Model Flags

HydroPol2D is controlled through a set of binary and categorical flags defined in General_Data.xlsx.

These flags determine:

• which physical processes are active
• how forcing is applied
• which numerical schemes are used
• how outputs are generated

Each flag must be set consistently with the selected modeling approach.

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Boundary Condition Flags

Flag	Description
$\mathrm{flag\_rainfall}$	Activates rainfall forcing over the domain
$\mathrm{flag\_spatial\_rainfall}$	Uses spatially distributed rainfall instead of uniform rainfall
$\mathrm{flag\_ETP}$	Activates evapotranspiration computation via meteorological forcing
$\mathrm{flag\_input\_rainfall\_map}$	Uses raster-based rainfall input (e.g., satellite or gridded products)
$\mathrm{flag\_rainfall\_multiple\_runs}$	Under Development
$\mathrm{flag\_data\_source}$	Under Development
$\mathrm{flag\_inflow}$	Activates inflow hydrograph boundary conditions
$\mathrm{flag\_satellite\_rainfall}$	Uses satellite-derived rainfall products
$\mathrm{flag\_alternated\_blocks}$	Activates Alternating Block design storm method
$\mathrm{flag\_huff}$	Activates Huff storm distribution method
$\mathrm{flag\_stage\_hydrograph}$	Applies stage (water level) boundary condition
$\mathrm{flag\_input\_ETP\_map}$	Uses raster-based evapotranspiration inputs

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Hydrologic–Hydrodynamic–Water Quality Flags

Flag	Description
$\mathrm{flag\_infiltration}$	Activates infiltration into the soil
$\mathrm{flag\_critical}$	Limits flow velocity to the critical flow (Froude = 1)
$\mathrm{flag\_D8}$	Activates D8 flow routing scheme
$\mathrm{flag\_CA}$	Activates Cellular Automata routing
$\mathrm{flag\_inertial}$	Activates Local Inertial shallow water equations (recommended default)
$\mathrm{flag\_waterbalance}$	Distributed mass balance errors in inflow cells (default 0)
$\mathrm{flag\_waterquality}$	Activates water quality transport module
$\mathrm{flag\_reservoir}$	Activates reservoir internal boundary conditions
$\mathrm{flag\_wq\_model}$	Defines which wash-off model to use
$\mathrm{flag\_groundwater\_modeling}$	Activates groundwater recharge computation
$\mathrm{flag\_real\_time\_satellite\_rainfall}$	Enables real-time satellite rainfall ingestion with Persiann
$\mathrm{flag\_dam\_break}$	(Under Development)
$\mathrm{flag\_human\_instability}$	Activates human stability hazard modeling
$\mathrm{flag\_boundary}$	Enforce all boundary cells as outlet cells
$\mathrm{flag\_numerical\_scheme}$	1: local inertial model, 2: upwind scheme, 3: central scheme
$\mathrm{flag\_outlet\_type}$	1: normal flow, 2: critical flow
$\mathrm{flag\_adaptive\_timestepping}$	Celerity-based, 2: Celerity + Advection-based stability criteria (1 as default)
$\mathrm{flag\_neglect\_infiltration\_river}$	Disables infiltration in river cells
$\mathrm{flag\_subgrid}$	Activates subgrid hydraulic representation
$\mathrm{flag\_spatial\_albedo}$	Uses spatially distributed albedo instead of uniform values
$\mathrm{flag\_river\_rasters}$	Uses raster-based river geometry inputs
$\mathrm{flag\_baseflow}$	Solves 2D Boussinesq Equation for Aquifers
$\mathrm{flag\_kinematic}$	Activates kinematic wave approximation
$\mathrm{flag\_diffusive}$	Activates diffusive wave routing
$\mathrm{flag\_DTM}$	Uses digital terrain model corrections or processing
$\mathrm{flag\_abstraction}$	Activates water abstraction or withdrawal processes
$\mathrm{flag\_overbanks}$	Activates floodplain overflow dynamics with a subgrid model
$\mathrm{flag\_snow\_modeling}$	Activates snow accumulation and melt processes
$\mathrm{flag\_WQ\_Rasters}$	Uses raster-based pollutant inputs

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Performance Flags

Flag	Description
$\mathrm{flag\_GPU}$	Enables GPU acceleration
$\mathrm{flag\_single}$	Uses single precision arithmetic for performance optimization

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Initial Condition Flags

Flag	Description
$\mathrm{flag\_warmup}$	Activates model warm-up period to stabilize initial conditions
$\mathrm{flag\_initial\_buildup}$	Initializes pollutant buildup conditions

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DEM Treatment Tools

Flag	Description
$\mathrm{flag\_resample}$	Activates raster resampling to target resolution
$\mathrm{flag\_smoothening}$	Applies DEM smoothing filter
$\mathrm{flag\_trunk}$	Smooth only the main river trunk from DEM
$\mathrm{flag\_fill\_DEM}$	Fills sinks in DEM for hydrological consistency
$\mathrm{flag\_smooth\_cells}$	Applies cell-level smoothing to terrain
$\mathrm{flag\_reduce\_DEM}$	Reduces DEM resolution at river cells

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Extra Flags

Flag	Description
$\mathrm{flag\_export\_maps}$	Enables export of raster outputs
$\mathrm{flag\_dashboard}$	Activates dashboard-style outputs or visualization
$\mathrm{flag\_elapsed\_time}$	Tracks simulation runtime
$\mathrm{flag\_obs\_gauges}$	Activates output extraction at observation gauge locations

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Notes

• Flags must be used consistently to avoid conflicting configurations
• Only one routing scheme should be active at a time (e.g., inertial vs diffusive vs kinematic)
• Subgrid and raster-based river options should not be combined unless explicitly supported
• Adaptive time stepping is strongly recommended for numerical stability
• GPU execution requires compatible data structures and hardware

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Summary

Flags define the structure of a HydroPol2D simulation.

They control:

• physics
• numerics
• forcing
• outputs

Correct configuration of these flags is essential for stable and physically meaningful simulations.