New design standards for stream crossings to help mitigate pollution
by Mariah LucasThis article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility:
fact-checked
trusted source
proofread
Since 2001, the Center for Dirt and Gravel Road Studies, housed in the Larson Transportation Institute in the Penn State College of Engineering's Department of Civil and Environmental Engineering, has worked to reduce the environmental impact of public dirt and gravel roads and undersized bridges and culverts by contributing to the Pennsylvania State Conservation Commission's Dirt, Gravel, and Low Volume Road Maintenance Program (DGLVR).
Most recently, the research center worked with the U.S. Forest Service to develop standards to replace stream crossings in Pennsylvania. "Stream crossings" is an inclusive term describing the variety of crossings in the commonwealth, including bridges—which typically have two concrete abutments and a large span between them—and culverts, which are smaller than bridges and are built using a variety of materials, shapes and sizes.
Standardizing when stream crossings are replaced, as well as the materials and specifications used, can help reduce pollution caused by runoff from dirt and gravel roads, according to researchers at the center. The first few stream crossings designed with the DGLVR's new standards were completed this past summer.
Penn State News met with Steve Bloser, associate research professor and director of the Center for Dirt and Gravel Road Studies, to discuss the new standards as well as the center's ongoing efforts to reduce pollution in the commonwealth.
How do dirt and gravel roads, as well as undersized bridges and culverts, contribute to water and soil pollution?
Pennsylvania has a comprehensive network of over 120,000 miles of public roads and tens of thousands of road and stream crossings. These roads are spread across the landscape and can serve not only as a source of erosion, but also as collectors of runoff and pollutants from adjacent land that then funnel stormwater directly into local streams.
Much of the state's stream crossing network is severely undersized compared to the stream channels they are in, which causes problems such as erosion, fragmentation of stream habitat, excessive maintenance and even complete road washouts. These concerns are only exacerbated by the trends we are seeing of increasing rainfall frequency and intensity.
What are the new stream crossing design standards, and how did the center contribute to designing them?
This new stream crossing replacement standards put the focus on stream continuity through the road, which allows a stream to behave more like a natural channel in terms of slope, shape, size, composition and access to the floodplain. Compared to traditional methodologies, these new design standards install larger structures and utilize a natural stream bottom.
These standards also typically require additional work in the stream channel above, below and through the structure. This additional work is done in an attempt to mimic the natural stream channel through the entire crossing area, making it continuous through the road area in terms of slope, width, shape, and function.
Penn State spearheaded this effort with partners at Pennsylvania's Conservation Commission, Fish and Boat Commission and Department of Environmental Protection, as well as Trout Unlimited and others. These design standards currently only apply to the Dirt, Gravel, and Low Volume Roads Program and its $28 million annual state allocation, but we are working closely with other state agencies to promote the benefits of stream continuity and flood resiliency, which are at the heart of these standards.
Can you give an example of how the new stream crossing standards were applied to a recent project?
The 2024 construction season saw the first few projects being installed under the new standards, and the Polly Pine Road crossing in Hartley Township, Union County, was one of the first structures to be replaced. This township-owned road previously had twin four-foot-wide pipes channeling a 15-foot-wide stream. The twin pipes frequently clogged, and the road flooded during heavy rain events.
The pipes were replaced with a 22-foot-wide concrete box culvert that allowed a natural streambed to be rebuilt through the road for habitat connectivity, while greatly increasing the capacity of the crossing. This is a great example site, as just two weeks after installation, the site saw six-to-eight inches of rain from Hurricane Debby, a flooding event that would have previously overtopped the road.
Discover the latest in science, tech, and space with over 100,000 subscribers who rely on Phys.org for daily insights. Sign up for our free newsletter and get updates on breakthroughs, innovations, and research that matter—daily or weekly.
Subscribe
How does the center offer year-round assistance to the commonwealth's Dirt, Gravel, and Low Volume Roads Program?
Our center provides a wide range of education, training and over 300 annual on-site technical assistance visits to assist local public road-owning entities through the DGLVR Program. The center also provides training and assistance to Pennsylvania's 66 conservation districts that administer the DGLVR Program locally within each county.
The goal of the DGLVR Program is to implement projects that reduce environmental impacts from the road, while also reducing future maintenance needs and providing a more sustainable road.
What are the other research and outreach efforts of the center?
Most of the center's efforts focus on education, outreach and technical assistance for public entities throughout Pennsylvania. The center also collaborates with other universities and state partners in research efforts regarding dust control, road durability, culvert replacements and sediment reduction.
These research efforts are led by Eric Chase, assistant teaching professor and researcher with the Larson Transportation Institute, who teaches Rural Road Ecology and Maintenance, a popular course with engineering, environmental resource management and forestry students. Over time, the center has become a nationally and internationally recognized leader in rural road maintenance and environmental issues.
Provided by Pennsylvania State University