-dimensional water-sediment-temperature coupled numerical model that achieves a rapid simulation of water-sediment-temperature processes along the entire lower Yellow mainstream, allowing to account for different cross-sectional geometries and various flow velocity distributions. We have conducted habitat suitability simulations based on the daily-scale flows and sediment data of 1999-2021, and the results reveal that in this reach, the total water volume is a dominant factor of its downstream ecological health. As the volume increases, the weighted usable area of habitats increases initially and then decreases, peaking in an optimal volume range of 25.5 - 36.5 billion m3. In the range of 20 - 25 billion m3, the weighted usable area is in quite scattering, highlighting the dominant role of flow and sediment changes in shaping the overall ecosystem health in this reach. The simulations further demonstrate high sediment concentrations in the flow-sediment regulation period reduce the weighted usable area drastically, yet the overall impact of its sediment remains limited because the duration of high-sediment transport in flood season is short. This study has developed a basic tool for assessing river ecosystem health that helps further exploration of ecological thresholds and sustainable water resource management of large sediment-laden rivers.

Key words: environmental hydrology, habitat suitability model, Yellow River carp, flow-sediment-temperature model, lower reach of the yellow river, river ecology