WMS:GSSHA Channel Routing

GSSHA is a two-dimensional finite difference rainfall/runoff model. A finite difference grid is used to establish the computational domain and parameters for surface runoff. The GSSHA model is fully coupled with hydraulic stream flow/routing models. Parameters for stream channels are defined using arcs and then mapped to the appropriate underlying grid cells.

In order to define GSSHA channel parameters using arcs, the current coverage type must be set to GSSHA.

Smoothing Stream Cells

Because elevation data used to define the surface runoff component of GSSHA does not contain the detailed resolution required to capture the actual stream bed elevation of the channels, the bed elevation profile can be highly irregular. These irregularities, or abrupt changes in elevation can cause instabilities in the channel routing computations, and therefore must be smoothed out.

The Smooth Stream Arcs command is used to adjust the elevation of the stream bed for GSSHA. Smoothing is done by first selecting a continuous set of arcs which represent the stream and then choosing the Smooth Stream Arcs command from the GSSHA menu.

Initially the bed elevation is assigned the same value as the grid. Whenever a profile is shown, the bed elevation profile is displayed in blue while the grid elevation of the cell is shown in red. Care should be taken to see that no bed elevation is higher than the grid cell elevation.

Renumber Links And Nodes

In order to properly execute the channel routing routines of GSSHA, the stream channel must have the proper order and connectivity. This ordering or numbering can be done automatically using the Renumber Links and Nodes command from the GSSHA menu.

Links define whole channel segments and must be numbered such that any segment has no "upstream" segments with a link number that is greater than itself. In other words all channel segments must "flow" into downstream segments with a higher link number.

Related Topics

• GSSHA Overview
• Grids