Surface source and sink
3Di does not cover all processes that can affect a water system. To allow users to add and extract water from the 2D surface domain, the Surface Sources and Sinks function is implemented. It allows users to define their own source and sink rates related to a certain process. An example would be to capture evaporation effects. These rates are treated similar to the other source and sink terms.
The Surface sources and sinks is part of the scenario forcings, it forces the system to react to the input and it can differ per simulation. Therefore, the input is not part of your schematisation, but is set in the API call. A more elaborate explanation about API calls and the specified input can be found here: 3Di Models & Simulations API.
In this first release, one can only use the option to add a time-series containing uniform values. In the near future, options to add temporally and spatially varying raster values will be released. In addition to those option, also an option for interpolation of these rates will become available. The input rates are defined in m/s, and will automatically scaled with the grid size.
The actual surface source and sink discharges per computational cell are recorded in the 3di_results.nc file Results 3Di. Especially, in case of extraction of water, the quantities can differ from the input values in case the cell becomes nearly empty. In addition to these results, one can also generate aggregated results Aggregated output. The positive and negative cumulated results are required in case for using the water balance tool.
Surface sinks (i.e. negative values in the time series) extract water from the model. If less water is available in the node or cell then what is to be extracted, 3Di will limit the extraction. Just before the cell becomes dry, the extraction rate will be less than the extraction rate in the user input. This is done to guarantee stability and capture reality better.
A Surface-Subsurface Model; balancing speed, accuracy and reality. Stelling and Volp (to be published)