Pennsylvania is home to more than 86,000 miles of streams and rivers, and over 75,000 miles of non-federal public roads which are owned by 2,500 local municipalities. This high density of streams and local roads creates an extensive network of stream culverts and bridges owned and maintained by a wide variety of entities. Unfortunately, a large percentage of these stream crossings, especially in rural areas, are inadequately sized for the streams they convey. Undersized crossings pose a host of problems for both the road and stream including channel erosion, road erosion, gravel aggradation, blockage of aquatic organism passage (AOP), road flooding, and even loss of structure.
Pennsylvania’s Dirt, Gravel, and Low Volume Road Maintenance Program (Program), provides $28 million annually in funding to public road owners to implement environmental improvements on unpaved and low volume paved roads. Starting in 2014, the Program increased its focus on stream crossing replacements, now funding approximately 100 replacements annually. Through the Program’s internal QAQC process it was determined that many stream crossing replacements were not meeting the goals of the program, including aquatic organism passage and stream channel continuity. Additionally, a Trout Unlimited (TU) study of 47 recently installed crossings found that 87% had reduced or no AOP as determined by the North Atlantic Aquatic Connectivity Collaborative crossing assessment protocol. The QAQC results coupled with the TU study identified the lack of a clear standard and design guidance as a major hurdle to successful projects. To address these concerns, an effort to define comprehensive standards and guidance was undertaken in 2021 leading to the Program’s new Stream Crossing Design and Installation Standard and accompanying Technical Manual adopted in July 2022.
Two of the biggest changes in the new standard are an increase the minimum structure size to >125% of the bankfull channel, and a requirement the structure pass the 100-year discharge (Q100) at 80 percent of the finished opening height. This allows for the construction of not only low-flow and bankfull channels and bank margins inside the structure, but additional flood capacity and increased resiliency of the structure. In addition, the following elements were added to ensure successful stream crossing replacement projects.
• Required longitudinal profile survey 150 feet upstream and downstream of the structure
• Streambed depth requirements in structures with bottoms
• Requiring bottomless structures over 4% stream slope
• Construction design plan requirements
• Increased oversight and inspection from engineers
• Engineer certification at completion
While there have been past issues resulting in less than desirable projects, the new standard and technical guidance should result in a higher number of successful stream crossing replacements. The experiences and lessons learned in Pennsylvania can benefit other entities as concerns about both aquatic organism passage and flood resilience in a changing climate gain traction across the United States.