River systems are schematised into a simplified river network using a node-link structure for modelling in Source. The river network begins and ends with a node, and all nodes are interconnected by links. Runoff is fed into the network as an inflow at the relevant location in the network.
Links represent a length of stream, which can be zero for near coincident processes, and are used for transfer of flow and constituents between two nodes with or without routing and transformation. Note that Source is generally a feed-forward model (from upstream to downstream), in that the only bi-directional flow is associated with the filling and emptying of wetlands, otherwise there are no bi-directional interactions with upstream elements. (Extracted from Welsh, et al, 2013, with adaptations to suit the needs of the SRG.)
Source provides functionality for routing of flows and water quality constituents, including decay and deposition, through links. More information on this functionality is available via Water quantity processes (Rivers) - SRG for flows and Link water quality processes (Rivers) - SRG for water quality, respectively.
Nodes represent a physical location along a river where flow and water quality constituents either enter the system or are stored, extracted, lost or measured and can be used for the application of management rules. Other modelling components are represented as nodes in the river network. A set of nodes has been designed to represent functions of various physical and regulatory flow control processes in a river network and they can be broadly classified into two types: i) physical nodes, which are used to define flow convergence, divergence, loss and measurement, and ii) regulation/management nodes, which are used to apply management rules that regulate the river and to keep account of the water ordered and extracted by users. More information on processes modelled at nodes (including water quality at some node types) is nodes is available via Water quantity processes (Rivers) - SRG.
The above material has largely been extracted from Welsh, et al (2013), with adaptations to suit the needs of the SRG.
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.