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U.S. Department of Transportation U.S. Department of Transportation Icon United States Department of Transportation United States Department of Transportation

Public Roads - Summer 2022

Summer 2022
Issue No:
Vol. 86 No. 2
Publication Number:
Table of Contents

Resources for Applying Resilience Concepts to Projects in River Environments

by Eric R. Brown, Laura Girard, and James Neighorn
"Aerial photo from a drone shows a road network, a bridge, railroad tracks, and commercial development in the floodplain of a river. The river has narrow tree-lined banks on both sides of its channel. Image Source: FHWA."
When in close proximity, rivers and roads interact in numerous ways, and frequently to the detriment of both natural and built environments.

A river presents a particular challenge for highway projects. Its complex natural conditions and functions vary with both time and location within the river corridor. Careful assessment and consideration of rivers is paramount for the safe, resilient, and ecologically sensitive planning, design, and operation of highways.

Federal, State, and local transportation project teams regularly build highway projects in river environments. To meet the needs of these diverse teams, FHWA is developing a variety of high-quality resources and engaging, interactive training—including online and instructor-led courses, immersive and virtual reality (VR) experiences, videos, and protocols—to help teams acquire the knowledge they need to be successful.

Waterway-Road Interactions and Resilient Design

Paul Wirfs, State hydraulic engineer for the Oregon Department of Transportation, has spent his career working on infrastructure projects. “It is vitally important to understand the dynamics of the natural and built environment,” says Wirfs. “Today’s hydraulic engineering professionals are challenged daily with balancing environmental and infrastructure considerations while also providing practical design solutions. The riverine environment must be treated like a living organism in order to provide resilient hydraulic engineering solutions.”

FHWA courses and related resources focus on core themes of river science. One prominent theme upholds that the preservation and enhancement of natural river functions may improve the resilience and sustainability of highway projects.

FHWA resources identify four primary, natural river functions as follows:

  1. Conveyance and storage of water, sediment, wood, and debris.
  2. Channel evolution, including side-to-side and vertical movements.
  3. Habitat within the channel, along the streambank (riparian) zones, and in the floodplain.
  4. Connectivity of the channel in the long-stream (direction of flow), lateral, and vertical directions.

The FHWA resources introduced in this article explain how project planning and design efforts that preserve and restore these river functions in a holistic manner may significantly reduce adverse interactions between rivers and infrastructure. Preserving natural river functions has many potential benefits, including lowered risk of roadway overtopping, less erosion and more stable stream banks, and reduced scour at bridge foundations.

"Table “Example Benefits of Preserving Natural River Functions”. Column Heads: Natural River Function; Description; Example Infrastructure Benefits by Preserving River Function. Row 1, Col. 1: Conveyance & storage (water, sediment, wood & debris). Col. 2: River channels move water, which carries sediment, wood, debris. Floodplains temporarily move & store water, sediment, wood during floods that crest channel banks. Col. 3: Maintaining channel & floodplain conveyance & storage may lower risks of bridges & culverts becoming plugged which could trigger roadway overtopping & other failures. Row 2, Col. 1: Evolution (changing location, planform shape, vertical profile). Col. 2: Natural rivers continually move from side-to-side (lateral migration) & adjust their bed elevations (aggradation is upward & degradation is downward movement) as soil is eroded in one location & deposited in another. Col. 3: Allowing for some space adjacent to existing channel for channel evolution to occur may avoid triggering unintended up- & downstream soil erosion & deposition resulting from infrastructure in & adjacent to channel. Row 3, Col. 1: Habitat (within channel, streambank riparian zone, floodplain). Col. 2: Vegetation, woody material, rocks, overhanging banks, other natural materials & features provide nutrients, shade, shelter, spawning areas to fish & other aquatic life. Col. 3: Natural habitat & features may promote stable stream banks, for example deep, dense root masses of vegetation hold soils in place. Stable vegetated banks have lower risk of erosion & movement. Row 4, Col. 1: Connectivity (long-stream, lateral, vertical). Col. 2: Rivers in natural conditions allow for movement of water, sediment, wood, nutrients, aquatic organisms up- & downstream (long-stream), into & out of floodplains (lateral), in & out of underlying aquifers (vertical). Col. 3: River connectivity allows flood flow energy to spread into floodplain, potentially lowering scour (erosion) potential at bridges & culverts. Image Source: FHWA."

Transportation Infrastructure and Aquatic Organism Passage

Another important theme covered by FHWA resources is Aquatic Organism Passage (AOP). Effective AOP (through stream reaches and bridge and culvert openings) relies on connectivity, and specifically long-stream connectivity. When bridges and culverts disrupt natural flow patterns, fish and other aquatic life may be cut off from large swaths of the habitat they use for spawning and feeding.

In the United States, restoring AOP at bridge and culvert locations is increasingly a priority, as evidenced by the proliferation of laws and regulations, design procedures, and increasing project expenditures aimed at improving ecological connectivity and restoring natural river conditions. Infrastructure owners and environmental agencies continue to seek improved AOP design approaches to road-stream crossings that produce measurable results.

Riverine Projects Require Multidisciplinary Teamwork

Highway projects in river environments require close collaboration among many offices, disciplines, and skill sets to realize successful outcomes. Multidisciplinary teamwork necessitates that project members with a wide range of experience and duties have knowledge of key river science vocabulary and concepts.

"A shaded, natural stream flowing through a forest. The stream bed is composed of various sizes of gravels, cobbles, and small boulders. Some tree branches are stored in the stream, and a large tree has fallen across the channel in the distance. The stream is bordered on the left and right by wooded streambanks. Image Source: FHWA."
Natural river functions include floodplain and long-stream connectivity, evolution, habitat, and conveyance and storage of water, wood, and sediment.

Greg Bergquist, environmental protection specialist with the FHWA Central Federal Lands Highway Division, recognizes how multidisciplinary teams develop holistic and resilient transportation projects, emphasizing the specialized knowledge required for river environments: “Understanding river and stream processes and considering how those processes affect the built environment are essential in the holistic design of transportation infrastructure in and around waterways.”

Bergquist notes teams that share a framework for understanding river functions can communicate and collaborate more effectively. “Interdisciplinary design teams can consistently assess the root causes of conflicts between infrastructure and the river environment by utilizing structured frameworks to evaluate river functions,” Berquist says. “These frameworks can foster opportunities for improved communication and collaboration in determining solutions that are both resilient and context sensitive.”

Engineers and environmental scientists may, through education and experience, be well equipped for working in and around river settings; however, other professions often lack the knowledge, tools, and confidence to practically apply key river science concepts to their projects. So how do transportation professionals new to river science and engineering get up to speed?

"These side-by-side photos were taken looking in the upstream direction and show two roadway culverts in a forest. One is a pipe culvert (circular shape) and the other is a box culvert. The culvert outlets, or downstream ends, each sit approximately two feet above the streambed. A small depth of water drops from the culvert outlets to the stream channel below. Image Source: FHWA."
These two “perched” (outlet higher than the streambed) culverts may act as barriers to AOP, thereby disrupting long-stream connectivity and habitat functions of a river or stream.  Fish trying to swim upstream would likely be unable to navigate the jump heights and the shallow water depths in the culverts.

FHWA Training and Resources

FHWA maintains an abundance of technical information and training resources related to river science and engineering, the majority of which may be accessed through the agency’s hydraulic engineering website ( The sheer volume of information may seem daunting to the inexperienced.

FHWA recognizes the specific needs of new learners. The Rivers and Roads (R&R) Connection initiative (introduced in the Autumn 2020 issue of Public Roads Magazine) is primed to help novices in river science and engineering quickly learn fundamental, practical knowledge and procedures.

A recently completed R&R product is the National Highway Institute (NHI) Web-based training course 135096, Roadway Interactions with Rivers and Floodplains: Basic Concepts. This free training introduces participants to river terminology and functions, river-infrastructure interactions, and resilient design in river environments.

A new FHWA technical manual, Hydraulic Engineering Circular 16 (HEC-16), Highways in the River Environment: Roads, Rivers, and Floodplains, Second Edition, will be available in fall 2022. Together, this new manual and course 135096 provide engaging entry points for learners with limited time and who may initially feel intimidated by river science. HEC-16 provides information for understanding, assessing, and addressing interactions between river functions and transportation infrastructure. The manual adopts a holistic assessment approach by illustrating not only the effects of rivers on roads and bridges, but also the effects of roads and bridges on rivers and their floodplains.

Instructor-led training course NHI 135097, Roadway Interactions with Rivers and Floodplains, is another companion course to HEC-16 that will be available in fall 2022. It provides overviews of the following topics:

  • Federal policy pertaining to highways in the river environment.
  • Concepts important for planning, design, construction, and maintenance of transportation infrastructure in river settings.
  • Practical tools in hydrology and hydraulics, fluvial geomorphology (i.e., river science), and sediment transport modeling.
  • River biology.
  • Specialty topics including flows at river confluences, ice flows, wood in rivers, human-generated debris, water quality, invasive species, beaver activity, mud and debris flows, alluvial fans, tidally influenced and tidally dominated rivers and streams, and inspection and monitoring.

HEC-16 and the two NHI courses constitute a “starter kit” for quickly training individuals in the basics of river science and engineering.

Field Scoping Videos

To complement the technical manual and courses, FHWA recently completed a series of five videos titled “Hydraulic Engineering: Field Scoping Videos” to help teams identify and categorize problems observed during project visits. The videos are intended to introduce good practices and procedures of project reconnaissance (such as visual field assessment, data collection, and data interpretation) necessary for the hydraulic design and maintenance of transportation infrastructure. The specific field scoping video topics cover bridges, river and stream channels, highway drainage (culverts, ditches, medians, pavements, and storm drains), drainage maintenance projects, and pre-field visit data collection. The videos are available at

"Drone photo looking down at an angle on the U.S. 101 bridge spanning the Elwha River in a heavily forested location. Rolling mountains are seen in the background. The flowing river water bends around a large point bar of sediment and then flows through the three spans of the bridge. Image Source: © 2021. Casey Kramer."
Large river crossings, such as the U.S. 101 bridge over the Elwha River in northern Washington State, present ideal opportunities to study river ecology, functions, and both positive and negative interactions with infrastructure.
"Screenshot from a virtual reality simulation shows a diorama (or three-dimensional model) of a long reach of the Elwha River in Washington State. The river reach lies within a valley between mountain ridges. Several locations in the diorama are labeled, coinciding with two dam removals, the U.S. 101 bridge, and other points of interest. Image Source: FHWA."
The Elwha River VR site visit provides workshop participants opportunities to explore several locations within the river to assess natural functions and changes resulting from two dam removals.

Elwha River Immersive Workshop

FHWA is also finalizing development of the one-day Stream Technology Immersive Learning Environment (STILE) workshop, currently scheduled for completion during summer 2022. This workshop will teach basics of river functions and river-road interactions through the use of a physical stream model (known as a stream table) and a VR site visit of a river crossing, the U.S. 101 bridge over the Elwha River in northern Washington State. To view a short stream table demonstration, please visit

The Elwha River offers an ideal learning environment to examine essential river system considerations and river-road interactions. Olympic National Park and the recently deconstructed Glines Canyon Dam lie upstream of the U.S. 101 bridge. Downstream of the crossing are the recently deconstructed Elwha Dam and the confluence with the Strait of Juan de Fuca.

The dam removals fostered the return of long-stream connectivity and salmon migration, sediment and wood conveyance, and habitat reestablishment. As natural river functions returned, flow conditions at the U.S. 101 bridge also changed. Through the VR experience, workshop participants will travel to the bridge site to explore river channel lowering, large wood material buildup at the bridge piers, and other results that necessitate actions by the bridge owner. They will also learn about tools and tips for conducting river assessments. The Elwha River VR site visit also touches on AOP, using salmon migration as an example.

AOP Monitoring Protocol

Another FHWA activity dives into the details and nuances of AOP.  To assess the effectiveness of culverts and bridges to pass aquatic organisms, FHWA Federal Lands Highway Division staff led an effort to develop a multi-stage AOP monitoring protocol. The protocol, which was field tested in 10 States, consists of a stream assessment based on observations and measurements by a multidisciplinary team of two or three trained staff (e.g., engineers and biologists) using available and easy to use tools. Required data includes channel and structure (bridge or culvert) geometry, slope, bed material composition, and features that may potentially limit passage. These data are collected in both up- and downstream channel reaches and within crossing structures.

"A bridge abutment in the foreground looking across the river. The bridge deck, railings, and piers are shown. At the upstream bases of the two bridge piers that are in the river, large branches and sediment have been deposited. Image Source: FHWA."
Large wood and sediment collect at the U.S. 101 bridge piers. Changes in any river system may alter local conditions at highways, bridges, and culverts, which may necessitate assessment and possible remediation by infrastructure owners.

The protocol developers created inspection forms compatible with mobile platforms and for use on tablets or phones. Future users may modify the forms to suit their specific needs. Use of readily available personal equipment and mobile devices with GPS capabilities allows teams to quickly and consistently complete multiple georeferenced inspections per day. Teams can upload data directly into their database and generate formatted reports.

Assessment team members can consolidate the collected information into a dataset to be used to identify sites with potential passage issues requiring either immediate action or a detailed analysis. Data may also be used to evaluate structure resiliency, life cycle costs, and other impacts to stream systems, and to inform improvements to design, construction, and maintenance practices.

“Although not typically part of the project delivery process, monitoring of various stream metrics is essential in understanding how a water crossing is achieving project goals and functioning over time. The FHWA AOP monitoring protocol is a great tool that that brings a multidisciplinary team together to assess how a crossing allows for the natural movement of water, sediment, and woody material, which is essential for maintaining natural processes and passage for various aquatic species,” says Casey Kramer, a civil engineer and codeveloper of the monitoring protocol. “With various geomorphic settings, species of interest, and acceptable risks to infrastructure, designing a water crossing that considers these and other metrics, on a project-by-project basis, is critical to achieve project goals and provide resilient transportation infrastructure to the traveling public.”

"A large corrugated metal culvert with a natural rock bottom. The culvert opening is approximately eighteen feet wide. A stream flows through the culvert and among the rocks. Two engineers are measuring and recording the flow depths along a line strung across the width of the culvert. The water depth is variable and the average depth is approximately six inches. Image Source: FHWA."
Using instructions provided by the FHWA AOP monitoring protocol, two engineers measure and record flow depths through a large culvert with a fish friendly natural rock bottom.

Looking Ahead

By using concepts presented by these resources and tools, design teams may enhance the resilient design and operation of transportation infrastructure in riverine settings. FHWA continues to develop resources for educating practitioners and students in the understanding, assessment, and application of natural river functions in their transportation projects. Planned future efforts include development of additional training resources and advanced assessment methods. For more information on R&R activities, please reach out to the authors or your FHWA hydraulic engineering point of contact.

"A gravelometer sitting on the coarse gravel and small cobbles of a riverbed. The gravelometer is a thin sheet of metal with square holes of various sizes cut out of it. This tool is used to measure the representative sizes of the gravels and cobbles that compose some riverbeds. Image Source: © 2021. Casey Kramer."
A gravelometer is used to measure the representative sizes of gravels and small cobbles found on river channel beds. Engineers use results of sediment analyses to inform project designs: for example, depths of bridge foundations.

Eric R. Brown, Ph.D., is a senior hydraulic engineer with the FHWA’s Office of Bridges and Structures, where he supports hydraulic engineering program areas. Dr. Brown holds a Ph.D. in civil engineering from Pennsylvania State University.

Laura Girard, P.E., MSCE, is a senior hydraulic engineer with the FHWA’s Resource Center, where she provides technical support on hydraulic design and modeling. Girard holds a M.S. in civil engineering from Colorado State University.

James Neighorn, P.E., is the hydraulic discipline champion with FHWA’s Office of Federal Lands Highway, where he supports the hydraulic discipline’s program and project delivery. Neighorn holds a B.S. in civil engineering from Oregon State University.

For more information, see or contact Eric R. Brown at 202–366–4598 or

FHWA Rivers and Roads Resources

FHWA’s latest learning resources:

  • Roadway Interactions with Rivers and Floodplains: Basic Concepts/135096: ( This free Web-based course from NHI presents fundamental river terminology and processes.
  • Roadway Interactions with Rivers and Floodplains/135097 (available fall 2022): This NHI three-day, instructor-led training targets all transportation professionals and emphasizes interdisciplinary and interagency collaboration.
  • A four-part Web-based training series (142081, 142082, 142083, and 142084) on resilient highway project development and design ( These free NHI Web-based courses can be completed as standalone training or in preparation for 142085.
  • Addressing Climate Resilience in Highway Project Development and Preliminary Design/142085 (available summer 2022). This course represents current understanding of the engineering approaches, and underlying physical relationships, on how extreme weather resilience can be incorporated into surface transportation project decisionmaking.
  • Highways in the River Environment: Roads, Rivers, and Floodplains/HEC-16 (available fall 2022): This reference manual presents practical planning, assessment, design and maintenance concepts, methods, and tools associated with river and road interactions.
  • Stream Technology Immersive Learning Experience (STILE) workshop (available fall 2022): This one-day workshop will feature hands-on activities with a physical stream model and a VR site visit to a major crossing of the Elwha River.
  • Field scoping/reconnaissance videos for bridges, river channels, culverts, and roadway drainage features (
  • Riverine Nature-Based Solutions (NBS) for Highway and Transportation Resilience: This white paper explores the use of riverine NBS in transportation projects and will inform the development of an implementation guide.
  • Written procedures and forms for conducting assessments of culverts designed for aquatic organism passage (available by request).

Please contact any of the authors to discuss these and related FHWA resources.