ABSTRACT
Many large rivers are experiencing a significant reduction in sediment flux owing to human activity. Sediment transport capacity directly affects the predictive accuracy of sediment concentration in morphodynamic modelling. A total of 1092 datasets with extremely low sediment concentrations in a quasi-equilibrium state were selected at five hydrometric stations of the Middle Yangtze River, and used to determine two parameters of a sediment transport capacity formula proposed by Zhang Ruijin. Firstly, the relationship between the effective sediment transport capacity and the comprehensive flow-sediment factor in the Middle Yangtze River was derived. Based on this relationship, Zhang’s sediment transport capacity formula was improved with its parameters being calculated according to varying flow and sediment conditions. Then the improved sediment transport capacity formula was successfully applied to other rivers with low sediment concentrations, also including a 347-km-long reach of the Middle Yangtze River.
Disclosure statement
No potential conflict of interest was reported by the authors.
Notation
C | = | comprehensive flow-sediment factor for suspended bed-material load (–) |
= | comprehensive flow-sediment factor for total suspended sediment (–) | |
dc | = | critical grain size (m) |
g | = | gravity acceleration (m s–2) |
h | = | water depth (m) |
k | = | coefficient (kg m–3) |
m | = | exponent (–) |
N | = | number of sediment fractions (–) |
Pb | = | per cent finer of bed material (%) |
PWD | = | portion of wash load (%) |
Q | = | discharge (m3 s–1) |
= | concentration of suspended bed-material load (kg m–3) | |
= | concentration of total suspended load (kg m–3) | |
= | concentration of wash load (kg m–3) | |
= | effective sediment transport capacity (kg m–3) | |
= | actual sediment transport capacity (kg m–3) | |
= | observed value of effective sediment transport capacity (kg m–3) | |
= | calculated value of effective sediment transport capacity (kg m–3) | |
= | theoretical sediment transport capacity (kg m–3) | |
T | = | temperature (°C) |
U | = | flow velocity (m s–1) |
= | friction velocity (m s–1) | |
Z | = | water level (m) |
= | correction coefficient (–) | |
= | vertical turbulence intensity (m s–1) | |
= | grain-size distribution of bed material (%) | |
= | grain-size distribution of suspended sediment (%) | |
= | grain-size distribution of sediment transport capacity (%) | |
Δt | = | time interval (s–1) |
= | Kármán constant (–) | |
ω | = | group settling velocity of non-uniform suspended sediment (m s–1) |
= | settling velocity of the kth fraction sediment (m s–1) |