Model units & connections

This page describes how modelling tools allow users to discretise catchments into modelled units in order to represent and calculate hydrological processes. Differentiating the catchment into separate components or units, such as subcatchments, patches of similar land cover, soil layers with distinct properties, allows hydrological processes to be modelled by algorithms that have been developed for that scale and type of unit.

Each modelling tool has a unique way of describing a catchment in terms of:

• The types surface and subsurface model units that can be included
• The connections that can be defined between these different units
• The process algorithms that are used to calculate inflows, storage, and outflows for each unit

This page summarises the unit types and connection options available across the tools, while their process algorithms are described here. Although described on separate pages the discretisation and process algorithms are inextricably linked. This page also summarises some implications of the structural differences across the tools, which are dealt with in more detail for some specific model application contexts here.