Assigns a water level to the cell(s) based on a water level versus time curve.
HX
Water Level (Head) from an eXternal Source (ie. a 1D model)
One or two 1D nodes provide a water level every half timestep. Automatically creates 1D QX boundaries at the node(s) (see Table 4 .22), which receive a flow from the 2D domain every half timestep. 2D HX boundaries are linked to 1D nodes using CN connections (see below).
Tip: A common cause for instabilities is that the starting water level in the 1D node is different to those in the adjacent 2D cells.
Treatment
Cell(s) can be wet or dry. It is not a requirement that at least one cell is wet.
HT lines can be oblique to the X-Y axes, in which case, Oblique Boundary Method should be set to “ON” (this is the default).
The water level can vary in height along a line of cells.
Tip: A common cause of instabilities at or near head boundaries at the start of a simulation is the initial water level specified at the adjacent cells is different to the head value. If your model immediately goes unstable at the boundary, check your initial water levels. If it is a 2D HX boundary the water levels in the 1D node and the 2D cells should be similar.
Combinations
Any number of water level boundaries can be assigned to the same cell(s). The water level used is the sum of the water levels assigned. For example, a storm tide may be specified as a combination of a tidal HS boundary, a HT boundary of the storm surge and another HT boundary of the wave setup. The HS boundary would be water elevations and the two HT boundaries water depths.
The exception is that a 2D HX boundary, being a dynamically linked one, cannot be summed with another H boundary. In earlier versions of TUFLOW, if you accidentally specify a 2D HX boundary and a 2D HT or HS boundary at the same cell, the 2D HX boundary prevails and no warning is given.
