Fact Sheet A2 – Prioritizing Ditches for Inspection
and Maintenance
Fact Sheet A2
Prioritizing Ditches
for Inspection
and Maintenance
Time and resource limitations prevent maintenance crews from conducting frequent inspections
and maintenance to every single ditch in their jurisdiction. To prioritize ditches for maintenance
activities, the relative importance of each ditch should be evaluated alongside its maintenance
urgency.
Inspection and maintenance prioritization can be simplified into two major questions:
Ditch Significance
How important is the ditch?
Ditch Condition
How immediate is the ditch maintenance
need?
Prioritize Ditches for Inspection
Desktop Evaluation
See Fact Sheet A1:
Ditch Mapping
Recommendations
Determine
Ditch Significance
Score
Field Evaluation
See Fact Sheet F1:
Field Evaluation of
Roadside Ditches
Determine
Ditch Condition
Score
Ongoing
Data Collection
and
Maintenance
Activities
Prioritize Ditches for
Maintenance
When prioritizing ditches for inspection, ditch condition is often unknown. Ditch Significance
may serve as the initial primary metric for sorting and ranking ditches for inspection and/or
routine maintenance. After Ditch Condition data is collected in the field, ditches can then be
prioritized for corrective maintenance.
February 7, 2019
Fact Sheet A2 – Prioritizing Ditches for Inspection
and Maintenance
Several key criteria can be used to determine the relative importance of a ditch. Data collection
to evaluate ditch significance typically requires a desktop assessment, as discussed in Fact
Sheet A1: Ditch Mapping Recommendations. The primary ditch significance criteria include:
Ditch Significance Score
Are there steep slopes in the general vicinity?
Are there erosion hazard areas or landslide hazard
areas in the general vicinity?
Does the ditch segment have a large drainage area?
(if drainage areas have been delineated)
Does this ditch have a high likelihood of capturing
polluted flows based on the road type or land use?
Does the ditch drain into a sensitive waterbody?
Does this ditch infiltrate to potential drinking water
sources?
How long ago was the last routine maintenance
action/inspection?
Is the ditch condition known?
Water Quality
Contributing Drainage Area Characteristics
Date of Last Maintenance/Inspection and Available Data
Fact Sheet A2 – Prioritizing Ditches for Inspection
and Maintenance
A streamlined evaluation for ditch significance with a standardized scoring system is
recommended as part of the desktop evaluation. Table 1 provides recommendations for
scoring ditch significance, and can be adjusted to add categories, ratings, and/or to adjust
threshold values that reflect local conditions and priorities.
*WHPA = Wellhead Protection Area
Table 1. Recommendations for Ditch Significance Scoring
Road Type/
Classification
Local Road
Minor Collector
Major Collector
Minor Arterial
Principal Arterial
Receiving Waterbody
Quality
No known
water quality
issues
No known water
quality issues,
but is within ¼
mile of receiving
water
303(d) listed for
phosphorus or
fecal coliform,
shellfish bed
closures, or beach
closure
Any 303(d) listed
parameter (other
than phosphorus
or fecal coliform)
TMDL
Located in WHPA*
No WHPA
10-year travel
time
5-year
travel time
1-year
travel time
6-month
travel time
Slope of Adjacent Road
Low
(< 5%)
Low to
Moderate
(5-10%)
Moderate
(10-15%)
Moderate to
Steep
(15-20%)
Steep
(> 20%)
Erosion/ Landslide
Hazard Areas
Not applicable
Yes, but not
directly adjacent
to ditch
Yes; directly
adjacent to ditch
Drainage Area Size
(in acres)
Small
(< 0.25)
Small to
Moderate (0.25-
0.50)
Moderate
(0.50-0.75)
Moderate to
Large
(0.75-1.0)
Large
(> 1.0)
Date Last Visited
< 1 year
1-3 years
3-5 years
5-10 years
>10 years
Adjacent Land Use
Undeveloped
(Forest,
Natural, or
Undisturbed)
Single Family
Residential
(Rural)
Single Family
Residential
(Urban)
Multi-Family
Residential
Light Commercial
Agricultural
Golf Course
Industrial
Heavy
Commercial
Livestock
Spill Frequency
None reported
Low
(1-2 spills/
accidents per
year)
Moderate
(3-5 spills/
accidents per
year)
Moderate-High
(6-9 spills/
accidents per
year)
High
(10 or more
spills/accidents
per year)
Category
Score
Ditch Significance Score
Fact Sheet A2 – Prioritizing Ditches for Inspection
and Maintenance
A score of 5 across several data fields would contribute to an overall high priority ditch
significance score, placing the ditch in the “Moderate-High” or “High” inspection priority
bracket. For specific high-urgency concerns, “red flag” items or weighted scores can be used to
improve accuracy of the calculated score to match real-world priorities.
Ditch Significance Score*
10-18
19-27
28-36
37-45
Inspection Priority
Low
Low-Moderate
Moderate
Moderate-High
High
Ditch Significance Score
Category
Rating
Score
Road Type/Classification
Major Collector
Receiving Waterbody Quality
On the 303(d) list for temperature
Located in WHPA
No WHPA
Slope of Adjacent Road
Low to Moderate (5-10%)
Erosion/Landslide Hazard Areas
Yes, directly adjacent to ditch
Drainage Area Size
Small to Moderate (0.25-0.50 acres)
Date Last Visited
3-5 years
Adjacent Land Use
Single Family Residential (Urban)
Spill Frequency
Moderate (3-5 spills/accidents per year)
Total Ditch Significance Score
*Scoring intervals can be customized, and will vary if weighting or additional criteria are added to the recommended
framework
Example of Mapped Landslide Hazard Areas
Ditch Significance Score Example
Fact Sheet A2 – Prioritizing Ditches for Inspection
and Maintenance
Table 2. Recommendations for Ditch Condition Scoring
Good (1)
Moderate (3)
Poor (5)
Capacity and
Conveyance
Ditch flows freely, no
debris build-up evident
Ditch flows freely, some
minor build-up evident
Ditch functions to < 25% of
capacity
No evidence of localized
flooding
Not applicable
Evidence of localized flooding
Structural
Components
No damaged components
present
Damaged components, but
not causing flow blockages
Damaged components
causing flow blockages
No debris buildup at inlet
or outlet
Debris buildup at inlet or
outlet blocking 25% of
inlet/outlet capacity
Debris buildup at inlet or
outlet blocking 50% of inlet/
outlet capacity
Vegetation
Covering 90% of ditch
bottom
Covering 75-90% of the
ditch bottom
Covering < 75% of ditch
bottom and/or causing line-
of-sight issues
Recently mowed
(< 1 year ago)
Mowed last year
(2 years ago)
Not recently mowed
(3 or more years ago)
No noxious weeds present
Noxious weeds present, but
are actively being managed
Noxious weeds present and
not being managed
Integrity
No bare spots
10-20% bare spots
> 40% bare spots
No evidence of nuisance
animals
Evidence of illegal dumping
Evidence of nuisance animals
or illicit connections
Assessment of ditch condition requires field data collection, which can occur during
adjacent road or ditch maintenance activities or as part of a proactive inspection program.
Field assessment for ditch condition is discussed in Fact Sheet F1: Considerations for Field
Evaluation of Roadside Ditches.
Table 2 provides recommendations for scoring ditch condition. The intent of the rating matrix
is to correlate the field condition assessment with a relative score that can be applied to all
ditches within the jurisdiction. This rating may be evaluated in further detail to prioritize the
ditch segment for ongoing inspections and to schedule routine and/or corrective maintenance.
This rating matrix can be adjusted to add categories, ratings, scoring values (e.g., 1 for good,
3 for moderate, and 5 for poor), and/or to adjust threshold values (e.g., 90% vegetation
coverage, < 25% capacity).
Rating (Score)
Category
Ditch Condition Score
Fact Sheet A2 – Prioritizing Ditches for Inspection
and Maintenance
Structural Component
Vegetation
Integrity
Capacity and Conveyance
Example: Ditch segment appears
recently maintained, with intact
structural components and
open conveyance. Vegetation is
not overgrown; however, ditch
segment is entirely bare and needs
urgent corrective maintenance to
avoid future erosion. No noxious
weeds are present.
Category
Rating
Score
Capacity and
Conveyance
Ditch flows freely, no debris
build-up evident
Ditch flows freely, some
minor build-up evident
Ditch functions to < 25% of
capacity
No evidence of localized
flooding
Not applicable
Evidence of localized flooding
Structural
Components
No damaged components
present
Damaged components, but
not causing flow blockages
Damaged components causing
flow blockages
No debris buildup at inlet or
outlet
Debris buildup at inlet or
outlet blocking 25% of
inlet/outlet capacity
Debris buildup at inlet or outlet
blocking 50% of inlet/outlet
capacity
Vegetation
Covering 90% of ditch bottom
Covering 75-90% of the
ditch bottom
Covering < 75% of ditch bottom
and/or causing line-of-sight
issues
Recently mowed (< 1 year
ago)
Mowed last year (2 years
ago)
Not recently mowed (3 or more
years ago)
No noxious weeds present
Noxious weeds present,
but are actively being
managed
Noxious weeds present and
not being managed
Integrity
No bare spots
10-20% bare spots
> 40% bare spots
No evidence of nuisance
animals
Evidence of illegal dumping
Evidence of nuisance animals or
illicit connections
Total Ditch Condition Score
The ditch condition score for this example would be calculated as follows:
Ditch Condition Score Example
Fact Sheet A2 – Prioritizing Ditches for Inspection
and Maintenance
A score of 5 across several data fields would contribute to an overall high ditch condition score.
For specific high-urgency concerns, “red flag” items or weighted scores can be used to improve
accuracy of the calculated score to reflect local priorities. This prioritization score can be used
to determine high-risk, high-need ditches based on local priorities and concerns. Ideally, this
rating system would be integrated with the ditch database and updated as inspections and
maintenance activities are performed.
Combined Ditch
Significance and Ditch
Condition Score*
18-34
35-51
52-68
69-85
Overall Maintenance
Priority
None
Minor
Routine
Major
Urgent
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 Condition Score Example
*Scoring intervals can be customized, and will vary if weighting or additional criteria are added to the recommended
framework.
The overall maintenance priority of a ditch should incorporate both the Ditch Significance
Score and the Ditch Condition Score. This combined score can be used to prioritize ditches for
maintenance on an ongoing basis.
Combined Ditch Significance and Ditch Condition Score
Mapped Ditch Significance Score
Mapped Ditch Condition Score
Mapped Maintenance Priority