February 2019
Roadside Ditch Maintenance Matrix
Table 1. Routine Ditch Maintenance Strategies.
Strategy
Description
Condition
Ditch
Surface Type
Water Flow
Common Equipment and Material Needs
Considerations
References
Ditch Vegetation Management Strategies
Mowing
Cutting vegetation
to a reasonable
height to allow for
proper water flow
and aesthetics
Tall vegetation is
impeding flow of
water through the
ditch or causing line
of sight issues
 Vegetated
 No flow
• Mower
• Specialized mower for steep slopes
• Brooms, scoops, shovels, and/or
handheld blowers
Additional Equipment and Materials for
Natural Flow
• Reflective markers (“fish sticks”)
Considerations Prior to Implementation
• Set the mowing height at the highest acceptable level. For standard turf grass, mowing
only the top 1/3 of the grass blade height is recommended. Where vegetation growth is
excessive, additional mowing may be necessary.
• Avoid operating in wet areas or rough terrain to minimize scalping and rutting.
• Strategize mowing direction to minimize spreading of cut material onto adjacent paved
surfaces.
• If vegetation is providing flow control or treatment, too much removal or trimming could
reduce these functions.
• If possible, retain vegetation on the south or west sides of the ditch to provide shading of
the ditch and reduce water temperature.
• If there is an opportunity to re-seed, low growing grass seed mix is recommended to
reduce mowing frequency and cost.
Steep Slope Considerations
• Use a specialized mower when steep slopes (≥ 15 percent) are present.
Disposal Considerations
• Turf grass may be mulch mowed and left in place; however, large quantities of turf grass
clippings may lead to outlet clogging and nutrient loading in downstream water bodies.
Refer to Invasive Species
and Noxious Weed
Removal (Table 1, page 3)
for additional
recommendations
regarding mowing.
Refer to Fact Sheet F3 –
Maintaining Ditches that
Convey Natural Flow for
natural flow considerations.
Refer to local codes and
regulations for additional
requirements.
Brush Cutting
(or Brushing)
Trimming woody
vegetation to
remove overgrown
and/or excessive
vegetation to allow
for proper water
flow and to restore
sight distance
• Overgrown/
excessive
vegetation
impeding flow or
storage of water
and sediments
• Safety or
structural integrity
of the roadway is
jeopardized
 Vegetated
 No flow
• Brush cutters
• Power saws
• Axes and/or machetes
• Pruning shears, loppers, and/or clippers
• Brooms, scoops, shovels, and/or rakes
• Truck cover (for securing load during
transport)
Considerations Prior to Implementation
• If vegetation is providing flow control or treatment, too much removal or trimming could
reduce these functions.
• If possible, retain vegetation on the south or west sides of the ditch to provide shading of
the ditch and reduce water temperature.
Disposal Considerations
• Remove cut branches/other vegetative debris after brushing to reduce outlet clogging
and spreading invasive species.
• Compost or stockpile vegetative matter in a clean green stockpile at your maintenance
facility, if possible.
Refer to local codes and
regulations for additional
requirements.
February 2019
Roadside Ditch Maintenance Matrix
Table 1 (continued). Routine Ditch Maintenance Strategies.
Strategy
Description
Condition
Ditch
Surface Type
Water Flow
Common Equipment and Material Needs
Considerations
References
Ditch Vegetation Management Strategies (continued)
Minor
Reseeding/
Replanting
Adding seed and/or
plants to stabilize
exposed soils.
Applies to
conditions affecting
a small section of a
ditch that can be
addressed as part of
routine
maintenance.
• Sparse
vegetation/
eroded patches
on ditch bottom
• Poor grass growth
 Vegetated
 Bare Soil
 No flow
• Seed mix
• Hydroseeder
• Post-seeding erosion control BMPs (e.g.,
straw mulch, biodegradable nets and
blankets, coir mats)
Considerations Prior to Implementation
• Ensure that erosion control BMPs are installed properly to avoid blockages.
• Low growing grass seed mix is recommended to reduce mowing frequency and cost.
• Confirm that there are no weed seeds or invasive plant seeds in the seed mixes.
• Seed and/or plant during the following optimum windows:
o Late spring (April 1 through June 30)
o Early fall (September 1 through October 1)
• Establishment of vegetation may not be feasible in coarse grained or mineral soils.
When major reseeding/
replanting is necessary to
correct poor conditions,
refer to Major Replanting/
Reseeding(Table 2, page 9).
Refer to Fact Sheet F3 –
Maintaining Ditches that
Convey Natural Flow for
natural flow considerations.
Refer to local codes and
regulations for additional
requirements.
Weed
Control
Control of weeds
through biological,
physical,
mechanical,
chemical, or cultural
methods
Weeds present in
ditch
 Vegetated
 Bare Soil
 Rock
 No flow
 Standing
water
 Low flow
• Required permits (keep documentation
on-site during work)
• Weeding tools
• Weed burner
• Brooms, scoops, shovels, and/or rakes
Considerations Prior to Implementation
• Verify that required permits have been obtained prior to beginning work.
• Review preferred implementation strategies documented in an Integrated Pest
Management (IPM) plan.
• Ensure that herbicide applications are performed by licensed, qualified staff.
• Use physical and/or mechanical methods of vegetation removal rather than applying
herbicides, where practical.
Disposal Considerations
• Compost or stockpile vegetative matter in a clean green stockpile at your maintenance
facility, if possible, and only if invasive species and noxious weeds are not present.
Refer to Invasive Species
and Noxious Weed
Removal (Table 1, page 3)
for disposal considerations
when invasive species and
noxious weeds are present.
Refer to Fact Sheet F3 –
Maintaining Ditches that
Convey Natural Flow for
natural flow considerations.
Refer to Fact Sheet A3 –
Permit Requirements for
Ditch Maintenance for
permitting considerations.
Refer to your local IPM plan,
local codes and regulations
for additional requirements.
February 2019
Roadside Ditch Maintenance Matrix
Table 1 (continued). Routine Ditch Maintenance Strategies.
Strategy
Description
Condition
Ditch
Surface Type
Water Flow
Common Equipment and Material Needs
Considerations
References
Ditch Vegetation Management Strategies (continued)
Invasive
Species and
Noxious
Weed
Removal
Control of invasive
species and noxious
weeds through
biological, physical,
mechanical,
chemical, or cultural
methods
• Invasive species
present
• Noxious weeds
present
 Vegetated
 Bare Soil
 Rock
 No flow
 Standing
water
 Low flow
• Required permits (keep documentation
on-site during work)
• Weeding tools
• Weed wrench
• Targeted herbicide applicator (woody
painter/herbicide wand)
• Garbage bags (to prevent seed
development and dispersal)
• Protective clothing and eye protection
(for toxic, noxious weeds)
Considerations Prior to and During Implementation
• Verify that required permits have been obtained prior to beginning work.
• Invasive species may need to be removed by hand.
• Pull plants when soils are moist and before seeds are produced.
• Identify invasive species that can and should be controlled or reduced by mowing.
• Ensure that herbicide applications are performed by licensed, qualified staff.
• Prior to mowing, implement the following for small populations of invasive plants:
o Use herbicides early in the summer.
o Physically remove flower or seed heads (cut and bag).
o Physically remove rootstock (mechanically excavate).
• Implement the following for large, mature invasive plants:
o Control large purple loosestrife plant populations with biocontrol beetles (Hylobias
sp. or Galrucella sp.) prior to mowing.
o Mow plants prior to seed maturation, allow the plants to regrow to a height of 2 to
4 feet and then treat with foliar herbicide.
• If mowing occurs after seed maturation, hand clean the upper parts of the mowing
equipment with a brush or broom prior to moving to a new location.
Disposal Considerations
• Ensure proper disposal per the Washington State Noxious Weed Control Board.
• Bag cut flowers and seed heads.
Refer to Fact Sheet F3 –
Maintaining Ditches that
Convey Natural Flow for
natural flow considerations.
Refer to Fact Sheet A3 –
Permit Requirements for
Ditch Maintenance for
permitting considerations.
Refer to the Washington
State Noxious Weed
Control Board for weed
identification, removal, and
disposal considerations:
www.nwcb.wa.gov
Refer to your local IPM plan,
local codes and regulations
for additional requirements.
Other Maintenance Strategies
Inlet/Outlet
Cleaning
Clean accumulated
sediment from
inlets and outlets
Accumulated
sediment or blockage
impeding flow
(≥ 50% blockage) at
inlet/outlet pipe
 Vegetated
 Bare Soil
 Rock
 Paved
 Metal
 No flow
 Standing
water
• Rake, hoe, or shovel
• Wheelbarrow or buckets
Steep Slope Considerations
• Consider adjusting threshold to ≥ 30% blockage when steep slopes (≥ 15%) are present.
Disposal Considerations
• Use or disposal options for the sediment removed from the inlet and/or outlet will
depend on the characterization of the waste.
Refer to Fact Sheet A3 –
Permit Requirements for
Ditch Maintenance for
permitting considerations.
Refer to local codes and
regulations for additional
requirements.
February 2019
Roadside Ditch Maintenance Matrix
Table 1 (continued). Routine Ditch Maintenance Strategies.
Strategy
Description
Condition
Ditch
Surface Type
Water Flow
Common Equipment and Material Needs
Considerations
References
Other Maintenance Strategies (continued)
Nuisance
Animal/
Insect
Control
Control of nuisance
animals/insects
through mechanical,
manual, or chemical
methods. Examples
of nuisance animals
and insects include:
• Beavers: May
block ditch
capacity with
dams
• Bees: Could
pose a hazard to
crews
maintaining the
ditch
• Moles:
Contribute to
erosion by
burrowing holes
• Mosquitoes:
May result from
stagnant flow in
ditch; nuisance
and public health
hazard
• Nutria:
Contribute to
erosion by
destroying the
banks of ditches
Nuisance animals/
insects present
 Vegetated
 Bare Soil
 Rock
 Paved
 Metal
 No flow
 Standing
water
• Animal guards (e.g., rods, flap gates, and
finger-type flap gates) for outlet pipes
• Traps (if allowed)
Considerations Prior to Implementation
Preferred implementation strategies should be documented in an Integrated Pest
Management (IPM) plan.
Refer to Fact Sheet F3 –
Maintaining Ditches that
Convey Natural Flow for
natural flow considerations.
Refer to Fact Sheet A3 –
Permit Requirements for
Ditch Maintenance for
permitting considerations.
Refer to your local IPM plan,
local codes and regulations
for additional requirements.
February 2019
Roadside Ditch Maintenance Matrix
Table 2. Corrective Ditch Maintenance Strategies.
Strategy
Description
Condition
Ditch
Surface Type
Water Flow
Common Equipment and Material Needs
Considerations
References
Ditch Cleaning Strategies
Hand Ditching
Removing
sediment and
debris manually
using a rake,
hoe, or shovel
• Sediment
accumulation
near inlet and/or
outlet
• Excess sediment
impeding flow or
causing erosion
 Vegetated
 Bare Soil
 Rock
 Paved
 Metal
 No flow
 Low flow
• Rake, hoe, or shovel
• Wheelbarrow or buckets
• Erosion control BMPs (e.g., wattles, check dams, silt
fences)
Additional Equipment and Materials for Natural Flow
• Required permits (keep documentation on-site during
work)
• Containment dams (e.g., water bladders, sand bags)
• Vactor truck (for non -fish bearing waters and low -flow
scenarios)
• Fish exclusion nets (9.5 mm stretched mesh)
• Pump and bypass setup (if ditch flow is significant)
• Spill kit, including containment for the pump
• Erosion control BMPs for pump outfall, channel
stabilization, etc.
Considerations Prior to Implementation
• Verify that required permits have been obtained prior to beginning work.
• Cleaning should be performed during low flow or no flow periods if
possible.
• Install erosion control BMPs prior to conducting sediment removal.
• Consider retaining vegetation near ditch outlet(s), also known as “skip
ditching.”
• Reseed and install erosion control BMPs after sediment has been removed
if needed.
Steep Slope Considerations
• Retain additional vegetation near ditch outlet(s) when steep slopes (≥ 15
percent) are present.
Disposal Considerations
• Sweep and collect dirt and debris remaining on the pavement at the
completion of work.
• Separate screenings into soil and vegetative matter (e.g., leaves, grass,
needles, branches, etc.) categories:
o Compost or stockpile vegetative matter in a clean green stockpile at
your maintenance facility, if possible.
o Use or disposal options for the soil portion will depend on the
characterization of the waste.
Refer to Minor Reseeding/
Replanting (Table 1,
page 2).
Refer to Fact Sheet F2 –
Ditch Cleaning Strategies
for additional information
on ditch cleaning.
Refer to Fact Sheet F3 –
Maintaining Ditches that
Convey Natural Flow for
natural flow considerations.
Refer to Fact Sheet A3 –
Permit Requirements for
Ditch Maintenance for
permitting considerations.
Refer to local codes and
regulations for additional
requirements.
February 2019
Roadside Ditch Maintenance Matrix
Table 2 (continued). Corrective Ditch Maintenance Strategies.
Strategy
Description
Condition
Ditch
Surface Type
Water Flow
Common Equipment and Material Needs
Considerations
References
Ditch Cleaning Strategies (continued)
Bucket Ditching
(Mechanical
Excavation)
Removing
sediment and
debris in deep
ditches where
hand ditching is
impractical
• Sediment
accumulation
near inlet and/or
outlet
• Excess sediment
impeding flow or
causing erosion
 Vegetated
 Bare Soil
 No flow
 Low flow
• Backhoe or excavator with ditching bucket or Ditch
Master
• Erosion control BMPs (e.g., wattles, check dams, silt
fences)
Additional Equipment and Materials for Natural Flow
• Required permits (keep documentation on-site during
work)
• Containment dams (e.g., water bladders, sand bags)
• Vactor truck (for non -fish bearing waters and low -flow
scenarios)
• Fish exclusion nets (9.5 mm stretched mesh)
• Pump and bypass setup (if ditch flow is significant)
• Spill kit, including containment for the pump
• Erosion control BMPs for pump outfall, channel
stabilization, etc.
Considerations Prior to Implementation
• Verify that required permits have been obtained prior to beginning work.
• Cleaning should be performed during low flow or no flow periods if
possible.
• Cleaning should utilize low-impact equipment if feasible.
• Install erosion control BMPs prior to conducting sediment removal.
• Consider retaining vegetation near ditch outlet(s), also known as “skip
ditching.”
• Reseed and install erosion control BMPs after sediment has been removed
if needed.
• Keep excavation equipment on the roadway and off the ditch bank.
Steep Slope Considerations
• Retain additional vegetation near ditch outlet(s) when steep slopes (≥ 15
percent) are present.
Disposal Considerations

ROADSIDE DITCH
MAINTENANCE IN
WESTERN WASHINGTON
FIELD GUIDE
February 7, 2019
Field Guide for Roadside Ditch Maintenance in Western Washington: Routine Maintenance
Ditch maintenance strategies fall into two categories: routine maintenance and corrective
maintenance. Some maintenance strategies can fall into both categories.
Different ditch types and different existing conditions require different
maintenance strategies, and appropriate maintenance strategies may
be limited by cost, space availability, and environmental regulations.
Some existing ditches may be so degraded that they require more
complicated and expensive source control or retrofit strategies.
This field guide focuses on the implementation of routine and
corrective maintenance strategies by municipal maintenance staff in
roadside ditches that convey stormwater.
Introduction
The reference bar at the bottom of most of the maintenance strategy pages refers to a set
of 8 fact sheets that were also developed as part of this project:
Fact Sheet A1 – Ditch Mapping
Recommendations
Fact Sheet A2 – Prioritizing Ditches for
Inspection and Maintenance
Fact Sheet A3 – Permit Requirements for
Ditch Maintenance
Fact Sheet A4 – Source Control Strategies
for Ditches
Fact Sheet A5 – Ditch Retrofit Strategies
Fact Sheet F1 – Considerations for Field
Evaluation of Roadside Ditches
Fact Sheet F2 – Ditch Cleaning Strategies
Fact Sheet F3 – Maintaining Ditches that
Convey Natural Flow
This guide is for reference only. All maintenance strategies must comply with local codes and regulations.
Maintenance strategies in ditches that convey natural flow require special considerations.
This field guide 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.
Fact sheets are boxed and shown in brighter text if they are directly applicable to the maintenance
strategy described on that page of the field guide.
Introduction
Field Guide for Roadside Ditch Maintenance in Western Washington: Routine Maintenance
What is ditch vegetation management?
Vegetation management includes the establishment and maintenance of healthy,
beneficial vegetation in ditches and the control of excess or unwanted vegetation.
Why is ditch vegetation management important?
Ditches are designed to transport water away from the roadway to prevent roadway
flooding. Vegetation can promote this essential ditch function, but can also inhibit
the capacity of a ditch to convey water. Vegetation can also capture pollutants from
stormwater runoff.
Routine maintenance strategies for vegetation management should ensure that vegetation
is healthy, but does not encroach on the adjacent roadway or cause ditch capacity issues.
Mowing (page 3)
Routine Maintenance
Weed Control
(page 6)
(page 8)
(page 9)
Invasive Species and
Noxious Weed Removal
(page 7)
Brush Cutting (or
Brushing)
(page 4)
Minor Reseeding/
Replanting
(page 5)
Ditch Vegetation
Management
Nuisance Animal/
Insect Control
Inlet/Outlet
Cleaning
Ditch Vegetation Management
In general, routine maintenance can be completed by municipal maintenance staff
without major analysis, engineering, or permits. Ideally, ditches that are in good
condition do not require corrective maintenance and can be maintained through
routine inspections and maintenance.
The routine maintenance strategies outlined in this field guide include:
Field Guide for Roadside Ditch Maintenance in Western Washington: Routine Maintenance
Ditch Vegetation Management Strategies
Mowing
Description
Cutting vegetation to a reasonable height to allow for proper water flow and aesthetics
Condition
Tall vegetation is impeding flow of water through the ditch or causing line of sight issues
Ditch Surface Types
Vegetated
Water Flow
No flow
Common Equipment
and Materials
Mower
Specialized mower for steep slopes
Brooms, scoops, shovels, and/or handheld blowers
Additional Equipment
and Materials for
Natural Flow
Reflective markers (“fish sticks”)
Considerations Prior to
Implementation
Set the mowing height at the highest acceptable level. For standard turf grass, mowing
only the top 1/3 of the grass blade height is recommended. Where vegetation growth is
excessive, additional mowing may be necessary.
Avoid operating mowers in wet areas or rough terrain to minimize scalping and rutting.
Strategize mowing direction to minimize spreading of cut material onto adjacent paved
surfaces.
If vegetation is providing flow control or treatment, too much removal or trimming
could reduce these functions.
If possible, retain vegetation on the south or west sides of the ditch to provide shading
of the ditch and reduce water temperature.
If there is an opportunity to re-seed, low growing grass seed mix is recommended to
reduce mowing frequency and cost.
Steep Slope
Considerations
Use a specialized mower when steep slopes (≥ 15 percent) are present.
Disposal
Considerations
Turf grass may be mulch mowed and left in place; however, large quantities of turf grass
clippings may lead to outlet clogging and nutrient loading in downstream water bodies.
Fact Sheet References
Additional References
Refer to Invasive Species and Noxious Weed
Removal (page 7) for additional recommendations
regarding mowing.
Refer to local codes and regulations for additional
requirements.
Photo source: King County
Field Guide for Roadside Ditch Maintenance in Western Washington: Routine Maintenance
Ditch Vegetation Management Strategies
Brush Cutting or “Brushing”
Description
Trimming woody vegetation to remove overgrown and/or excessive vegetation to allow for
proper water flow and to restore sight distance
Condition
Overgrown/ excessive vegetation impeding flow or storage of water and sediments
Safety or structural integrity of the roadway is jeopardized
Ditch Surface Types
Vegetated
Water Flow
No flow
Common Equipment
and Materials
Brush cutters
Power saws
Axes and/or machetes
Pruning shears, loppers, and/or clippers
Brooms, scoops, shovels, and/or rakes
Truck cover (for securing load during transport)
Considerations Prior
to Implementation
If vegetation is providing flow control or treatment, too much removal or trimming
could reduce these functions.
If possible, retain vegetation on the south or west sides of the ditch to provide
shading of the ditch and reduce water temperature.
Disposal
Considerations
Remove cut branches/other vegetative debris after brushing to reduce outlet
clogging and spreading invasive species.
Compost or stockpile vegetative matter in a clean green stockpile at your
maintenance facility, if possible.
Vegetation management demonstration
Photo source: Kitsap County
Additional References
Refer to local codes and regulations
for additional requirements.
Field Guide for Roadside Ditch Maintenance in Western Washington: Routine Maintenance
Ditch Vegetation Management Strategies
Minor Reseeding/Replanting
Description
Adding seed and/or plants to stabilize exposed soils. Applies to conditions affecting a small
section of a ditch that can be addressed as part of routine maintenance (see Additional
References below).
Condition
Sparse vegetation/ eroded patches on ditch bottom
Poor grass growth
Ditch Surface Types
Vegetated
Bare Soil
Water Flow
No flow
Common Equipment
and Materials
Seed mix
Hydroseeder
Post-seeding erosion control BMPs (e.g., straw mulch, biodegradable nets and
blankets, coir mats)
Considerations Prior
to Implementation
Ensure that erosion control BMPs are installed properly to avoid blockages.
Low growing grass seed mix is recommended to reduce mowing frequency and cost.
Confirm that there are no weed seeds or invasive plant seeds in the seed mixes.
Seed and/or plant during the following optimum windows:
Late spring (April 1 through June 30)
Early fall (September 1 through October 1)
Establishment of vegetation may not be feasible in coarse grained or mineral soils.
Fact Sheet References
Examples of sparse or absent vegetation that could be classified as poor (left),
moderate (center), and good (right) vegetation coverage.
Additional References
When major reseeding/replanting is
necessary to correct poor conditions, refer
to Major Reseeding/Replanting (page 16)
in the Corrective Maintenance section of
this field guide.
Refer to local codes and regulations for
additional requirements.
Field Guide for Roadside Ditch Maintenance in Western Washington: Routine Maintenance
Ditch Vegetation Management Strategies
Weed Control
Description
Control of weeds through biological, physical, mechanical, chemical, or cultural methods
Condition
Weeds are present in a ditch
Ditch Surface Types
Vegetated
Bare Soil
Rock
Water Flow
No flow
Standing water
Low flow
Common Equipment
and Materials
Required permits (keep documentation on-site during work)
Weeding tools
Weed burner
Brooms, scoops, shovels, and/or rakes
Considerations Prior
to Implementation
Verify that required permits have been obtained prior to beginning work.
Review preferred implementation strategies documented in an Integrated Pest
Management (IPM) plan.
Ensure that herbicide applications are performed by licensed, qualified staff.
Use physical and/or mechanical methods of vegetation removal rather than
applying herbicides, where practical.
Disposal Conditions
Compost or stockpile vegetative matter in a clean green stockpile at your maintenance
facility, if possible, and only if invasive species and noxious weeds are not present.
Fact Sheet References
Reed canarygrass, Photo source: WA State Noxious Weed
Control Board
Additional References
Refer to Invasive Species and Noxious Weed
Removal (page 7) for disposal considerations
when invasive species and noxious weeds are
present.
Refer to your local IPM plan, local codes and
regulations for additional requirements.
Field Guide for Roadside Ditch Maintenance in Western Washington: Routine Maintenance
Ditch Vegetation Management Strategies
Invasive Species and Noxious Weed Removal
Description
Control of invasive species and noxious weeds through biological, physical, mechanical,
chemical, or cultural methods
Condition
Invasive species present Noxious weeds present
Ditch Surface Types
Vegetated Bare Soil Rock
Water Flow
No flow Standing water Low flow
Common Equipment
and Materials
Required permits (keep documentation on-site during work)
Weeding tools
Weed wrench
Targeted herbicide applicator (woody painter/ herbicide wand)
Garbage bags (to prevent seed development and dispersal)
Protective clothing and eye protection (for toxic, noxious weeds)
Considerations Prior to
Implementation
Verify that required permits have been obtained prior to beginning work.
Invasive species may need to be removed by hand.
Pull plants when soils are moist and before seeds are produced.
Identify invasive species that can and should be controlled or reduced by mowing.
Ensure that herbicide applications are performed by licensed, qualified staff.
Prior to mowing, implement the following for small populations of invasive plants:
Use herbicides early in the summer.
Physically remove (cut) flower or seed heads.
Physically remove rootstock (mechanically excavate).
Implement the following for large, mature invasive plants:
Control large purple loosestrife plant populations with biocontrol beetles
(Hylobias sp. or Galrucella sp.) prior to mowing.
Mow plants prior to seed maturation, allow the plants to regrow to a height of 2 to
4 feet and then treat with foliar herbicide.
If mowing occurs after seed maturation, hand clean the upper parts of the mowing.
equipment with a brush or broom prior to moving to a new location.
Disposal Conditions
Ensure proper disposal per the Washington State Noxious Weed Control Board.
Bag cut flowers and seed heads.
Fact Sheet References
Common invasive species that thrive in ditches include reed canarygrass and
Himalayan blackberry. These species can make ditches difficult to access and
inspect and can reduce ditch flow capacity.
Additional References
Refer to the Washington State Noxious
Weed Control Board (www.nwcb.wa.gov) for
weed identification, removal, and disposal
considerations.
Refer to your local IPM plan, local codes and
regulations for additional requirements.
Field Guide for Roadside Ditch Maintenance in Western Washington: Routine Maintenance
Inlet/Outlet Cleaning
Description
Clean accumulated sediment and blockages from inlets and outlets
Condition
Accumulated sediment or blockage impeding flow (≥ 50% blockage) at inlet/outlet pipe
Ditch Surface Types
Vegetated Bare Soil Rock
Paved Metal
Water Flow
No flow Standing water
Common Equipment
and Materials
Rake, hoe, or shovel
Wheelbarrow or buckets
Steep Slope
Considerations
Consider adjusting threshold to ≥ 30% blockage when steep slopes (≥ 15 percent) are
present.
Disposal Conditions
Use or disposal options for the sediment removed from the inlet and/or outlet will depend
on the characterization of the waste (see Fact Sheet A3 – Permit Requirements for Ditch
Maintenance).
Fact Sheet References
Culvert outlet is partially buried in sediment (left). Inlet blocked by structure (right).
Additional References
Refer to local codes and regulations for
additional requirements.
Field Guide for Roadside Ditch Maintenance in Western Washington: Routine Maintenance
Nuisance Animal/Insect Control
Description
Control nuisance animals/insects through mechanical, manual, or chemical methods. Examples
of nuisance animals and insects include:
Beavers: May block ditch capacity with dams
Bees: Could pose a hazard to crews maintaining the ditch
Moles: Contribute to erosion by burrowing holes
Mosquitoes: May result from stagnant flow in ditch; nuisance and public health
hazard
Nutria: Contribute to erosion by destroying the banks of ditches
Condition
Nuisance animals/insects present
Ditch Surface Types
Vegetated
Bare Soil
Rock
Paved
Metal
Water Flow
No flow
Standing water
Common Equipment
and Materials
Animal guards (e.g., rods, flap gates, and finger-type flap gates) for outlet pipes
Traps (if allowed)
Considerations Prior
to Implementation
Preferred implementation strategies should be documented in an Integrated Pest
Management (IPM) plan.
Fact Sheet References
Evidence of moles in a roadside ditch.
Additional References
Refer to your local IPM plan, local codes and regulations
for additional requirements.
Field Guide for Roadside Ditch Maintenance in Western Washington: Corrective Maintenance
Corrective Maintenance
Corrective maintenance may require analysis, engineering, or permitting prior to implementation. The
corrective maintenance strategies outlined in this field guide include:
Trees of Concern
(page 17)
Ditch Cleaning
Minor Ditch Reshaping/
Regrading (page 15)
Ditch Stabilization
(page 14)
Major Replanting/
Reseeding (page 16)
Hand Ditching (page 11)
Bucket Ditching (page 12)
Shoulder Ditching (page 13)
Minor Inlet/Outlet Repair
(page18)
What is ditch cleaning?
Ditch cleaning is a…