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Document Author: Herrera Environmental Consultants

Guide to Roadside Ditch Inventory and Assessment Tools

Summary: Ditch inventory and assessment tools, ditch inventory, ditch assessment,

TECHNICAL MEMORANDUM
2200 Sixth Avenue | Suite 1100 | Seattle, Washington | 98121 | p 206 441 9080 | f 206 441 9108
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.

Ditch Cleaning Strategies Fact Sheet

Summary: Ditch cleaning, strategies for ditches,

Fact Sheet F2 – Ditch Cleaning Strategies
What is Ditch Cleaning?
Ditch Cleaning
Strategies
Fact Sheet F2
Ditch cleaning is a corrective maintenance activity for ditches focused on sediment and debris removal.
The three types of ditch cleaning methods and an inventory of equipment needed are summarized in
the table below.
Method
Description
Common Equipment
and Materials
Photo Example
Hand Ditching
Removing sediment
and debris manually
using a rake, hoe, or
shovel.
Rake, hoe, or shovel
Wheelbarrow or buckets
Erosion control BMPs
(e.g., wattles, check dams,
silt fence)
Bucket Ditching
(Mechanical
Excavation)
Removing sediment
and debris using a
backhoe, excavator,
or front-end loader
in deep ditches
where hand ditching
is impractical.
Backhoe or excavator
with ditching bucket or
DitchMaster
Erosion control BMPs
(e.g., wattles, check dams,
silt fence)
Shoulder
Ditching
(Blade Ditching
or Shoulder
Pulling)
Reshaping and
cleaning ditches by
removing excess sod
from the shoulder.
Grader
Belt loader
Erosion control BMPs
(e.g., wattles, check dams,
silt fence)
Photo source: King County
February 7, 2019
Fact Sheet F2 – Ditch Cleaning Strategies
Surface
Type
Description
Applicable Ditch Cleaning
Methods
Photo Example
Vegetated
Typically seeded or
sodded grasses placed in
and along the channel.
Hand Ditching
Bucket Ditching
Shoulder Ditching
Bare Soil
Soils without established
vegetation (e.g., due to
overcompaction, low
organic content, nutrient
deficiencies, etc.);
typically located in areas
where slopes are mild,
flow depths are shallow,
and there is a low risk
for erosion.
Hand Ditching
Bucket Ditching
Shoulder Ditching
Rock
Small rounded cobbles
with a uniform gradation
or riprap.
Hand Ditching
Paved
Concrete or asphalt-
lined.
Hand Ditching
Metal
Half-culvert; typically
located in areas with
steep slopes and a high
risk of erosion.
Hand Ditching
Where is Ditch Cleaning Applicable?
Fact Sheet F2 – Ditch Cleaning Strategies
Field Tips
Cleaning should be performed during low flow
or no flow periods if possible.
Install erosion control best management
practices (BMPs) prior to conducting sediment
removal.
Consider “skip ditching” where vegetation is
retained in portions of the ditch near outlets to
help preserve water quality.
Cleaning should utilize low-impact equipment if
feasible.
Keep excavation equipment on the roadway and
off the ditch bank.
Reseed and install erosion control BMPs after
sediment has been removed if needed.
Ensure runoff can sheet flow into the ditch. Avoid
creating a “curb of sod” along the road shoulder
during ditch cleaning activities.
Ditches should be cleaned to ensure that they are functioning as designed to convey runoff away from
road surfaces and minimize high flows, erosion, and pollution. Excess sediment and debris buildup
in ditches can limit vegetation growth, contribute to the pollutant loads carried by runoff in ditches
to water bodies, decrease ditch capacity, and cause flooding. Ditch cleaning may be necessary when
excess sediment is impeding flow and/or causing erosion. Ditch cleaning may also be needed for spill
response to remove contaminated soils.
Dispose of dirt and debris from road surfaces after completing ditch cleaning activities.
Separate removed material into soil and vegetative matter (e.g., leaves, grass, needles,
branches) categories.
Accumulated sediment removed during ditch maintenance may be reclaimed, recycled, or
reused when allowed by local codes and ordinances.
Vegetative matter may be composted or placed in a clean green stockpile at your
maintenance facility.
Roadside ditch cleanings contaminated by spills or other
releases known or suspected to contain dangerous
waste must be handled following the Dangerous Waste
Regulations (Chapter 173-303 WAC). Soils that are identified
as contaminated pursuant to Chapter 173-350 WAC shall be
disposed at a qualified solid waste disposal facility. If testing
determines materials are not designated as a dangerous
waste, but contaminants are present, consult with your
local health department to determine the most appropriate
disposal option.
If invasive species or noxious weeds are present in waste, consult the Washington State Noxious
Weed Control Board.
Why is Ditch Cleaning Important?
Disposal Considerations
Compost, Photo source: King County
This fact sheet was developed by Herrera Environmental Consultants with input from King County and the Regional Operations and Maintenance
Program (ROADMAP). Project funding was provided by a National Estuary Program grant from the Washington State Department of Ecology.

Ditch Mapping Recommendations Factsheet

Summary: ditch mapping, ditch recommendations

Fact Sheet A1 – Ditch Mapping Recommendations
Why Should Ditches be Mapped?
NPDES Municipal Stormwater Permit Requirements
Fact Sheet A1
February 7, 2019
Ditch mapping is used by jurisdictions to understand their overall stormwater drainage systems. Ditch
mapping is also used to facilitate efficient tracking and prioritization of ditches for inspection and
maintenance.
Mapping ditches is required by the National Pollutant Discharge Elimination System (NPDES) Phase
I and Phase II municipal stormwater permits if they drain to an outfall or discharge point that has
a specified diameter. Ditch attributes that must be mapped according to the NPDES municipal
stormwater permit include:
Conveyance type (e.g., pipe, ditch)
Material
Size (if known)
Associated drainage area
Land use
Phase I and Phase II
Municipal Stormwater
Permit References
Phase I: S5.C.2.a and S5.C.2.b
Phase II: S5.C.3 (S5.C.4 in
2019-2024 permit)
Ditch
Mapping
Recommendations
Measuring and mapping ditches
Refer to Ecology's GIS Standards to ensure compatibility
for data sharing:
https://ecology.wa.gov/Research-Data/Data-resources/
Geographic-Information-Systems-GIS/Standards
Fact Sheet A1 – Ditch Mapping Recommendations
How to Map Ditch Segments
Many jurisdictions already have partial or complete roadside ditch (and culvert) mapping for their
roads. For jurisdictions with data gaps, or unmapped ditches, there are a few different options for
creating ditch features in GIS:
Manually digitize ditches from available as-built drawings (or import from CAD record
drawings, if available)
Sketch ditches in desktop GIS based on topographic data like LiDAR or contours
Map ditches in the field using mobile global positioning system (GPS) technology to capture
the upstream and downstream end points
Fact Sheet A1 – Ditch Mapping Recommendations
A single centralized database is recommended for tracking ditch data, with a unique ID assigned to each
ditch. Databases can be supplemented with existing spatial mapping for a specific jurisdiction or can
rely on datasets provided by state or national entities where local data is not available. Some examples
of open data sources include:
Aerial imagery can also provide details about the road (e.g., road width, number of lanes) and
surrounding area for each ditch segment. Aerial imagery is available statewide at various scales and
resolutions, with a good starting point being the U.S. Department of Agriculture National Aerial
Imagery Program (NAIP).
Building a Centralized Database
Washington State Department of Ecology: Hydrography, Water Resource Inventory Areas
(WRIAs), watershed boundaries, jurisdiction boundaries, permitted facilities, etc.
Washington State Department of Health: Wellhead Protection Areas (WHPA)
Washington State Department of Natural Resources, Natural Heritage Program: Rare or
imperiled plants
Washington State Department of Transportation: Transportation infrastructure
Map Tip
Ditch data can also be integrated
into off-the-shelf asset
management software and
inspection workflows.
Additional resources and templates for mapping ditches, procedures, clarifying terminology, etc. can be
found on the Washington Stormwater Center Stormwater Infrastructure Framework web page:
www.wastormwatercenter.org/stormwater-infrastructure-framework-resources/
Fact Sheet A1 – Ditch Mapping Recommendations
During a desktop analysis, attributes can be assigned to individual ditch segments using various
GIS tools. One approach is to use the Select by Location tool in ArcGIS to identify where certain key
background layers (e.g., land use, property ownership) intersect the ditch layer. It may be helpful
to generate a “study area” such as a 100-foot buffer or a ¼-mile buffer around each linear ditch to
capture nearby attributes for each ditch segment.
Table 2 lists recommended data to include in a desktop analysis and the type of prioritization category
that each attribute applies to. For further guidance on how to integrate desktop analysis criteria into a
ditch prioritization matrix, see Fact Sheet A2: Prioritizing Ditches for Inspection and Maintenance.
Desktop Analysis
Table 1. Recommended Ditch Attributes to Include in a Centralized Database
Attributes
Water Quality
Prioritization
Maintenance
Prioritization
Type of Maintenance
Property Owner
Ditch Segment Length
Road Type/Classification
Date Last Visited (if known)
Date Last Retrofitted (if applicable)
Table 2. Recommended Ditch Attributes to Include in a Desktop Analysis
Attributes
Water Quality
Prioritization
Maintenance
Prioritization
Type of
Maintenance
Drainage Area Size
Direct Discharge (e.g., within ¼ mile)
Adjacent Land Use
Landslide Hazard Area (e.g., within 100 feet)
Erosion Hazard Area (e.g., within 100 feet)
Wellhead Protection Area
Rare/Imperiled Plant Habitat (e.g., within 100 feet)
Noxious Weed Presence
Spill Frequency (e.g., illegal dumping, vehicle accidents)
Receiving Waterbody Quality
Building a Centralized Database
Fact Sheet A1 – Ditch Mapping Recommendations
One of the most important criteria for prioritizing ditch maintenance is the volume
of runoff collected by the ditch. When possible, contributing drainage areas should
be identified for every ditch segment. Potential methods for generating these
contributing drainage areas include:
A manual desktop delineation (e.g., determination of the area that drains to each
ditch segment) based on available topographic data and stormwater drainage
infrastructure.
Using the spatial analysis tools built into GIS software. These tools can be used
with stormwater infrastructure mapping to identify the potential area draining to
each ditch endpoint.
How to Determine Contributing Drainage Areas
How to Assess Downstream Runoff
To better understand the water quality significance of a specific ditch segment, it is
important to determine what happens after runoff leaves the ditch:
There are several methods for collecting and analyzing downstream runoff
information, depending on the quality and completeness of the ditch mapping and
the location of the ditch:
Does the ditch segment discharge directly to surface water
(e.g., wetland, stream, lake)?
Does this ditch segment discharge to a stormwater facility
(e.g., detention pond, bioretention facility)?
Is the ditch segment located in fast-draining soils that
primarily infiltrate into the ground?
Desktop path tracing (ideally with field verification) is a time-intensive
method used to evaluate the specific discharge point of a ditch system.
Tools built into GIS software may be employed to collect information on
batches of ditches, when the quality and completeness of the existing ditch
mapping data is good.
Referencing the larger watershed or drainage basin where the ditch is located,
rather than tracing the specific outfall location for each ditch segment, can be
used to make a quick determination of the downstream receiving water.
This fact sheet was developed by Herrera Environmental Consultants with input from King County and the Regional Operations and Maintenance
Program (ROADMAP). Project funding was provided by a National Estuary Program grant from the Washington State Department of Ecology.

Considerations for Field Evaluation of Roadside Ditches Fact Sheet

Summary: Ditch Field evaluation, considerations for ditch evaluation

Fact Sheet F1 – Considerations for Field Evaluation of Roadside Ditches
Configure Mobile Data Collection
Data Collection Methods
This fact sheet will support inspection and maintenance staff in conducting a field evaluation
of roadside ditches to efficiently document ditch status and maintenance needs. The workflow
for completing a ditch field evaluation is shown below:
Electronic data collection is
recommended for efficiently capturing
detailed data. Electronic devices
streamline the data collection process by:
Desktop Evaluation
(See Fact Sheet A1 –
Ditch Mapping
Recommendations)
Configure Mobile
Data Collection
Prepare Field
Equipment
Assess Ditch
Condition
Minimizing post-processing or typing data
into spreadsheets after a long field day.
Allowing field crews to attach photos directly to
the database, therefore avoiding the need to sort and
re-label.
Using checkboxes and drop-downs to standardize
data entries by multiple people and prevent
misspellings and other data entry errors.
Data collection: Handheld GPS and mobile
device units
Data Collection Methods
Considerations for
Field Evaluation of
Roadside Ditches
Fact Sheet F1
February 7, 2019
Fact Sheet F1 – Considerations for Field Evaluation of Roadside Ditches
Ideally, a large-screen tablet is recommended for readability and quick data
entry; however, smaller devices such as mobile phones can also be used to
collect electronic data and store field photos. Mobile devices can be paired
with various brands of global positioning system (GPS) satellite receivers to
improve location accuracy, if desired.
Configure Mobile Data Collection
Getting Started with a Mobile App
Electronic data collection may sound complicated, but if your municipality is
already using geographic information system (GIS) software to map ditches,
set-up and rollout of electronic data collection can be relatively easy.
Talk to your local GIS staff
to see what options are
available for bringing ditch
data online. Field crews will
need access to an online
account.
Enable database
photo attachments.
Find a mobile device suitable for field work.
Download ESRI’s free mobile data
collection applications
(e.g., Collector, Survey123).
Consider offline data collection for
remote areas without cell service.
Other specialized survey or questionnaire-focused
mobile applications and other asset management
software is available with varying cost-structures and
functionalities.
Field Tip: Include a notes field
in your field form or data collection
matrix to capture unique circumstances
that field crews may encounter.
Data collection by using both a hand-drawn field map and a handheld GPS
device in areas with limited cell service.
Data Collection Methods
Fact Sheet F1 – Considerations for Field Evaluation of Roadside Ditches
Many ditches do not
have safe nearby parking
or wide shoulders. High-
visibility safety vests/
jackets and traffic cones
are critical. Gloves are
also recommended for
potentially hazardous
or unsanitary materials,
noxious vegetation,
etc. Hard hats may be
required when working
near roads. Defer to local
jurisdiction for safety
requirements.
Be prepared for
dangerous conditions
in erosion/slope hazard
areas. The roadside ditch
may be wedged between
a busy road with a high-
speed limit and a steep
slope, leaving field crews
without much distance
between fast moving
traffic. These ditches are
not recommended for field
evaluation without proper
traffic control in place.
When Himalayan
blackberries or other
aggressive vegetation
is encountered, field
crews cannot make an
accurate assessments
and have limited space
to conduct evaluations.
If encountered, it is
recommended to
schedule these ditches
for brush cutting prior
to completing field
evaluations.
Wearing Personal Protective
Equipment (PPE)*
Safety Concern:
Narrow road shoulders
Safety Concern:
Steep slopes on high traffic roads
with overgrown vegetation
For quick and safe field evaluation of roadside ditches, field crews should note the following:
Safety First
Prepare Field Equipment
*Defer to local jurisdiction PPE requirements
Fact Sheet F1 – Considerations for Field Evaluation of Roadside Ditches
If ditches are missing basic characterization
data (e.g., length, width, etc.), the following
equipment is also recommended:
Field Tip: In some cases, safety concerns may make
it difficult to collect characterization measurements.
Because these measurements are only informative
and not critical to prioritizing and implementing a
maintenance program, it is recommended to skip
these measurements in unsafe areas.
Prepare Field Equipment
Equipment and Materials Recommendations
Personal Protective Equipment (PPE) (e.g., high-
visibility vest/jacket, hardhat, gloves)
Traffic cones and other traffic control equipment
Large-screen tablet equipped with a glare-resistant
screen protector and a protective (waterproof, drop-
proof) field case
The roadside ditch field evaluation is primarily based on visual observations and does not
require any high-tech equipment. Recommended equipment and materials include:
Measuring tape (short)
Eastern Washington Field Guide
Washington State Noxious Weed Control Board
www.nwcb.wa.gov
N o x i o u s W e e d s
That Harm Washington State
Backup paper forms and pencils/pens
Noxious Weeds that Harm Washington State, Western Washington Field Guide. You
can request free hard copies of this pocket guide from the Washington State Noxious
Weed Control Board (www.nwcb.wa.gov)
WA Invasives mobile app
(https://invasivespecies.wa.gov)
Measuring tape (long)
Slope measurement device
(e.g., electronic, surveying rod)
Field Tip: Always bring a
portable backup battery and/
or a car charger when using a
tablet or mobile phone for data
collection. The battery may
drain quickly!
Planning ahead and bringing proper equipment can promote
safety and efficiency in remote or high-risk locations
Fact Sheet F1 – Considerations for Field Evaluation of Roadside Ditches
A streamlined inspection for maintenance
needs is also recommended as part of the field
evaluation. Due to the variety of ditch shapes,
surface types, and other unique conditions that
might be encountered at a ditch, it is recommended to focus on broad categories related to
critical ditch function (e.g., conveyance, water quality, etc.) and road safety. If needed, specific
details can be recorded in an open notes field within the database. Categories that should be
assessed include:
Can the ditch convey flow freely?
Have blocked culverts or failed
structural components caused
localized flooding of nearby
property or roadways?
Is there evidence of the ditch
conveying natural flows?
Field Tip: Always take photos in the field.
Geolocated photos can be attached to the ditch
database and used to confirm ditch condition or
to communicate specific maintenance needs.
Is there evidence of erosion,
channelization, or scouring?
Are there nuisance animals
(e.g., moles, beavers)
present that may put ditch
flow capacity or structural
integrity at risk?
Are ditch side slopes intact
and stabilized?
Is there evidence of a
potential illicit connection or
illegal dumping?
Does the ditch need to be
mowed?
Are there line-of-sight issues
associated with overgrown
ditch vegetation?
Is vegetation sparse or
absent?
Is lack of vegetation causing
erosion?
Are invasive or noxious
species present?
Capacity and Conveyance
Vegetation
Integrity
Structural Components
Are structural components
broken or damaged?
Are structural components
causing flow blockages?
See Fact Sheet A2 – Prioritizing Ditches for Inspection and Maintenance for guidance on
how to incorporate field data into a scoring matrix that can be used for ditch maintenance
prioritization.
This fact sheet was developed by Herrera Environmental Consultants with input from King County and the Regional Operations and Maintenance
Program (ROADMAP). Project funding was provided by a National Estuary Program grant from the Washington State Department of Ecology.
Assess Ditch Condition

Permit Requirements for Ditch Maintenance Fact Sheet

Summary: Permitting ditch maintenance, permit requirements ditch maintenance

Fact Sheet A3 – Permit Requirements for Ditch Maintenance
Fact Sheet A3
Permit
Requirements for
Ditch Maintenance
This fact sheet provides an overview of regulatory requirements and guidance related to:
Permitting for ditches with natural flow
Other local permits that may apply
NPDES Municipal Stormwater Permit Requirements
Mapping
Mapping ditches is required by the National
Pollutant Discharge Elimination System (NPDES)
Phase I and Phase II municipal stormwater
permits if they eventually drain to an outfall or
discharge point that has a specified diameter.
Ditch attributes that must be mapped according
to the NPDES municipal stormwater permit
include:
Standard Operating Procedures (SOPs)
The following ditch-related activities shall be
addressed as part of a Municipal Operation and
Maintenance (O&M) Program according to the
NPDES municipal stormwater permit:
Cleaning of culverts that convey stormwater in
ditch systems
Ditch maintenance
Maintaining roadside areas, including
vegetation management
Erosion and sediment control
Landscape maintenance and vegetation
disposal
Conveyance type (e.g., pipe, ditch)
Material
Size (if known)
Associated drainage area
Land use
Ditch and roadside vegetation maintenance,
Photo source: WSDOT
Ditch maintenance
Recordkeeping
Proper disposal
February 7, 2019
Phase I and Phase II
Municipal Stormwater
Permit References
Phase I: S5.C.2.a and S5.C.2.b
Phase II: S5.C.3 (S5.C.4 in
2019-2024 permit)
Fact Sheet A3 – Permit Requirements for Ditch Maintenance
Phase I NPDES Municipal
Stormwater Permit References
Phase II NPDES Municipal
Stormwater Permit References
NPDES Municipal Stormwater Permit Requirements
Regulated municipal stormwater permit areas as of 2018
Figure source: Washington Department of Ecology
Mapping: S5.C.2.a and S5.C.2.b
SOPs: S5.C.9.e (S5.C.10.e in 2019-2024 permit)
Recordkeeping: S5.C.9.h
(S5.C.10.h in 2019-2024 permit)
Disposal: G10 and Appendix 6
Mapping: S5.C.3.a. (S5.C.4.a in
2019-2024 permit)
SOPs: S5.C.5.f (S5.C.7.e in 2019-
2024 permit)
Recordkeeping: S5.C.5.i (S5.C.7.h
in 2019-2024 permit)
Disposal: G10 and Appendix 6
Recordkeeping
Permittees must maintain records of inspections and
maintenance or repair activities for up to five years.
Disposal
Street waste solids (including sediment accumulations
removed during ditch maintenance) may be reclaimed,
recycled, or reused when allowed by local codes and
ordinances. Soils that are identified as contaminated
pursuant to Chapter 173-350 WAC must be disposed at a
qualified solid waste disposal facility.
Fact Sheet A3 – Permit Requirements for Ditch Maintenance
Use or disposal options for the sediment removed from ditches will depend on the characterization of
the waste. Roadside ditch cleanings contaminated by spills or other releases known or suspected to
contain dangerous waste must be handled following the Dangerous Waste Regulations (Chapter 173-
303 WAC). If testing determines materials are not dangerous waste, but contaminants are present,
consult with your local health department for disposal options.
Stormwater Management Manual for Western Washington
The Volume IV of the Stormwater Management Manual for Western Washington (SWMMWW)
describes best management practices (BMPs) for maintenance of roadside ditches (S416 BMPs):
“Maintain roadside ditches to preserve the condition and capacity for which they were originally
constructed, and to minimize bare or thinly vegetated ground surfaces. Maintenance practices should
provide for erosion and sediment control.” Operational BMPs include:
Remove vegetation when flow is blocked
or excess sediment has accumulated
Appropriately dispose of dirt and debris
from road surfaces after completing ditch
cleaning activities
Do not apply fertilizer unless needed
Perform seeding, fertilizer application,
and harvesting in late spring and/or early
fall, where possible
The frequency of ditch inspections and cleaning is not specified in the NPDES municipal stormwater
permit or SWMMWW and can be set by the local jurisdiction. Considerations for establishing
inspection and maintenance frequencies include road type, land use type, and previous maintenance
records. See Fact Sheet A2 – Prioritizing Ditches for Inspection and Maintenance for more
information.
Disposal Considerations
Inspect ditches regularly to identify
sediment accumulations and
localized erosion
Inspect culverts regularly for scour or
sedimentation at inlet and/or outlet
Clean as needed
Remove trash and debris
Note: Several Phase I jurisdictions (e.g., King County, Pierce County, City of Seattle) and the
Washington State Department of Transportation (WSDOT) have developed their own stormwater
manuals which have been reviewed for equivalency to the SWMMWW by Ecology. Refer to the
stormwater manual that your jurisdiction has adopted to determine if additional requirements related
to maintenance of roadside ditches apply.
Fact Sheet A3 – Permit Requirements for Ditch Maintenance
Plans must be submitted with the Simplified
Application for HPA and should address the following:
Permitting for Ditches that Convey Natural Flow
For regulatory purposes, a ditch that conveys natural flow should be treated as a stream. This may
include ditches that are hydraulically connected and within ¼ mile of a stream or wetland (see
local codes and ordinances). In some cases, a ditch may not be properly mapped as natural flow
conveyance. If maintenance crews encounter a ditch that appears to be conveying natural flow,
planned maintenance should be put on hold until:
(1)
Appropriate permits are obtained, and
(2)
Crews are trained on stream-specific
Hydraulic Project Approval (HPA)
A Washington State HPA is required for projects that
will use, divert, obstruct, or change the natural flow or
bed of any of the salt or fresh waters of the state. HPA
is administered by the Washington Department of Fish
and Wildlife (WDFW) under Chapter 220-660 WAC.
A Simplified Application for HPA can be submitted
for road maintenance work which includes, but is not
limited to:
Culvert cleaning Ditch maintenance
Plan and cross-view drawings
Project location in relation to the ordinary
high water mark (OHWM) for freshwater,
the mean higher high water line (MHHW)
for saltwater, the channel migration zone,
and the 100-year floodplain
Equipment that will be used and where
it will be operated
Construction sequencing
Sediment and erosion control BMPs
Plan for removal (if any) of riparian
vegetation
WDFW uses an Aquatic Permitting System (APPS) for the HPA application. This application will include
proof of State Environmental Policy Act (SEPA) compliance, and can be converted to a Joint Aquatic
Resource Permit Application (JARPA) if needed (several permitting agencies accept this form). A copy
of the HPA or Federal Permit for the maintenance activity must be on site during the work.
Natural flow in ditch at upstream road crossing
Natural flow in ditch
maintenance practices (see Fact Sheet F3 –
Maintaining Ditches that Convey Natural
Flow)
Fact Sheet A3 – Permit Requirements for Ditch Maintenance
Other Potential Permits
Consult local codes and ordinances for additional specific requirements related to ditch maintenance
activities. Code requirements that regulate activities, such as vegetation management, in and near
streams may vary by jurisdiction. When natural flow is present, additional local permits and submittals
may be necessary, including the following:
Critical areas permit
Clearing and grading permit
Shoreline permit
Habitat permit (for proposed cleaning in
riparian areas that are priority habitat
areas designated by the local jurisdiction)
Vegetation management plan
NPDES permit for herbicide applications
(note: herbicide applications should
always be performed by a licensed,
qualified professional)
U.S. Army Corps of Engineers Seattle
District regional conditions for NWPs
Natural flow in ditch
Nationwide Permit (NWP)
In 2017, the U.S. Army Corps of Engineers established 52 Nationwide Permits that regulate dredging
and placement of fill in wetlands, streams, lakes, and marine waters and may apply to ditch
maintenance activities if maintenance is performed in ditches with natural flow. Some activities that
may require a permit include, but aren’t limited to:
Placement of sandbags Dredging sediment Reshaping ditches
Permitting for Ditches that Convey Natural Flow
The NWP does not apply to activities that only involve cutting or removing vegetation above the
ground, where the activity neither substantially disturbs the root system nor involves mechanized
pushing, dragging, or other similar activities that redeposit excavated soil. The following NWPs may
apply to ditch maintenance activities:
This fact sheet was developed by Herrera Environmental Consultants with input from King County and the Regional Operations and Maintenance
Program (ROADMAP). Project funding was provided by a National Estuary Program grant from the Washington State Department of Ecology.
Maintenance – NWP 3
Bank Stabilization – NWP 13
Linear Transportation Projects – NWP 14
Reshaping Existing Drainage Ditches – NWP 41

Source Control Strategies for Ditches Fact Sheet

Summary: ditch source control strategies, ditch strategies

Fact Sheet A4 – Source Control Strategies for Ditches
Method
Description
Manage Soil Erosion from Uplands
Minimize sediment entering ditches by controlling soil erosion at the source
through increased infiltration or sediment management practices such as:
Designate a Ditch Buffer
Restrict or exclude agricultural crop and livestock production from the
public road right-of-way and its associated roadside ditch to prevent direct
applications of fertilizer, manure, or pesticides in the ditch zone.
Street Sweeping
Perform street cleaning (typically sweeping with a regenerative air or
vacuum sweeper) to clean the adjacent roadway surface and to reduce
sediment loading into ditches.
Catch Basin Cleaning
Clean catch basins that may be associated with a ditch inlet to reduce
sediment loading into ditches.
No-till or conservation tillage
Contour farming
Contour buffer strips
Cover crops
Direct seeding
Field borders
Design of agricultural ditches
to avoid pollution sources
What is Source Control?
Source Control
Strategies for
Ditches
Fact Sheet A4
Source control refers to practices that prevent or reduce pollutant generation rather than treating or
removing pollutants already captured by stormwater runoff. Methods for preventing pollutants from
entering a ditch and preventing generation of pollutants in a ditch are described in this fact sheet.
Prevent Pollutants from Entering a Ditch
February 7, 2019
Fact Sheet A4 – Source Control Strategies for Ditches
Method
Description
Minimize Cleaning Activities
During the Wet Season
Conduct ditch maintenance in the later spring, summer, or early fall, where possible to
allow re-establishment of vegetative cover and minimize erosion.
Control Sediment Loading
During Vegetation
Establishment
Install preventative measures (e.g., check dams, straw mulch, or silt fence) to reduce
downstream sediment loading while establishing new vegetation. Seed and/or plant
during the following optimum windows:
Late spring (April 1 through June 30)
Early fall (September 1 through October 1)
Eliminate or Reduce
Herbicide Use
Use physical and/or mechanical methods of vegetation removal rather than applying
herbicides, where practical. If herbicides must be used, apply early in the summer.
Guidelines for Stream and Ditch Maintenance (Oregon Department of Agriculture, 2018): www.oregon.
gov/ODA/shared/Documents/Publications/NaturalResources/GuidelinesStreamDitchMaintenance.pdf
Re-plumbing the Chesapeake Watershed: Improving Roadside Ditch Management to Meet TMDL Water
Quality Goals (Schneider and Boomer, 2016):
www.chesapeake.org/pubs/349_Boomer2016.pdf
Draft Options for Crediting Pollutant Reduction from Roadside
Ditch Management Practices (RDM) in the Chesapeake Bay
Watershed (Chesapeake Bay Roadside Ditch Management
Team, 2017): www.chesapeakebay.net/channel_files/24809/
attach_b_062017_rdm_memo_draft.pdf
Drainage water management for water quality protection
(Strock et al., 2010):
www.jswconline.org/content/65/6/131A.full.pdfestablishment.
Why is Source Control Important?
When is Source Control Needed?
Source control is the first step in reducing pollutant loads that enter ditches or are generated in ditches through
installation and maintenance activities. The goal of source control is to implement cost-effective approaches to
improve stormwater runoff quality. Source control strategies may result in an improvement in water quality in
ditches without installing more costly treatment practices downstream.
When ditches receive direct runoff from pollutant-generating land
uses such as agricultural fields.
When ditches lack natural buffers to prevent stormwater runoff
with high pollutant loads from entering ditches.
When routine maintenance such as ditch cleaning, ditch reshaping/
regrading, and vegetation establishment is being implemented.
Additional Resources
Prevent Generation of Pollutants in a Ditch
This fact sheet was developed by Herrera Environmental Consultants with input from King County and the Regional Operations and Maintenance Program (ROADMAP).
Project funding was provided by a National Estuary Program grant from the Washington State Department of Ecology.

Ditch Retrofit Strategies Fact Sheet

Summary: ditch retrofit, retrofit strategies for ditches

Fact Sheet A5 – Ditch Retrofit Strategies
Overview
Factors to Consider
Ditch Retrofit
Strategies
Fact Sheet A5
Retrofitting ditches provides an opportunity to improve water quality treatment and/or increase conveyance
capacity within existing ditches. In areas that have already been developed, especially where ditches are
underperforming, retrofitting existing infrastructure may provide the most cost-effective opportunity to remove
pollutants prior to discharge to surface waters. Ditch retrofit strategies described in this fact sheet include:
Ditch retrofits may not always be possible or advised due to existing site conditions and feasibility limitations.
Limitations may include:
Certain retrofit strategies may be more appropriate for water quality improvements,
while others are better suited for increasing conveyance capacity.
Lack of right-of-way space may prevent flow redirection, ditch modifications, or adjacent enhancements
Established plants, which should not be disturbed if they provide water quality treatment and ditch
stabilization
Steep slopes that prevent planting improvements or other strategies for regulating ditch velocity
Enhance Ditch
Enhance ditch vegetation
Enhance filtration media
Add ditch buffer
Enhance ditch buffer
Add an underdrain elbow
Add an upturned elbow
Convert/Eliminate Ditch
Replace ditch with a water quality treatment and flow control BMP
Replace ditch with a water quality treatment or flow control BMP
Convert ditch to a closed system with water quality treatment
Regulate Ditch Velocity
Modify Ditch Shape/Grade
Modify Inlet/Outlet
Scour at ditch inlet
Scour at ditch outlet
Redirect ditch outfall
Refer to the potential retrofit strategies listed below to determine which strategies are most appropriate for
addressing various ditch issues.
February 7, 2019
Fact Sheet A5 – Ditch Retrofit Strategies
Intended
Outcome
Issue
Potential Retrofit Strategy
Ditch could benefit from and
has suitable conditions to slow
water, reduce erosion, and
increase plant uptake.
Plant ditch vegetation with wetland vegetation
(see Ditch Conversion/ Elimination) or meadow habitat vegetation.
Pollutant build-up in soil media
Amend the soil media in portions of the ditch.
Prior to installation of soil amendment, confirm that nutrients of
concern will not be exported by the amended soil media.
Note: Several soil amendments are under development.
Replace existing soil media with filtration media
See Ditch Conversion/ Elimination on page 3 of this fact sheet
Install nutrient removal check dams or in-ditch bioreactors.
Products are under development to target specific nutrients (e.g.,
woodchip socks).
Note: In-ditch nutrient removal may cause low dissolved oxygen
in ditch flows. Water quality treatment systems should be paired
with rock splash pads.
Larger-scale off-line bioreactors for denitrification have been
used in agricultural ditch networks; smaller bioreactors are under
development.
Pollutants entering ditch from
adjacent property
Add a narrow-width vegetative buffer (15 to 30 feet), such as a filter
strip or grass, between the adjacent property and the ditch.
Fill slope roadway
embankment is long and wide
and could provide additional
water quality treatment.
Amend roadside embankment with compost similar to a compost
amended vegetated filter strip.
Roadway flooding in areas
with low permeability soils,
sensitive side slopes, and/or
low ditch slopes
Install a buried conduit (e.g., underdrain or French drain) to collect
water.
Receiving water is sensitive to
nitrogen
Use upturned elbow for internal water storage to increase retention
time for denitrification
Additional Resources:
Chesapeake Bay Roadside Ditch Management Team, 2017
Chesapeake Stormwater Network, 2018
Needelman et al., 2007
Issues and Potential Retrofit Strategies
Enhance Ditch
Fact Sheet A5 – Ditch Retrofit Strategies
Intended
Outcome
Issue
Potential Retrofit Strategy
Stormwater runoff entering
ditch could benefit from
infiltration or water quality
treatment.
Replace ditch with a water quality treatment and/or flow control BMP:
Dispersion
Wetland
Biofiltration swale
Wet biofiltration swale
Bioretention area
Sand filter
Ditch segment is located
along urban roadway with
limited space for water quality
treatment BMP.
Convert ditch to closed system with water quality treatment:
Tree box filters
Modular sand filters
Infiltration trench
Boxed treatment can also be added at existing piped segments
in urban ditch networks.
Ditch erosion, high-velocity
ditches, and high sediment
loads from rural ditches
This practice involves reconfiguring roadside drainage to promote
sheet flow into adjacent forested buffers. Techniques include:
Raising the road profile
Remove roadside berms
Out-sloping the road
If steep slopes are present, consider ditch elimination only on the
down-slope side; cross pipes may be installed to convey drainage
across the road.
Additional Resources:
Chesapeake Bay Roadside Ditch Management Team, 2017
Chesapeake Stormwater Network, 2018
Examples of ditch enhancement Photo Source: Kitsap County
Enhance Ditch
Convert/Eliminate Ditch
Fact Sheet A5 – Ditch Retrofit Strategies
Intended
Outcome
Issue
Potential Retrofit Strategy
Steep longitudinal slope with
a high potential for erosion
Reduce ditch slope-length by adding:
Cross-pipes (culverts)
Turnouts (bleeders or lead-off ditches)
Broad-based dips or grade breaks
Single inlet with high velocity
resulting in scour and erosion
Add a flow spreader to distribute the water across the ditch surface
area:
Flow dispersion trench
Alternative flow dispersion trench
Tee type energy dissipater
Approved engineered flow spreading BMP
Channelized, incised flow in
ditches with steep slopes and
uneven vegetation
Add internal energy dissipation mechanisms (e.g., check dams).
Guidance from Kitsap County (2012) recommends:
Soft (e.g., straw wattle, coir log, coir netting) or rock check
dams for 2.5-10% slope
Rock-lined ditch with hard check dams for 10-15% slope
Cascade check dam > 15% slope
Additional Resources:
Chesapeake Bay Roadside Ditch Management Team, 2017
Kitsap County, 2012
Steep longitudinal slopes and high velocities flowing through ditches can lead to numerous issues, but they
may be easily addressed through a ditch retrofit.
Adding check dam to regulate ditch velocity
Photo Source: Kitsap County
Cascade Weir
Regulate Ditch Velocity
Fact Sheet A5 – Ditch Retrofit Strategies
This section summarizes major modifications to the ditch shape and/or grade. For corrective maintenance
strategies for excavating minor amounts of accumulated sediment in order to restore original ditch slope and/
or grade line, refer to the Field Guide for Roadside Ditch Maintenance in Western Washington.
Intended
Outcome
Issue
Potential Retrofit Strategy
High flow rate in a V-shaped
ditch is resulting in erosion
Reshape to U-shape or trapezoidal ditch with wider bottom than
the original V-shape.
Reshape to a natural channel (2-stage ditch with a low-flow channel
and vegetated floodplain bench).
Storage capacity has been
substantially reduced by
accumulated sediment
Excavate/remove sediment to restore to original proposed grade.
Refer to the Field Guide for Roadside Ditch Maintenance in
Western Washington for specific ditch cleaning and reshaping/
regrading methods.
Additional Resources:
University of Minnesota, 2014
Stabilizing ditch during reshaping
Photo source: Kitsap County
Ditch sediment removal prior to stabilization
Photo source: King County
Modify Ditch Shape/Grade
Fact Sheet A5 – Ditch Retrofit Strategies
Intended
Outcome
Issue
Potential Retrofit Strategy
Scour at inlets and/or outlets
Realign culverts or provide headwalls and endwalls at crossings.
Outfall from ditch discharges
directly to a stream
Disconnect direct outfalls to streams by:
Redirect ditch outlets away from streams
Redirect ditch outlets through vegetated area
Unfiltered ditch flow
discharges to receiving water
through cross-culvert under
road
Install structure to intercept and treat flow at ditch outlet.
Examples:
Tree-box filter (for urban settings)
Type II Catch Basin with sump and internal water quality
treatment component
Additional Resources:
Kitsap County, 2012
This section summarizes major modifications to the inlet and/or outlet structures. For corrective maintenance
strategies for inlets and outlets, such as installing or repairing riprap, aprons, and/or rock plunge pools, refer to
the Field Guide for Roadside Ditch Maintenance in Western Washington.
Additional Resources
Chesapeake Bay Roadside
Ditch Management Team
(2017)
Draft Options for Crediting Pollutant Reduction from Roadside Ditch Management
Practices (RDM) in the Chesapeake Bay Watershed.
Chesapeake Stormwater
Network (2018)
Roadside Ditch Management Guidance Webcast, Part 1 and Part 2
Kitsap County (2012)
Roadside Ditch and Shoulder Water Quality Enhancement Plan
Needelman et al. (2007)
Improved Management of Agricultural Drainage Ditches for Water Quality Protection:
An Overview
Schneider and Boomer (2016)
Re-plumbing the Chesapeake Watershed: Improving Roadside Ditch Management to
Meet TMDL Water Quality Goals, STAC Workshop Report
Strock et al. (2010)
Drainage Water Management for Water Quality Protection
University of Minnesota (2014) Field Guide for Maintaining Rural Roadside Ditches: Protecting Lakes and Streams
through Proper Ditch Maintenance
Modify Inlet/Outlet
This fact sheet was developed by Herrera Environmental Consultants with input from King County and the Regional Operations and Maintenance
Program (ROADMAP). Project funding was provided by a National Estuary Program grant from the Washington State Department of Ecology.

Maintaining Ditches that Convey Natural Flow Fact Sheet

Summary: Natural flow ditches, maintaining natural flow, natural flow conveyance ditches

Fact Sheet F3 – Maintaining Ditches that Convey Natural Flow
Maintaining Ditches
that Convey Natural
Flow
Fact Sheet F3
Ditches with natural flow should be identified, mapped, and assigned specialized
maintenance procedures. If natural flow is observed or suspected in a ditch,
maintenance activities must be put on hold until the appropriate permits are obtained.
Maintenance activities may also require special permitting and coordination with local,
state, and federal agencies (see Fact Sheet A3 – Permit Requirements for Ditch Maintenance).
For ditches that are (1) known to have natural flow or (2) located in proximity to a waterbody or wetland:
Confirm if ditch is hydraulically connected to
a stream. Ditches that are within ¼ mile of a
stream may also require special permitting and
procedures.
Prior to beginning maintenance activities,
confirm that the site and maintenance
activity are properly permitted. A copy of the
appropriate permit must be present on site
during the maintenance activity.
Ensure that field crews are aware of specialized
procedures (see Working in Fish-Bearing Waters
and General Maintenance Procedures on pages
2-3 of this fact sheet).
Use reflective markers (“fish sticks”) to identify
stream or wetland buffers where mowing
activities should be limited.
Limit maintenance to areas near ditch outlets
to control overgrowth and allow access for
inspection and repair, when possible.
Determine if proposed BMPs for erosion and
sediment control are appropriate (e.g., check
dams should not be used in locations that
could reduce actual or potential areas where
fish can seek refuge during high flows).
If fish are suspected or known to be present,
postpone all work until further direction is
given by a crew lead or project manager.
Ditches that convey natural flow can be identified by their flow patterns and historical
drainage patterns. If a ditch only flows during storm events or periods of site discharge
and/or was specifically build to convey stormwater or discharge water, then it is not
typically considered to be a ditch that conveys natural flow. If a ditch is located in an area
where there historically was a stream, then it is likely that the ditch still conveys some
natural flows.
February 7, 2019
Does the Ditch Convey Natural Flow?
Considerations for Ditches that Convey
Natural Flow
Fact Sheet F3 – Maintaining Ditches that Convey Natural Flow
Perform maintenance activities during low flow or no flow periods if possible, and only during the period
defined by the Hydraulic Project Approval (HPA) or federal permit (if applicable).
Scheduling Maintenance Activities
Working in Fish-Bearing Waters
Before beginning maintenance activities,
isolate the maintenance work area
using fish block nets and upstream and
downstream containment dams.
Place all in-water materials within the
isolated area.
If fish are present, herd fish and
remove using electroshocking. Fish
removal can only be performed by a
qualified and permitted consultant or
crew member.
Any flow diversion intake structures
should be equipped with a screening
apparatus to prevent fish (and debris)
from entering the system.
Ditch with Natural Flow
Reflective Markers (“Fish Sticks”) for letting crews know when
they are working close to a stream
Photo source: Kitsap County
Fact Sheet F3 – Maintaining Ditches that Convey Natural Flow
Prior to Work
Source Control
Begin Work
Isolate and
Divert Flow
Around the
Work Area
During Work
Minimize
Disturbance
End of Work
Carefully
Reintroduce
Flow
Prevent oil
and other
pollutants
from migrating
offsite and
entering water
bodies.
Prevent
mobilization of
sediment.
Reduce risk of site
disturbance and
soil compaction
Reduce risk of site
disturbance and
soil compaction
Perform equipment maintenance/service
Remove buildup of oils and grease on equipment prior to transporting
them to the site.
Flag work area to minimize disturbance to riparian vegetation
Isolate maintenance work area with upstream and downstream
containment dams.
For non-fish bearing waters and low-flow scenarios, use a vactor truck.
For fish-bearing waters and/or higher flow scenarios, use a pump and
bypass system.
– Install an intake screening apparatus to prevent fish and/or debris
from entering the hose.
– Provide secondary containment for potential fuel spills from pump
system.
If a pump and bypass system is not feasible, isolate half the channel at
one time, allowing flow to pass through the other half.
Monitor the area downstream of the maintenance activity for turbidity. If
high turbidity is observed, stop work and address the source.
Keep excavation or other heavy equipment on the roadway and off the
ditch bank.
Utilize low-impact equipment if feasible (see Equipment and Materials
on page 4 of this fact sheet).
Protect side slopes from erosion.
Leave vegetation in place where sediment buildup does not impede flow
or filtration.
If maintenance equipment must be serviced in the field, use drip pans
and non-toxic solvents when possible. Clean surfaces following any
discharge or spill.
Remove built-up sediment from containment dams.
Slowly reintroduce water to the work area. Ensure sufficient energy
dissipation when reintroducing flow to minimize turbidity. Consider
allowing flow to build-up and spill gradually over the upstream
containment dam or remove top layer of upstream dam.
Once area has stabilized, slowly remove any in-water containment or
other materials used during maintenance activities.
If vegetation disturbance (e.g., trampled or uprooted plants, exposed
soil) has occurred, consult a habitat restoration expert (additional
permitting may be required).
Remove and recycle or dispose of any waste materials.
Clean equipment and tools offsite where pollutants can be contained.
The following general maintenance procedures may apply to maintenance activities in and near ditches that
convey natural flow.
General Maintenance Procedures
Objective
Maintenance Procedures
Fact Sheet F3 – Maintaining Ditches that Convey Natural Flow
These types of corrective maintenance activities are not typically implemented in ditches that convey natural
flow; however, ditch cleaning may be considered when sediment accumulation near the inlet and/or outlet is
impeding flow or causing erosion. Ditch reshaping/grading may be necessary if ditch storage capacity is limited
by accumulated sediments; maintenance would require excavation of sediment to restore the ditch slope or
grade line.
When using a vactor truck, keep backwash out of the work area by maintaining suction until the vactor line has
cleared. If subsurface water enters the work area, use an additional vactor truck or pump and sediment tank to
manage flow without causing turbidity downstream.
Ditch Cleaning and Minor Reshaping/Regrading
Ditch Stabilization
Ditch stabilization may be required when erosion damage has occurred, or if high flows have caused ditch
bottom erosion or scour. Corrective maintenance activities may include installing additional vegetative cover or
riprap on steep side slopes or installing check dams to slow flow.
Additional equipment not used for routine ditch maintenance activities may be necessary to complete
maintenance activities when natural flow is present.
Maintenance Activity
Common Equipment and Materials
Work Area Isolation
Containment dams (e.g., water bladders, sand bags)
Fish exclusion nets (9.5 mm of stretched mesh, only for work in fish-bearing waters)
Pump and bypass setup* (if ditch flow is significant)
Spill kit, including containment for the pump
Ditch Cleaning and
Minor Reshaping/
Regrading
Hand tools (e.g., rakes, hoes, shovels)
Backhoe or excavator with ditching bucket or DitchMaster
Front end loader
Grader
Belt loader
Vactor truck
Ditch Stabilization
Riprap
Check dams (note restrictions for fish presence)
Minor and Major
Replanting/Reseeding
Riprap
Check dams (note restrictions for fish presence)
*Includes pump, backup pump, hoses, pump intake screen to keep fish and debris out of pump, and energy dissipation
for outflow back into drainage system
Considerations for Corrective Maintenance
Equipment and Materials
This fact sheet was developed by Herrera Environmental Consultants with input from King County and the Regional Operations and Maintenance
Program (ROADMAP). Project funding was provided by a National Estuary Program grant from the Washington State Department of Ecology.