How to select the TUFLOW link-type to use

One of your first decisions when creating any integrated model is which link type to choose. When linking to TUFLOW, HX connections are recommended when you have natural flood embankments. SX connections are recommended when you have artificial flood defences (e.g. a flood defence wall).

Further details about the available link-types are provided below.

1. Lateral HX connection

   For an HX (H [water level] supplied eXternally to TUFLOW) connection, Flood Modeller allows every RIVER (and INTERPOLATED and REPLICATED RIVER) unit to be a potential donor/recipient of flow to/from the 2D domain.Thus it is the HX connection in TUFLOW which determines whether there is a connection to the 2D domain and no amendment to a 1D data file is necessary, provided the cross sections have already been trimmed to the extent of the 1D domain.

   The water level calculated in the 1D domain is obtained by TUFLOW, which determines the discharge (if any) across the HX connection line based on the water levels on either side. As with a 1D lateral spill or lateral inflow, the discharge is distributed laterally across the length of the HX unit. Importantly it is the elevation of the HX line that determines when the spill starts to occur- not the cross section within 1D. As soon as the elevation of the water surface exceeds the elevation of the HX line, water will pass between the 1D and 2D domain.

   The flow exchange between the 2D and 1D domains over an HX connection at each node and same interval may be output to the supplementary results (*.zzx) file by:

   1. Ticking 2D Flow Box (found on the Additional Output Tab of the Run Forms Interface)

   2. Or by directly adding the line "2DFlow=1" to the Flood Modeller Event File (*.ief)

2. SX connection

   For an SX (S [source flow] supplied externally to TUFLOW) connection, the discharge into/from the 2D domain is calculated by Flood Modeller, taking into account the water level in the 2D domain which is returned by TUFLOW. Any two-noded 1D unit in theory can be linked to an SX connection, although a typical application would be as the lateral HX configuration above, with HX connection replaced by a lateral spill connected in 1D, and the node on the 2D side linked to the SX connection. In such instances, a relatively shorter spill may be preferable since effectively a point discharge is being applied to the 2D domain and consideration would be needed as to how this is distributed in the 2D domain. The node on the 2D side of the connecting unit (e.g. the downstream node of the spill) must be connected to a [dummy] HTBDY. Since this node will be linked to an SX connection in TUFLOW, Flood Modeller will ignore any data in the HTBDY unit and override it dynamically with the water level returned by TUFLOW.

   The water level returned by TUFLOW can be accessed from the "stage" variable as normal in Flood Modeller; similarly, the flow exchange between the 1D and 2D can be viewed via the "flow" variable.