Center for Environmental Excellence by AASHTO CENTER HOME  
skip navigation
CEE by AASHTO Home | Compendium Home | Online Compendium Help | Recent Updates | Inquiries | FAQs | State DOT Links
About Best Practices | Comment on Best Practices | Suggest A Best Practice | Volunteer to Vet Best Practices
Printer Friendly Version Print This Page    
« Back to Chapter 9 | Go to Chapter 11 »
Chapter 10
Roadside Management and Maintenance: Beyond Vegetation
10.11. Maintenance Stewardship Practices for Slopes, Drainage Ditches, Swales, and Diversions

Maintenance activities related to slopes, drainage and associated vegetation include repair, replacement and clearing of channels, ditches, culverts, underdrains, horizontal drains and other elements of the stormwater drainage system. Protective measures such as soil stabilization using vegetation or rock on stream banks, slopes, benches or ditches are also part of the these activities.


10.11.1 Drainage Ditch and Channel Maintenance

Channels and drainage ditches are maintained to avoid obstruction and maintain flow. Ditch cleaning includes use of equipment for cleaning and reshaping of ditches including loading, hauling, and disposing of excess materials. Vegetation located in the ditch is removed during cleaning. Material is removed to an appropriate location for disposal or storage. Subtasks include vehicle operation, mechanically cleaning, and stockpiling and disposal of removed material. Fill material may be imported to repair eroded channel walls.

  • Use water quality management practices to control potential pollution from disturbed soil, leaks and stockpiles, and release of pollutants such as sediment, litter, fuel, hydraulic fluid and oil. Such pollution prevention practices may include scheduling and planning, illegal spill discharge control, illicit connection/illicit discharge reporting and removal, vehicle and equipment fueling, vehicle and equipment maintenance, solid waste management, liquid waste management, concrete waste management, contaminated soil management, sanitary/septic waste management, sandbag or gravel bag barrier, straw bale barrier, fiber rolls, check dam, hydroseeding/ handseeding, compaction, clear water diversion, material use, tire inspection and sediment removal, baseline stormwater drainage facilities inspection and cleaning and water conservation practices. [N]

Ditch Cleaning Practices

A summary of other state DOT environmental stewardship practices for ditch or swale cleaning are outlined below:

  • Maintenance ditch cleaning is only done in areas where the ditch's function is impaired. The ditch length, width and height should be dredged back to its original dimensions. At NYSDOT, ditches are mowed to control vegetation rather than mechanically cleaning ditches with heavy equipment because mowing causes less erosion of exposed soil and can result in improved water quality. [N]
  • In general, culverts and ditches are cleaned, repaired or replaced only during periods of low water flow and not during intense rainfall events
  • Dredging should be conducted during low water periods and during dry weather, avoiding rainfall events.
  • Evaluate and modify, where feasible and appropriate, existing ditch slopes to trap sediments, and support development of vegetation
  • Use best management practices identified in the local Integrated Vegetation Management plan.
  • All efforts should be made to retain existing vegetation, especially along the ditch slopes to maintain slope stability.
  • Consider excavating only the first three quarters of the ditch and retaining vegetation in the remainder. WSDOT assessed routine highway ditch cleaning alternatives or service levels for water quality benefits, surveyed biofiltration swales to evaluate conditions promoting water quality benefits, and assessed restabilization and revegetation options for use after ditch cleaning and for restoring biofiltration swale vegetation. Of the options explored, the study found the greatest water quality benefits when the first three quarters of the ditch were excavated and vegetation was retained in the remainder. The ditch treated in this manner was capable of reducing TSS by approximately 40 percent, total phosphorus by about 50 percent, and total and dissolved Cu and Zn each by roughly 20 to 25 percent. Analysis of survey data also showed that biofiltration swales with broad side slopes, wide bases, and total storage volumes equivalent to 3 inches of runoff from the impervious drainage area consistently supported good vegetation cover and showed few signs of damage. For assisting grass growth, straw held in place with stapled jute mat had a clear advantage in effectiveness over the alternatives and a slight economy advantage over the coconut mat. [N]
  • Dispose of removed material above the bank line and not in any waterway or wetland. Recycle excavated material when feasible.
  • Adequate siltation control measures should be in place before dredging operations begin. Use erosion control devices such as check dams, silt fences and other acceptable techniques, when the potential exists to have sediment or other materials enter a water of the State. Install check dams on steep slopes, as necessary, to slow water velocity reduce erosion and sedimentation. Consult with DOT Environmental Specialists if silt devices are inadequate to filter water prior to draining to watercourses.
  • When feasible, begin dredge at fixed flow elevation points (i.e. culvert inlets/outlets, catch basin inlets, etc.).
  • Cleaned ditches should be seeded and mulched at the end of each work day. Monitor daily for subsequent erosion until area is stable. Repair as necessary.
  • Temporary conveyances should be completely removed as soon as the surrounding drainage area has been stabilized or at the completion of construction.
  • The measure should be inspected after every storm and repairs made to the dike, flow channel and outlet, as necessary. Approximately once every week, whether a storm has occurred or not, the measure should be inspected and repairs made if needed. Damages caused by construction traffic or other activity must be repaired before the end of each working day.
  • Check the channel lining, embankments, and bed for erosion and accumulating debris and sediment buildup. Remove debris and repair linings and embankments as required.
  • If channelized flow is too strong for the surrounding environment, energy dissipaters may be needed. If vegetation or rock lined ditches reduces the ditch flow capacity, the road may be endangered. Native material curbs, or berms can be developed using a grader. Vegetating these berms will enhance the durability of these constructed features. Hardened curbs such as asphalt or concrete will require a construction crew and an engineer. The softest approach to developing vegetated ditches is to not heel or pull the ditch with a grader, except when absolutely necessary. Roadside ditches should be large enough, and have adequate relief drain spacing, to carry runoff from moderate storms. Ditch gradient between 2 and 8 percent slopes are usually better performers. Slopes greater than 8 percent provide runoff waters with too much momentum and erosive force and will require more ditch relief. Slopes of less than 2 percent drain water too slowly, or not at all.


10.11.2 Evaluating Ditches and Culverts for Water Quality and Function
< back to top >

DOTs track the need to maintain and replace culverts before they contribute to flood damage on roads and bridges. To do so, many state DOTs rely on time-consuming manual systems to record information on inventory, condition, and work needs. Other agencies have no formal system in place and consequently find themselves reacting to immediate or impending problems, rather than proactively managing maintenance and replacement.

Culvert Management Systems

To help agencies manage their culvert inventories, condition assessments, and improvement programs, FHWA developed a computer-based "Culvert Management System" under the Local Technical Assistance Program (LTAP). The system provides an automated tool to facilitate the coordination of culvert maintenance and replacement operations on a system-wide basis. With the software, state DOTs can create an inventory of their culverts, assess them, and schedule repairs and replacements. It also helps agencies to develop maintenance plans and to estimate costs for installing, repairing, or replacing culverts. The system consists of five modules, which an agency can phase in individually. The inventory module enables the agency to record information about each culvert under its jurisdiction, such as size and location, while the condition module maintains a record of each culvert's condition. The schedule module helps the agency develop a culvert work plan for the year. The work needs module enables the agency to define maintenance and rehabilitation options, determine costs, and rank work by type and priority. With the work funding module, agencies can project culvert deterioration over time and develop long-term work programs.

Drainage Ditch Evaluation

NYSDOT has developed the following rating system for drainage ditches and maintenance: [N]

  • 4 - Sides well shaped, clean, properly graded, smooth transition to inverts of culverts or drainage structures, environmentally friendly particularly in sensitive areas
  • 2- Slopes slightly oversteepened, minor erosion or material build-up around headwalls, end sections or structures, minor invert erosion, meets environmental guidelines
  • 0 - Slopes significantly oversteepened, significant vegetation impacting flow, standing water, significant erosion or material build-up around headwalls, end sections or structures, significant invert erosion, or one or more violations of the Department's environmental guidelines.

Mn/DOT developed a Ditch Stabilization Matrix that identifies appropriate BMPs to stabilize different kinds and lengths of slopes and ditches:

Figure 18 : Mn/DOT Ditch Stabilization Matrix with Recommended Treatment Methods

Mn/DOT Ditch Stabilization Matrix with Recommended Treatment Methods
*click image to see larger version

Evaluation of Other Drainage Structures

NYSDOT has developed the following rating system for other drainage structures and maintenance: [N]

Drainage Structures
  • 4 - Clean and in very good structural condition, frames and grates in very good condition, no erosion or material build-up, environmentally compatible
  • 2 - Some material present not affecting flow characteristics, some aging of structure or frame / grate - but not enough to pose structural problems, minimal scour or invert loss
  • 0 - Significant material build-up or erosion impacting flow, significant structural loss, frame / grate separated or missing, undermining of frame / grate
Closed Drainage System
  • 4 - Clean and in very good structural condition, inverts at structures in very good condition, no erosion or material build-up
  • 2 - Some material present not affecting flow characteristics, some aging of pipe, end sections or headwalls - but not enough to pose structural problems, minimal scour or invert loss
  • 0 - from structure
Litter and Debris
  • 4 - No appreciable litter present within segment
  • 2 - Small concentrations of litter or two or more pieces of large debris present
  • 0 - Significant concentrations of litter or debris exceeding 5 large pieces

NYSDOT developed an inspection form for open channels, as seen in the Appendix that also includes space to identify needed actions, further comments, etc.


10.11.3 Drain and Culvert Maintenance for Water Quality and Fish Passage
< back to top >

Drain and culvert maintenance includes the maintenance of under drains, horizontal drains, down drains, gutters, overside drains, scuppers and deck drains. Drains are maintained to prevent flooding and allow unobstructed flow. Subtasks include vehicle operation, cleaning (backhoe or Vactor TM may be used) and stockpiling and disposal of removed material.

  • Use water quality management practices to control potential pollutant sources such as disturbed soil, leaks and stockpiles create the possible pollutants of sediment, litter, fuel, hydraulic fluid and oil. Recommended environmental stewardship practices include: illicit connection/illicit discharge reporting and removal, scheduling and planning, illegal spill discharge control, vehicle and equipment fueling, vehicle and equipment maintenance, solid waste management, liquid waste management, concrete waste management, contaminated soil management, sanitary/septic waste management, sandbag or gravel bag barrier, straw bale barrier, fiber rolls, hydroseeding/handseeding, compaction, baseline stormwater drainage facilities inspection and cleaning and water conservation practices. [N]
  • Stenciling should be applied to urban drain inlets to discourage public dumping.
  • Litter is a high priority pollutant in some receiving waters and is a pollutant listed on the CWA Section 303(d) lists for receiving waters in a few areas. Storm drain inlets that contain 12 inches or more of accumulated material should be cleaned.
  • When Illicit Connection/Illicit Discharges are discovered, they should be referred to the District Maintenance or NPDES Stormwater Coordinator for initial investigation and reporting. Illegal dumping that may impact stormwater quality should be removed. All cleanup activities should be reported to the DOT or District Maintenance Stormwater Coordinator, as well as all illegal-dumping incidents found but not cleaned.

Drift removal is an aspect of culvert maintenance that involves either using boats to maneuver the drift, hydraulic tongs to reach over the side of the structure and dislodge the material, or pulling the drift from the side of the bridge (bank) and cutting it into pieces. Environmental stewardship practices for drift removal include:

  • Cut and turn drift to allow it to flow through and under the structure only where doing so would not endanger any other crossing structures downstream.
  • Repair and restore riparian areas temporarily impacted by machinery during drift removal. Coordinate long-term access for drift removal with the appropriate staff and agencies.

With regard to maintenance to ensure fish passage, post-construction evaluation of culvert improvements is important to assure the intended results are accomplished, and that mistakes are not repeated elsewhere. There are three parts to this evaluation: 1) Verify the culvert is installed in accordance with proper design and construction procedures. 2) Measure hydraulic conditions to assure that the stream meets these guidelines. 3) Perform biological assessment to confirm the hydraulic conditions are resulting in successful passage. Staff and resource agency biologists may assist in developing an evaluation plan to fit site-specific conditions and species. The goal is to generate feedback about which techniques are working well, and which require modification in the future. [N]

Any physical structure will continue to serve its intended use only if it is properly maintained. Hence the following practices should be employed.

  • Ensure timely inspection and removal of debris for culverts to continue to effectively move water, fish, sediment, and debris.
  • Inspect all culverts should be inspected at least annually to assure proper functioning. Summary reports should be completed annually for each crossing evaluated. An annual report should be compiled for all stream crossings and submitted to the resource agencies. A less frequent reporting schedule may be agreed upon for proven stream crossings. Any stream crossing failures or deficiencies discovered should be reported in the annual cycle and corrected promptly addressed.


10.11.4 Evaluating and Ranking Slope Stability and Chronic Environmental Deficiencies
< back to top >
Washington State DOT Chronic Environmental Deficiencies (CED ) Program & Rating to Prioritize Sites

Washington State (WSDOT)'s Unstable Slope Management System helps rate and prioritize problem slopes. WSDOT has also developed a Chronic Environmental Deficiencies (CED) Program with a rating form to prioritize sites. The agency performs detailed inventories of roadside problem areas and other routine roadside vegetation maintenance needs. Corrective action is implemented with secured funding.

WSDOT was the first agency in the United States to fully develop and implement an unstable slope management system (USMS), an internal WSDOT database and application designed for all participants in the unstable slope management process to view and enter data pertaining to their respective job functions. In addition, data from other WSDOT databases such as TARIS (traffic and accident data) can be downloaded automatically into the USMS database, while other information required by other WSDOT databases, such as PATS (Priority Array Tracking System) can be uploaded from the USMS database. WSDOT's system:

  • Rationally evaluates all known unstable slopes along WSDOT highway facilities utilizing a numerical rating system for both soil and rock instabilities.
  • Develops an unstable slope rank strategy, based on highway functional class that would address highway facilities with the greatest needs.
  • Provides for early unstable slope project scoping, conceptual designs for mitigation, and project cost estimates that could be used for cost benefit analysis.
  • Prioritizes the design and mitigation of unstable slope projects, statewide, based on the expected benefit.


10.11.5 Slope Repair Practices
< back to top >

Slope repair involves repairing water damage to roadway slopes, including import and shaping of material to restore slope and grade lines. In-water work can include replacement of riprap, rock or gabions which have been removed due to bank erosion. Slope repair may include repair of settlements/slide repairs done primarily when a road is in danger of collapse, and to forestall an emergency.

  • Avoid changes or increases in the material profile, whenever possible.
  • Place riprap within in-water work periods, in non-emergency situations.
  • Consider use of bioengineering solutions where practicable. Practicable use areas include areas not shaded by bridge elements, outside of the two-year flood plain where success is probable and safety of the structural elements are assured.
  • Coordinate any erosion repair activities (responses and cleanup of erosion problems, not the erosive action itself) which cause significant changes in the topography or vegetation within the riparian management area with DOT environmental staff and/or other regulating agencies. Also coordinate when placing riprap that is in addition to existing conditions and within the two-year floodplain of waters of the State.
  • Dispose of removed material at appropriate stable sites so the material will not be washed into wetlands or waterways.
  • Use erosion control methods in a timely manner, including seeding and mulching specific areas with non-invasive species, installing silt fences and installing other devices as appropriate.
  • Take precautionary measures on erodible areas (chicken wire, chain link, rock matting) where eroding areas are identified, and where precautionary measures can be successfully and safely applied.


< back to top >
Continue to Section 10.12 »
Table of Contents
Chapter 10
Roadside Management and Maintenance: Beyond Vegetation
10.1 Environmental Enhancement Practices and Partnership Efforts
10.2 Protection of Historic and Other Cultural Resources
10.3 Maintenance in Wetlands
10.4 Maintenance Near Waterbodies
10.5 Maintenance of Structures for Wildlife
10.6 Maintenance of Stormwater Facilities
10.7 Maintenance of Roadside Public Facilities
10.8 Management of Portable Sanitary/Septic Waste Systems
10.9 Maintenance of Shoulders and Roadway Appurtenances
10.10 Sweeping and Vacuuming of Roads, Decks, Water Quality Facilities, and Bridge Scuppers
10.11 Maintenance Stewardship Practices for Slopes, Drainage Ditches, Swales, and Diversions
10.12 Erosion and Sediment Control in Maintenance
10.13 Recycling in Roadside Maintenance Operations
10.14 Preserving Air Quality in Maintenance and Operations
10.15 Painting Operation Stormwater BMPs
10.16 Road Waste Management
10.17 Stockpiling, Spoil Disposal or Placement of Inert Fill
10.18 Maintenance of Soils
10.19 Emergency Actions
10.20 Field Review of Roadside Maintenance Operations
Lists: Examples | Tables | Figures
Website Problems Report content errors and/or website problems
PDF Document Download Adobe Acrobat Reader