2.2.2. Channel Sediment Routing

The Engelund and Hansen (1967) [24] equation is applied to calculate the sediment transport capacity for each sediment size group in channels. For each size group, the suspended part is transported by advective process first and the transport capacity will be subtracted by the amount of the suspended sediment transported. Then, the excessive capacity is used to transport deposited material. The amount of the deposited material that can be transported is limited by excessive transport capacity as well as advective processes. After the transport of suspended material and deposited material, if there is still any transport capacity left, it won't be used as channel erosion is not considered in the current version of the model.

$$T\_i = \frac{Q \times C\_i \times d\_t}{2.65} \tag{9}$$

$$C\_i = 0.05 \times \left(\frac{G}{G-1}\right) \times \frac{V \times S\_f}{\sqrt{(G-1) \times g \times d\_i}} \times \sqrt{\frac{R\_l \times S\_f}{(G-1) \times d\_i}}\tag{10}$$

where *Ti* is the sediment transport capacity in the channel for sediment type *i* (L3), *Q* is the flow discharge (L<sup>3</sup> T<sup>−</sup>1), *Ci* is the sediment concentration of type *i* by weight, *dt* is the time step of channel routing (T), *G* is the specific gravity of sediment and was set to 2.65 in this study, *V* is the depth-averaged velocity in channel (L T−1), *Sf* is the friction slope, *Rh* is the hydraulic radius (L), *g* is the gravity acceleration (L T<sup>−</sup>2), *di* is the diameter of sediment type *i* (L). Calculated transport capacity is used to transport the suspended sediment first and then the previously deposited sediment.
