Abstract: How to determine the sediment carrying capacity of water flow significantly influences the calculations of sediment transport in rivers. Since the operation of the Xiaolangdi reservoir in 2000, low sediment concentration floods have occurred frequently in its lower reach, and changes in flow-sediment relationship have emerged, yet the existing methods for sediment carrying capacity calculation remain unimproved under these new conditions. Starting from the energy conservation theory, this study derives a formula for calculating sediment carrying capacity. By the criteria for channel erosion and deposition, we calibrate its parameters using 360 sets of relatively balanced flow-sediment data selected from the 2000-2010 records of the lower Yellow. And, additional 208 sets of balanced water-sediment data of 2011-2022 are used to validate its reliability and applicability. Results demonstrate the calculations align closely with measurements, confirming the formula’s accuracy in estimating this reach’s sediment transport capacity. A comparative analysis with classical sediment carrying capacity formulas, using 171 published water-sediment datasets, highlights the superiority of our new formula in application to low sediment concentration conditions. It is simple in structural form and enjoys a relatively high calculation accuracy; It is applicable to estimating the capacity of sediment transport in a low sediment river such as the lower Yellow, useful in practical river channel management and riverbed evolution analysis.

Key words: new flow and sediment condition, sediment transport capacity, energy theory, lower Yellow River, low sediment?laden flows