HydroGeoSphere/Surface Flow

You can assign a critical depth or zero depth gradient boundary condition, as described in Section 3.7.2 to segments in the specified set. These segments should be part of the overland flow domain and are typically located on the outer boundary. The following instructions can be used as input to the Type instruction inside the Boundary condition...End instruction group to assign critical depth boundary conditions: Critical depth Sets the input type to be a critical depth boundary condition. • • • For example: boundary condition type critical depth segment set outflow end This example shows that a time-value table is not mandatory. However, if you wish to turn the critical depth boundary condition on or off, then this can be accomplished by including a time value table instruction: boundary condition type critical depth segment set outflow time value table 0.0 1.0 10.0 -99999. end end The value 1.0 at time zero is ignored, but the NODATA value -99999 at time 10.0 causes the boundary condition to be turned off and the nodes become unconstrained. Zero-depth gradient Sets the input type to be a zero-depth gradient boundary boundary condition. • • • For example: boundary condition type zero-depth gradient segment set outflow end If you wish to turn the zero-depth gradient boundary condition on or off, then this can be accomplished by including a time value table instruction. NOTE: zero-depth gradient boundaries used to include variables defining the direction of boundary gradient and the bed slope at the boundary.