# boundaries Section

This section configures **open boundary conditions (OBCs)**, **relaxation zones**, **river inputs**, and **buffer zones** for the model.

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 | **Parameter** | **Description** |
 |---------------|----------------|
 | `type` | Type of open boundary condition (`1`=clamped, `2`=Flather, `3`=Orlanski, `7`=delayed Flather, etc.). |
 | `mode` | Mode for boundary conditions (`LOCAL`, `VARIATIONAL`). |
 | `relax_time` | Relaxation time for boundary conditions (default: `2.0 hours`). |
 | `archived_BC_use` | Flag to use archived boundary conditions (`TRUE`, `FALSE`). |
 | `archived_BC_directory` | Directory for archived boundary condition files. |
 | `archived_BC_format` | Format of archived boundary condition files (`BINARY`, `NETCDF`). |
 | `archived_BC_input-settings` | Input settings for archived boundary conditions (e.g., `file=ROOTNAME.YYYY.MM.nc ssh=XXX u=XXX v=XXX mode=UNSTRUCTURED`). |
 | `archived_BC_offset` | Offset for archived boundary condition elevation. |
 | `archived_BC_units` | Units system for archived boundary conditions (`MKS`, `CGS`). |
 | `archived_BC_transport` | Transport variable for boundary conditions (`u`, `U`, `null`). |
 | `CirculationOBCs_Flag` | Flag to enable/disable circulation OBCs (`TRUE`, `FALSE`). |
 | `CirculationOBCs_Directory` | Directory for circulation OBC files. |
 | `CirculationOBCs_Format` | Format of circulation OBC files (`BINARY`, `NETCDF`). |
 | `CirculationOBCs_InputSetting` | Input settings for circulation OBCs. |
 | `CirculationOBCs_Offset` | Offset for circulation OBC elevation. |
 | `CirculationOBCs_Units` | Units system for circulation OBCs (`MKS`, `CGS`). |
 | `CirculationOBCs_Transport` | Transport variable for circulation OBCs (`u`, `U`, `null`). |
 | `PermanentTide_Flag` | Flag to add permanent tide in OBCs and tidal potential (`TRUE`, `FALSE`). |
 | `periodic_conditions_file` | File containing instructions for boundary condition periodicity. |
 | `sponge_flag` | Flag to enable/disable sponge layer (`TRUE`, `FALSE`). |
 | `PML_factor` | Attenuation factor in PML absorbing zone (default: `0.0 s⁻¹`). |
 | `RelaxationFlag` | Flag to activate relaxation in buffer zone (`TRUE`, `FALSE`). |
 | `RelaxationTimeScale` | Relaxation time scale for buffer zone (default: `0.0 decimal days`). |
 | `RelaxationLengthScale` | Relaxation length scale for buffer zone (default: `0.0 m`). |
 | `LinearityFlag` | Flag to activate model linearity in buffer zone (`TRUE`, `FALSE`). |
 | `LinearityLengthScale` | Linearity length scale for radiative buffer zone (default: `0.0 m`). |
 | `BufferZoneFile` | File containing instructions for open boundary buffers. |
 | `rivers_flag` | Flag to enable/disable river discharge (`TRUE`, `FALSE`). |
 | `rivers_file` | File containing river discharge information (default: `rivers.dat`). |
 | `solid_boundary_condition` | Solid boundary condition type (`FREE-SLIP`, `CONDITIONAL-NO-SLIP`). |
 | `no_slip_size` | Size for no-slip condition (default: `100.0 m`). |