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|Federal Highway Administration > Publications > Public Roads > Vol. 73 · No. 2 > National Highway Institute(NHI)|
Publication Number: FHWA-HRT-09-006
The National Highway Institute (NHI)
901 N. Stuart Street, Suite 300
Arlington, VA 22203
by Rachel Grant
Reducing the Impact of Roads On Stream Ecosystems
Building a roadway near a stream poses a variety of risks to the local ecosystem. Where a road alignment encroaches on the stream channel or its floodplain, construction can affect the availability and quality of the riparian habitat. Runoff from newly graded slopes and ditches can carry clay and silt into the stream, where it causes turbidity, which is dangerous to fish and can smother aquatic vegetation and invertebrate life. On the other hand, through erosion, scour, and flooding, rivers and streams can affect the safety and stability of roadway infrastructure.
"Where roads intersect rivers, they almost always interfere with the river's and the ecosystem's integrity," says Kevin Moody, an ecologist with the Federal Highway Administration's (FHWA) Resource Center in Atlanta. "Rivers adjust to road-related and other perturbations in ways that can threaten infrastructure like roads and other property."
Understanding how stream ecosystems work can help transportation professionals make better decisions during planning, construction, and maintenance to protect these sensitive environments--and ensure the long-term stability of the roadways and bridges themselves.
The National Highway Institute (NHI) offers a variety of courses designed to address the transportation industry's growing focus on reducing the environmental impacts of roadways. For example, NHI's course Managing Road Impacts on Stream Ecosystems: An Interdisciplinary Approach (FHWA-NHI-142048) examines how roadways affect stream ecosystems and underscores environmentally sound countermeasures that can minimize those impacts.
Mitigating Effects, Practical Solutions
Unlike roads and bridges, rivers and streams are nonstationary entities and can move in four dimensions: One is temporal (flow volumes change seasonally and due to weather events), and three are spatial (lateral or cross section, longitudinal or up- and downstream, and elevation or depth). Streams continuously change to flow more efficiently, which means they engage the entire landscape from all directions. Because streams interact with their environment from these four dimensions, the introduction of permanent, unyielding structures such as roads can result in undesirable effects on the ecosystem.
Because of technological developments, transportation professionals now are able to monitor the effects of roads on nearby stream ecosystems using electronic sensors and biological surveys. "The continued improvements in technology and computational capacity have enhanced our ability to understand the cause-and-effect relationships between roads and streams, and make our predictions much more robust than just 10-15 years ago," Moody says.
Managing Road Impacts on Stream Ecosystems introduces the basic concepts. The 3-day course highlights the physical and ecological characteristics of stream environments, examines the impacts of roadways, and discusses ways practitioners can avoid and limit adverse effects. For example, the course includes a strong focus on environmentally sound ways to guide a stream's flow and velocity, such as using root wads, stone weirs, or log cribs. These options, unlike traditional approaches such as concrete aprons, are more likely to maintain or restore the integrity and natural infrastructure of a stream.
About the Course
The course targets staff at FHWA, State departments of transportation, environmental resource agencies, and consultants involved in the design, construction, operation, and maintenance of roadway facilities. The training is intended to benefit engineers and environmental specialists involved in highway design, planning, and maintenance.
Through case examples and group discussions, participants have the opportunity to use critical thinking to develop solutions and identify preventive measures. The case studies feature lessons learned from around the country and include examples of both successful and failed attempts.
The most important thing that participants will take away from the course, according to Moody, is that all decisions regarding road and stream interaction must be context sensitive and made on a case-by-case basis. "There is no one-size-fits-all solution to managing road impacts on streams," Moody says.
Rachel Grant is a contractor for NHI.
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