Low-water crossings (LWCs) are roads over small creeks and streams and are designed to be overtopped by water during a high flow event. These LWCs are located on low-volume roads with fewer than 25 vehicles per day—typically access roads to farm fields. For these crossings, it is not necessary or feasible for the local highway department to install a bridge. Therefore, a LWC can be designed and constructed to provide a safe, economical, and environmentally friendly pathway to endure overtopping events.
Design guidelines for LWCs are not currently included in the Illinois Department of Transportation (IDOT) Local Roads Manual, which is used by local agencies in the construction of roads and bridges. The lack of design guidelines has made it difficult for local jurisdictions to determine the best location and method for installing a safe and effective LWC. In addition to addressing safety and traffic needs, LWCs should be environmentally friendly, maintaining the natural channel function and permitting water, sediment, debris, and wildlife to move freely through the crossing.
A research study was initiated by IDOT and conducted by the Illinois Center for Transportation (ICT) in collaboration with the U.S. Army Corps of Engineers’ Construction Engineering Research Laboratory (CERL) to identify best practices and guidelines for the safe, cost-effective, and environmentally friendly design of LWCs on low-traffic routes.
The research study, “Development of Low-Water Crossing Design Guidelines for Very Low ADT Routes in Illinois” (R27-148), was overseen by an IDOT Technical Review Panel chaired by Thomas Winkelman, Local Program Development Engineer at IDOT’s Bureau of Local Roads and Streets and co-chaired by Jayme Schiff, Engineer of Design at IDOT’s Bureau of Bridges and Structures. Professor Prasanta Kalita and Assistant Professor Rabin Bhattarai of the Department of Agricultural and Biological Engineering at the University of Illinois at Urbana-Champaign served as the project’s principal investigator and co-principal investigator, respectively. CERL Research Agronomist Heidi Howard and Agricultural Engineer Niels Svendsen also served as co-principal investigators.
According to Winkelman, “This project used other state DOT experience and Illinois-specific case studies to help develop design guidelines and identify policy implementation issues.” IDOT should be able to use these design guidelines to develop policy and design procedures for the implementation of low water crossings, says Winkelman.
The research team conducted several case studies and surveyed county engineers across the state as part of the project, which was initiated in January 2015 and completed in December 2016. This information provided an overview of the existing LWCs in Illinois and reflected the experience of local public agencies with LWC design, construction, and maintenance issues. The researchers developed a final report on commonly installed LWCs, site considerations, prevailing selection criteria, and signage requirements.
“The implementation of proper LWC design guidelines could save local agencies significant funding and provide better adaptability and storm-proofing characteristics, as well as reduce impacts to aquatic organism passage,” says Kalita.
The project’s final report, Development of Low-Water Crossing Design Guidelines for Very Low ADT Routes in Illinois, is available on ICT’s website.