Create Breach Lines

Description

Create straight line that breaches the local impediment to flow. The method loops through input breach area points and applies the following steps to each point at a time (points are treated independently from each other):

• Identify all elevation cells in the DEM within search radius that are lower than the elevation at the breach area point (specified by the ELEVATION field in the input point feature class) and group them into contiguous, non-overlapping regions.
• If there are no candidate regions, tool does not create a breach line for that point. Using larger value for "Maximum Allowed Line Length" parameter could find a candidate(s).
• If multiple candidate regions exist for a location, the closest region to the point is selected, and a breach line is constructed from the point of interest to the closes point on the region boundary (straight distance). Direction of "flow" for the constructed line is from the point of interest towards the region point.

The constructed line is a 2D line whose from node elevation will always be higher than the to node elevation. The input points must have the following fields:

• POINT_X - x coordinate of the point.
• POINT_Y - y coordinate of the point.
• ELEVATION - elevation used to identify lower neighborhood area.

If input points have HydroID assigned, the output breach line feature class will have field "FeatureID" containing the HydroID of the point for which this is the breach line.

The intent of the tool is to generate potential breach lines from depression areas representing man-made drainage structures (culverts/bridges). Not all identified locations might need or have such structures, so other selection criteria can be used for further selection (such as proximity to roads, existing flow paths, etc.). Ideally that would be applied on the selection of the input points, but the resulting breach lines can be also used for additional selection criteria (e.g. based on the length or slope of the resulting breach line).

The intent of this tool is to be used in conjunction with the "Identify Breach Area" tool and its resulting Breach Area Point. Other techniques for identifying starting points for the analysis can be used as well, as long as the resulting point feature class has required fields.

Usage

Parameters

Parameter Name	Type	Direction	Data Type	Dialog Reference
Input Breach Area Point	Required	Input	Feature Layer	Point feature class for which to find breach lines. Needs to have fields POINT_X, POINT_Y, and ELEVATION populated. It is recommended that HydroID is populated as well.
Input DEM Raster	Required	Input	Raster Layer	Input elevation raster.
Maximum Allowed Line Length	Required	Input	Double	Maximum length used to identify candidate regions around point of interest (in map units). Note that the actual length of generated line will almost always be less than this distance.
Output Breach Line	Required	Output	Feature Layer	Output potential breach 2D line feature class. Besides properties of the end points, line will also have attributes: NEAR_FID - OBJECTID of the breach (starting) point. FeatureID (optional) - HydroID of the breach point (if available).