Additional Spatial Inputs

Beyond the core DEM, LULC, and soil rasters, HydroPol2D can ingest a wider set of optional raster and initial-state inputs. This page documents the supported file-based inputs that were historically under-described in the docs.

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Supplemental Raster Inputs

Input	Public path key	When used	Notes
Initial groundwater table	GW_table_path	When groundwater is active and an initial head raster is supplied	Raster is interpreted as initial groundwater table elevation/head in meters, aligned to the DEM. If missing, the model falls back to a shallow default water table above bedrock.
Fractional imperviousness	ImperviousFraction_path	When a fractional impervious raster is supplied	Values can be in [0,1] or [0,100] percent. This refines imperviousness for non-built-up cells. Cells classified as built-up/impervious by LULC remain fully sealed.
Spatial LAI	LAI_path	When LAI is used by the active configuration	Optional vegetation raster aligned to the DEM.
Spatial albedo	Albedo_path	When flag_spatial_albedo = 1	Optional albedo raster aligned to the DEM.
River width	RiverWidths_path	When the Neal (2012) channel-subgrid mode uses raster geometry	Channel width in meters. Values must be positive and smaller than the model-cell resolution.
River depth	RiverDepths_path	When the Neal (2012) channel-subgrid mode uses raster geometry	Rectangular channel depth or bank height in meters. A positive depth is required wherever river width is positive.
Water-quality coefficient rasters	B1_path, B2_path, W1_path, W2_path	When water quality is active and raster coefficients are enabled	Optional pollutant buildup / washoff coefficient rasters.

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Initial-State Raster Inputs

Input	Public path key	When used	Notes
Initial surface water depth	Warmup_Depth_path	When flag_warmup = 1 and a warmup-depth raster is provided	Raster is read as initial ponded depth in meters and converted internally to millimeters.
Initial soil storage	Initial_Soil_Moisture_path	When flag_warmup = 1 and an initial soil raster is provided	Despite the legacy name, the current code interprets this raster as initial active soil storage above residual water content in millimeters, not raw volumetric $\theta$.
Initial pollutant buildup	Initial_Buildup_path	When water quality uses an initial buildup raster	Used to initialize pollutant mass/buildup states.

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Groundwater Table Input

If GW_table_path is supplied, HydroPol2D uses that raster as the initial groundwater table elevation:

• it is aligned to the DEM,
• clipped so a minimum vadose thickness is preserved,
• masked to the active domain,
• and locally backfilled only where the raster has missing values.

If no groundwater-table raster is provided, the model falls back to a simple default initial head slightly above bedrock. This means GW_table_path is a true optional initial-condition input, not a required groundwater raster.

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Fractional Imperviousness Input

If ImperviousFraction_path is supplied, HydroPol2D reads a cellwise impervious fraction raster and converts it to:

• impervious fraction frac_imp,
• pervious fraction frac_perv,
• and a fully impervious mask for cells that are effectively sealed.

Important current behavior:

• values may be supplied as fractions or percents,
• the raster refines imperviousness mainly outside the built-up LULC class,
• cells already classified as impervious/built-up by the LULC table are forced to remain fully impervious.

So the impervious raster should be documented as a fractional imperviousness override/refinement, not as a separate standalone land-cover map.

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Alignment and Resampling

These supplemental rasters are expected to be consistent with the DEM, but HydroPol2D also performs alignment work internally:

• rasters are resampled to the DEM grid when needed,
• invalid values are masked out of the active domain,
• some optional rasters are only loaded when the corresponding flags are active.

That makes them flexible, but it does not remove the need for sensible preprocessing on the user side.

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Neal (2012) Channel Geometry

The Neal (2012) channel-subgrid mode uses the coarse DEM as the floodplain elevation. RiverDepths_path lowers the embedded rectangular channel bed below that elevation, while RiverWidths_path defines the channel width within each active river cell. The two rasters must be supplied together.

The channel width must remain smaller than the model-cell resolution. A channel as wide as or wider than the cell should be resolved by the ordinary grid instead of represented as a subgrid channel. Channel and floodplain roughness are assigned separately through the river and LULC parameter inputs.

See Model Flags for the required routing combination.

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Recommended Public Interpretation

The easiest way to think about the input surface is:

1. DEM, LULC, and SOIL define the base domain.
2. DTB, GW table, LAI, albedo, and impervious fraction refine that base domain.
3. Warmup, initial soil storage, and initial buildup set the starting state.
4. Water-quality rasters support optional specialized modules.

That is the current implemented input story the docs should follow.

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Root Depth

Root depth is part of the current model input surface, but not as a standalone raster path.

Current implemented behavior:

• root depth is read from the LULC parameter table as root_depth_m,
• that class-based value is expanded to the grid through the categorical LULC map,
• the resulting root depth is then truncated by bedrock depth and water-table position when the layered vadose profile is built.

So yes, HydroPol2D can ingest root-depth information, but the supported public path today is:

1. LULC raster for class identity,
2. root_depth_m in the LULC parameter table for per-class root depth.

There is no separate RootDepth_path raster input in the current code.