Following the definition given in the Arc Hydro book, HydroJunction is a feature class that contains all points of strategic hydrologic interest. The fact it is a Junction is telling us it belongs to the Hydrologic Network (it is a Network feature) and therefore represent connecting nodes that exist as elements of the network.

The fundamental definition given above is telling us that you must select your very own points of strategic hydrologic interest. Once you select them you can load all of them inside a point feature class called HydroJunction which will be the container for points of diverse hydrologic nature. Below there is a list of points that are normally considered of strategic hydrologic interest. Some of them already have a standard name inside the Arc Hydro Data Model.

• Streamflow or Discharge stations, named as MonitoringPoint in Arc Hydro

• Water Rights or Water Allocation Points, named as some of the seven HydroPoints in Arc Hydro

• Watershed Outlets, you may call it, WshOutlet

• Waterbody Outlets, you may call it, WbdOutlet

• Catchment Outlets, you may call it, CatOutlet

In short, you must load into the HydroJunction point feature class all the points of interest for your project following a procedure similar to the one outlined below:

In ArcCatalog (right click on feature dataset > new feature class) Generate a new feature class with POINT geometry importing the fields from any existing Point feature class as needed and call it HydroJunction.

Note: Before loading make sure the layers contain the following fields: Name, HydroID, HydroCode, and FType with the right Arc Hydro format.

4.1-Load MonitoringPoint into HydroJunction:

Because of the line representation of the river network in GIS or because of the type of station, the gauging stations may not lie exactly on the HydroEdge feature class. Thus, for network purposes it is needed to dual representation of the stations in the Arc Hydro model. One representation at their exact location as given by the MonitorinPoint Layer and another correspondent representation on the Network as HydroJunctions. To accomplish this, you can not only load the stations to HydroJunctions but also snap them to the network during the loading process as explained below:

Using the Load Features Process (shown below) load all MonitoringPoints to HydroJunction (with snapping option active)

If the Load Objects Tool is not loaded and active on ArcMap do:

Right click on gray background > Customize… > Commands > Data Converters > Load Objects…

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Process to Load Features that have a dual representation inside the Geodatabase

That is, only for Point features “not” on river network that should have a Junction representation on the network. Like MonitoringPoints of discharge

In MonitoringPoint do:

Add Fields: HydroID, GageID, JunctionID

In HydroJunction do:

Add fields: GageID, FType

In MonitoringPoint do:

Populate HydroID

Copy HydroID to GageID

 In ArcMap:

Set snapping environment:

Snap to Edges in HydroEdges

Perpendicular to sketch

Note: Make sure the snapping tolerance is appropriate for your dataset based on the biggest distance to be snapped!

Set Snapping tolerance = Number of  map units appropriate for your dataset based on the biggest distance to be snapped

Set Target = HydroJunction

Load Objects using snapping option

From MonitoringPoint to HydroJunction

In HydroJunction do:

Add field HydroID

Assign HydroID

In MonitoringPoint do:

align="justify"Join MonitoringPoint attribute table with HydroJunction attribute table using GageID as common field

Copy HydroJunction.HydroID to MonitoringPoint.JunctionID

Save Edits

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Select HydroJunction that intersects MonitoringPoint (the ones that failed to snap) and snap them manually (~Edit > Modify feature)

Add Ftype = GageUSGS, GageNSIP, GageHCDN (or other similar descriptor based on the source of your points)

Check and correct any superposition of gages and avoid multiple junctions for coincident gages (you must have only one Junction for all coincident gages)

4.2-Generate Outlet Junctions for Watersheds:

Intersect HydroEdge and Watershed using the Geoprocessing wizard in ArcMap and call the output WshI

Build a Network called NetWshI from the previous WshI to get NetWshI_Junctions

Note: If you have Drainage Point Processing from a previous DEM Terrain Analysis you may use that point layer as Outlets for your Watersheds.

Besides the needed intersection points you also have generic junctions that you do not want to include in your Network. Follow Process for Exclusion of Generic Junctions to leave the Intersections only.

Process for Exclusion of Generic Junctions (To leave Intersections ONLY)

Build Network from HydroEdge and call it NetEdges to get NetEdges_Junctions (To get the Generic Junctions)

Intersect HydroEdge with Watershed to get WshI

Build Network from WshI to get NetWshI_Junctions (Generic + WshOutlets)

In NetWshI_Junctions Select Intersection with NetEdges_Junctions

Switch the selection and export selection to a new layer (WshOutlet1)

Add Ftype = “WshOutlet”

Load WshOutlet1 to HydroJunction without snapping

4.3-Generate Outlet Junctions for Waterbodies:

Select Waterbodies that intersect HydroEdge

Generate a new layer from selection, WbdOnly

Note: If HydroEdge and Waterbody come from NHD (inArc or inGeo formats) the intersection with Waterbody already exists and the following step is NOT necessary.

If Edges have no Ends at Waterbody intersections then, Generate Outlet Junctions for Waterbodies (Intersect HydroEdge and WbdOnly with Geoprocessing wizard) to get WbdI, then build Network (NetWbdI) from WbdI to get NetWbdI_Junctions (with snapping using default values)

Follow Process for Exclusion of Generic Junctions as described below:

Intersect HydroEdge with Waterbody to get WbdI

Build Network from WbdI to get NetWbdI_Junctions (Generic + WbdOutlets)

In NetWbdI_Junctions Select Intersection with NetEdges_Junctions

Switch the selection and export selection to a new layer (WbdOutlet1)

Add Ftype = “WbdOutlet”

Load WbdOutlet1 to HydroJunction without snapping

 4.4-Load Outlet Junctions

Load Outlet Junctions (For Watersheds and Waterbodies) into HydroJunction with no snapping (HydroJunction already contains the MonitoringPoints)

Set Target = HydroJunction

Load without snapping

4.5-Assign HydroID to all layers

Using the Arc Hydro Tool bar in ArcMap assign HydroIDs to all existing layers in your geodatabase: Watershed, HydroJunction, Waterbody, HydroEdge, MonitoringPoint, Catchment

Save Edits

Go onto next phase