Scope: what’s covered (and not!) in this wiki

This wiki is aimed at readers who a have at least a basic background in hydrology and exposure to catchment hydrological modelling. It is not intended to replace courses or foundational instructional material on hydrology and modelling, or on the use of specific modelling tools. One needs a solid grounding in hydrology before getting into catchment modelling. It is also necessary to go through the theory and user manuals or other documentation of a modelling tool being used. This wiki describes and compares various aspects of different modelling tools, but is by no means an exhaustive coverage, and cannot replace reading the tool's supporting material.

This wiki focuses on catchment-scale hydrological modelling, rather than plot-scale, hillslope-scale, or global-scale modelling of water movement.

Modelling tools intended for catchment hydrological modelling necessarily include some level of representation of groundwater storage and fluxes and of river channel flows. However this is generally far more simplified than groundwater-focused modelling tools and hydraulic modelling tools. Recognising the need for more detailed representation of groundwater and channel/floodplain hydraulics in some catchment modelling contexts has led to integration of these model types, as offered in the MIKE-SHE modelling platform for example. At present this wiki doesn't cover specifically groundwater-focused tools (e.g. MODFLOW) or hydraulics-focused tools (e.g. HEC-RAS).

At present this wiki does not cover modelling of sediment transport or other water quality parameters, although some of the focus modelling tools do have these capabilities.

Modelling software tools & versions covered

The modelling tools included in the detailed comparison in this wiki are:

Modelling tool	Version	References
ACRU, Agricultural Catchment Research Unit model	ACRU4	Schulze, 1986, 1995; Schulze and Davis, 2018
WRSM-Pitman, Water Resources System Model	WRSM2000	Pitman, 1973; Bailey and Pitman, 2015
SPATSIM-Pitman, Spatial and Time Series Information Modelling	IWR (GWv3)	Pitman, 1973; Hughes, 2005
SWAT, Soil and Water Assessment Tool	ArcSWAT2012	Arnold et al., 1998;
MIKE-SHE (& MIKE-Hydro), Système Hydrologique Européen	MIKE-SHE 2020	Abbott et al., 1986; DHI, 2014; Refsgaard and Storm, 1995

These were chosen as commonly used, accessible, and/or promoted versions of the modelling platforms at the time of the project (2019-21) from which this wiki was developed. Both ACRU, SPATSIM-Pitman, and SWAT are curated by university research groups and there are many versions of these platforms that were developed by researchers for specific studies. These may appear in published research articles, but not be easily accessible for a general user.

A new generally accessible version of SWAT, called SWAT+ was newly launched during the inception of this project. Most of it's core algorithms are the same as ArcSWAT2012, however it's user interface has changed and SWAT+ includes runoff routing from specified hillslope areas to floodplain areas. This is a significant change to the landscape process representation.

For the Pitman model tools, WRSM-Pitman and SPATSIM-Pitman, two different algorithms have been developed for groundwater processes, generally referred to by their primary developers: the Sami method and the Hughes method. These algorithms separate the representation of aquifers from storage in soils and interflow compared to the lumped subsurface representation in the original Pitman model (Pitman, 1973). The WRSM-2000 version allows users to choose the original Pitman, Sami, or Hughes groundwater representation, while the SPATSIM GWv3 version uses the Hughes method. As such, the WRSM-Pitman tool is described with the Sami method groundwater algorithm in this material to allow coverage of both approaches.