InfoWorks ICM has full Water Quality available as standard, which can be simultaneously applied to both the 1D and 2D domains (i.e. the Sewers, the Rivers and right across the surface of the catchment). The 2D water quality engine is able to model advection and diffusion of the same pollutants that can be modelled in the 1D network. Available sources of pollutants in the 2D zone include river banks, manholes, point sources and external boundaries.
This functionality was first introduced in the v1.5 release in February 2011, but only included conservative pollutants in that release. This was extended for v2.0 (September 2011) to include non-conservative interactions across the Domain.
The 1D Water Quality engine (which can be applied to stormwater networks, sewer/wastewater systems and river models) has the following properties:-
- Advection (Holly-Preissmann)
- Multiple dissolved conservative pollutants
- Two sediment fractions and attached pollutants
- Erosion/deposition (including updating bed geometry) with multiple equations (Ackers-White, Velikanov, KUL)
- Non conservative pollutants (available from v2.0)
- Built-in Processes (e.g. Dissolved Oxygen and Temperature)
- User-defined processes
The Implementation of non-conservative pollutants and User-defined processes in the 1D engine is the same as the approach used in the 2D Water Quality Engine (see below). The built-in processes for Dissolved Oxygen and Temperature also apply in the 2D engine. The 1D Water Quality engine doesn’t yet do dispersion (aka diffusion). However, we plan to introduce this functionality in one of the forthcomming release cycles.
The 2D Water Quality model is based on a Finite Volume Conservative scheme to model advection-diffusion of multiple pollutants. A non-conservative approach applies for pollutants using a decay rate based on:-
- Constant rate
- Half-life period (exponential decay function based on time)
- Concentration (exponential decay function based on concentration)
- A combination of Half-life period and Concentration.
The 2D water quality process module is very flexible and the user is able to implement their own processes by means of standard reaction equations like Arrhenius terms or equilibrium equations. Special emphasis has been put into implementing the type of equations required to model DO, although at the moment, there are no plans to include Lakes.
Where users include their own processes in the 2D Water Quality module, they don’t replace decay-rate alternatives. The processes represent interactions between different substances, whereas decay rate only involves an individual substance. As noted above, user-defined processes are also available in the 1D engine.
Sediment transport is not yet considered on the 2D side, so erosion/deposition simulation on the ground surface is not possible at the moment. However, we do plan to enhance InfoWorks ICM so that sediment transport in the 2D module will allow for loss of sediment (and attached pollutants) from a river channel after major flow events.