Providing Geography for Topology;A Schematic View of the National

Watershed Boundary Dataset (WBD)

James E. Mitchell, Ph.D.

IT GIS Manager

Kurt L. JohnsonIT GIS Technical Specialist

2012 ESRI International User’s ConferenceSan Diego, California – July, 2012 (Revised January, 2013)

The Watershed Boundary Database

• A national database defining hydrologic boundaries– Based on the USGS Hydrologic Unit Codes

• Hierarchical organization that aggregates basins into– Regions – “HUC 2”– Subregions – “HUC 4”– Basins – “HUC 6”– Subbasins – “HUC 8”– Watersheds – “HUC 10”– Subwatersheds – “HUC 12”

• An areal depiction of the organization of watersheds and the flow of water across the landscape

Lake Pontchartrain Basinfrom the WBD Database

Lake Pontchartrain Basinfrom the

Watershed Boundary Dataset (WBD)

“Out of the box,” it is easy to see basin delineations. However, flow direction is less evident. As complexity increases and topography decreases relationships are unclear.

Lake Pontchartrain BasinSymbolized by HUC 10 Basins

Lake Pontchartrain Basinshaded by WBD HUC 10

Watersheds

HUC 12 Subwatersheds

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Open Water

Drainage patterns are more evident, using symbology. However detail is still lacking and relationships in complex areas are not clearly revealed.

Lake Pontchartrain BasinShowing WBD Downstream Topology

Lake Pontchartrain BasinWBD Downstream Flow Topology

HUC 12 Basin Centroids

HUC 12 Downstream Link

Gulf of Mexico

A schematic visualization of the Lake Pontchartrain Basin drainage pattern. This clearly depicts the drainage network in geographic space.

Creating a Schematic Diagram to Using Schematics to Represent the

Hierarchical Topology of Adjacent WBD Polygons

• Use the downstream HUC 12 attribute (ToHUC) to define the flow relationship between WBD Basins

• Create a centroid point to represent each WBD basin polygon (Feature to Point Tool, in ArcToolBox)– Force the centroid to lie within the polygon

• Create a schematic diagram – Use the basin centroids to define the schematic nodes– Use the ToHUC field to develop the link to the next

downstream node• Examine diagram for topology errors and “loose ends”

Step 1 – Create Basin CentroidsLake Pontchartrain Basin

WBD HUC 12 Basin Centroids

Centroids placed within each HUC 12 basin polygon contain the attribute information form their originating polygon. This is used to create links between up and down stream.

Step 2 – Identify a Schematic DatasetIn a geodatabase, create a new Schematic Datasetor use an existing Diagram Template

The Diagram Template defines the style and elements in the diagram

The first element of this template is a schematic node feature that captures the X,Y position of each centroid point from its Shape field

The second element of this template is a schematic link (line) feature that uses a query to select a starting point (centroid) and end point (downstream centroid from ToHUC) and transfers the X,Y position of each to the link origin and extremity nodes

Step 3 – Schematic Node Featureclass Created from Basin Centroids

The new features will be a “Node” type schematic feature

The geometry of the schematic features will be “Point” type

Properties of the schematic nodes

Step 4 – Transfer X,Y to Schematic Nodes from Basin Centroids

The new “InitialXPosition” attribute is named and set to a Type of “Geo Geometry”

The Field dropdown is set to “Shape” and “X Coordinate” is selected for Geometry

The same process is used to create the “InitialYPosition” attribute

Create attributes for the schematic nodes – “InitialXPosition” and “InitialYPosition”

Step 5 – Schematic Link Featureclass Created from Basin Centroids

The new features will be a “Link” type schematic feature

The geometry of the schematic features will be “Polyline” type

Properties of the schematic links

Step 6 – Create Schematic Links by Defining Origin and Extremity Nodes

The new “OriginNode” attribute is named and set to a Type of “Field”

The Field is used to define a query to erect the centroid node at the beginning of the link (HUC12)

The same process is used to create the “ExtremityNode” attribute, specifying the ToHUC field, to select the node (centroid) at the end of the link

Create attributes for the schematic links – “OriginNode” and “ExtremityNode”

Lake Pontchartrain BasinInitial Schematic Diagram

Lake Pontchartrain BasinInitial Flow Schematic

Based onWBD HUC 12 Downstream Attribute

Detail of Initial DiagramFull Extent of Initial Diagram

Terminal nodes have no downstream element with which to link. This can be used as a means to examine, diagnose, and correct topological errors and anomalies.

Lake Pontchartrain BasinExamining and Correcting Topology

Lake Pontchartrain BasinCorrecting WBD HUC 12 Topology

PROBLEM This centroid is froma polygon outside ofthe Pontchartrain Basinand drains directly into the the Mississippi Riv er

SOLUTION Delete the centroidfrom the input datasetand regenerate thediagram

OR

Edit the diagram anddelete this link

PROBLEM : These are terminal nodesand have no downsteamnode with whigh to createa connection link

PROBLEM These are terminal nodesand have no downsteamnode with whigh to createa connection link

SOLUTION Delete the links and createa new point in the centroidsdata representing a locationfor the Gulf of Mexico

PROBLEM This is the centroid forLake Borgne and hasa downstream HUC 12designted as "OCEAN"

The correct downstreamHUC 12 is actually"Chandeleur Sound"

SOLUTION Edit the centroids attributetable to reflect:

HU_12_DS = "080902030900"

Then regenerate the diagram

Four topology errors become immediately apparent. One is a basin outside of Lake Pontchartrain. The others relate to missing or incorrect downstream links.

Lake Pontchartrain BasinAfter Correcting Topology

Lake Pontchartrain BasinDiagram After Topology Corrections

HUC 12 Basin Centroids

HUC 12 Downstream Link

Path from terminal node (Gulfof Mexico) to an arbitrary point(0,0) at end of diagram

Point added to centroids torepresent the topological position of the Gulf of Mexico

Corrected flow path from Lake Borgne toChandaleur Sound

Created by editing the HU_12_DS field inthe WBD

This ling has been edited to route it aroundHUC 12 basins that lie between the LakeBorgne node and the Chandaleur Sound node

After correcting the topology errors, the new diagram is complete and only requires the removal of the arbitrary terminal node.

What Can Be Done with this Schematic Diagram?

• WBD QA/QC

• Identify flow relationships– Upstream/downstream (including multiple pourpoints– Flow accumulation– Diversions and interbasin transfers

• Visualize the flow network in different formats (styles)

• Trace flow paths– Connect pollution sources to water quality impacts

Flow Topology ApplicationsConnecting Upstream and Downstream

Applications from the Lake Pontchartrain Basin Flow Topology Diagram

Jones Creek

Clay Cut Bayou

King George Bayou

Bayou Barbary

Lake Maurepas

North Pass-Manchac Pass

Lake Pontchartrain

What drainage systems connectJones Creek to Lake Pontchartrain?

Which basins are downstreamfrom downtown Baton Rouge?

What drainage systems connectto Lake Pontchartrain?

Which watersheds are locatedupstream from Lake Maurepas?

HU_12_NAME

Skulls Creek-Tangipahoa River

Ponchitalaw a Creek-Tchefuncta River

Bayou Chinchuba

Liberty Bayou-Bayou Bonfouca

Big Branch Bayou-Lacombe Bayou

Bayou Castine-Cane Bayou

North Pass-Manchac Pass

Bayou Vincent-Bayou Bonfouca

Illinois Central Gulf

Lake Pontchartrain

Salt Bayou

Schematic diagrams can be “traced” and selections propagated into the data frame

Lake Pontchartrain BasinGeographic and Schematic Diagrams

Lake Pontchartrain BasinGeographic and Schematic Diagrams

Maps and diagrams are linked allowing selections to be propagated between them. The schematic depiction of these basins provides a clear view of their topology

Lake Pontchartrain BasinHierarchical Smart Tree Diagram

Lake Pontchartrain BasinPure Schematic Diagram

Lake Maurepas

Lake Pontchartrain

Lake Borgne

The diagram provides a simplified depiction of the topology of the Lake Pontchartrain Basin. Up and downstream traces can be executed and transferred to the map.

Lake Pontchartrain BasinHierarchical Diagram/Orthogonal Corners

Lake Pontchartrain BasinPure Schematic Diagram wih Orthogonal Connections

Lake Maurepas

Lake Pontchartrain

Lake Borgne

Diagrams can be edited and reformatted using varies options. Using this capability, diagrams can be designed to satisfy essential operational and functional requirements.

Interbasin TransferThe Bonnet Carré Spillway

The Bonnet Carré Spillway is opened to relieve pressure on New Orleans’ levees from the Mississippi River and moves water into the Lake Pontchartrain Basin.

Interbasin Transfers in theWatershed Boundary Dataset

Interbasin Transfer into the Lake Pontchartrain Basinfrom the Bonnet Carré Spillway

Bonnet Carré Spillway

An interbrain transfer can be accommodated by adding two additional records (nodes) to the “centroids” database, at the location of the diversion. For the point representing the diversion, the HUC_12 is set to the originating HUC_12 plus a sequence number, and the HU_12_DS is set to the receiving basin. The sequence number will represent the position of the diversion, relative to the centroid, which will also have to have its HUC_12 modified to represent its position. This must be repeated for each diversion.

Interbasin transfers or diversions can be accounted for by adding additional points to the centroids data and modifying the WBD attribute table for proper routing.

Conclusions• Schematics provide a powerful tool for visualizing

topological relationships– “Geographic” space– “Logical” space

• Schematics can be used to investigate, reconcile, and ensure topological integrity (QA/QC)

• Schematics can be used to extend the capabilities of geospatial data, such as the Watershed Boundary Dataset by:

– Creating a logical network representing the flow through geographic elements– Augmenting simple topology with complex networks

– Extending the capabilities of the data with tools that can navigate through the network