ah-docs

Extract N Values

Description

Create Manning table in the HEC-GeoRAS format from cross-section and land use feature classes. Mannings N values are defined as a field in the input land use table.

Input layers need to have the following fields populated:

2D Cross-sections:

• HydroID

Land Use:

• N_Value (field can be named anything and is selectable as input in the tools UI).

While the land use polygon feature class must have a field with n values, that field name is not hard-coded and will not be checked for before the tool is run. User will be able to select which field to use for n-value extraction through user interface. This enables the same polygon feature class to have multiple value fields representing different n-value alternatives.

The output table will have the following fields:

• XS2DID - contains the HydroID of the matching cutline (2D cross-section representation).
• Fraction - fraction along the cut line at which the roughness value changes. Note that initial value is always 0 indicating the starting roughness along the cut line. If the value does not change, that will be the only entry for that cut line. The end value (1) is not explicitly stored in the table as it is understood that the last change in roughness propagates till the end of the cut line.
• N_Value - roughness value

Usage

Parameters

Direction	Type	Parameter Name	Data Type	Dialog Reference
Input	Required	Input 2D Cross Section Feature Class	GPFeatureLayer	Cut line feature class (2D cross-section). It must have HydroID correctly populated.
Input	Required	Input Landuse Feature Class	GPFeatureLayer	Land use polygon feature class. It must have required attributes correctly populated.
Input	Required	Input Manning's N Value Field	Field	Field in the land use polygon feature class containing roughness coefficient for that polygon. Field has to be of a non-integer number type.
Output	Required	Output Manning's N Table	GPTableView	Table with roughness coefficient values per cut line.