TECHNICAL MEMORANDUM
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SEATTLE, WA | PORTLAND, OR | MISSOULA, MT | OLYMPIA, WA | BELLINGHAM, WA
pjj—16-06278-001_tm_guide_rdsideditchinvandassmnttools.docx
Date:
April 3, 2019
To:
Jessica Engel, King County
From:
Jennifer Schmidt and Rebecca Dugopolski, PE,
Herrera Environmental Consultants, Inc.
Subject:
Guide to Roadside Ditch Inventory and Assessment Tools
INTRODUCTION
This guide provides instructions on using a set of GIS and field data collection tools to support a
roadside ditch inventory and assessment. These tools were developed as part of a National
Estuary Program (NEP) grant from the Washington State Department of Ecology (Ecology)
received by King County. The overall goal of the project is to improve the condition of roadside
ditches (and associated water quality) by improving maintenance procedures, and by improving
tracking and prioritization methods for inspection and maintenance efforts.
The GIS and field data collection tools outlined in this guide include:
1. Geodatabase framework to facilitate desktop GIS evaluation of ditch significance.
2. Survey123 field form template to facilitate collecting data on ditch condition in the field.
3. ArcGIS toolbox for processing the desktop ditch significance and field evaluation ditch
condition data to produce cumulative scores and assign maintenance priorities.
These tools are accompanied by a series of eight fact sheets and a field guide for roadside ditch
maintenance in Western Washington for maintenance crews and administrative/office staff. Four
of the eight fact sheets provide information related to mapping recommendations and
requirements and include:
Technical Memorandum (continued)
Guide to Roadside Ditch Inventory and Assessment Tools
April 2019
Fact Sheet A1: Ditch Mapping Recommendations
o Spatial data resources
o Recommendations for desktop analysis
Fact Sheet A2: Prioritizing Ditches for Inspection and Maintenance
o Example of ditch significance scoring
o Example of ditch condition scoring
Fact Sheet A3: Permit Requirements for Ditch Maintenance
o Mapping requirements for the National Pollutant Discharge Elimination System
(NPDES) Municipal Stormwater Permit
Fact Sheet F1: Considerations for Field Evaluation of Roadside Ditches
o Mobile data collection
o Ditch condition assessment criteria
Technical Memorandum (continued)
Guide to Roadside Ditch Inventory and Assessment Tools
April 2019
PROCESS OVERVIEW
The figure below provides an overview of the steps involved with using this set of tools to
prioritize ditches for inspection and maintenance. More detail and guidance on each step are
provided in the following sections.
Step 1: Confirm Ditch Mapping
The workflow outlined in this guide assumes that roadside ditches have already been mapped as
linear features and assigned a unique identifier. If ditch mapping has been completed, proceed
to Step 2. If ditch mapping is not available, please refer to the following resources for additional
guidance on building a ditch database:
Fact Sheet A1: Ditch Mapping Recommendations
Washington Stormwater Center Stormwater Infrastructure Framework web page
Step 1: Confirm Ditch Mapping
Step 2: Desktop Evaluation of Ditch
Significance
Step 3: Field Evaluation of Ditch
Condition
Step 4: Assign Maintenance
Priority
Technical Memorandum (continued)
Guide to Roadside Ditch Inventory and Assessment Tools
April 2019
Step 2: Desktop Evaluation of Ditch Significance
Ditch significance (i.e., ditch importance) can be used to prioritize ditches for inspection and
maintenance activities. A geodatabase (DitchMaintenanceTool.gdb) with a linear feature class
(Ditch_Significance) is provided as part of this toolset to help support assessing ditch
significance in desktop GIS. The attributes recommended for data collection and the drop-down
values associated with each field in the template are documented in detail in Table 1 of Fact
Sheet A2: Prioritizing Ditches for Inspection and Maintenance.
Procedure
1. Load your mapped ditch polylines into the Ditch Significance feature class. This can be
done by manually copying and pasting the ditch polylines in ArcMap into the provided
feature class or by using the Simple Data Loader tool in ArcCatalog. This second option
will allow you to map the fields in your existing ditch dataset into the appropriate fields
in the Ditch_Significance feature class.
2. Make sure that each ditch has been assigned a unique identifier in the Ditch ID field.
This can be an ID from your asset management system or just a sequential identifier (i.e.,
1, 2, 3, etc.).
3. Download and compile the GIS data sources for your area of interest that will allow you
to populate each field from the drop-down values provided. See Fact Sheet A1: Ditch
Mapping Recommendations for recommendations on where to obtain data if you do
not already have it available.
Technical Memorandum (continued)
Guide to Roadside Ditch Inventory and Assessment Tools
April 2019
4. Use the appropriate GIS datasets to assign values for each ditch significance category to
each ditch by selecting the appropriate drop-down value for each one.
5. Add the Ditch Maintenance Priority toolbox (Ditch Maintenance Priority.tbx) to
ArcToolbox and open the Calculate Ditch Significance tool.
6. Select the ditch significance dataset and click OK. The tool will add a new field to your
dataset and assign each ditch an inspection priority based on your desktop analysis and
the prioritization scoring criteria from Fact Sheet A2: Prioritizing Ditches for
Inspection and Maintenance.
Applying the Results
The ditch significance scoring results can then be used for planning inspection and maintenance
activities:
1. Prioritize ditches for inspection. When deciding which ditches should be inspected
first, focus on ditches with known issues and/or a high ditch significance score.
2. Prioritize ditches for maintenance. See Step 4.
Step 3: Field Evaluation of Ditch Condition
Evaluating ditch condition requires a visual assessment in the field to identify current
maintenance issues that may reduce ditch capacity or ditch integrity, potentially leading to
issues with flooding or transport of pollutants to waterways. The geodatabase included with this
documentation (DitchMaintenanceTool.gdb) contains a table for storing ditch condition
information collected in the field (Ditch_Condition). There are two options for populating this
table:
Technical Memorandum (continued)
Guide to Roadside Ditch Inventory and Assessment Tools
April 2019
1. Use Survey123 to collect field data using an electronic field form.
2. Collect the data using other methods and then manually entering it into the
Ditch_Condition table in the geodatabase.
Note: The following instructions are specific to users with access to an ArcGIS Online (AGOL)
account. Speak with your GIS Administrator to confirm your AGOL access and policies.
Alternatively, other questionnaire-format mobile applications may be used to collect this data in
the field, but the results will need to be uploaded into the Ditch_Condition table to run the
scoring tools.
Procedure
1. Download the Survey123 Ditch_Condition_Assessment.xlsx file provided with this
toolkit.
2. Download and install the Survey123 Connect for ArcGIS desktop application:
www.arcgis.com/home/item.html?id=9a0a850521174e78b8d08d3a66cbf34c.
3. Launch Survey123 Connect for ArcGIS and log in using your AGOL credentials.
4. Select New Survey and the File radio button from the list. Click on Browse for XLSForm
and navigate to the location where you saved Ditch_Condition_Assessment.xlsx.
Change the title of the survey to Ditch Condition Inspection and click Create Survey.
Technical Memorandum (continued)
Guide to Roadside Ditch Inventory and Assessment Tools
April 2019
5. To publish the survey to your AGOL account so that it is available on your mobile device,
click the cloud on the left side of the form preview and then click Publish Survey.
6. Download the free Survey123 data collection app to your mobile device from your
device’s app store. Log in using the same AGOL credentials that you used to publish the
form.
7. Complete ditch inspections in the field by filling out the form for each ditch. The ditch
ID that you enter must match the ditch ID from the desktop evaluation in Step 2.
Make sure to:
a. Identify your location using the interactive map.
b. Take detailed notes and photos for any ditch components that require follow-up
action. Schedule the ditch for urgent or routine maintenance, if needed.
c. If maintenance needs are addressed during the field visit, be sure to update the
condition status as needed.
8. After completing the ditch inspections in the field, log in to http://survey123.arcgis.com
using your AGOL credentials and click on your published form.
9. Click on the Data tab on the top of the page and then select Export and File
Geodatabase. This will download all of your inspection data (point locations) and any
attached photos. This may take several minutes depending on the number of photos you
have taken.
Technical Memorandum (continued)
Guide to Roadside Ditch Inventory and Assessment Tools
April 2019
Applying the Results
The ditch condition scoring results can then be used for planning maintenance activities. See
Step 4.
Step 4: Assign Maintenance Priority
Planning for and allocating resources to ditch maintenance requires consideration of both ditch
significance and ditch condition. Ditch significance will influence the order of ditch inspections,
but can also inform planning for maintenance activities later on. Immediate maintenance needs
may also be apparent based on the ditch condition determined through a field evaluation in
Step 3. Ditch significance and ditch condition should be combined and evaluated together when
planning maintenance activities and assigning maintenance priorities.
Procedure
1. To assign a ditch condition score and maintenance priority to each ditch, open the Ditch
Maintenance Priority toolbox in ArcMap and select the Calculate Maintenance
Priority tool.
2. If you completed Step 3 using Survey123, select the Ditch Condition point file that you
exported from the Survey123 website. This file is named surveyPoint by default. If you
entered your information manually into the Ditch Condition table included with the
template geodatabase, select that file.
3. Select the Ditch Significance line feature class that you created in Step 2.
Technical Memorandum (continued)
Guide to Roadside Ditch Inventory and Assessment Tools
April 2019
4. Hit OK. Three new fields will be added to your Ditch Significance line feature class:
a. Ditch Condition Score: Ditch condition scores can be used to determine which
ditches require the most urgent maintenance attention and to plan maintenance
activities accordingly. A high ditch condition score indicates poor condition and
therefore high maintenance priority.
b. Combined Ditch Score: This score reflects the sum of your ditch significance and
ditch condition scores.
c. Maintenance Priority: This field indicates the maintenance priority of each ditch
based on the combined ditch score ranging from None to Urgent.