Research Idea Details

Research Idea Scope

This research idea was developed as part of NCHRP Project 24-27(03) “Evaluation of Bridge-Scour Research: Geomorphic Processes and Predictions,” and addresses three Focus Areas (Environmental Considerations in Planning, Project Delivery/Streamlining, Wildlife and Ecosystems).  State Departments of Transportation (DOT) have numerous hydraulic design standards for bridges over waterways. These include flow frequency, road overtopping, deck freeboard, abutment setback, scour event, and scour check flood.  DOTs also have an obligation to meet regulatory requirements and obtain relevant permits and resource agency approvals for construction of bridges and countermeasures.  These requirements address potential impacts on flood insurance, flood hazards, navigation, water quality, environmental protection, and protection of fish and wildlife.  Agency involvement can include FHWA oversight, FEMA backwater and floodplain encroachment limits, local “no-rise” certification, local floodplain use permit, US Army Corps of Engineers (USACE) 404 permit, US Coast Guard (USCG) permit, and coordination and approvals from State environmental agencies, US Fish and Wildlife Service (USFWS), and National Oceanic and Atmospheric Administration (NOAA) Fisheries Service.  The permitting and approval process is often cited as a major impediment for efficient delivery of new bridges, bridge replacements, and countermeasures.Bridge hydraulic design focuses on hydraulic efficiency, which often involves minimizing the bridge length while not causing excessive backwater, velocity, scour and erosion.  Environmental agencies have additional concerns that include aquatic, riparian, and floodplain habitat, fish passage, and wildlife passage.  This project would focus on meeting the environmental concerns related to bridge design and construction with the goal of developing AASHTO model agreements that can be tailored by individual DOTs in coordination with State environmental agencies, NOAA Fisheries, and USFWS.  These agreements would establish performance criteria that, if met, would significantly streamline the agency approval process by directly addressing environmental concerns.  The criteria may include minimum setback distances between abutments and channel banks, requirements for clear spanning certain channels, limits on the location and number of piers in channels, constraints on exposed riprap aprons, limits on additional scour protection, minimum deck clearance for wildlife passage, and limits on increased velocities and shear stresses for frequent (2- to 10-year recurrence interval) flood conditions.

The proposed research has 4 objectives: (1) Contact State DOTs, USFWS, and NOAA Fisheries at national and regional levels and State environmental agencies to develop a list of environmental concerns specifically related to bridge hydraulic design (length, location, foundation locations, countermeasures, clearance, etc.). (2) Categorize the concerns based on environmental impact, bridge component, and regional or physiographic tendencies. (3) Develop rational, process-based criteria for addressing the concerns. (4) Develop model standards that address these concerns.  These standards could be adopted by DOTs or could serve as a starting point for individual DOTs to negotiate agreements for streamlining the permitting and approval process.  An example of this type of agreement is the fluvial performance standard, which is part of the Oregon DOT (2005) OTIA III State Bridge Delivery Program Environmental Performance Standards.  The fluvial performance standard is intended to allow normative physical processes within the stream-floodplain corridor that promote natural sediment transport, provide unaltered debris movement, and allow longitudinal continuity and connectivity of the stream and floodplain for fish and wildlife passage.

Urgency and Payoff

In addition to the benefits of streamlined permitting and reduced environmental impacts, there are other, long-term benefits that DOTs can expect from this research.  These include bridges with (1) fewer debris problems, (2) reduced scour, (3) fewer stream instability problems, (4) reduced long-term maintenance, (5) extended service life, (6) fewer stream instability and scour countermeasures, and (7) greater long-term resilience in the face of climate change.