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Welcome to the next generation MIKE+ Documentation

2D Initial Conditions

The initial values for the hydrodynamic variables can be specified in three ways:

  • Dry Domain
  • Uniform Water Level
  • Varying in Domain.

To avoid the generation of shock waves and potential model instabilities, it is recommended that your initial surface elevation matches the boundary conditions at the start of the simulation.

Dry Domain

In this case, the simulation will start with zero water depth and velocity across the entire domain.

Uniform Water Level

A single water level value can be specified to be applied across the domain. Elements where the topography is higher than this level will therefore be initially dry.

Varying in Domain

To define spatially varying 2D initial conditions, the following sources of information can be used:

  • MIKE+ 2D Initial Conditions Layer of Water Level
  • Background Layer of Water Level
  • 2D File with Water Level
  • 2D File with Water Depth and Velocities

When using an external 2D file (water level or water depth and velocity), the area in the data file must cover the model area. If a *.dfsu file is used, piecewise constant interpolation is used to map the data. If a dfs2 file is used, bilinear interpolation is used to map the data. If the input data file contains a single time step, this field is used. In the case where the file contains several time steps, e.g. from the results of a previous simulation, the actual starting time of the simulation is used to interpolate the field in time. Therefore, the starting time must be between the start and end time of the file. Delete values (used in empty elements of the file) will be ignored and the value will be interpolated only from existing data.

MIKE+ 2D Initial Conditions Layer of Water Level

This option enables an initial conditions layer with specified water levels to be graphically defined in the "Map" view using the tools available in the "2D overland" ribbon.

Steps to define initial conditions layer:

  • Select the Target layer as "2D initial conditions"
  • Click on "Create" and define polygons. Utilise the various editing tools to refine the polygons if necessary. Tip: specify a default water level in the 2D initial conditions table to automatically populate the water level value of a polygon as soon as it is digitised.
  • In the 2D initial conditions table, the digitised polygons will be listed. Specify the initial water level values for each of these polygons, and prioritise them using the up and down buttons (important if there are overlaps)
  • Where the model domain is not covered by the initial condition polygons the default value will be used in this area.

Clicking on "Review initial conditions file on map" will build a 2D initial conditions *.dfs2 or *.dfsu file and add the layer to the map. This layer will also be saved in your project directory for use in the simulation. This file will also be created when starting the simulation, if it doesn't exist in the project directory of if input data have been modified.

Background Layer of Water Level

Utilize predefined information to define the 2D initial water level, e.g. from shape files or text files.

Steps to define the Initial conditions details:

  • Layer: Select the appropriate layer that has already been loaded into the MIKE+ interface as a background layer (available in the drop-down list) or browse to a saved file.
  • Water level Item: Select the field in the layer that contains water level values
  • Unit: specify the unit of the water level item
  • Default water level: Value to be used if no water level value exists in the layer

Clicking on "Review initial conditions file on map" will build a 2D initial conditions *.dfs2 or *.dfsu file and add the layer to the map. This layer will also be saved in your project directory for use in the simulation. This file will also be created when starting the simulation, if it doesn't exist in the project directory of if input data have been modified.

2D File with Water Level

Use a previously defined *.dfs2 or *.dfsu  file with a "Water level", "Elevation" or "Surface Elevation" item type as the 2D initial condition.

2D File with Water Depth and Velocities

Use a previously defined *.dfs2 or *.dfsu file. The file must contain the total water depth and the velocity components in the x- and y-directions.

The initial conditions can be the result from a previous simulation in which case the initial conditions effectively act as a hot start of the flow field.