## 2 Digital Platform--DNS with SWAT Module
### Riverbed Phase  
This phase controls the movement of water and suspended sediment generation through the channel network of the watershed to the outlet [81, 112, 113]. The water is routed through the main canal network using the Muskingum routing method using Manning's Equation (5), and the suspended sediment transported with the water is subject to deposition and degradation processes (6-9) [114]. These two processes are computed with a simplified version of the Bagnold stream power equation, where the maximum amount of sediment transported from each sub-basin is a function of the peak channel velocity. If the concentration of sediment in the basin area, at the beginning of the time step, exceeds the maximum concentration of sediment that can be transferred by the water, additional sediment is deposited; if not, degradation occurs, which is a function of the channel erosion and the channel vegetation cover [115]. The average flow velocity, \(v_{ch}\) (m/s), is calculated using [PERSON]'s equation:  
\[v_{ch}\ =\ \frac{R_{ch}^{2/3}*slp_{ch}^{1/2}}{n} \tag{5}\]  
where: \(slp_{ch}\) is the riverbed phase of each sub-basin slope (m/m), and \(n\) is the Manning coefficient. The maximum concentration of sediment that can be transported through in the riverbed phase of each sub-basin is closely related to the peak channel velocity at the daily time step. The peak channel velocity (m/s) and the maximum sediment concentration are calculated as:  
\[v_{ch,pk}=PRF*\ v_{ch} \tag{6}\]  
\[conc_{sed,ch,mx}=C_{sp}*\ v_{ch,pk}^{spexp} \tag{7}\]  
where: \(PRF\) is the peak rate adjustment factor, \(v_{ch}\) is the mean flow velocity, \(C_{sp}\) is a coefficient, and \(spexp\) is an exponent. The \(conc_{sed,ch,mx}\) (t/m\({}^{3}\)) is compared to the actual concentration of sediment in the riverbed phase of each sub-basin (t/m\({}^{3}\)). If \(conc_{sed,ch,i}\) > \(conc_{sed,ch,mx}\), deposition dominates in the riverbed phase of each sub-basin, sediment routing and the sediment deposition \(sed_{dep}\) is calculated as:  
\[sed_{dep}=(conc_{sed,ch,i}-conc_{sed,ch,mx})*Q_{ch} \tag{8}\]  
However, if \(conc_{sed,ch,mx}\) > \(conc_{sed,ch,i}\), degradation or erosion dominates in the riverbed phase of each sub-basin, sediment routing and the sediment degradation \(sed_{deg}\) is calculated as:  
\[sed_{deg}=(conc_{sed,ch,i}-conc_{sed,ch,\ m2})*Q_{ch}*K_{ch}*C_{ch} \tag{9}\]  
where: \(K_{ch}\) is the erodibility factor in the riverbed phase of each sub-basin, and \(C_{ch}\) is the cover factor in the riverbed phase of each sub-basin. However, the Bagnold equation, the default in the SWAT module, is considered impractical to apply across the entire streaming network [116]. The SWAT module also offers three alternative sediment tracking methods to the Bagnold method (Kodoatie, Molinas and Wu, and Yang Sand and Gravel). All these equations share the same in-stream sediment routing (sediment transport capacity is routed in main reaches/channels), but calculate the maximum sediment transport capacity (maximum concentration of transportable sediment) differently [117], and allow for the analysis of individual sediment fractions. The Yang equation was developed to simulate large particles such as sand and gravel. The Molinas and Wu equation and the Kodoatie equation are better suited for simulating small particles forming suspended sediments. In all four equations, bed erosion exceeded bank erosion [118; 119; 120]. Despite this choice of equations for sediment tracking in the riverbed phase, studies show that SWAT does not have a solid representation of the sediment processes in the stream [121]. The mechanisms associated with the transport of cohesive and non-cohesive sediment fractions in stream systems are different. The mentioned empirical and physical methods implemented in SWAT for the erosion, deposition, and transport of sediment in a stream system are universally applied across all sediment fractions.