The Trace Downstream tool uses a hosted digital elevation model (DEM) to trace downstream flow paths. For analysis purposes, hydrologic information has been precomputed by Esri using standard hydrologic models.
The output is a hosted feature layer.
Example
Many mining sites drains are connected to rivers, lakes, oceans, or other waterways, making anything entering the drain a potential pollutant for areas downstream. The Trace Downstream tool can be used to determine where the water entering the drain originated.
Usage notes
Trace Downstream includes configurations for the input layer, downstream path settings, and the result layer.
Input layer
The Input layer group includes Input point features, which specifies the points that will be used as the starting location for each downstream trace line. You can choose a layer using the Layer button, or use the Draw input features button to create a sketch layer to use as the input. For feature inputs, a count of features is displayed below the layer name. The count includes all features in the layer, except features that have been removed using a filter. Environment settings, such as Processing extent, are not reflected in the feature count.
Downstream path settings
The Downstream path settings group includes the following parameters:
- Split distance divides the trace line into multiple lines in which each line is the length provided.
- Split distance units are the linear units for the Split distance parameter value.
- Maximum downstream trace distance is the total length of the trace line that will be returned.
- Downstream trace distance units are the linear units for the Maximum downstream trace distance parameter value.
- Clip output to is the area to which the trace line will be clipped using a polygon feature layer.
Result layer
The Result layer group includes the following parameters:
Output line name is the name of the output polyline feature layer representing the downstream trace path.
The name must be unique. If a layer with the same name already exists in your organization, the tool will fail and you will be prompted to use a different name.
- Save in folder specifies the name of a folder in My content where the result will be saved.
Limitations
The following limitations apply to the tool:
- The input must be point features.
- The input has a limit of 1,000 features. If more input features are provided, the tool will return an error and will not run.
Environments
Analysis environment settings are additional parameters that affect a tool's results. You can access the tool's analysis environment settings from the Environment settings parameter group.
This tool honors the following analysis environments:
- Output coordinate system
- Processing extent
Note:
The default processing extent is Full extent. This default is different from Map Viewer Classic in which Use current map extent is enabled by default.
Outputs
This tool creates an output feature layer containing the downstream trace line or lines. The line features layer will contain the same attributes as the points and the following additional fields:
- PourPtID—The unique ID field from the input points feature.
- Description—The description of the source database used in the analysis. The options are as follows:
- US30m, which is derived from the 30m NHDPlusV2.1 for the continental United States
- 90m HydroSHEDS for the world between 60 degrees North and 56 degrees South, as well as some areas in Canada and Alaska north of 60 degrees
- Length—The length of the line in the units specified in the analysis. If no units are specified, the units in your profile, which are either miles or kilometers, will be used.
- DataResolution—The data source resolution that was used in the analysis.
- From Distance—The distance down the trace line where each line segment starts. The first From Distance attribute value for each trace line is always zero because the first trace segment starts at the origin. This field will only be added to the attribute table if a value was provided for the Split distance parameter.
- To Distance—The distance down the trace line where each trace segment stops. The last segment in a trace line will have a value that equals the total distance. This field will only be added to the attribute table if a value was provided for the Split distance parameter.
- Total Distance—The total distance of the trace line. This field will only be added to the attribute table if a value was provided for the Split distance parameter or the Maximum downstream trace distance parameter. It will be equal to the Maximum downstream trace distance value if specified.
Usage requirements
This tool requires the following user type and configurations:
- Creator, Professional, or Professional Plus user type
- Publisher or Administrator role, or an equivalent custom role
Resources
Use the following resources to learn more:
- Trace Downstream in ArcGIS REST API
- trace-downstream in ArcGIS API for Python
- Trace Downstream in ArcGIS Pro in the Ready to Use toolbox