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.