Surface Polygon
Several polygon element types are now available for 2D modeling: Building, Land Use Area, Road, Adjustment Area, and Void Area. Each of these 2D Grid Adjustments can be drawn on the map as an area of similar overland characteristics. Where the polygon’s area overlaps with a 2D Grid, the underlying grid cells will be adjusted as specified by the 2D Polygon. To declare how these polygon elements will intersect computational grid cells, refer to the calculation option Polygon Intersection Type.
- Building – is representative of a building’s footprint upon the 2D computational grid.
- Land Use Area – will model a parcel of land with similar hydrologic attributes.
- Adjustment Area – provides the ability to simulate a proposed land use or elevation adjustment to portion of a catchment or 2D grid area.
- Road (2D Polygon) – designates a portion of the 2D submodel as an impermeable surface area.
- Void (2D Polygon) – allows for user defined and irregular polygon-shaped portions of the grid to be excluded from 2D computational space.
The following attributes are used to model the properties of Surface
Polygons:
- Elevation Adjustment Operation: Allows you to specify how you want to adjust the surface elevations of the corresponding grid cells. Choices are Add, Subtract, or Set.
- Elevation Adjustment: Is the amount of change in elevation that will be added to, or subtracted from, the current surface elevation of each matching grid cell. The operation of Set To will directly assign this value as the new surface elevation for each grid cell that is encompassed by the area.
- Impermeability Fraction Adjustment Type: Lets you select how the value for Impermeability Fraction that will be overridden for the corresponding 2D grid cells; using a User Defined amount or a value from a referenced catalog item.
- Impermeability Fraction: When the Impermeability Fraction Adjustment Type is User Defined, enter the value to assign to each of the 2D grid cells contained by this area.
- Manning’s n Adjustment Type: Lets you select how the value for Manning’s n will be assigned to each grid cell. Either a User Defined value, or referencing a value defined within a catalog item.
- Manning’s n: The value for overland roughness that will be assigned to the corresponding portion of the computational grid.
- SCS CN Adjustment Type: Lets you select how the value for SCS Curve Number will be provided; using a User Defined amount or a value from a referenced catalog item.
- SCS CN: Applicable when the SCS CN Adjustment Type is User Defined, enter the value that you wish to allocate to the corresponding 2D grid cells. The default value is 98.
- Priority: Is used to determine which adjustment area governs when two areas overlap.