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The biggest thematic group covers the area of modelling. Hydrodynamic-numerical, water quality, ecosystem and data-driven models are being developed, extended and coupled in order to describe processes in interface systems within the urban water cycle. If possible, open source software tools are used. In the following, some examples are given. However, for comprehensive information on all modelling activities please visit the project websites.
For some research areas, coupled model approaches are used. In order to evaluate the impact of remaining wastewater constituents on the sediment-water interface in urban lakes (Project T4 ) two coupled hydrodynamic-biogeochemical models are developed to either simulate lakes as one- or two-dimensional systems. The hydrodynamics of the model are described by using respectively the 1D-General Lake Model or TELEMAC-MASCARET whereas biogeochemical processes are modelled using either the Aquatic Ecodynamics Model Library or the Delft Water Quality module.
In other areas, models are being extended. Within the Computational Fluid Dynamics model OpenFOAM, a multiphase solver is being extended by transport and mass transfer processes in order to describe fluxes of hydrogen sulphide across the water-air interface in sewer systems (Project T3 ). In another project, an integral solver for groundwater-surface water interactions is being extended for transport processes in OpenFOAM (Project N7 ). For the first time, this integral solver is being applied to the hyporheic zone which can be described as the groundwater-surface water interaction space.
Data-driven models are being developed in order to describe the complex processes at the surface water – atmosphere as well as the urban soil – atmosphere interface. At the urban soil – atmosphere interface relationships and feedbacks between evapotranspiration processes and surface sealing are modelled (Project N2). The carbon and nitrogen cycle across the surface water – atmosphere interface are being modelled in order to quantify greenhouse gas formations and fluxes (Project N3) as well as ecosystem metabolism (Project N4).
Katharina Teuber (corresponding doctoral student) 
Anne Timm 
- sediment – surface water (T4 - Robert Ladwig )
- surface water – groundwater (N5 - Mikael Gillefalk , N6 – Jonas Schaper , N7 - Tabea Broecker )
- surface water – atmosphere (N3 - Sonia Herrero , N4 - Clara Romero )
- urban soil – atmosphere (N2 - Kyle Pipkins , T1 - Anne Timm )
- wastewater – sewer atmosphere (T3 - Katharina Teuber )
- Berliner Wasserbetriebe (BWB) 
- Netherlands Institute of Ecology (NIOO), Wageningen 
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