Development of Alternative Desert Tortoise Crossing Criteria and Designs (NDOT 494-24-803)

The Nevada Department of Transportation (NDOT) maintains many hundreds of miles of highway in the habitat of the Mojave Desert tortoise, 450 miles of which are protected by tortoise exclusionary fencing. While the exclusionary fencing protects desert tortoises from highway mortality, it does not address the issue of habitat fragmentation, and in fact may add to the problem. Since exclusionary fencing restricts desert tortoise movement even further than the highway itself, it can inhibit or prevent access to seasonal resources, alter tortoise behavior, and can be detrimental to the larger population through reduced gene flow. In some areas, drainage culverts that pass under roadways have been retrofitted into desert tortoise crossings by connecting tortoise exclusionary fencing to the culvert wingwalls. Desert tortoises have been documented using some of these crossings. However, it appears that the design requirements of these drainage features, especially those in high-flow areas, commonly conflict with the movement abilities of the desert tortoise. Many of these culverts have large rocks (rip rap) placed at the openings to minimize the potential for erosion, but the large voids within the rip rap are a major obstacle for tortoise movement, an entrapment hazard, and have been known to cause mortality. NDOT maintenance has attempted to mitigate this issue by backfilling the rip rap with a mix of native gravel and soil. This has limited utility as it does well on flat terrain but is regularly carried away in steeper areas by the voluminous water flows commonly observed in desert flood events. The native soil must be replaced often, which is a burden for NDOT maintenance. Therefore, there is a need to develop criteria and plans for retrofitting culverts into desert tortoise crossings that can withstand multiple large hydraulic events while also being easily navigated by desert tortoises. The objectives of this research include: (1) Identify four culvert crossings along Nevada State Route 160 (SR 160) to evaluate and retrofit into desert tortoise culvert crossings with low maintenance requirements. (2) Obtain topographical surveys to develop creative designs, including engineered plans. (3) Produce one report for each crossing and one final report that provide details of the design efforts performed. The four culvert reports will focus on strengths and weaknesses of each and a design summary. (4) The final report will summarize the design effort, lessons learned, and considerations by each location on what works and what other entities have tried. The reports may include single-purpose crossing design success compared to dual-purpose crossing design. (5) Provide implementation-ready construction plans, specifications, and estimates. Will attempt to develop standard details, proposed designs, and treatment types as applicable and directed.

    Language

    • English

    Project

    • Status: Active
    • Funding: $289,801.00
    • Contract Numbers:

      494-24-803

    • Sponsor Organizations:

      Nevada Department of Transportation

      1263 South Stewart Street
      Carson City, NV  United States  89712

      Federal Highway Administration

      1200 New Jersey Avenue, SE
      Washington, DC  United States  20590
    • Managing Organizations:

      Nevada DOT Research

      1263 South Stewart St
      Carson City, Nevada  United States  89712
    • Project Managers:

      Holcomb, Kristi

      Ison, Mitch

    • Principal Investigators:

      Nussbaumer, Matthew

    • Start Date: 20250103
    • Expected Completion Date: 20260131
    • Actual Completion Date: 0

    Subject/Index Terms

    Filing Info

    • Accession Number: 01944756
    • Record Type: Research project
    • Source Agency: Nevada Department of Transportation
    • Contract Numbers: 494-24-803
    • Files: RIP, STATEDOT
    • Created Date: Jan 31 2025 6:06PM