As previously stated in Rivers - SRG, Source uses a link-node structure to represent river systems for modelling. In links, lag time and storage routing concepts are used for routing. Two flow routing methods are available to model travel time and attenuation: pure lag or translation, and a generalised streamflow storage routing method, which can represent linear, non-linear, and variable parameter Muskingum routing (details on all these are available in Link storage routing - SRG). In the routing algorithm, river water (in-bank flow) fills the dead storage in a reach first before propagating through the reach. Overbank flow is considered for modelling interactions between surface water and groundwater. The surface water-groundwater (SW-GW) interaction component in Source (see for details) is integrated into the river network through links. (Extracted from Welsh, et al, 2013, with adaptations to suit the needs of the SRG.)
Source has 14 node types available and these are listed in together with an overview of the processes modelled at each node type, and references to where details on each type can be found.
Reference
Welsh, W.D., Vaze, J., Dutta, D., Rassam, D., Rahman, J.M., Jolly, I.D., Wallbrink, P., Podger, G.M., Bethune, M., Hardy, M.J., Teng, J., Lerat, J. (2013) An integrated modelling framework for regulated river systems. Environmental Modelling & Software, 39: 81-102.