Setting up Initial Conditions

The domain class incorporates a number of important quantities:

stage — absolute water-surface elevation (m)

elevation — bed elevation / bathymetry (m)

xmomentum — depth-integrated momentum in the x-direction (m²/s)

ymomentum — depth-integrated momentum in the y-direction (m²/s)

friction — Manning roughness coefficient n (dimensionless)

Water depth is the derived quantity stage - elevation (a cell is dry where these are equal). Elevation and stage are measured from the same vertical datum, so stage is not the water depth.

These variables are stored in the domain as quantities. The quantities are stored as a dictionary with the key being the name of the quantity and the value being the quantity itself. They all have default values of 0.0.

The setting of the initial conditions is done by setting the values of these quantities. The values can be set by using the set_quantity method of the domain object.

For instance, to set the elevation to a function of x and y, and the stage to a constant value, the following code can be used:

domain.set_quantity('elevation', function = lambda x,y : x/10)
domain.set_quantity('stage', expression = "elevation + 0.2" )

The set_quantity method can also be used to set the initial conditions for the xmomentum, ymomentum and friction, indeed any quantity that is stored in the domain.