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2.0.0b10
catchment modelling framework
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2.0.0b10
catchment modelling framework
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Cells are the units of the horizontal discretization. Cells are defined by the position of their center in space and their area. Each cell references its soil layers, a surfacewater storage, a snow storage, a water storage for the vegetation canopy. Vegetational parameters are also defined for cells, and used by models for evapotranspiration. Upon creation, the cell consists of a boundary condition for evaporation and transpiration, and a flux node for the surface water (not a water storage). The geometric shape of a cell is not saved and not relevant for cmf. For models with lateral fluxes, saved information on the topology (spatial relation) of the cells can be helpful. The API documentation can be found here: Cell.
Cells are created for a project with the following command. The position in space is given with the x,y,z coordinates (cartesian coordinates in m, eg. UTM or from a user defined origin) and the area is given in m². For 1D and lumped models, an area of 1000m² is helpful to use any volume in m³ as mm.
The cell c has a standard vegetation (short grass) which can be changed with c.vegetation and the boundary conditions noted above.
Adds a new soil layer up to the depth of 10cm below ground (d in m) with a default paramterized van Genuchten - Mualem retention curve. The usage of retention curves in cmf is discussed here, but it is recommended to read about that later in the CMF-1Dtutorial" <h3>Adding a surface water storage</h3> @icode{py} c.surfacewater_as_storage() @endicode converts the flux node surfacewater into an openwater storage. This is '''strongly recommended''' for all model setups, except for very conceptual models. If you are not sure, create it. Routing is much simpler to understand, if a surfacewater storage is present, '''even if you do not expect to have infiltration or saturation excess'''. And cmf is much better tested for models with surfacewater storage. <h2>Topology</h2> Lateral flux connections between water storages and boundary conditions, like soil layers, surface water, and outlets are usually defined by just creating them (see eg. @ref cmfTutFirstModel "here"). Most of the flux connections require a notion of the distance between the water storages, and the crosssection of the flux. Calculating these values can be cumbersome, if many lateral connections need to be created. To facilitate this task, you can save the topologic relation of cells. There are tools available (see CmfFluxCreationTools), to create many connections based on the topological information. Cell topology defines neighborhood relation between 2 cells by saving the length of the shared boundary of the cells. @icode{py} c1.topology.AddNeighbor(c2,5.0) @endicode defines c1 and c2 as neighbors with a shared boundary of 5m. Topology is used in [[wiki:CmfTutDarcianLateralFlow]|and [wiki:CmfTutSurfaceRunoff]]. <h1>Rivers and reaches</h1> Rivers can cross cells or run along cells, depending your setup, or if you only need a 1D model of flow in rivers, they can be created without cells, see [[wiki:CmfTutChannel].|Rivers need to be discretized to reaches according to your needs of numerical precision, the heterogenity of the channel form and to match the size of the cells. The reaches are implemented in cmf by the @ref cmf::river::Reach "Reach"] water storage. <h2>Crossectional geometry</h2> If you create a reach for the project, you must give the crossectional geometry of the river. The different basic geometries are: - @ref cmf::river::TriangularReach "TriangularReach" - T, a river with a triangular crosssection - @ref cmf::river::SWATReachType "SWATReachType" - S, a river with a trapezoidal crossection, with a flat flood plain, as in the model SWAT - @ref cmf::river::RectangularReach "RectangularReach" - R, a rectangular crosssection - @ref cmf::river::PipeReach "PipeReach" - P, a circular pipe More crossection types can be implemented on demand. <h2>Creating a river</h2> <h3>Creating the reaches</h3> As a general type, @ref cmf::river::Channel "Channel" is used, denoting the crosssection by the shortcuts listed above:
This command creates a new reach with a trapezoidal crossection, a bank width of 50cm, a depth of 10 cm using (per default) a kinematic wave approach. The center of the reach is located at x,y,z.
The two reaches can be connected with any connection suitable for open water storages. However, in most cases a kinematic or diffusive wave approach, using Manning's roughness as the friction term will be used for modelling channeled flow (see CmfTutChannel), hence the two reaches can be connected by definining r2 as the downstream reach of r1:
r2 should be connected to the area outlet:
CmfTutChannel will show a full running example.