Hydrography Event Management Tools

Version 2.0

Prepared by:

U.S. Department of the Interior

Bureau of Land Management

Oregon State Office

333 SW 1^st^ Avenue

Portland, Oregon 97208

Last Updated:

01/30/2009

Table of Contents

[Getting Started with HEM 1](#__RefHeading___Toc221070362)

> [HEM Event Types 1](#hem-event-types)
>
> [Creating Event Featureclasses 2](#creating-event-featureclasses)
>
> [Configuring ArcMap for HEM 5](#configuring-arcmap-for-hem)
>
> [HEM ArcMap Toolbar Overview 5](#hem-arcmap-toolbar-overview)

[Point Events 8](#__RefHeading___Toc221070367)

> [Create Point Events 8](#create-point-events)
>
> [Update Point Events 10](#update-point-events)
>
> [Copy Point Events 11](#copy-point-events)
>
> [Delete Point Events 12](#delete-point-events)
>
> [Import Point Events 13](#import-point-events)

[Line Events 16](#__RefHeading___Toc221070373)

> [Create Line Events 16](#create-line-events)
>
> [Update Line Events 19](#update-line-events)
>
> [Create Multiple Line Events Upstream
> 20](#create-multiple-line-events-upstream)
>
> [Create Multiple Line Events Down.
> 21](#create-multiple-line-events-downstream)
>
> [Copy Line Events 23](#copy-line-events)
>
> [Delete Line Events 24](#delete-line-events)
>
> [Merge Line Events 24](#merge-line-events)
>
> [Split Line Events 26](#split-line-events)
>
> [Import Line Events 28](#import-line-events)
>
> [Import Selected Flowlines 30](#import-selected-flowlines)

[Area Events 31](#__RefHeading___Toc221070384)

> [Area Event Validation 31](#area-event-validation)
>
> [Create Area Events -- Entire
> 33](#create-area-events-entire-waterbody)
>
> [Create Area Events -- Partial
> 35](#create-area-events-partial-waterbody)
>
> [Update Area Events 38](#update-area-events)
>
> [Copy Area Events 40](#copy-area-events)
>
> [Delete Area Events 41](#delete-area-events)
>
> [Merge Area Events 42](#merge-area-events)
>
> [Split Area Events 44](#split-area-events)
>
> [Import Area Events 46](#import-area-events)

[Other HEM Functions 48](#__RefHeading___Toc221070394)

> [Measure Linear Distance 48](#measure-linear-distance)
>
> [Go X Distance 50](#go-x-distance)
>
> [Select by Selected 52](#select-by-selected)
>
> [Check Continuous Events 53](#check-continuous-events)
>
> [Repair Continuous Events 57](#repair-continuous-events)
>
> [Interactive Event Synchronization
> 59](#interactive-event-synchronization)
>
> [Batch Event Synchronization 63](#batch-event-synchronization)

[HEM Tips and Tricks 74](#__RefHeading___Toc221070402)

> [Customizing the HEM Toolbar 74](#customizing-the-hem-toolbar)
>
> [Snap Environment 75](#snap-environment)
>
> [Using Barriers 76](#using-barriers)
>
> [Upgrading HEM 1.x Featureclasses
> 76](#upgrading-hem-1.x-featureclasses)

[Appendix I HEM Event Table Structure 79](#__RefHeading___Toc221070407)

[]{#__RefHeading___Toc221070362 .anchor}Getting Started with HEM

The purpose of this document is to provide technical instructions on how
to operate the Hydrography Event Management (HEM) Tools. These tools are
a set of shared components to allow for creation, management, and
refresh of event data that is referenced to hydrography data in the NHD
format. In order for the HEM tools to function, the user must add
NHDinGEO Hydrography data to their ArcMap session. While there are many
useful tables and featureclasses within the NHDinGEO dataset, at a
minimum, the user must add the NHDFlowline featureclass (with a built
network) to the map. For more information about the National Hydrography
Dataset, go to: http://nhd.usgs.gov.

Chapter Overview:

-   HEM Event Types

-   Creating Event Featureclasses

-   Configuring ArcMap for HEM

-   HEM ArcMap Toolbar Overview

-   HEM Candidate Form

-   Upgrading HEM 1.x Featureclasses

# HEM Event Types

The HEM event structure is based on the National Hydrography Dataset
(NHD) data model for event featureclasses. The event data are ArcGIS
featureclasses with geometry and each record contains route and measure
information. HEM supports editing point, single-route line, multi-route
line, and area events. For more information about the attributes
associated with each event type, see Appendix I.

-   Point Events -- contains zero-dimensional information that can be
    located at a discrete location on an NHD Flowline feature.

-   Single-Route Line Events -- contains one-dimensional information
    that can be located along a portion of a single NHD Flowline
    feature.

-   Multi-Route Line Events -- contains one-dimensional information that
    can be located along a portion of multiple NHD Flowline features.
    *This data type is not supported by the NHD data model.*

-   Area Events -- contains two dimensional information that be located
    coincident with an NHD Waterbody feature.

Note

> While not supported by the NHD, the multi-route event structure is
> important for users who have implemented event databases based on a
> longer route feature and who do not plan to submit data to the NHD
> repository. Advantages of this data format include ease in migrating
> existing event data to the HEM format and more flexibility in creating
> data that crosses multiple flowline features without being
> artificially broken into multiple records.

# Creating Event Featureclasses

The Event Table Manager is provided to manage the event featureclasses.
Using this tool for creating, modifying, and deleting event
featureclasses ensures that they are created in the correct format and
the tracking tables that are used in conjunction with the editing tools
are properly maintained.

The Hydro Event Management Tools toolbar in ArcCatalog allows you to
create and manage hydro events that are contained inside of a
geodatabase (Personal or SDE). Most of the features on the toolbar are
inactive until you select a geodatabase that contains your events.

To access the event table manager:

1.  Launch ArcCatalog.

```{=html}
<!-- -->
```
1.  Add the Hydro Event Management toolbar to your ArcCatalog session
    (View ToolbarsHydro Event Management Tools).

2.  Click the Event Featureclass Manager button to open the Event Table
    Manager dialog box.

![](media/image1.png){width="1.75in" height="0.8541666666666666in"}

Note

> The following examples show the creation of a new geodatabase to store
> point, line, and area events. New events can also be created in an
> existing NHD geodatabase. Users should consult their agency spatial
> database administrators for guidance on organizing their spatial data.

The Event Table Manager will allow you to add a new featureclass to the
geodatabase that you have selected. By using this tool the featureclass
will be created with all of the required fields that are needed for an
event featureclass. The Event Table Manager window can also be used to
modify existing featureclasses that have already been created.

**To create a new event featureclass:**

1.  From the Event Table Manager, select Tools -- Add New.

2.  Once you select Add New, the lower half of the Event Table Manager
    form will appear.

> ![](media/image2.png){width="3.303472222222222in"
> height="3.2194444444444446in"}

3.  Type in the name of the new featureclass.

> ![](media/image3.png){width="3.4680555555555554in"
> height="0.3333333333333333in"}

4.  Select if the featureclass will contain point, line, or area data.

> ![](media/image4.png){width="3.113888888888889in" height="0.34375in"}

5.  Choose if you want the schema of the new featureclass to include all
    fields (Full) or only required fields. Selecting Full will add all
    fields specified in the NHD Event Table structure.

> ![](media/image5.png){width="3.0930555555555554in"
> height="0.3541666666666667in"}

6.  If Line is selected, specify if the event featureclass contains
    multi-route events.

> ![](media/image6.png){width="3.0305555555555554in" height="0.375in"}

7.  If Line is selected, specify if the event featureclass contains
    continuous events.

> ![](media/image7.png){width="1.5208333333333333in"
> height="0.3645833333333333in"}

8.  Optional: if an EventType domain has been created, select it from
    the list.

> ![](media/image8.png){width="3.457638888888889in"
> height="0.3854166666666667in"}

9.  Optional: specify an ArcSDE configuration keyword.

> ![](media/image9.png){width="3.6555555555555554in"
> height="0.4166666666666667in"}

10. Click the Create New button. Clicking the Create New button will
    open the ArcCatalog New Spatial Reference dialog. You must complete
    the spatial reference information before continuing. For more
    information on designating a spatial reference, see the ArcCatalog
    user help. If the spatial reference is not correctly assigned, you
    may experience problems using the event editing tools.

> ![](media/image10.png){width="1.1041666666666667in"
> height="0.2916666666666667in"}

11. After the spatial reference is selected, the featureclass will be
    created and the event table manager will display the new
    featureclass properties.

There are some actions that can be performed once an event featureclass
has been created. These are:

-   To modify the name, click on the name of the featureclass to select
    it, and then click on the name a second time. This will allow you to
    type over the name with a new value.

-   To modify if a line event featureclass is continuous, right-click on
    the name of the featureclass and select Set Continuous  Yes or No.

> ![](media/image11.png){width="2.6041666666666665in"
> height="1.2291666666666667in"}

-   To delete a featureclass, click on the name of the featureclass and
    from the Tools menu, select Delete.

> ![](media/image12.png){width="1.6145833333333333in"
> height="1.3020833333333333in"}

# Configuring ArcMap for HEM

In order for the HEM editing tools to function correctly in ArcMap, the
following items must be true:

-   Event Featureclasses must be created using the HEM tools and added
    to the map. Event data may be stored in personal, file, or SDE
    geodatabases. If you are using SDE, the data must be versioned and
    you must have create/edit/delete permissions on the data.

-   NHD Flowline (for point and line events) and NHD Waterbody (for area
    events) must be added to the map. NHD Flowline must have the
    geometric network built and flow direction set.

-   The coordinate system for the map data frame must match the NHD
    feature dataset.

-   The NHDReachCode_ComID table must be available in the same
    geodatabase as the NHD data and populated in order for the
    ReachSMDate to be inserted into event records. If it is not
    available, the ReachSMDate will not be populated and this will cause
    problems for the event synchronization tools.

-   The HEM toolbar has been added to the map (ArcMap  View  Toolbars
     Hydro Event Management Tools) and you are in an edit session.

# HEM ArcMap Toolbar Overview

The bulk of HEM functionality has been consolidated onto the Hydro Event
Management Tools toolbar in ArcMap. This section provides a brief
overview of each of the toolbar items.

![](media/image13.png){width="6.41875in" height="0.5444444444444444in"}

![](media/image14.png){width="0.3229166666666667in" height="0.28125in"}
Event Selection Tool -- Used for selecting existing event records;
useful for copying and deleting events. Draw a box or click to select a
feature

![](media/image15.png){width="0.2916666666666667in"
height="0.2916666666666667in"} Event Sketch Tool -- Used for defining
the point location or end points for event records.

Event Tasks -- List of edit options.

![](media/image16.png){width="3.0097222222222224in" height="1.75in"}

![](media/image17.png){width="2.4583333333333335in" height="0.28125in"}

![](media/image18.png){width="2.2083333333333335in"
height="3.926388888888889in"}

![](media/image19.png){width="0.25in" height="0.25in"} Clear HEM
Elements -- Clears HEM flags and HEM line elements from the map that are
created while editing data with the tools.

![](media/image20.png){width="0.23958333333333334in"
height="0.2604166666666667in"} Snap Environment -- Sets a default snap
environment for the edit session and then opens the ArcMap snapping
window.

![](media/image21.png){width="0.25in" height="0.23958333333333334in"}
Select by Selected -- Opens the HEM selection dialog using the currently
selected features.

![](media/image22.png){width="0.25in" height="0.25in"} Interactive
Synchronize Events -- Tool that facilitates the manual update of event
data that has become out of alignment with the underlying hydrography
data.

![](media/image23.png){width="0.20833333333333334in" height="0.21875in"}
Batch Synchronize Events -- Tool that automates the update of event data
that has become out of alignment with the underlying hydrography data.

![](media/image24.png){width="0.19791666666666666in"
height="0.19791666666666666in"} Batch Synchronize QA/QC -- Tool for
reviewing and approving the edits made by the Batch Synchronize Events
tool.

![](media/image25.png){width="0.25in" height="0.25in"} Check Continuous
Events -- Makes sure that if the event is continuous it does not have
any gaps or overlaps.

![](media/image26.png){width="0.25in" height="0.25in"} Repair Continuous
Events -- Creates new linear events for all gaps that are detected by
the Check Continuous Events tool.

![](media/image27.png){width="0.25in" height="0.25in"} Import Points --
Tool that imports point features into a point event featureclass.

![](media/image28.png){width="0.25in" height="0.25in"} Import Lines --
Tool that imports line features into a line event featureclass.

![](media/image29.png){width="0.25in" height="0.25in"} Import Areas --
Tool that import area features into an area event featureclass.

![](media/image30.png){width="0.25in" height="0.25in"} Import Selected
Flowlines -- Creates new line events from a selected set of NHD Flowline
features.

![](media/image31.png){width="0.25in" height="0.25in"} Toggle
SourceFeatureID -- Determines if new events will be assigned a Source
Feature ID value from an input table or text file.

Options -- Opens the HEM Options dialog box. This allows the user to
customize some aspects of how the HEM tools behave; includes the option
for not displaying HEM graphics and for turning off area event
validation routines.

[]{#__RefHeading___Toc221070367 .anchor}Point Events

Point events contain information that can be located at a discrete
location on an NHDFlowline feature. This chapter discusses how to use
the HEM functionality for editing point events.

Chapter Overview:

-   Create Point Events

-   Update Point Events

-   Copy Point Events

-   Delete Point Events

-   Import Points

# Create Point Events

To create new point features:

1.  Set the HEM Task to Create Point Event.

> ![](media/image32.png){width="2.2083333333333335in" height="0.3125in"}

2.  Set the HEM Target to the featureclass where you would like to add
    new records.

![](media/image33.png){width="2.4895833333333335in"
height="0.3020833333333333in"}

3.  Activate the HEM Event Sketch tool.
    ![](media/image34.png){width="0.3125in" height="0.28125in"}

4.  Click at a point along a stream.

> ![](media/image35.png){width="1.5729166666666667in"
> height="1.1458333333333333in"}

5.  If there are multiple Route Location Candidates at the selected
    point, select the correct Route Location and click the OK button. If
    you need assistance determining the correct Route Feature, select
    one of the location candidates from the list and click the Flash
    Feature button.

> ![](media/image36.png){width="3.7909722222222224in"
> height="3.3430555555555554in"}

6.  If the Toggle Source Feature ID option is selected, a second window
    will open allowing you to assign a value to the Source_FeatureID
    field. Select a value from the list and click OK or click Cancel to
    skip this step.

> ![](media/image37.png){width="2.7805555555555554in"
> height="2.988888888888889in"}

Note

> An existing DBF or text file can be used to import values to the
> Source_FeatureID field. If you use a DBF, it needs to contain a field
> named SrcID; a text file only needs a single column of values. There
> is a 40 character limit for each value in the Source_FeatureID field,
> although values over 40 characters can still be present in your list
> as long as they are not selected.

7.  A new point event record will be added to the target featureclass.
    Repeat the above steps as needed to complete data entry. Be sure to
    save your edits using the ArcMap  Editor  Save Edits button.

> ![](media/image38.png){width="1.4270833333333333in"
> height="1.34375in"}

# Update Point Events

To update existing point event features:

1.  Change the HEM Task to Update Point Event.

![](media/image39.png){width="2.2395833333333335in" height="0.3125in"}

2.  Activate the Event Selection tool.
    ![](media/image40.png){width="0.28125in"
    height="0.2708333333333333in"}

3.  Using the Event Selection tool as you would the ArcMap Selection
    tool, select an existing point event.

4.  The Select Event dialog box will open. Select the event record to
    update from the list and click the OK button.

> ![](media/image41.png){width="4.480555555555555in"
> height="2.2868055555555555in"}

5.  The HEM Sketch tool should automatically activate. Using this tool,
    click on a stream to define the new location for the point.

> ![](media/image42.png){width="1.5416666666666667in"
> height="1.53125in"}

6.  The record will be moved to its new location and its HEM/NHD
    attributes will be updated accordingly.

> ![](media/image43.png){width="1.3229166666666667in"
> height="1.6770833333333333in"}

# Copy Point Events

To copy an existing point event feature into a new record:

1.  Change the HEM Task to Copy Event.

![](media/image44.png){width="2.2395833333333335in"
height="0.2916666666666667in"}

2.  Select HEM Target event featureclass for the new record. The target
    can be the same featureclass as the record to be copied or a
    different point event featureclass.

![](media/image33.png){width="2.4895833333333335in"
height="0.3020833333333333in"}

3.  Activate the Event Selection tool.
    ![](media/image40.png){width="0.28125in"
    height="0.2708333333333333in"}

4.  Using the Event Selection tool as you would the ArcMap Selection
    tool, select an existing point event.

5.  The Select Event dialog box will open. Select the event record to
    update from the list and click the Copy button.

> ![](media/image45.png){width="5.520833333333333in"
> height="2.6534722222222222in"}

6.  The existing point feature will be copied into the target
    featureclass. It is important to note that the copied feature will
    now stack on top of the original feature. Repeat the above steps to
    copy additional features.

# Delete Point Events

To delete an existing point event features:

1.  Change the HEM Task to Delete Event.

![](media/image46.png){width="2.2395833333333335in" height="0.3125in"}

2.  Activate the Event Selection tool.
    ![](media/image40.png){width="0.28125in"
    height="0.2708333333333333in"}

3.  Using the Event Selection tool as you would the ArcMap Selection
    tool, select an existing point event.

4.  The Select Event dialog box will open. Select the event record to
    delete from the list and click the Delete button.

> ![](media/image47.png){width="5.779166666666667in"
> height="2.7222222222222223in"}

5.  The selected point feature will be deleted. Repeat the above steps
    to delete additional records.

# Import Point Events

The Import Point Events button creates new HEM events from existing
point features. Import features can be from a variety of sources and do
not have to be in the NHD format.

To import point features:

1.  Add an NHD Flowline featureclass and the import point dataset to the
    map document and using the ArcMap selection tool, select the point
    features to be imported. If no features are selected, all records in
    the dataset will be imported.

2.  Set the HEM Task to Create Point Event.

> ![](media/image48.png){width="2.21875in" height="0.3125in"}

3.  Set the HEM Target to the point event featureclass you want to
    import into.

> ![](media/image49.png){width="2.4583333333333335in" height="0.3125in"}

4.  Select the source featureclass in the ArcMap table of contents.

> ![](media/image50.png){width="2.3854166666666665in"
> height="1.0104166666666667in"}

5.  From the HEM Edit Tools menu, select Import Points.

> ![](media/image51.png){width="1.0416666666666667in"
> height="0.2916666666666667in"}

6.  The tool will offer the opportunity to transfer a unique identifier
    into the new point event records. This is useful for relating the
    new point events back to the original data source. Select Add IDs to
    transfer the identifier to the new record. Don't Add IDs skips this
    step. Stop Import exits the tool.

> ![](media/image52.png){width="3.0722222222222224in"
> height="2.4895833333333335in"}

7.  The tool will cycle through points to import and attempt to snap
    them to a flowline record. Depending on how close the points are to
    a flowline, some may not be imported. A report is generated
    outlining how many points were successfully imported and which OIDs
    failed. This report can be saved to a text file.

> ![](media/image53.png){width="4.572222222222222in"
> height="2.9159722222222224in"}

Note

> If the points to be imported are close to stream confluences, you may
> be prompted by the HEM application to select a route location for one
> or more records.

[]{#__RefHeading___Toc221070373 .anchor}Line Events

Line events contain information that can be located along a portion of
an NHDFlowline feature. This chapter discusses how to use the HEM
functionality for editing line events.

Chapter Overview:

-   Create Line Events

-   Update Line Events

-   Create Multiple Events Upstream

-   Create Multiple Events Downstream

-   Copy Line Events

-   Delete Line Events

-   Merge Line Events

-   Split Line Events

-   Import Lines

-   Import Selected Flowlines

# Create Line Events

To create new line features:

1.  Set the HEM Task to Create Line Event.

> ![](media/image54.png){width="2.21875in" height="0.3125in"}

2.  Set the HEM Target to the featureclass where you would like to add
    new records.

![](media/image55.png){width="2.4375in" height="0.2916666666666667in"}

3.  Activate the HEM Event Sketch tool.
    ![](media/image34.png){width="0.3125in" height="0.28125in"}

4.  Click at a point along a stream. The first point clicked will be
    considered the downstream extent of the line event.

> ![](media/image56.png){width="4.740972222222222in"
> height="1.7868055555555555in"}

5.  If there are multiple Route Location Candidates at the selected
    point, select the correct Route Location and click the OK button. If
    you need assistance determining the correct Route Feature, select
    one of the location candidates from the list and click the Flash
    Feature button.

> ![](media/image57.png){width="3.7909722222222224in"
> height="3.3430555555555554in"}

6.  While holding the Shift key on your keyboard, click on a location on
    a stream to define the upper extent of the line event. If there are
    multiple Route Location Candidates at the selected point, follow the
    process identified in step 5.

![](media/image58.png){width="5.001388888888889in"
height="1.4215277777777777in"}

7.  If the Toggle Source Feature ID option is selected, a second window
    will open allowing you to assign a value to the Source_FeatureID
    field. Select a value from the list and click OK or click Cancel to
    skip this step.

> ![](media/image37.png){width="2.7805555555555554in"
> height="2.988888888888889in"}

Note

> An existing DBF or text file can be used to import values to the
> Source_FeatureID field. If you use a DBF, it needs to contain a field
> named SrcID; a text file only needs a single column of values. There
> is a 40 character limit for each value in the Source_FeatureID field,
> although values over 40 characters can still be present in your list
> as long as they are not selected.

8.  A new line event record will be added to the target featureclass.
    Repeat the above steps as needed to complete data entry. Be sure to
    save your edits using the ArcMap  Editor  Save Edits button.

> ![](media/image59.png){width="4.740972222222222in"
> height="1.7916666666666667in"}

# 

# Update Line Events

To update existing line event features:

1.  Change the HEM Task to Update Line Event.

![](media/image60.png){width="2.21875in" height="0.3020833333333333in"}

2.  Activate the Event Selection tool.
    ![](media/image40.png){width="0.28125in"
    height="0.2708333333333333in"}

3.  Using the Event Selection tool as you would the ArcMap Selection
    tool, select an existing line event.

4.  The Select Event dialog box will open. Select the event record to
    update from the list and click the OK button.

> ![](media/image61.png){width="5.389583333333333in"
> height="2.7645833333333334in"}

5.  The HEM Sketch tool should automatically activate. Using this tool,
    click on a stream to define the new downstream location for the
    line. You may be prompted to select a route location candidate.

> ![](media/image62.png){width="4.764583333333333in" height="1.16875in"}

6.  While holding the Shift key on your keyboard, click on a location on
    a stream to define the new upper extent of the line event. You may
    be prompted to select a route location candidate.

7.  The record will be moved to its new location and its HEM/NHD
    attributes will be updated accordingly.

> ![](media/image63.png){width="4.740972222222222in"
> height="1.7916666666666667in"}

# Create Multiple Line Events Upstream

The Create Multiple Events Upstream tool creates line events that cover
all NHDFlowlines upstream from the point that is clicked on a map. This
tool uses a network trace to determine the upstream flowlines and is the
equivalent of "Trace Upstream" in the ArcMap Utility Network Analyst
Trace Tasks list. If the event geometry is "single-route" then multiple
events will be created -- one for each separate flowline in the trace
result. If the event geometry is "multi-route," then the tool will
create a single multi-part feature that covers all of the flowlines in
the trace result. To run this tool:

1.  Change the HEM Task to Create Multiple Events Upstream.

![](media/image64.png){width="2.8534722222222224in" height="0.71875in"}

2.  Select the HEM target event featureclass.

3.  Using the HEM Sketch Tool, click on the map at the downstream point.
    Linear event(s) will be created for all flowlines above this point.

> ![](media/image65.png){width="4.768055555555556in"
> height="2.176388888888889in"}

4.  When the process has completed, the map will refresh and the new
    record(s) will be displayed.

> ![](media/image66.png){width="4.768055555555556in"
> height="2.176388888888889in"}

Note

> The time it takes the Create Multiple Events Upstream tool to complete
> is increased by the number of records in the upstream network trace.
> If needed, barriers can be created to prevent flowlines from being
> included in the trace results.

# Create Multiple Line Events Downstream

The purpose of the Create Multiple Events Downstream tool is to create
line events that cover all NHDFlowlines downstream from the point
identified on the map. This is the equivalent of "Trace Downstream" in
the ArcMap Utility Network Analyst Trace Tasks list. If the event
geometry is "single-route" then multiple events will be created -- one
for each separate flowline in the trace result. If the event geometry is
"multi-route," then the tool will create a single multi-part feature
that covers all of the flowlines in the trace result. To run this tool:

1.  Change the HEM Task to Create Multiple Events Downstream.

![](media/image67.png){width="2.65625in" height="1.03125in"}

2.  Select the HEM target event featureclass.

3.  Using the HEM Sketch Tool, click on the map at the upstream point.
    Linear event(s) will be created for all flowlines downstream from
    this point.

> ![](media/image68.png){width="4.768055555555556in"
> height="2.176388888888889in"}

4.  When the process has completed, the map will refresh and the new
    record(s) will be displayed.

> ![](media/image69.png){width="4.768055555555556in"
> height="2.176388888888889in"}

Note

> The time it takes the Create Multiple Events Downstream tool to
> complete is increased by the distance to the furthest downstream point
> in the NHDFlowline dataset you are using. If needed, barriers can be
> created to prevent flowlines from being included in the trace results.

# Copy Line Events

To copy an existing line event feature into a new record:

1.  Change the HEM Task to Copy Event.

![](media/image44.png){width="2.2395833333333335in"
height="0.2916666666666667in"}

2.  Select HEM Target event featureclass for the new record. The target
    can be the same featureclass as the record to be copied or a
    different line event featureclass.

> ![](media/image70.png){width="1.96875in"
> height="0.3020833333333333in"}

3.  Activate the Event Selection tool.
    ![](media/image40.png){width="0.28125in"
    height="0.2708333333333333in"}

4.  Using the Event Selection tool as you would the ArcMap Selection
    tool, select an existing line event.

5.  The Select Event dialog box will open. Select the event record to
    update from the list and click the Copy button.

> ![](media/image71.png){width="5.51875in"
> height="2.2395833333333335in"}

6.  The existing line feature will be copied into the target
    featureclass. It is important to note that the copied feature will
    now stack on top of the original feature. Repeat the above steps to
    copy additional features.

# Delete Line Events

To delete an existing line event feature:

1.  Change the HEM Task to Delete Event.

![](media/image46.png){width="2.2395833333333335in" height="0.3125in"}

2.  Activate the Event Selection tool.
    ![](media/image40.png){width="0.28125in"
    height="0.2708333333333333in"}

3.  Using the Event Selection tool as you would the ArcMap Selection
    tool, select an existing line event.

4.  The Select Event dialog box will open. Select the event record to
    delete from the list and click the Delete button.

> ![](media/image72.png){width="4.395833333333333in"
> height="3.0083333333333333in"}

5.  The selected line feature will be deleted. Repeat the above steps to
    delete additional records.

# Merge Line Events

For line events, the Merge Event task takes two line event records and
attempts to consolidate them into a single line event record. To merge
line events:

1.  Change the HEM Task to Copy Event and change the HEM Target to the
    featureclass to be edited.

> ![](media/image73.png){width="4.707638888888889in"
> height="0.3020833333333333in"}

2.  Activate the HEM Event Selection Tool and select two existing line
    events.

3.  The Select Two Events form will open with two or more events listed.
    While holding the shift key on the keyboard, select the two events
    to be merged in the list and click the Merge button.

> ![](media/image74.png){width="5.457638888888889in"
> height="3.3430555555555554in"}

4.  Select which attributes should be assigned to the merged record and
    click the OK button.

> ![](media/image75.png){width="4.228472222222222in"
> height="3.832638888888889in"}

5.  A new record will be created in the edit target that has the merged
    geometry from the two input records and the attributes selected in
    Step 4. The original records will be deleted. When completed, the
    following message box will display.

> ![](media/image76.png){width="4.582638888888889in" height="1.65625in"}

# Split Line Events

For line events, the Split Event task divides a single line event record
into two different records based on the user defined split location. To
split a line event:

1.  Change the HEM Task to Split Event.

![](media/image77.png){width="2.21875in" height="0.3229166666666667in"}

2.  Activate the Event Selection tool.
    ![](media/image40.png){width="0.28125in"
    height="0.2708333333333333in"}

3.  Using the Event Selection tool as you would the ArcMap Selection
    tool, select an existing line event.

4.  The Select Event dialog box will open. Select the event record to
    split from the list and click the Split button.

> ![](media/image78.png){width="4.121527777777778in"
> height="2.553472222222222in"}

5.  Using the HEM Sketch tool, click on the line event at the point
    where it should be split into two records. It is helpful to have
    snapping turned on to the event or flowline data when splitting
    events.

> ![](media/image79.png){width="4.905555555555556in"
> height="2.2395833333333335in"}

6.  The results of the split task will be reported in a message box.

> ![](media/image80.png){width="5.8in" height="1.4520833333333334in"}

# Import Line Events

The Import Line Events button creates new HEM events from existing line
features. Import features can be from a variety of sources and do not
have to be in the NHD format.

To import point features:

1.  Add an NHD Flowline featureclass and the import line dataset to the
    map document and using the ArcMap selection tool, select the line
    features to be imported. If no features are selected, all records in
    the dataset will be imported.

2.  Set the HEM Task to Create Line Event.

> ![](media/image81.png){width="2.2083333333333335in" height="0.3125in"}

3.  Set the HEM Target to the point event featureclass you want to
    import into.

> ![](media/image82.png){width="2.4375in" height="0.2708333333333333in"}

4.  Select the source featureclass in the ArcMap table of contents.

> ![](media/image83.png){width="2.0520833333333335in"
> height="1.4895833333333333in"}

5.  From the HEM Edit Tools menu, select Import Lines.

> ![](media/image84.png){width="0.9791666666666666in"
> height="0.23958333333333334in"}

6.  The tool will offer the opportunity to transfer a unique identifier
    into the new line event records. This is useful for relating the new
    line events back to the original data source. Select Add IDs to
    transfer the identifier to the new record. Don't Add IDs skips this
    step. Stop Import exits the tool.

> ![](media/image52.png){width="3.0722222222222224in"
> height="2.4895833333333335in"}

7.  The tool will cycle through the lines to import and attempt to snap
    them to a flowline record. Depending on how close the end points are
    to a flowline, some may not be imported. A report is generated
    outlining how many features were successfully imported and which
    OIDs failed. This report can be saved to a text file.

> ![](media/image85.png){width="4.1194444444444445in"
> height="3.017361111111111in"}

Note

> If the lines to be imported are close to stream confluences, you may
> be prompted by the HEM application to select a route location for one
> or more records.

# Import Selected Flowlines

The Import Selected Flowlines tool creates new HEM line events from
selected NHD flowline features. This is useful functionality for
creating new event data in an area that does not have events.

To import selected flowlines:

1.  Select one or more flowline records. Records can be selected using
    the ArcMap selection tool, querying by attributes, or any other
    method for selecting records.

2.  Set the HEM Task to Create Line Event and set the HEM target to a
    line featureclass.

> ![](media/image86.png){width="4.686805555555556in"
> height="0.3229166666666667in"}

3.  Select the NHDFlowline layer in the map table of contents.

4.  From the HEM Edit Tools menu, select Import Selected Flowlines.

> ![](media/image87.png){width="1.5729166666666667in"
> height="0.2916666666666667in"}

5.  The application will cycle through the selected flowline records and
    create line events for them. Depending on how many flowline records
    are selected, this may take a few minutes. When the import is
    completed, you will be presented with the Import Flowlines Report
    which details which records were successfully created. This report
    can be saved by clicking the save button.

![](media/image88.png){width="4.593055555555556in"
height="2.988888888888889in"}

[]{#__RefHeading___Toc221070384 .anchor}Area Events

Area events contain information that can be located along all or a
portion of an NHD Waterbody feature. This chapter discusses how to use
the HEM functionality for editing area events.

Chapter Overview:

-   Area Event Validation

```{=html}
<!-- -->
```
-   Create Area Events -- Entire Waterbody

-   Create Area Events -- Partial Waterbody

-   Update Area Events

-   Copy Area Events

-   Delete Area Events

-   Merge Area Events

-   Split Area Events

-   Import Areas

# 

# Area Event Validation

By default, the application requires that area events follow the
following rules:

-   Area events cannot cross multiple waterbody features.

-   Area events cannot extend outside of its related waterbody feature.

-   Area cannot be created on NHD Waterbody features that do not have an
    assigned ReachCode (ex. Swamp/Marsh).

If you are not submitting your data to the NHD repository and choose not
to follow the area validation rules, you may turn this functionality off
by opening the HEM Edit Tools  Options menu.

![](media/image89.png){width="1.9777777777777779in" height="3.49375in"}

To turn off area validation rules, select the No option underneath the
Validate Area Events section of the form and click the checkbox next to
Allow Null or Blank values for ReachCode. Click the Apply and Close
button to apply the changes.

![](media/image90.png){width="3.5097222222222224in"
height="3.770138888888889in"}

# Create Area Events -- Entire Waterbody

To create a new area feature that covers the entire extent of an NHD
Waterbody feature:

1.  Set the HEM Task to Create Area Event -- Entire Waterbody.

> ![](media/image91.png){width="2.7395833333333335in"
> height="0.4583333333333333in"}

2.  Set the HEM Target to the featureclass where you would like to add
    new records.

![](media/image92.png){width="2.4479166666666665in"
height="0.3020833333333333in"}

3.  Activate the HEM Select Event tool.
    ![](media/image93.png){width="0.3125in" height="0.3125in"}

4.  Using the HEM Select Event tool, select an NHD Waterbody feature by
    clicking on it.

> ![](media/image94.png){width="4.768055555555556in"
> height="2.046527777777778in"}

5.  When the Select Waterbody dialog box opens, select the correct
    feature and click the Create button. If you need assistance
    determining the correct feature, select one of the candidates from
    the list. This will flash the feature on the map. You can also click
    the flash feature button to flash it again.

> ![](media/image95.png){width="4.768055555555556in"
> height="2.5506944444444444in"}

6.  If the Toggle Source Feature ID option is selected, a second window
    will open allowing you to assign a value to the Source_FeatureID
    field. Select a value from the list and click OK or click Cancel to
    skip this step.

> ![](media/image37.png){width="2.7805555555555554in"
> height="2.988888888888889in"}

Note

> An existing DBF or text file can be used to import values to the
> Source_FeatureID field. If you use a DBF, it needs to contain a field
> named SrcID; a text file only needs a single column of values. There
> is a 40 character limit for each value in the Source_FeatureID field,
> although values over 40 characters can still be present in your list
> as long as they are not selected.

7.  A new area event record will be added to the target featureclass.
    Repeat the above steps as needed to complete data entry. Be sure to
    save your edits using the ArcMap  Editor  Save Edits button.

> ![](media/image96.png){width="4.768055555555556in"
> height="2.046527777777778in"}

# Create Area Events -- Partial Waterbody

To create a new area feature that covers only part of the extent of an
NHD Waterbody feature:

1.  Set the HEM Task to Create Area Event -- Partial Waterbody.

> ![](media/image97.png){width="2.7083333333333335in" height="0.4375in"}

2.  Set the HEM Target to the featureclass where you would like to add
    new records.

![](media/image92.png){width="2.4479166666666665in"
height="0.3020833333333333in"}

3.  Activate the HEM Select Event tool.
    ![](media/image93.png){width="0.3125in" height="0.3125in"}

4.  Using the HEM Select Event tool, select an NHD Waterbody feature by
    clicking on it.

> ![](media/image94.png){width="4.768055555555556in"
> height="2.046527777777778in"}

5.  When the Select Waterbody dialog box opens, select the correct
    feature and click the Create button. If you need assistance
    determining the correct feature, select one of the candidates from
    the list. This will flash the feature on the map. You can also click
    the flash feature button to flash it again.

> ![](media/image95.png){width="4.768055555555556in"
> height="2.5506944444444444in"}

6.  Using the HEM Sketch tool, sketch the extent of the new area
    feature. Double-click the mouse to finish the sketch.

> ![](media/image98.png){width="4.768055555555556in"
> height="2.046527777777778in"}

7.  If the Toggle Source Feature ID option is selected, a second window
    will open allowing you to assign a value to the Source_FeatureID
    field. Select a value from the list and click OK or click Cancel to
    skip this step.

> ![](media/image37.png){width="2.7805555555555554in"
> height="2.988888888888889in"}

Note

> An existing DBF or text file can be used to import values to the
> Source_FeatureID field. If you use a DBF, it needs to contain a field
> named SrcID; a text file only needs a single column of values. There
> is a 40 character limit for each value in the Source_FeatureID field,
> although values over 40 characters can still be present in your list
> as long as they are not selected.

8.  A new area event record will be added to the target featureclass.
    Repeat the above steps as needed to complete data entry. Be sure to
    save your edits using the ArcMap  Editor  Save Edits button.

> ![](media/image99.png){width="5.363888888888889in"
> height="2.3020833333333335in"}

# Update Area Events

To update existing area event features:

1.  Change the HEM Task to Update Line Event.

![](media/image100.png){width="2.21875in" height="0.3125in"}

2.  Activate the Event Selection tool.
    ![](media/image40.png){width="0.28125in"
    height="0.2708333333333333in"}

3.  Using the Event Selection tool as you would the ArcMap Selection
    tool, select an existing area event.

4.  The Select Event dialog box will open. Select the event record to
    update from the list and click the OK button.

> ![](media/image101.png){width="5.436805555555556in"
> height="3.3430555555555554in"}

5.  The HEM Sketch tool should automatically activate. Using this tool,
    define the new shape of the area feature. Double-click the mouse to
    finish the sketch.

> ![](media/image102.png){width="5.363888888888889in"
> height="2.3020833333333335in"}

6.  When the sketch is completed, the area validation checks will be
    performed. If there are any errors the Invalid Area Event dialog box
    will open. To continue creating the event, select the option Clip to
    Waterbody button. Otherwise, click the Delete and Recreate button to
    start over.

> ![](media/image103.png){width="2.34375in"
> height="3.7493055555555554in"}

7.  If there were no validation errors or if you selected Clip to
    Waterbody, the area event will be updated.

> ![](media/image104.png){width="5.363888888888889in"
> height="2.3020833333333335in"}

# 

# Copy Area Events

To copy an existing line event feature into a new record:

1.  Change the HEM Task to Copy Event.

![](media/image44.png){width="2.2395833333333335in"
height="0.2916666666666667in"}

2.  Select HEM Target event featureclass for the new record. The target
    can be the same featureclass as the record to be copied or a
    different line event featureclass.

> ![](media/image105.png){width="2.4583333333333335in"
> height="0.2708333333333333in"}

3.  Activate the Event Selection tool.
    ![](media/image40.png){width="0.28125in"
    height="0.2708333333333333in"}

4.  Using the Event Selection tool as you would the ArcMap Selection
    tool, select an existing area event.

5.  The Select Event dialog box will open. Select the event record to
    update from the list and click the Copy button.

> ![](media/image106.png){width="5.436805555555556in"
> height="3.3430555555555554in"}

6.  The existing area feature will be copied into the target
    featureclass. It is important to note that the copied feature will
    now stack on top of the original feature. Repeat the above steps to
    copy additional features.

# Delete Area Events

To delete an existing area event feature:

1.  Change the HEM Task to Delete Event.

![](media/image46.png){width="2.2395833333333335in" height="0.3125in"}

2.  Activate the Event Selection tool.
    ![](media/image40.png){width="0.28125in"
    height="0.2708333333333333in"}

3.  Using the Event Selection tool as you would the ArcMap Selection
    tool, select an existing area event.

4.  The Select Event dialog box will open. Select the event record to
    delete from the list and click the Delete button.

> ![](media/image107.png){width="5.436805555555556in"
> height="3.3430555555555554in"}

5.  The selected area feature will be deleted. Repeat the above steps to
    delete additional records.

# Merge Area Events

For line events, the Merge Event task takes two line event records and
attempts to consolidate them into a single line event record. To merge
line events:

1.  Change the HEM Task to Copy Event and change the HEM Target to the
    featureclass to be edited.

> ![](media/image73.png){width="4.707638888888889in"
> height="0.3020833333333333in"}

2.  Activate the HEM Event Selection Tool and select two existing area
    events.

3.  The Select Two Events form will open with two or more events listed.
    While holding the shift key on the keyboard, select select the two
    events to be merged in the list and click the Merge button.

> ![](media/image108.png){width="5.436805555555556in"
> height="3.3430555555555554in"}

4.  Select which attributes should be assigned to the merged record and
    click the OK button.

> ![](media/image109.png){width="4.228472222222222in"
> height="3.9680555555555554in"}

5.  An area record will be created in the edit target that has the
    merged geometry from the two input records and the attributes
    selected in Step 4. The original records will be deleted. When
    completed, the following message box will display.

> ![](media/image110.png){width="4.582638888888889in"
> height="1.65625in"}

# Split Area Events

For area events, the Split Event task divides a single area event record
into two different records based on the user defined split location. To
split a line event:

1.  Change the HEM Task to Split Event.

![](media/image77.png){width="2.21875in" height="0.3229166666666667in"}

2.  Activate the Event Selection tool.
    ![](media/image40.png){width="0.28125in"
    height="0.2708333333333333in"}

3.  Using the Event Selection tool as you would the ArcMap Selection
    tool, select an existing area event.

4.  The Select Event dialog box will open. Select the event record to
    split from the list and click the Split button.

> ![](media/image111.png){width="5.436805555555556in"
> height="3.3430555555555554in"}

5.  Using the HEM Sketch tool, sketch a line through the area feature
    where it should be split into two records. Double-click the mouse to
    finish the sketch.

> ![](media/image112.png){width="5.363888888888889in"
> height="2.3020833333333335in"}

6.  The results of the split task will be reported in a message box.

> ![](media/image113.png){width="5.031944444444444in"
> height="1.6263888888888889in"}

# Import Area Events

The Import Area Events button creates new HEM events from existing area
features. Import features can be from a variety of sources and do not
have to be in the NHD format.

To import area features:

1.  Add an NHD Waterbody featureclass and the import area dataset to the
    map document and using the ArcMap selection tool, select the area
    features to be imported. If no features are selected, all records in
    the dataset will be imported.

2.  Set the HEM Task to Create Area Event -- Partial Waterbody.

> ![](media/image114.png){width="2.2083333333333335in"
> height="0.3229166666666667in"}

3.  Set the HEM Target to the area event featureclass you want to import
    into.

> ![](media/image115.png){width="2.46875in" height="0.3125in"}

4.  Select the source featureclass in the ArcMap table of contents.

> ![](media/image116.png){width="2.25in" height="1.4583333333333333in"}

5.  From the HEM Edit Tools menu, select Import Areas.

> ![](media/image117.png){width="1.0625in" height="0.25in"}

6.  If there are no selected features in the import dataset, all
    features will be imported.

7.  The tool will offer the opportunity to transfer a unique identifier
    into the new area event records. This is useful for relating the new
    area events back to the original data source. Select Add IDs to
    transfer the identifier to the new record. Don't Add IDs skips this
    step. Stop Import exits the tool.

> ![](media/image118.png){width="3.0409722222222224in"
> height="2.4895833333333335in"}

8.  The tool will cycle through the areas to import and attempt to
    overlay them with an NHD Waterbody. If the feature to import does
    not follow the area validation rules, the Invalid Area Event dialog
    box will open. Select Clip to Waterbody to adjust the import feature
    to the shape of the underlying NHD Waterbody and continue with the
    import. A report is generating detailing how many features were
    successfully imported and which OIDs failed.

9.  This report can be saved to a text file.

> ![](media/image119.png){width="4.009722222222222in" height="2.7in"}

[]{#__RefHeading___Toc221070394 .anchor}Other HEM Functions

The purpose of this chapter is to discuss the other tools that are
provided with the HEM tools.

Chapter Overview:

-   Measure Linear Distance

-   Go X Distance

-   Select by Selected

-   Check Continuous Events

-   Repair Continuous Events

-   Interactive Event Synchronization

-   Batch Event Synchronization

# 

# Measure Linear Distance

The purpose of this tool is to provide a method for calculating the
stream linear distance between two user-identified points along a
stream. To use this functionality:

1.  Set the HEM Task to Measure Linear Distance. You do not need to set
    an HEM Target.

> ![](media/image120.png){width="2.1875in" height="0.3125in"}

2.  Activate the HEM Event Sketch tool.
    ![](media/image34.png){width="0.3125in" height="0.28125in"}

3.  Click at a point along a stream.

> ![](media/image121.png){width="4.768055555555556in"
> height="2.046527777777778in"}

4.  While holding the Shift key on your keyboard, click on a location on
    a NHD Flowline to define the other end of the line you wish to
    measure.

> ![](media/image122.png){width="4.768055555555556in"
> height="2.046527777777778in"}

5.  The path between the two points will be solved using a network trace
    and the measure results dialog box will open.

> ![](media/image123.png){width="2.4270833333333335in"
> height="2.34375in"}

Note

> The measure box by default opens using the US Survey Foot conversion
> between units of measure. The input value (in either feet or meters)
> is then calculated to the other units of measure. The input unit of
> measure is based on the unit of measure for the data projection. If
> the data uses the Geographic coordinate system, the polyline created
> by the network solve is first projected to the Albers projection and
> then the length of the feature is calculated. To toggle between the US
> Survey Foot and the International conversion standards, select the
> conversion constants pull-down menu from the top of the form. The
> values on the form will change based on the constant selected.

6.  When the measure results dialog box is closed, you will be presented
    with the option to convert the measure results to a line event. If
    you select yes, a new feature will be added to the featureclass
    identified in the HEM Target box.

> ![](media/image124.png){width="1.9270833333333333in"
> height="1.1145833333333333in"}

# Go X Distance

The purpose of this tool is to provide a mechanism to travel up or
downstream a user-defined distance.

1.  Set the HEM Task to Go X Distance. You do not need to set an HEM
    Target.

> ![](media/image125.png){width="2.1979166666666665in"
> height="0.2916666666666667in"}

2.  Activate the HEM Event Sketch tool.
    ![](media/image34.png){width="0.3125in" height="0.28125in"}

3.  Click at a point along a stream. This will serve as the point from
    which the distance will be measured.

> ![](media/image126.png){width="4.768055555555556in"
> height="2.046527777777778in"}

4.  Going in the distance you would like to travel, while holding down
    the shift key, click somewhere up or downstream beyond your estimate
    of the distance.

Note

> Clicking the second point on the stream helps establish the path of
> where the trace should go. If you need assistance estimating where the
> second point should be, use the ArcMap measure distance tool to
> provide a rough estimate of the distance.

5.  The measure distance box will open. Input a distance using the unit
    of measure from the projection that your NHD data (and the data
    frame) utilizes and then press the Enter key on your keyboard.

> ![](media/image127.png){width="1.125in" height="0.5in"}

6.  A red cross-hair graphic will appear on the stream at the user
    defined distance.

> ![](media/image128.png){width="4.768055555555556in"
> height="2.3222222222222224in"}

7.  You will be presented with the option to convert the measure results
    to a point event. If you select yes, a new feature will be added to
    the featureclass identified in the HEM Target box.

> ![](media/image129.png){width="1.9583333333333333in"
> height="1.1145833333333333in"}

8.  When the measure results dialog box is closed, you will be presented
    with the option to convert the measure results to a line event. If
    you select yes, a new feature will be added to the featureclass
    identified in the HEM Target box.

9.  The HEM graphics created by the tool can be cleared from the map by
    clicking the HEM Edit Tools  Clear Elements button.

# Select by Selected

The Select by Selected tool will select a point or line event in your
map based on an existing selection. This tool will allow you to use the
ArcMap selection tools (such as an attribute query) to select an event,
and then pass that selection set to the HEM tools.

1.  Select one or more events using any of the ArcMap tools for
    selecting records.

2.  Change the HEM Task to Copy Event or any other tasks that uses a
    selected event. This includes Delete Event, or any of the update
    tasks.

![](media/image44.png){width="2.2395833333333335in"
height="0.2916666666666667in"}

3.  Select HEM Target event featureclass for the new record. The target
    can be the same featureclass as the record to be copied or a
    different point event featureclass.

![](media/image33.png){width="2.4895833333333335in"
height="0.3020833333333333in"}

4.  From the HEM Edit Tools menu, select the Select by Selected button.

> ![](media/image130.png){width="1.3541666666666667in"
> height="0.19791666666666666in"}

5.  Using the Event Selection tool as you would the ArcMap Selection
    tool, select an existing point event.

6.  The Select Event dialog box will open. Select the event record to
    copy/update/delete from the list and click the Copy/Update/Delete
    button.

> ![](media/image131.png){width="4.772222222222222in"
> height="3.045138888888889in"}

7.  The edit task selected will complete.

Note

> The greatest use of the Select by Selected tool is for users who call
> the HEM edit functionality programmatically from agency specific .NET
> applications. For more information about how to use this
> functionality, see the "Calling the Hydro Event Management Tools from
> Other Applications" document or contact the HEM development team.

# Check Continuous Events

The Check Continuous Events button provides a way to verify that events
that should be continuous do not have any gaps or overlaps. This tool
can be run from ArcCatalog on an entire featureclass or in ArcMap on a
selected set of features. Any errors that are found are put into a text
report as well as a new personal geodatabase table that can be joined to
the route featureclass and used to display errors in the map. This tool
only functions on an event featureclass that contains continuous events
as specified when the featureclass was created using the HEM Event Table
Manager.

To use the Check Continuous Events tool in ArcCatalog:

1.  Open ArcCatalog and select the geodatabase that contains the event
    featureclass.

2.  Click the Check Continuous Events buttons to launch the tool.
    ![](media/image132.png){width="0.23958333333333334in"
    height="0.2604166666666667in"}

3.  A select featureclass dialog box will open with a list of the
    continuous event featureclasses. Select the featureclass that you
    want to run the tool on and click the Return button.

> ![](media/image133.png){width="3.332638888888889in" height="1.75in"}

4.  Next, select the NHDFlowline featureclass that will be used to check
    the continuous events.

> ![](media/image134.png){width="3.9881944444444444in"
> height="2.7131944444444445in"}

5.  The last step is to specify an output folder to store the QC
    geodatabase and tables.

> ![](media/image135.png){width="3.9895833333333335in"
> height="2.979861111111111in"}

6.  Tool progress will be displayed in a progress box.

> ![](media/image136.png){width="3.207638888888889in"
> height="2.3333333333333335in"}

Once processing has completed (either in ArcCatalog or ArcMap), a window
will open informing you the process has finished. The text file that was
created in the output folder contains a list of all of the errors that
were encountered in your event featureclass, what the ReachCode is where
the error was found, and what the error is. The name of the text file
generated by the tool is HEMContEvtQC followed by a date and time stamp
of when the error report was created.

![](media/image137.png){width="5.436805555555556in"
height="1.5208333333333333in"}

The output text file can be used to inspect the data to see if there are
any errors.

![](media/image138.png){width="6.832638888888889in"
height="5.447222222222222in"}

Once it is determined that the data has errors, the personal geodatabase
table that is created by the tool can be added to ArcMap to view the
errors. Open ArcMap and add the event featureclasses that were checked
and the NHD linework. Then add the personal geodatabase error report
table located in the tool output directory. The personal geodatabase
uses the same naming convention as the text file: HEMContEvtQC followed
by the date and time stamp and the .mdb extension. The table that ends
with "\_err" is the error table.

![](media/image139.png){width="6.836805555555555in"
height="2.672222222222222in"}

Once the table is added to ArcMap it can be joined to the NHD Flowline
using the ReachCode field and symbolized on the Error_Type field.
Standard ArcMap tools can be used for these steps.

The HEM editing tools or the Repair Continuous Events tool can be used
to fix errors.

Note

> The Check Continuous Events tool performs similarly in ArcMap as it
> does in ArcCatalog with a few exceptions. When running the tool in
> ArcMap you can select the features in the NHD Flowline featureclass to
> be checked for errors. You also need to select the event workspace
> using the Table of Contents source tab before the tool becomes
> enabled.

# Repair Continuous Events

The Repair Continuous Events tool provides a user interface for easily
reviewing and fixing errors detected by the Check Continuous Events
tool. This tool uses the error table created by the Check Continuous
Events tool.

To run the Repair Continuous Events tool:

1.  Open ArcMap and add NHD Flowline and the continuous event theme to
    the map; start editing.

2.  From the HEM Edit Tools menu, select Repair Continuous Events.

> ![](media/image140.png){width="1.75in" height="0.23958333333333334in"}

3.  The Repair Continuous Events dialog will open.

4.  Select the Continuous Check Workspace. This is the personal
    geodatabase created by the Check Continuous Events tool.

> ![](media/image141.png){width="3.0930555555555554in"
> height="0.5625in"}

5.  Select the featureclass to be repaired using the Select Event
    Feature Class drop down menu.

> ![](media/image142.png){width="2.8222222222222224in"
> height="0.4895833333333333in"}

6.  Once a featureclass has been selected, you can identify which errors
    to inspect: All, Gaps, Overlaps, or No Events. This option will
    control which errors will appear in the Event Error grid.

> ![](media/image143.png){width="1.96875in"
> height="1.0208333333333333in"}

7.  The Event Errors grid will now display the records to be fixed. The
    buttons next to the grid perform the following functions:

> Zoom to Event -- focuses the map display on the selected record.
>
> Outline Errors -- creates a graphic on the map to display the error.
>
> Auto Repair -- attempts to automatically resolve the error.
>
> Manual Repair -- activates the HEM edit environment so that the fix
> can be manually completed.
>
> ![](media/image144.png){width="4.25in" height="1.7090277777777778in"}

8.  Select a record in the grid to repair. Click the Zoom To Event and
    Outline Errors button to better display the error:

> ![](media/image145.png){width="5.740972222222222in"
> height="1.8493055555555555in"}

9.  Click the Auto Repair button to attempt to automatically fix the
    error. If the application can fix the record, it will be fixed.

> ![](media/image146.png){width="1.0625in"
> height="0.2708333333333333in"}

10. If the application cannot automatically fix the error, the Manual
    Repair button can be activated. This button will set up the HEM
    task/target and activate the HEM sketch tool so that you can create
    a new event manually.

11. Repeat steps as needed to fix all errors. Be sure to Stop Editing
    and Save Edits to keep the updates.

# Interactive Event Synchronization

The Event Synchronization Tool that was developed to assist users with
updating records that have become out of alignment with the NHD Flowline
data due to edits to the stream network. Typically, this tool would be
run on event data when updated hydrography data has been downloaded from
the NHD. The tool will detect which event records have a potential error
based on the date of the last spatial edit to the NHD Flowline data
compared to the date of the last spatial edit to the event. This tool
uses the location of the event to determine the new location on the
refreshed flowline data. This tool does not utilize the NHD Flow or
Reach Cross Reference tables when processing the data and users must
approve each edit.

To use the Interactive Event Synchronization tool:

1.  Open ArcMap and add the NHD Flowline and event data to the map.

2.  Select the event records to synchronize; records from multiple event
    featureclasses may be selected.

3.  From the HEM Edit Tools menu, select Synchronize Events.

> ![](media/image147.png){width="1.9375in" height="0.25in"}

4.  Select the event featureclasses to be synchronized and click the
    Return button.

> ![](media/image148.png){width="3.332638888888889in"
> height="1.7291666666666667in"}

5.  The Synchronize Events form will then open. Depending on the number
    of records selected, this may take a few moments. When the form
    opens, the event records displayed are those that need
    synchronization.

![](media/image149.png){width="6.620138888888889in"
height="1.9361111111111111in"}

Synchronize Form Overview:

-   Events to Synchronize Grid -- a table of records that need to be
    updated.

-   Zoom to Record -- zooms the map display to the event record selected
    in the grid.

-   Auto-Match -- for the event record selected in the grid, the
    application will attempt to automatically update the geometry of the
    event to match the underlying NHDFlowline records.

-   Edit Points -- facilitates the manual update of the event record
    selected in the grid.

-   Preview Trace -- previews the automatic match results. This provides
    the user the opportunity to view the update before the edit is
    committed to the dataset.

-   Accept Match -- if the Preview Trace is acceptable, Accept Match
    will complete the edit to the selected record.

To perform an Auto-Match:

1.  Select one of the records in the grid. Selecting the record in the
    grid will highlight it on the map. Observe how the selected event
    has become out of alignment with the underlying NHD Flowline.

![](media/image150.png){width="3.201388888888889in"
height="2.466666666666667in"}

2.  Click the Auto-Match button. If the Auto-Match is successful, the
    event record will be re-aligned to the stream and the event record
    will disappear from the records in the grid

> ![](media/image151.png){width="1.0833333333333333in"
> height="0.2604166666666667in"}

Occasionally you may encounter an event that cannot be auto-matched.
This occurs because one or more of the endpoints of the event record no
longer fall within the selection tolerance of the underlying stream
network. When this occurs the auto-match function will return the
message: "No route was found within the search tolerance of the entered
point." In order to synchronize a record that cannot be auto-matched,
you will need to perform a manual edit.

![](media/image152.png){width="4.582638888888889in"
height="1.5208333333333333in"}

![](media/image153.png){width="3.970833333333333in" height="3.25in"}

To do this:

1.  Select the event record in the grid.

2.  Click the Edit Points button. This will automatically set up the
    edit -- selecting the event record, changing the task to Update
    Line/Point Event, and activating the HEM Sketch Tool.

> ![](media/image154.png){width="1.09375in"
> height="0.2604166666666667in"}

3.  Click on the map where the location (point) or start and end points
    (line) should be located. This is the same process used when
    updating events. The event record will be updated and the event
    record will disappear from the records in the grid.

If you would like to preview the trace results before using the
Auto-Match tool:

1.  Select the event record in the grid.

2.  Click the Preview Trace button. This will create a blue preview
    graphic of what the Auto-Match results would be for the record.

![](media/image155.png){width="3.71875in" height="2.842361111111111in"}

3.  If the results are acceptable, you may click the Accept Match button
    to accept the change to the event record.

> ![](media/image156.png){width="1.09375in"
> height="0.2708333333333333in"}

When all records have been synchronized, the form can be closed using
the X button in the corner of the dialog box. Be sure to Save Edits from
the ArcMap Editor toolbar to save all changes to the dataset.

# Batch Event Synchronization

In version 2.0 of the HEM Tools, a more robust tool has been added for
synchronizing events to changes in the NHD data. This tool attempts to
provide an automated tool for refreshing the data that utilizes the NHD
Reach Cross Reference and Flow tables to provide a more accurate end
result. Batch Event Synchronization is a two-stage process. First, the
synchronize process must be run on the geodatabase in either ArcMap or
ArcCatalog. Once this is completed, the user can review, edit, and post
changes in ArcMap. The Batch Event Synchronization tool cycles through
the selected event tables and exports those events that have ReachSMDate
values that are earlier than their underlying NHD data and that fall
within the extent of the selected NHD Flowline dataset. For each of the
exported records, the tool will attempt to synchronize the records.

To synchronize the database (ArcCatalog or ArcMap):

1.  Click the Batch Synchronize Events button
    ![](media/image157.png){width="0.23958333333333334in"
    height="0.23958333333333334in"} to open the user interface.

2.  Select the NHD Flowline featureclass. If the Waterbody featureclass
    is in the same workspace it will be populated automatically. If it
    is not, add it manually.

> ![](media/image158.png){width="3.6243055555555554in"
> height="0.8854166666666666in"}

Note

> The batch synchronization tool requires that the NHDReachCrossRef,
> NHDFlow, and NHDReachCode_ComID tables be present in the same
> workspace as the NHDFlowline data.

3.  Select the HEM workspace. If the data is versioned the tool will ask
    you to select a version to evaluate.

> ![](media/image159.png){width="3.676388888888889in"
> height="0.5208333333333334in"}

4.  Define the maximum search tolerance. This is the maximum distance a
    point geometry (either point event or line endpoints) will search to
    snap to a set of NHD Flowlines. This field defaults to 50 meters.

> ![](media/image160.png){width="2.4583333333333335in"
> height="0.3645833333333333in"}

5.  Select the event featureclasses that will be processed. Items that
    are not checked will be skipped.

> ![](media/image161.png){width="3.6972222222222224in"
> height="1.9166666666666667in"}

6.  Create the temporary file geodatabase for processing events that
    need update. If the database already exists, you will be prompted to
    overwrite the existing file.

> ![](media/image162.png){width="3.6555555555555554in"
> height="0.5520833333333334in"}

7.  Click the Run Synchronization button. Progress will be reporting in
    the Progress area of the form.

> ![](media/image163.png){width="3.8743055555555554in"
> height="0.8645833333333334in"}

8.  When the tool has completed, a text report of the results will be
    presented.

> ![](media/image164.png){width="3.990972222222222in"
> height="3.167361111111111in"}

After the database synchronization completes successfully, you need to
review, edit if necessary, and apply updates back to the source data.

To perform QA/QC steps on the synchronized records (ArcMap):

1.  Click the Batch Synchronize QA/QC
    ![](media/image165.png){width="0.22916666666666666in"
    height="0.23958333333333334in"} button to open the user interface.

2.  On the QA/QC Options tab:

    a.  Select the QA/QC file geodatabase for review.

    b.  Click the Add Events to Map button to add the data to the map or
        you can add it manually. You will also need to add the NHD
        Flowline and Waterbody featureclasses to the map if you plan to
        use the HEM tools for editing.

    c.  Select threshold distances, currently in decimal degrees.

    d.  Select the cross reference classes to review (regardless of
        thresholds).

    e.  Using the ArcMap Edit menu, start editing the synchronized
        (temporary) workspace.

> ![](media/image166.png){width="5.366666666666666in"
> height="4.9222222222222225in"}

Note

> All checked classes will be listed in the datagrid for review and
> approval. All non-checked classes that are within the defined distance
> thresholds will be set to approved and will not be listed in the
> datagrid for review. You can always return to this tab and reset what
> is approved and what is not approved.

3.  Click the Review QA/QC button.

> ![](media/image167.png){width="1.2083333333333333in"
> height="0.28125in"}

4.  On the Review QA/QC tab:

    a.  Click Next or Previous to navigate through the records in the
        data grid. Or simply click a row in the datagrid and it will
        Zoom and Flash the record.

    b.  Click the Approved column to approve a synchronized event or use
        the HEM tools to update the record. (Important -- use HEM Update
        Point, Update Line, or Update Area to fix records.)

    c.  Continue to approve and fix records for each of the event tables
        listed. When you are satisfied with the results, click the Apply
        Synchronization button.

    d.  Save edits and stop editing when finished.

> ![](media/image168.png){width="4.829861111111111in"
> height="4.471527777777778in"}

5.  The Apply Synchronization tab is where you apply the synchronized
    geometry for the source event featureclasses. **The edit workspace
    for this step must be set to the source event workspace.** (If
    source data is stored in ArcSDE, be sure to create an edit version
    before continuing.) Click the Apply Synchronized Updates button.

> ![](media/image169.png){width="4.190972222222222in"
> height="2.7680555555555557in"}

6.  The tool will cycle through the temporary event featureclasses and
    update the source data accordingly. When it has completed a text
    report will display with the results. Be sure to stop editing and
    save edits.

> ![](media/image170.png){width="3.2881944444444446in"
> height="4.011805555555555in"}

7.  Click the Close button when completed.

[]{#__RefHeading___Toc221070402 .anchor}HEM Tips and Tricks

Chapter Overview:

-   Customizing the HEM Toolbar

-   Snap Environment

-   Using Barriers

-   Upgrading HEM 1.x Featureclasses

# Customizing the HEM Toolbar

Commonly used buttons or tools can be added to the HEM toolbar using the
ArcMap customize window. To open the customize window select View 
Toolbars  Customize from the ArcMap menu. As long as the customize
window is open you can add and remove commands from toolbars.

![](media/image171.png){width="3.9722222222222223in" height="3.1in"}

Activate the Commands tab to find commands to add to the toolbar. Once
you locate a command to add, click and drag it from the commands box
onto the toolbar. In the example below, the ArcMap Start Editing, Stop
Editing, and Save Edits commands have been added to the HEM toolbar.

![](media/image172.png){width="6.835416666666666in"
height="0.5208333333333334in"}

![](media/image173.png){width="1.6354166666666667in"
height="0.6458333333333334in"}If you want your customizations to apply
to all future ArcMap sessions, make sure that the "Save In:" box at the
bottom of the customize window is set to Normal.mxt. Otherwise you can
set it to the name of your current map document and the changes that you
make to the toolbar will only be applied to the current map document.
When finished, click the Close button.

# Snap Environment

The application provides a tool that automatically sets up the snap
environment for editing. The snap environment can help establish exact
locations in relation to other features. Once the default settings have
been established, the ArcMap snapping window opens so the user can
review those settings and adjust as necessarily. This is an optional
tool that is meant to facilitate snapping event data to the NHD data.

To use this tool:

1.  Open ArcMap and add the NHD data and event featureclasses that will
    be edited to the map.

2.  Start Editing.

3.  From the HEM Edit Tools menu, select Snap Environment.

> ![](media/image174.png){width="1.2604166666666667in"
> height="0.2708333333333333in"}

4.  The snap environment will be set and the snapping window will open.
    Review the environment and adjust as needed to meet your editing
    needs. The snapping window can be left open or closed.

> ![](media/image175.png){width="3.332638888888889in"
> height="1.2291666666666667in"}

HEM Snapping Tips:

-   If point and line events should snap to stream junctions, select the
    End checkbox for the Flowline featureclass.

-   If you are creating Area events, turn off snapping for Flowline, and
    turn on snapping for Waterbody edge. This will prevent the mouse
    from trying to snap to Flowline artificial paths.

-   If the endpoints of linear events should snap to each other, then
    turn on End snapping for the event featureclass. This also applies
    to points.

-   To adjust the Snapping Tolerance and Snapping Priority, open the
    ArcMap Editor Menu  Options  Editing Options. Snap Tips can also
    be turned on using this tab.

-   For more detailed information about the ArcMap snapping environment,
    see ArcGIS Desktop Help Snapping Environment.

# Using Barriers 

The HEM application relies on the network tracing capability of ArcGIS.
Occasionally in some areas, such as braided streams, the tools may not
return the path that you intended. In this case, you will want to
utilize the Add Junction Barrier and Add Edge Barrier tools located on
the ArcMap Utility Network Analyst toolbar.

![](media/image176.png){width="6.833333333333333in"
height="0.5090277777777777in"}

![](media/image177.png){width="0.6458333333333334in"
height="0.8541666666666666in"}The Add Junction and Edge Barrier tools
are in the dropdown tool palette represented with the blue flag. To
activate one of the tools, select it using your mouse.

Both types of barriers define places in the network past which traces
cannot continue. When performing trace operations, ArcMap treats the
underlying network features as if they are disabled, preventing the
trace from continuing beyond these features. Junction Barriers
![](media/image178.png){width="0.2708333333333333in"
height="0.2708333333333333in"} can be placed at NHD Flowline junctions
(where one or more features meet). Edge Barriers
![](media/image179.png){width="0.23958333333333334in"
height="0.23958333333333334in"} can be placed anywhere along an NHD
Flowline feature.

When using barriers, be sure to clear them from the map when you no
longer need them. To clear barriers, select Clear Barriers from the
Utility Network Analyst  Analysis menu.

# Upgrading HEM 1.x Featureclasses

The HEM application utilizes and maintains a field in the event
featureclasses called ID. In the HEM 1.x releases, this field was
created as a text field with a length of 34 characters. In HEM 2.0, the
field has been expanded to 40 characters in order to accommodate
inserting a GUID (Globally Unique Identifier) value. In order for you to
use the HEM 2.0 tools on data created using HEM 1.x, you must upgrade
the featureclasses. A tool has been provided to perform this upgrade for
you.

Note

> This tool only functions on personal and file geodatabases. To upgrade
> HEM featureclasses that are stored in ArcSDE, export the
> featureclasses, any related \_M tables, and the HEM Tracking Table to
> a personal or file geodatabase, perform the upgrade, then replace the
> data in ArcSDE with the upgraded featureclasses/tables.

To upgrade HEM 1.x featureclasses to HEM 2.0:

1.  Open ArcCatalog and select the event geodatabase.

2.  Click the Update to GUID
    ![](media/image180.png){width="0.2604166666666667in"
    height="0.2604166666666667in"} button on the HEM toolbar.

3.  The Update HEM Tables to GUID dialog box will open.

4.  Select the HEM Tracking Table for the geodatabase. (Note: if data is
    stored in SDE, there can be multiple HEM tracking tables.)

> ![](media/image181.png){width="3.4993055555555554in"
> height="0.53125in"}

5.  Then select the tables to be upgraded and click the Update button.

> ![](media/image182.png){width="3.5104166666666665in"
> height="3.6868055555555554in"}

6.  If you would like to preserve existing ID values, then check this
    option. This is useful if you have other datasets that have been
    related to the event table using the ID field.

> ![](media/image183.png){width="1.7083333333333333in"
> height="0.1875in"}

7.  When the tool has completed, a report will be displayed.

> ![](media/image184.png){width="4.615972222222222in"
> height="5.384722222222222in"}

[]{#__RefHeading___Toc221070407 .anchor}Appendix I HEM Event Table
Structure

The following is the structure of the event tables and featureclasses
that are compatible with the HEM tools. Event tables can be created with
either the Full or Compressed schema. The Full Schema includes all
attributes identified by the NHD Data Model for event data and those
attributes needed for the HEM tools to function. The Compressed Schema
includes only those attributes that were identified as the minimum
required attributes for the HEM tools to function. This data format
should not be used for data that will be submitted to the NHD
Repository.

**Point Event Data**

  ------------------- ---------- ---------- ------------ ------------ -------------------------------- ------------
  **Field Name**      **Data     **Allow    **Domain**   **Length**   **Description**                  **Schema**
                      Type**     Nulls?**                                                              

  OID                 Object ID                                       ESRI system maintained           Both
                                                                      identifier.                      

  ComID               Long       No                                   Uniquely identifies the record.  Both
                      Integer                                                                          

  Event Date          Date       Yes                     8            The date the event record was    Both
                                                                      created or last modified.        

  ReachCode           String     No                      14           The ReachCode value for the      Both
                                                                      NHDFlowline record that the      
                                                                      event record references.         

  ReachSMDate         Date       No                      8            The reach spatial modification   Both
                                                                      date.                            

  ReachResolution     Long       No         Resolution                Code for the source resolution.  Both
                      Integer                                                                          

  FeatureComID        Long       Yes                                                                   Full Only
                      Integer                                                                          

  FeatureClassRef     Long       Yes                                                                   Full Only
                      Integer                                                                          

  Source_Originator   String     Yes                     130                                           Full Only

  Source_DataDesc     String     Yes                     100                                           Full Only

  Source_FeatureID    String     Yes                     40                                            Full Only

  FeatureDetailURL    String     Yes                     255                                           Full Only

  Measure             Double     No                      0            The measure along the            Both
                                                                      NHDFlowline record where the     
                                                                      event record is located.         

  Offset              Double     No                      0                                             Both

  EventType           Long       No                                                                    Both
                      Integer                                                                          

  ID                  String     No                      34           HEM unique identifier.           Both
                                                                      Maintained by the editing tools. 

  Shape               Geometry                                        Point geometry for the event     Both
                                                                      record.                          
  ------------------- ---------- ---------- ------------ ------------ -------------------------------- ------------

**Single-Route Linear Events**

Single-route events are linear event records that do not cross multiple
NHD Flowline records.

  ------------------- ---------- ---------- ------------ ------------ -------------------------------- --------------
  **Field Name**      **Data     **Allow    **Domain**   **Length**   **Description**                  **Schema\***
                      Type**     Nulls?**                                                              

  OID                 Object ID                                       ESRI system maintained           Both
                                                                      identifier.                      

  ComID               Long       No                                   Uniquely identifies the record.  Both
                      Integer                                                                          

  Event Date          Date       Yes                     8            The date the event record was    Both
                                                                      created or last modified.        

  ReachCode           String     No                      14           The ReachCode value for the      Both
                                                                      NHDFlowline record that the      
                                                                      event record references.         

  ReachSMDate         Date       No                      8            The reach spatial modification   Both
                                                                      date.                            

  ReachResolution     Long       No         Resolution                Code for the source resolution.  Both
                      Integer                                                                          

  FeatureComID        Long       Yes                                                                   Full Only
                      Integer                                                                          

  FeatureClassRef     Long       Yes                                                                   Full Only
                      Integer                                                                          

  Source_Originator   String     Yes                     130                                           Full Only

  Source_DataDesc     String     Yes                     100                                           Full Only

  Source_FeatureID    String     Yes                     40                                            Full Only

  FeatureDetailURL    String     Yes                     255                                           Full Only

  FMeasure            Double     No                      0            The measure along the            Both
                                                                      NHDFlowline record where the     
                                                                      start point of the event record  
                                                                      is located.                      

  TMeasure            Double     No                      0            The measure along the            Both
                                                                      NHDFlowline record where the end 
                                                                      point of the event record is     
                                                                      located.                         

  Offset              Double     No                      0                                             Both

  EventType           Long       No                                                                    Both
                      Integer                                                                          

  ID                  GUID       No                      34           HEM unique identifier.           Both
                                                                      Maintained by the editing tools  

  Shape               Geometry                                        Polyline geometry for the event  Both
                                                                      record.                          
  ------------------- ---------- ---------- ------------ ------------ -------------------------------- --------------

**Multi-Route Linear Events**

Multi-route linear events refer to events that may cross one or many NHD
Flowline records. Detailed ReachCode and Measure data is stored in the
related "\_M" table.

  ------------------- ---------- ---------- ------------ ------------ -------------------------------- --------------
  **Field Name**      **Data     **Allow    **Domain**   **Length**   **Description**                  **Schema\***
                      Type**     Nulls?**                                                              

  OID                 Object ID                                       ESRI system maintained           Both
                                                                      identifier.                      

  ComID               Long       No                                   Uniquely identifies the record.  Both
                      Integer                                                                          

  Event Date          Date       Yes                     8            The date the event record was    Both
                                                                      created or last modified.        

  FReachCode          String     No                      14           The ReachCode value for the      Both
                                                                      NHDFlowline record that the      
                                                                      start point of the event record  
                                                                      references.                      

  TReachCode          String     No                      14           The ReachCode value for the      Both
                                                                      NHDFlowline record that the end  
                                                                      point of the event record        
                                                                      references.                      

  ReachSMDate         Date       No                      8            The reach spatial modification   Both
                                                                      date.                            

  ReachResolution     Long       No         Resolution                Code for the source resolution.  Both
                      Integer                                                                          

  FeatureComID        Long       Yes                                                                   Full Only
                      Integer                                                                          

  FeatureClassRef     Long       Yes                                                                   Full Only
                      Integer                                                                          

  Source_Originator   String     Yes                     130                                           Full Only

  Source_DataDesc     String     Yes                     100                                           Full Only

  Source_FeatureID    String     Yes                     40                                            Full Only

  FeatureDetailURL    String     Yes                     255                                           Full Only

  FMeasure            Double     No                      0            The measure along the            Both
                                                                      NHDFlowline record where the     
                                                                      start point of the event record  
                                                                      is located.                      

  TMeasure            Double     No                      0            The measure along the            Both
                                                                      NHDFlowline record where the end 
                                                                      point of the event record is     
                                                                      located.                         

  Offset              Double     No                      0                                             Both

  EventType           Long       No                                                                    Both
                      Integer                                                                          

  ID                  GUID       No                      34           HEM unique identifier.           Both
                                                                      Maintained by the editing tools. 

  Shape               Geometry                                        Polyline geometry for the event  Both
                                                                      record.                          
  ------------------- ---------- ---------- ------------ ------------ -------------------------------- --------------

> **M Table Structure**

  ------------- -------- ---------- ------------ ----------------------------------- --------------
  **Field       **Data   **Allow    **Length**   **Description**                     **Schema\***
  Name**        Type**   Nulls?**                                                    

  OID           Object                           ESRI system maintained identifier.  Both
                ID                                                                   

  ReachCode     String   No         14           The ReachCode value for the         Both
                                                 NHDFlowline record that the event   
                                                 record references.                  

  ReachSMDate   Date     No         8            The reach spatial modification      Both
                                                 date.                               

  FMeasure      Double   No         0            The measure along the NHDFlowline   Both
                                                 record where the start point of the 
                                                 event record is located.            

  TMeasure      Double   No         0            The measure along the NHDFlowline   Both
                                                 record where the end point of the   
                                                 event record is located.            

  ID            GUID     No         34           HEM unique identifier. Maintained   Both
                                                 by the editing tools.               
  ------------- -------- ---------- ------------ ----------------------------------- --------------

**Area Events**

Area events are polygon event records that are coincident with all or
part of an NHD Waterbody feature.

  ------------------ ---------- ---------- ------------ ------------ -------------------------------- --------------
  **Field Name**     **Data     **Allow    **Domain**   **Length**   **Description**                  **Schema\***
                     Type**     Nulls?**                                                              

  OID                Object ID                                       ESRI system maintained           Both
                                                                     identifier.                      

  ComID              Long       No                                   Uniquely identifies the record.  Both
                     Integer                                                                          

  Event Date         Date       Yes                     8            The date the event record was    Both
                                                                     created or last modified.        

  ReachCode          String     No                      14           The ReachCode value for the NHD  Both
                                                                     Waterbody record that the event  
                                                                     record references.               

  ReachSMDate        Date       No                      8            The reach spatial modification   Both
                                                                     date.                            

  ReachResolution    Long       No         Resolution                Code for the source resolution.  Both
                     Integer                                                                          

  FeatureComID       Long       Yes                                                                   Full Only
                     Integer                                                                          

  FeatureClassRef    Long       Yes                                                                   Full Only
                     Integer                                                                          

  SourceOriginator   String     Yes                     130                                           Full Only

  SourceDataDesc     String     Yes                     100                                           Full Only

  Source_FeatureID   String     Yes                     40                                            Full Only

  FeatureDetailURL   String     Yes                     255                                           Full Only

  EventType          Long       No                                                                    Both
                     Integer                                                                          

  ID                 GUID       No                      34           HEM unique identifier.           Both
                                                                     Maintained by the editing tools. 

  Shape              Geometry                                        Polyline geometry for the event  Both
                                                                     record.                          
  ------------------ ---------- ---------- ------------ ------------ -------------------------------- --------------

**Synchronization Fields**

This is a summary of the fields contained in the tables created by the
EPA Synchronization tool.

+--------+------------------------------------------------------+-----+
| *      | **Description**                                      | **S |
| *Field |                                                      | che |
| Name** |                                                      | ma\ |
|        |                                                      | *** |
+--------+------------------------------------------------------+-----+
| Sync   | Distance point moved during synchronization.         | Poi |
| Score1 |                                                      | nts |
+--------+------------------------------------------------------+-----+
| Sync   | Distance From point moved during synchronization.    | L   |
| Score1 |                                                      | ine |
+--------+------------------------------------------------------+-----+
| Sync   | Distance To point moved during synchronization.      | L   |
| Score2 |                                                      | ine |
+--------+------------------------------------------------------+-----+
| Sy     | Percent change in length between source geometry and | L   |
| ncPerc | synchronized geometry.                               | ine |
| Change |                                                      |     |
+--------+------------------------------------------------------+-----+
| Sy     | Percent change in area between source geometry and   | P   |
| ncPerc | synchronized geometry.                               | oly |
| Change |                                                      |     |
+--------+------------------------------------------------------+-----+
| S      | Coefficient of area correlation.                     | P   |
| yncCAC |                                                      | oly |
+--------+------------------------------------------------------+-----+
| Sy     | Sync successful (0=no, 1=yes)                        | All |
| ncSucc |                                                      |     |
+--------+------------------------------------------------------+-----+
| Sync   | An event for update is supposed to look for a set of | All |
| Status | targets to try and sync to rather than just trying   |     |
|        | to snap to the closest feature in the entire         |     |
|        | dataset. To find these targets you navigate to       |     |
|        | NHDReachCrossRef table and try to find a subset of   |     |
|        | reaches.                                             |     |
|        |                                                      |     |
|        | Use these if you can. If you cannot snap to this     |     |
|        | subset then try the whole dataset.                   |     |
|        |                                                      |     |
|        | Values:                                              |     |
|        |                                                      |     |
|        | XRefTargets: found and successfully synchronized to  |     |
|        | targets via XRef table.                              |     |
|        |                                                      |     |
|        | XRefNotValid: found but did not successfully sync to |     |
|        | targets via XRef table. Used whole dataset and       |     |
|        | synchronized successfully to something.              |     |
|        |                                                      |     |
|        | NHDTargets: XRef table did not generate targets.     |     |
|        | Synchronized entire dataset successfully.            |     |
|        |                                                      |     |
|        | NoTargetsFound: Could not synchronize to anything    |     |
|        | from any source.                                     |     |
+--------+------------------------------------------------------+-----+
| Syn    | Values:                                              | All |
| cClass |                                                      |     |
|        | O -- used same reach                                 |     |
|        |                                                      |     |
|        | S -- used XRef tab and found only one reach          |     |
|        |                                                      |     |
|        | M -- used XRef tab and found multiple reaches        |     |
|        |                                                      |     |
|        | I -- XRef not used. Used entire dataset (I think     |     |
|        | these are the suspicious ones)                       |     |
+--------+------------------------------------------------------+-----+
| SyncDi | Max distance moved by point or endpoints (point and  | All |
| stance | lines only)                                          |     |
+--------+------------------------------------------------------+-----+
| SyncAp | Approved status (0=no, 1=yes)                        | All |
| proved |                                                      |     |
+--------+------------------------------------------------------+-----+
| Sync   | original ID of source event                          | All |
| OrigID |                                                      |     |
+--------+------------------------------------------------------+-----+