Saturation Recovery Coefficient

The sediment saturation recovery coefficients are important parameters of the non-equilibrium sediment transport equation in the mathematical models. A wide range of the saturation recovery coefficient, ranging from 0.01 to 1000, has been proposed in various studies. Chapter 6 presents the expressions of the saturation recovery coefficient from the transition intensities (from rest state to suspension state and vice versa), including: and the saturation recovery coefficients for equilibrium and non-equilibrium sediment transport, respectively, and the composite saturation recovery coefficient. Four theoretical characteristics of the saturation recovery coefficient are illustrated. The saturation recovery coefficients are related with the upward and settling velocities of suspended load, the single-step distance, the suspension height, and the flow discharge involved in sediment suspension. A formula is derived for the saturation recovery coefficient for equilibrium sediment transport. The numerical results are consistent with the empirical values. The calculation of the saturation recovery coefficient for non-equilibrium sediment transport is difficult, because the suspension height depends on the vertical distribution of sediment concentration, which is complicate for the non-equilibrium sediment transport. Based on the simplified assumption for vertical distribution of sediment concentration in scour and deposition the saturation recovery coefficients is computed for non-equilibrium sediment transport. Under the general hydraulic and sediment conditions, the saturation recovery coefficient can be greater or less than 1 and is less than 1 for most cases, and can even be 0.01 or less. This theoretically solves the past dispute for the reasonable values of the saturation recovery coefficient. The composite saturation recovery coefficient is relatively stable. It shows less variation with the scour or deposition process, while it varies significantly with ω/u∗. Hence, it is more convenient to utilize the composite saturation recovery coefficient. The theoretical values of the composite saturation recovery coefficient show good agreement with the field data of the lower Yellow River.