New guidance available soon to help communities reduce the risks of fluvial erosion hazards

Indiana’s cities and towns work hard to protect their communities from the hazards associated with flooding. They study flood maps and develop ordinances to limit the potentially devastating impacts that flooding can have on their residents. But, it’s not just floodwaters that are worrisome. Fluvial erosion – the erosion caused by flowing water and moving streams – can also be a big concern. Erosion and sedimentation are normal stream processes. However, during flood events, the high, fast moving water in a stream can scour away large sections of its bank, posing significant hazards to nearby structures and infrastructure such as roads, bridges or utilities – compromising their structural integrity and in some cases, washing them away.

Soon, Indiana communities will have a new tool in their toolbox of resources to support more comprehensive planning and mitigation of the hazards related to fluvial erosion. Christopher B. Burke Engineering, LLC (CBBEL), with assistance from Indiana University-Purdue University at Indianapolis’ (IUPUI) Center for Earth and Environmental Science (CEES), is developing the Indiana Fluvial Erosion Hazard (FEH) Mitigation Manual to offer municipalities, in vulnerable areas, new strategies for mitigating the risks associated with fluvial erosion hazards.

A new awareness of the hazards associated with fluvial erosion

The FEH Guidance Manual is part of a program initiated by the Indiana Silver Jackets – a group of federal, state, and regional agencies and universities working together to mitigate hazards associated with natural disasters. Funding for the program is provided by the Indiana Office of Community and Rural Affairs (OCRA), a long-time member of the Indiana Silver Jackets.  The FEH Program was initiated in response to the flooding of 2008, which resulted in widespread damage to homes, businesses, and critical infrastructure and one of the costliest natural disasters in Indiana history.  Fluvial erosion was a significant factor in the devastation, making it clear that a better understanding of FEH – where they exist and the threats they pose – was needed in order to better protect vulnerable areas.

Three members of the Indiana Silver Jackets – IUPUI CEES, the Polis Center at IUPUI, and the U.S. Geological Survey Indiana Water Science Center – have teamed up to implement the program in three phases:

Phase 1 – During the first phase of the program, the implementing team worked to develop tools that can be used to determine whether an area is vulnerable to fluvial erosion hazards. They also conducted outreach to introduce Indiana communities to FEH and help them better understand the associated risks.

Phase 2 – Using the tools developed in the first phase, the team identified FEH zones throughout the state and developed maps to show where areas of vulnerability are located.

Phase 3 – Now, for the third phase of the program, the FEH team has brought in CBBEL as part of the team to turn what they have learned about FEH in Indiana into actionable information that cities and towns can use to better protect their communities.

Jeff Fox, a water resources engineer with CBBEL, said the Indiana FEH Mitigation Manual will be geared toward local agencies and community officials, consultants, and state agencies and will contain the maps developed in the second phase of the project along with a set of recommended best practices that communities can use to mitigate their risk from FEH.

Putting best practices to the test

In addition to writing the book on fluvial erosion hazard mitigation in Indiana, Fox mentioned CBBEL will also be able to vet some of the mitigation practices in the manual prior to its release.  “We have the opportunity to work with a couple of communities dealing with fluvial erosion,” said Fox. “We’ll use these opportunities as pilot projects to show us how well the practices we’ve developed will work.”

One of the pilot projects will be located on an actively migrating stream that has caught the attention of a nearby community whose wellfield is used to draw water for public water supply.  The community’s concern is that if the stream continues to migrate, the functionality of the wellfield could potentially be compromised.  “This is a good site to acknowledge the natural fluvial processes that are going on and how they may be threatening a critical piece of a community’s infrastructure,” said Fox.

The other project will focus on a site where the stream’s fluvial processes are threatening the integrity of a portion of a highway embankment. Fox said the complexity of the site, with a highly mobile stream adjacent to a gravel pit on one side and a roadway on the other, makes it a great candidate for testing some of the practices developed for the manual.

Every site is unique

Fox said the Indiana FEH Mitigation Manual won’t provide a recipe for how to mitigate every hazard. Instead, it will offer a suite of options that a community can consider given its unique circumstances and resources. “Every site is going to be different,” said Fox. “The options in the manual will provide a starting point for communities to begin working on mitigation,” he said, adding that “they’ll still have to be evaluated by people who are doing the work and know the specifics of what they’re dealing with.”

Fox noted that mitigating FEH is a difficult science due to the natural dynamics of each individual stream. “There’s always the risk that the stream will respond differently than what you expect. A stream is a living thing in a way. When you do these projects, you try to take into account all the changes that might happen and hope that the measures create an impact immediately.”

“We didn’t want to rewrite the book on stream restoration” Fox said. “There’s already a lot of good information out there. So, our approach is to build on that. Specifically, we want to focus on how to identify the hazards and mitigate them.” The manual will include a number of different measures that communities can take to address different types of fluvial erosion hazards and will cite other relevant sources of useful information where possible.

The big picture

The concept of FEH seems to amplify the message, “Keep your structures and infrastructure out of the floodplain.” But, Fox said, “For many communities it comes back to the age-old question – what do you do to mitigate risk when you already have existing structures and infrastructure in a hazardous area? Is the answer always going to be the use of engineered controls over a naturally dynamic system? Is there a better way?”

That’s what Fox and the CBBEL team want to find out. “When it comes to hazard mitigation,” he said, “the main objective is always avoidance. The manual is really about what our options are when avoidance isn’t an option.”

Fox said that the maps developed for the FEH mitigation manual can be used with floodplain mapping to better assess flood-related risks. “They’re both critical tools in how we evaluate the areas adjacent to waterbodies. They show different pieces of the picture.” Fox explained that floodplain maps show the probable extent of inundation during the 100-year flood event while FEH zones illustrate the areas prone to natural stream erosion processes.  He noted that the FEH  zones add a new level of information that cities and towns can use to help evaluate their current risk and inform future development through flood resilience planning.

The Indiana FEH Mitigation Manual is expected to be finalized later this year, after the pilot projects are complete and will be rolled out through regional workshops to be held by IUPUI CEES to educate communities about FEH and introduce the tools and documents that are now available.