Managing Environmental Impacts of Erosion and Sedimentation from Local Rural Roads in the Federal Aid Program Due to New Agricultural, Mining and Logging Economies
Over 3 years
Research Idea Scope
Many local rural roads were designed to provide land access, with little thought given to high traffic or heavy loadings. In some areas this includes higher classified “farm to market” or collector routes on which bridges and pavements were designed for infrequent heavy loading, even then only seeing those larger loads during harvest when roads were not subject to the effects of spring thaw. Even unpaved roads are seeing much heavier and more frequent heavy loadings in many rural areas with the advent of large livestock confinement operations, new biofuel plants, and wind power generation development.
The growth of ethanol plants, large livestock operations, wind farms and rural subdivisions is causing a change to traffic patterns and significant traffic growth in areas with roads that were designed for light traffic and infrequent heavy truck loads. Increasing demand for coal and aggregate has led to additional low volume road truck traffic demand for mining operations that are exploring new areas and deposits of needed material. Logging operations press new demands upon low volume roads as well with the increased demand for building materials sending timber companies into new areas. In addition to the increased weight of many of these loads, some of the vehicles using the roads are extremely long or wide in the case of wind farm development and the geometrics of roads last improved in the 1940-1960 period are not designed to accommodate their turning movements of very long or wide vehicles. In some states transportation patterns for grain are changing from going to elevators to going to ethanol plants.
The transportation infrastructure may be used differently than in the past such as: a) Going to different locations; b) Continuous grain, feed, or material movement throughout the year; or c) Different routes may be utilized than the historic “farm to market” or collector highway system. These factors have all lead to accelerated deterioration of road surfacing material and higher rates of sedimentation. Erosion (runoff) and sedimentation of and from local rural (low-volume) roads can adversely impact the environment. Many low-volume roads are soil or aggregate surfaced, have steeper grades than many paved roads, and are designed and maintained on narrower rights-of-way with steep fill slopes and back slopes and narrow or non-existent ditches. Runoff from rainfall can lead to erosion of the road surface or ditch bottoms. Drainage channels leading from the roads to nearby watercourses are receptors of soil and rock eroded from unsealed surfaces of these roads. Eroded sediments can adversely affect upland streams, damaging the aquatic ecosystem or increasing the risk of flooding. Low-volume roads can act as 4th order intermittent streams in times of high rainfall, and can significantly contribute to peak flows in higher order streams. When these roads are the receptors of agricultural runoff, roadside drainage is clogged, leading to road grade instability. Some agricultural runoff is contaminated with manure and/or chemicals, which can reach downstream receptors and/or kill roadside vegetation, thus exacerbating erosion problems within the right-of-way. Stream crossings may have been adequately designed to carry the hydraulic capacity, however, fish passage and debris flows are often a concern for embankment stability and species habitat. Not all roads, and not all segments of a given road, cause such problems. However, methods need to be developed to assist road planners and managers in identifying problem segments of roads and applying appropriate mitigation measures to those segments.
Objective The objectives of this research need are to develop simplified tools and procedures to:
- Measure offsite adverse impacts of runoff from low-volume rural roads, in particular erosion and sedimentation of adjacent drainage channels and watercourses.
- Assess adverse effects of agricultural runoff to roadside drainage ditches and subsequent problems created for downstream watercourses, roadbed stability, and roadside vegetation. (This includes concerns with disposal of the sediment excavated from the roadside when contaminated by manure and/or chemical runoff.)
- Identify critical parameters such as changing use patterns, heavier and wider truck loads, road layout and geometry, site soils and geology, regional rainfall intensity and frequency and inappropriate drainage design contributing to the problem(s).
- Develop tools for identifying problem segments of roads during planning and/or review stages.
- Identify cost-effective mitigation measures that rely on: (a) appropriate modifications to road siting, layout and design (b) structural and non-structural (bioengineering/ roadside vegetation management) measures to minimize the adverse impacts of road runoff and (c) traffic and pavement management systems for analyzing alternate route strategies.
Urgency and Payoff
Currently there is considerable public concern about the impacts of rural low-volume roads on the environment. Most of these roads are designed, constructed and maintained by local governmental agencies with partial federal funding. The public now expects these agencies to minimize the environmental impacts of such roads. There is much litigation and public debate concerning low-volume road environmental impacts. Thus, this problem has become a high priority for the general public. Road managers need the resources to address this problem. Environmental impacts related to water quality issues other than eroded sediment will likely be site-specific in nature and not warrant a national program. However, such problems may be locally severe and require local funding to be solved.
The primary individuals that could address this problem are county and state road engineers, Local Technology Assistance Program (LTAP) centers, university extension specialists and federal agency specialists, including the Federal Highway Administration, the Environmental Protection Agency and the U.S. Fish and Wildlife Service. Some cooperation has already begun between the federal agencies and universities on developing some of this technology. Effectiveness Society is very concerned about the environmental impacts of low-volume roads. This source of conflict could be reduced if road designers and managers could demonstrate environmental awareness and concerns, in planning, design, operations and monitoring.
With easily applied predictive tools road managers could determine the problem segments of low-volume roads and runoff and sedimentation from these roads would be significantly reduced. The monitoring program itself will provide measures of effectiveness for mitigation practices. For example, past work has shown that gravel can decrease road erosion by over 80 percent on some road segments but have little impact on other segments that may be far from watercourses. The ability to target problem sections, and to demonstrate the effectiveness of such targeting, will lead to reduced runoff and sedimentation problems and
TRB Committee on Low-Volume Roads, Michael T. Long, Chair, Oregon D.O.T. and Mark Nahra, County Engineer, Transportation Research Board, Telephone: 503-986-6935