National Hydrography Dataset and Networks in
ArcGIS
Prepared by Oscar Robayo, David R. Maidment
and Victoria Samuels
Center for Research in Water Resources
September 2002
Contents
·
Computer and Data Requirements
Part 1. The National Hydrography Dataset
·
Obtaining National Hydrography
Dataset Data
·
Viewing
and Inspecting NHD Feature Classes
·
Building a Geometric Network in
ArcCatalog
·
Using the Utility Network
Analyst Toolbar in ArcMap
Part
3. Generating an Arc Hydro Data Model
·
Applying
the Schema framework
·
Applying
Arc Hydro Tools
Goals of the Exercise
The
study area selected for this exercise corresponds to the San Marcos River basin
(8-digit HUC #12100203), which is part of the Guadalupe River Basin already
used for exercise 2.
This
exercise has three parts:
Part
1 introduces you to map
hydrography data depicting water features of the landscape, and specifically
hydrography data from the National Hydrography Dataset. There is a
voluntary addendum to this part in which you can learn to symbolize and
differentiate between the feature and reach data layers. The attributes
accompanying the hydrography data are also described.
Part
2 uses the network
capabilities in ArcGIS to allow you to:
·
Build
a Geometric Network of river and coastline features
·
Assign
Sinks and Set Flow Direction on the Network
·
Perform
Traces traversing the Network upstream and downstream
Part
3 contains the
application of the Arc Hydro schema to create an Arc Hydro Framework dataset
and the execution of a set of Arc Hydro tools to fill in some of the attributes
contained in the dataset.
Computer and Data Requirements
To carry out this exercise, you need to use the ArcInfo version of ArcGIS. The first part of this exercise can be carried out using ArcView, but the construction of a geometric network in the second part of this exercise cannot be done with ArcView. In order to download the National Hydrography Dataset data, you need Internet access. The data files used in the exercise consist of ArcInfo coverages from NHD and prepared shapefiles. All of the NHD data being used is in the Geographic projection, NAD 83 datum. The following files are required for this exercise and are stored in the file Ex4Data.zip
For
UT Austin students, the files are located on the LRC NT network in the
directory class\maidment\giswr\SanMarcos\.
·
12100203
zip file: the NHD
data for
·
HydroEdge,
HydroJunction, MonitoringPoint, Waterbody, Watershed: shapefiles for the
·
ArcHydroFrameworkSchema.mdb:
The schema to be applied
to your data model.
Part 1: The National
Hydrography Dataset
Obtaining National Hydrography Dataset Data
The
National Hydrography Dataset (NHD) is a substantial set of digital data and
contains information about the surface water drainage network of the
The
NHD is available at the website http://nhd.usgs.gov.
At this web site, click on the Data tab on the left side of the screen
and then click on the first bullet, Obtaining NHD Data. The NHD is
organized by Hydrologic Cataloging Unit (HUC). You will see a map of the
Zoom
in several times on
Press
the Download button on the lower right of the window. Fill out the NHD
Download screen information and Continue. Click Yes to
the Security Warning and click Download on the Download
page. Navigate to the location you want to place the 12100203 file,
and click OK to the Successful Download window. You should
now have all the 12100203.tgz files, a compressed set of folders with
the NHD data.
It
can occur that you get the response:
If
so, you can go to the Trouble Downloading? link, and choose Alternative Download
Methods and go to Medium
Resolution Data. Scroll down the
list to the 12100203.tgz link; click on it, then choose Save this
file to a disk. Navigate to the directory you want to place the data
in.
Now
you have the NHD data for the HUC that makes up the
Structure of the
National Hydrography Dataset
To
explore the structure of the NHD dataset unzip the 12100203.tgz file using the
Windows utility Winzip. Extract the file to the 12100203 folder.
Click Yes to the Winzip window asking if Winzip should decompress
12100203.arc.tar to a temporary folder. In Windows Explorer, navigate to
the 12100203 folder. Please note that using Winzip for uncompressing the
NHD files has some limitations not important to this exercise.
These limitations are important if you want to append or join NHD files for
several adjacent HUC units. In that event, use the uncompression software
provided on the NHD website.
The
NHD is organized as three ARC/INFO coverages (nhd, nhduu, and nhdpt), many
related INFO tables, and text files containing metadata. The nhd coverage
contains the line and polygon features. This coverage has line, polygon
and node topology, which together form a type of network topology. The nhdpt
coverage contains point features related to the hydrography. The third
coverage, nhdduu, contains metadata and information about sources and
updates of the hydrographical information. The spatial elements of the
surface water network are found in the nhd and nhdpt coverages.
An
addendum to this exercise NHDSanMarcos.doc
explores the National Hydrography Dataset for the
Part 2: Networks in
ArcGIS
Building a Geometric Network in ArcCatalog
We
can build a geometric network from the route.drain coverages in the NHD
files. Within the network functionality
of ArcGIS, the ability to trace along networks based on flow directions and
relationships is central. Open ArcCatalog and navigate to your data
folder containing the files for exercise 4. Right-click on the Ex4 folder in
the Table of Contents on the left. Drag down to New, and then drag
over to Personal Geodatabase.
Name
the geodatabase SanMarcos. Right-click on SanMarcos.mdb and
drag down to New and then to Feature Dataset....
Enter
the Name: for the Feature Dataset as ArcHydro (make sure that
ArcHydro is one word and not two words). Click Edit.. for the Spatial
Reference Properties and click on Import... a coordinate
system and X,Y,Z, M domains Navigate to the data folder and select Watershed.shp.
This sets the spatial extent for the feature dataset the same as the extent for
the Watershed.shp data layer, which contains a layer with raster-derived
catchments for the
At
this point, you want to enter all the data layers directly into the feature
dataset ArcHydro. Right-click on the feature dataset ArcHydro
and drag down to Import and to Shapefile to Geodatabase.
For the Input shapefile: browse to the HydroEdge.shp data layer
(an enhanced version of the NHD route.drain layer for the San Marcos River
basin) and keep the name of the new feature class as HydroEdge to be
consistent with the ArcHydro geodatabase structure. Click OK.
The software then converts the shapefile into data within the feature
dataset.
Add
the remaining shapefiles HydroJunction.shp, Waterbody.shp, and MonitoringPoint.shp
shapefiles from the Ex4Data.zip file to the ArcHydro feature
dataset by importing from Shapefile to Geodatabase in ArcCatalog
and keeping the standard names of all new feature classes. These five feature classes are the ones
contained in the Arc Hydro Framework dataset, which is the simplest form
of the Arc Hydro data model. The files
have been prepared for you in this exercise to simplify its execution but in
reality it takes quite a significant amount of data preparation to get the
files you are using.
·
HydroEdge.shp contains the river network for
·
HydroJunction.shp contains Junctions on the NHD network
representing Stream gages, Outlets for waterbodies, and Outlets for watersheds.
IN addition, you can introduce new Junctions based on other points of interest
(Control Points, Water Rights, Ecological monitoring points, Water withdrawals,
etc.).
·
MonitoringPoint.shp contains the USGS stream gages for the
·
Waterbody.shp contains the waterbody regions as
contained in the NHD layer region.rch.
·
Watershed.shp contains watersheds delineated for each
USGS streamgage from a raster analysis using a DEM (you’ll learn how to do this
in Exercise 5 in this course).
Ok,
now for the cool part, we are going to create a geometric network!!!
From
the Network feature dataset, right-click and drag down to New and to Geometric
Network...
This
launches a “Build Geometric Network Wizard” to help you create a network
from existing feature classes in a feature dataset. Click Next.
Because
you now have the HydroEdge data layer as the arcs, which you want to use
as your network and HydroJunction to determine flow direction, you want
to Build a geometric network from existing features. Make sure
this radial button is highlighted and click Next.
The
next screen determines which existing features should be incorporated in the
network. Because you have entered some feature classes into the feature
dataset, they are listed as defaults. Check only HydroEdge and HydroJunction
and enter the name HydroNetwork. (don’t forget to name this network
as HydroNetwork as the default name of ArcHydro_Net does not allow you to apply
the Arc Hydro Schema later in this exercise). Click Next. Click OK
to the ArcCatalog Warning about the "Enabled" field.
For
Do you want to preserve existing enabled values? Say yes. Enabled edges and junctions permit flow
through them.
For
Do you want complex edges in your network?, Select the radial button for
Yes to allow complex edges in HydroEdge. Click Next.
The
Junctions in HydroJunction accompanying the network fall exactly on the network
and do not need to be snapped. Highlight the radial button No for Do
your features need to be snapped? And click Next.
The
Junctions in HydroJunction can be used to contain the sinks for the San
Marcos River basin. Click Yes for the network to contain sinks and
make sure that HydroJunction is checked. Click Next. If
there is a Warning, click OK.
The
network you are working with has no weights assigned to it, so make sure the
radial button has No highlighted and click Next.
A
summary is then displayed of the input information. Check over this
information to ensure it is correct, and click Finish. The
elements of the feature classes are then converted to have network
topology. If you get an error message saying that some features cannot be
built into a network, don’t worry about this, just continue on. Voila!! Congratulations. You have
just created a geometric network! What this means is that lines are
transformed to network edges, edges meet at points called junctions,
and the connectivity of lines and junctions is defined by an internal data
structure called a logical model (as distinct from the geometric
model of the lines and edges which defines where they are located in
geographic space). Sinks are special kinds of junctions where flow
terminates or drains out of the network.
In
ArcCatalog, look in the feature dataset ArcHydro. A new icon and
new feature classes are added, the HydroNetwork network and its
accompanying HydroNetwork_Junctions, which are automatically created
when the feature classes are converted to have topology. Close
ArcCatalog. Now you want to look at the network within ArcMap to use the
network functionality.
Lets
Preview the Network that you've just created. Click on the Network Icon
and select Preview in the adjacent right window tabs. Click individually on the
four feature classes HydroEdge, HydroJunction, HydroNetwork, and
HydroNetwork_Junctions to see the individual elements that make up the
network. Pretty cool! Now we're going to assign flow
direction on the network edges and do some trace tasks on the network.
Using the Utility Network Analyst Toolbar in
ArcMap
Open
the ArcMap and make a new project. Add
the Arc Hydro geodatabase that you’ve just created. Recolor the themes to make them more
natural. There is a Symbol for “River”
that is well suited for representing the HydroEdge feature class. Turn off the HydroNetwork_Junctions because
otherwise they clutter up the display.
To
be turned in: A map showing the Arc
Hydro framework dataset for the San Marcos Basin
To
generate the flow direction along the network, the junctions representing sinks
must have an Ancillary Role value of 2, indicating a sink.
In this case the junction representing the Outlet of the San Marcos River basin
at the lower right corner of the window must have and Ancillary Role value of
2. The other available Ancillary Role values are 0 for None and 1 for
Source. You will now assign the Ancillary Role value of 2 to the Outlet
in the HydroJunction feature class. Add the Editor toolbar by
going to the View menu, Toolbars, and make sure there is a check
next to Editor. On the Editor Toolbar, click on Editor and drag
to Start Editing. Select SanMarcos.mdb as the dataset to
edit. Set the Edit Target box to HydroJunction.
Go
to Selection, Set Selectable Layers… and check the box only for HydroJunction
as shown below.
Zoom
in to the Outlet of the basin (lower right corner) and select the Junction.
Click on the attributes icon 
and set the Ancillary Role equal to Sink.
Close
the attributes window and click again on Editor. Drag to Save
Edits.
Arc
Hydro Tools
We
are now going to use the Arc Hydro tools for the first time. Add the Arc Hydro toolbar by going to the View
menu, Toolbars, and make sure there is a check next to Arc Hydro
Tools. If you don’t see any
entry on the toolbar for Arc Hydro Tools, it means that the tools are not
installed on your computer. If that is
the case, the tools are contained in the zip file that you downloaded to start
this exercise, in the folder arcHydroSetup.
If
an older instance of the Arc Hydro tools are installed on your machine, you
have to first uninstall them by using the Windows/Settings/Control Panel
option for Add/Remove Programs.
Use this tool to Remove the currently installed Arc Hydro Tools.
Then,
in the arcHydroSetup folder, run the setup application and when prompted
to run the msxml 3.0 installation say No. Finally, in the arcHydroSetup folder, run the
msxml Windows installer package, and you should have a correctly
installed set of Arc Hydro tools ready to use with ArcMap. If you go to View/Toolbars and don’t see Arc
Hydro tools, go to Tools/Customize and click on the Arc Hydro tools icon.
Setting
the Flow Direction
Normally,
when you build a geometric network, you set the flow direction by using the
ArcGIS Network Utility Analyst to direct the flow on all the network edges
towards the HydroJunction sink you just created. In this dataset, however, there are some
loops and other network features to which flow direction cannot be assigned
automatically in this way. The NHD has a flow table that tells for each reach
what is the next downstream reach, and by using this table and doing some hand
editing, the correct flow direction has already been assigned to each of the
HydroEdges in the attribute value FlowDir.
The Flow Direction in a
network is stored as an esriFlowDirection value for each Edge and may have the
following values:
·
esriFDUninitialized
0 Uninitialized
·
esriFDWithFlow 1 In the direction of digitization of the edge
·
esriFDAgainstFlow 2 Opposite
to the direction of digitization of the edge
·
esriFDIndeterminate 3 Indeterminate
flow direction
This is an example of a method
of assigning values to an ArcGIS attribute called a Coded Value Domain
in which each of the admissible attribute values has a number and also a text
description.
For this exercise, these
predefined values have already been stored in the HydroEdge attribute table
under the field FlowDir. In the ArcHydro Tools Toolbar select Network
Tools and Set Flow Direction… Be
careful not to use the tool Store Flow Direction, or you’ll overwrite the
correct flow direction values with uninitialized values.
Set the Flow Direction for the HydroEdge feature class and Assign the Flow based on the existing attribute field called FlowDir. If you have a disaster at this point because you set the flow direction incorrectly, go back to Arc Catalog, delete your geometric network, delete the HydroEdge feature class, reimport the HydroEdge shape file, and start the process again by rebuilding your geometric network.
ArcGIS
Network Tools
ArcGIS
has a set of powerful tools called the Utility Network Analyst. From the ArcGIS View menu, go to Toolbars
and check the Utility Network Analyst toolbar.
Click
on the Flow dropdown menu and go to Display Arrows. The arrows
may not all appear and only some black circles may appear. The software
is still not foolproof when displaying the arrows. If you have a problem,
try turning on and off display arrows, and that may work.
The
picture below shows how the arrows should appear. Turn on your HydroNetwork_Junctions
feature class. Notice how there is a
generic junction of this kind at the end of every edge.
Each
reach in the network may have an arrow or a circular "blob" on it to
indicate the flow direction along that reach. A circular "blob"
indicates that the flow direction is indeterminate along that reach. This
is caused by looping in the network, in which the flow path of water cannot be
chosen. Zoom into an area to see the arrows and how the flow progresses
down the network. The area studied in this exercise does not have many
indeterminate flow paths because it is not along the coast. Coastal areas
generally have more looping in the network, leading to undetermined flow
directions.
Because
it takes longer for the screen to redraw with the arrows, turn them off by
going back to the Flow dropdown menu and click again on Display
Arrows.
Network
Tracing
Now
that the flow direction has been determined, it is possible to perform traces
on the network to determine topology relationships between reaches. The Trace
Task menu lists the options that are available:
|
|
|
We
first want to set some Analysis/Options in the Utility Network Analyst
toolbar.
On
the Results tab, change the Results format from Drawing to
Selection. Now the trace results will be shown immediately as a
selection, which can then be exported to a feature class if desired.
Click OK.
Tracing
tasks are defined by first placing flags and barriers
along the network to indicate where the trace should start and stop
respectively. The icon after the Analysis menu places the flags and
barriers. There are four options:
Junction
flags and barriers are placed at junctions, while edge flags and barriers are
placed along edges. When using an edge flag or barrier, the trace either
begins or ends and includes that entire edge, as opposed to only a portion of
the edge.
Lets
suppose we want to trace upstream and downstream of the USGS Gage on Plum Creek
near Luling, Texas. Label the features
in the MonitoringPoint feature class and zoom in to this gage. You’ll see that there is a HydroJunction on
the network where this gage is located, and also a DEM-derived watershed whose
outlet is at this location.
Put
a Junction flag on top of the HydroJunction
Before
you do the trace, make sure that you make all the layers selectable by using
the ArcMap Selection/Set Selectable Layers/Select All.
To
perform the trace function, you must set the Trace Task from the drop
down menu as Trace Upstream and then click the Solve icon 
. The solution appears as a
selection. From the Selection menu, drag down to Zoom to
Selected Features to see the selected reaches upstream from the Plum Creek
Gage.
To be turned in: A map of the features selected by the Trace Upstream
task. How many features are selected by this trace? (Look at the selected features in the
attribute tables)
You
can see that all connected reaches were selected as the solution to the trace
upstream from the position of the flag. We can search for loops in the
area by using the Find Loops trace tasks by doing the following
procedure: First, clear the existing Flags:
Locate
the Junction in HydroJunction representing the sink at the outlet of the San
Marcos basin and place a Junction Flag on it. From the Analysis dropdown
menu, go to Options... and the Results tab. Change the
radial button for Results format to Drawings. By returning
the results as a drawing, you cannot use the results for anything other than
viewing. With the results as a selection, it is possible to convert that
selection to a new feature class, or look at the selected features in the
attribute table. Change the trace task to Find Loops and click the
Solve icon. This selection shows the loops from the selected
junction. In some cases the connectivity obtained by tracing to or from
any Junction can be affected by loops. The important thing is to bear this in
mind when trying to explain inconsistent results from any Trace analysis.
Zoom in to some loops and explore them closely.
Notice
how the flow direction is still correctly set on the loops.
Another
important Trace Task is the Find Path trace. This trace will normally
yield unambiguous results. Suppose we want to find the path between the
stream gages on the Blanco River near Wimberley and the San Marcos River near
Luling. Place Junction flags on the
HydroJunctions next to these gages. Change the Trace Task to Find
Path and click the Solve icon. The results are different to the
Trace Upstream results because now only the connecting path between the two
junctions is selected.
Notice
how all of the edge on which the downstream gage is located is selected even
though the junction lies on its interior.
The
final trace task you will perform will be a Trace Downstream from the
apparent headwater junction in HydroNetwork_Junction. Clear the flags and the
selected features. Place a new flag only at the headwater junction (most
upstream junction on the network). You will also utilize the other method
of returning results in a tracing task. Change the Trace Task to Trace
Downstream and click the Solve icon. Again, the results are
different to the Trace Upstream results because only the connecting downstream
path for the upstream junction is selected.
To be turned in: A map of the features selected by the Trace
Downstream task. How many features are selected by this trace?
To
clear the results as a drawing, go to the Analysis menu and go to Clear
Results. Save your ArcMap document. Be creative and try other
traces from other junctions. Experiment using barriers on both edges and
junctions. When you are finished, close the Edit Session by going to the Editor
menu and Stop Editing. Say Yes to saving the edits, and
save and close the ArcMap document.
You
have now finished this part of the exercise. Congratulations!
Part 3: Creating an Arc Hydro Framework
Dataset
In
this part of the exercise we will apply the Arc Hydro Schema and some of the
Arc Hydro tools. This portion of the exercise assumes that you’ve
already prepared the data for schema application and you have available a set
of prepared files in an Arc Hydro geodatabase (which you have done by preparing
the San Marcos geodatabase!). For the
last part of this exercise you will apply some of the Arc Hydro tools, which
requires a completely connected geometric network.
The
required files for this part are:
ArcHydroSetup
folder: a folder that
contains the Arc Hydro Tools Setup, the XML parser (msxml) and a readme
file that explains how to install the tools.
SanMarcos.mdb
-- the geodatabase you have just prepared (shown below).
ArcHydroFrameworkSchema.mdb – the
schema that will be applied to this geodatabase.
This
portion of the exercise also requires that you have available and have
installed the Arc Hydro Tools.
These tools can be obtained from the attached zip file (Ex4Data)
or from http://arconline.esri.com/arconline/datamodels_one.cfm?PID=1&id=15. The proper functioning of these tools
requires an Application Framework to be first installed on the computer
where ArcMap runs. This should already
be working in the computers in ECJ 3.400 but if you need to install it, you can
copy the files from the ArcHydroSetup folder and follow the instructions
contained in the readme file.
Ok,
lets get started!!!
What
you are beginning with is a draft of the SanMarcos.mdb geodatabase that
looks like this:
Applying the Schema
Add the schema creation wizard to ArcCatalog
The Arc Hydro Schema is a blank geodatabase that contains assigned
attribute names for the Arc Hydro feature classes and creates relationships
between them. By applying this Schema
to your existing San Marcos dataset, your feature classes will acquire these
attribute names and relationships. To
this, we need the Schema Creation Wizard. 
If the schema creation
wizard has already been added to ArcCatalog, skip to next step, Connect to
the Repository.
(1) Right click in the gray area in ArcCatalog where the buttons are and select Customize. You can also click Customize under the Tools menu.
(2) Click the Commands tab.
(3) If “Case Tools” appears in the categories list, skip to
step (4) of this section. If “Case
Tools” is not in the categories list, click “Add from file” and browse
to the Bin directory where ArcGIS was installed (/arcexe82/bin). Select SchemaWiz.dll and click Open,
then click OK. If you don’t see
the SchemaWiz.dll in /arcexe/bin, it may still be there but
invisible. Use Tools/Find File
in Windows Explorer to locate the file, and then register the .dll using RegCat.exe,
which is also located in /arcexe82/bin (This may also be invisible). Use Tools/Find File to locate RegCat.exe,
right click on it and create a shortcut on your desktop. Drag the SchemaWiz.dll file onto the RegCat.exe
shortcut and you’ll be prompted with a dialog to define where to register the
.dll. Select ArcMap, ArcCatalog and
ArcTools. Now, when you go to the
Categories list you will see that the Case Tools option is now available and
the Schema Wizard icon is visible.
(4) Click “Case Tools” in the categories list.
(1) Drag the Schema Wizard command onto a toolbar (adjacent to any existing icon).
(2) Click Close.
(3) Close ArcMap so that only ArcCatalog is open.
Connect to the Repository
(1) In the ArcCatalog tree, click the SanMarcos geodatabase to which you will apply the schema, so that it opens and you can see the Arc Hydro feature dataset it contains.
(2) Click
the Case Schema Creation button to launch the Schema
Creation Wizard. You may get a message
saying that this action requires an ArcGIS or ArcEditor version of ArcGIS. In that event, go to Programs/ArcGIS/Desktop
Administrator and set the seat to ArcGIS or ArcEditor.
(3) Click Next to skip the introduction step, and then click Browse to select the repository database (in this exercise, ArcHydroFrameworkSchema.mdb). Ignore User Name and Password Requirements. Click Next to continue.