Boundary Conditions¶

XBeach requires boundary conditions for flow and tide/surge at domain edges. This page covers the flow_boundary and tide_boundary components in Config.

For wave boundary conditions, see Data Interfaces > Wave Boundaries.

Flow Boundaries¶

Control how flow behaves at domain edges using Config.flow_boundary:

from rompy_xbeach.components.boundary.parameters import FlowBoundaryConditions

flow_bc = FlowBoundaryConditions(
    front="abs_2d",      # Offshore boundary
    back="wall",         # Onshore boundary
    left="neumann",      # Left lateral boundary
    right="neumann",     # Right lateral boundary
)

Boundary Types¶

Front (offshore) boundary:

Value	Description
`abs_1d`	1D absorbing-generating (default)
`abs_2d`	2D absorbing-generating
`wall`	Reflective wall
`wlevel`	Water level specified
`nonh_1d`	Non-hydrostatic 1D
`waveflume`	Wave flume mode

Back (onshore) boundary:

Value	Description
`wall`	Reflective wall (default)
`abs_1d`	1D absorbing
`abs_2d`	2D absorbing
`wlevel`	Water level specified

Left/Right (lateral) boundaries:

Value	Description
`neumann`	Zero-gradient (default)
`wall`	Reflective wall
`no_advec`	No advection

Tide Boundaries¶

Configure tide and surge boundary conditions using Config.tide_boundary:

from rompy_xbeach.components.boundary.parameters import TideBoundaryConditions

tide_bc = TideBoundaryConditions(
    tideloc=2,           # Number of tide locations
    tidetype="velocity", # Tide boundary type
    zs0=0.5,             # Initial water level (m)
    paulrevere="land",   # Sea/land specification
)

Tide Locations¶

`tideloc`	Description
0	No tide boundary
1	Single tide location (uniform)
2	Two corners (interpolated)
4	Four corners

Tide Types¶

`tidetype`	Description
`instant`	Instantaneous water level
`velocity`	Velocity-based
`hybrid`	Hybrid approach

Complete Example¶

from rompy_xbeach.config import Config
from rompy_xbeach.components.boundary.parameters import (
    FlowBoundaryConditions,
    TideBoundaryConditions,
)

config = Config(
    grid=grid,
    bathy=bathy,

    # Flow boundaries
    flow_boundary=FlowBoundaryConditions(
        front="abs_2d",
        back="wall",
        left="neumann",
        right="neumann",
    ),

    # Tide boundary
    tide_boundary=TideBoundaryConditions(
        tideloc=2,
        zs0=0.0,
    ),

    # Wave boundaries are specified via input.wave
    # See Data Interfaces > Wave Boundaries
)

YAML Configuration¶

flow_boundary:
  front: abs_2d
  back: wall
  left: neumann
  right: neumann

tide_boundary:
  tideloc: 2
  zs0: 0.0