Determining the scales for NI to mitigate coastal and riverine flood risks
Project Overview
Traditional approaches to reducing the risk of coastal and riverine floods include the construction of conventional infrastructure (CI) such as levees and floodwalls. Over the last decade, there has been a push towards Engineering With Nature (EWN) and the use of natural infrastructure (NI) (wetlands, barrier islands, coastal dunes, forest, riparian buffers) into resiliency and risk management planning to reduce flood impacts rather than relying on gray infrastructure alone. However, the relevant spatial scales and dimensions of NI need to be assessed to maximize flood protection benefits for a range of flood hazards and related risks. The spatial scale refers to how large or small a NI project must be to be most effective. High-performance, high fidelity, computer models of coastal and riverine floods provide a means to develop strategic and controlled digital environments to test how different NI features, combinations, and their size can provide flood risk reduction.


As climate change causes an increase in adverse weather events, coastal communities around the world will face new challenges from flooding and storms. Our team is working hard to understand how best we can put tools like natural infrastructure to work for our communities.
objective
This project aims to answer the following questions:
1) Traditionally, what types of NI have been used to reduce coastal and riverine flooding?
2) What NI characteristics are important to reduce flooding for a range of flood magnitudes?
3) What non-local effects do NI have outside the immediate region?
4) How should NI be configured for optimal configuration, including hybrid solutions?
what we’re doing


methods
We plan to test how coastal and inland hazards respond to NI at various sizes and conditions through idealized numerical experiments. An idealized study allows controlled experiments to take place. For example, a single parameter can vary (tidal creek depth, for example) and we can assess how that change (different tidal creek depths) changes the system (change in water level or wave energy). In a similar way, we can vary channel sinuosity (curvature or bend), the height of the marsh surface, and marsh slope (how quickly does the marsh surface increase over a certain distance – think rise over run).
deliverables
We will identify recommendations for length-scaling needed to accomplish risk reduction goals using NI. Idealized coastal and fluvial model studies will be analyzed, as well as a “what if” scenario for the North Carolina OBX, and military bases.
How can riverine natural infrastructure benefit water quality?
Riverine natural infrastructure such as levee setbacks provide benefits beyond flood risk reduction, particularly for improving water quality. Reconnected floodplains can store and remove nutrients, sediment, and other pollutants, reducing pollution for downstream communities. When flows are slowed down and spread out, excess sediment can deposit in the floodplain. The slower flows also increase contact among the floodwater, soil, and vegetation. The floodplain vegetation can uptake and store the nutrients and pollutants, while microbial processes in the soil can permanently remove nutrients such as nitrogen via denitrification, thereby reducing algal blooms, improving drinking water treatment, and enhancing habitat for fish and other wildlife. We are planning to explore how natural infrastructure can be designed for water quality benefits, specifically studying how these benefits scale with different levee setback scenarios.

PUBLICATIONS
Re-imagining Infrastructure for a Biodiverse Future
van Rees, C.B., Hernandez-Abrams, D.D., Shudtz, M., Lammers, R., Byers, J., Bledsoe, B., Bilskie, M.V., Calabria, J., *Chambers, M., Dolatowski, E., Ferreira, S., Naslund, L., Nelson, D.R., Nibbelink. N., Suedel, B., Tritinger, A., Woodson, C.B., McKay, S.K., Wenger, S.J. (2023), Proceedings of the National Academy of Sciences (PNAS), 120(46).
Civil infrastructure will be essential to face the interlinked existential threats of climate change and rising resource demands while ensuring a livable Anthropocene for all. However, conventional infrastructure planning largely neglects the contributions and maintenance of Earth’s ecological life support systems, which provide irreplaceable services supporting human well-being. The stability and performance of these services depend on biodiversity, but conventional infrastructure practices, narrowly focused on controlling natural capital, have inadvertently degraded biodiversity while perpetuating social inequities. Here, we envision a new infrastructure paradigm wherein biodiversity and ecosystem services are a central objective of civil engineering. In particular, we reimagine infrastructure practice such that 1) ecosystem integrity and species conservation are explicit objectives from the outset of project planning; 2) infrastructure practices integrate biodiversity into diverse project portfolios along a spectrum from conventional to nature-based solutions and natural habitats; 3) ecosystem functions reinforce and enhance the performance and lifespan of infrastructure assets; and 4) civil engineering promotes environmental justice by counteracting legacies of social inequity in infrastructure development and nature conservation. This vision calls for a fundamental rethinking of the standards, practices, and mission of infrastructure development agencies and a broadening of scope for conservation science. We critically examine the legal and professional precedents for this paradigm shift, as well as the moral and economic imperatives for manifesting equitable infrastructure planning that mainstreams biodiversity and nature’s benefits to people. Finally, we set an applied research agenda for supporting this vision and highlight financial, professional, and policy pathways for achieving it.
The Effects of Coastal Marsh Geometry and Surge Scales on Water Level Attenuation
V.H. Hewageegana, M.V. Bilskie, C.B. Woodson, B.P. Bledsoe (2022), Ecological Engineering. https://doi.org/10.1016/j.ecoleng.2022.106813.
Coastal wetlands are an effective natural and nature-based feature to mitigate coastal flood hazards. While the sheltering and attenuation offered by wetlands are recognized, the protection level varies based on wetland and storm characteristics. Here we focus on the effects of the spatial scales of the coastal wetlands (i.e., channel geometry, marsh elevation-gradient) and the temporal scales of storm forcing (i.e., storm surge amplitude and duration) on peak water level attenuation. The study was conducted by performing hydrodynamic simulations on an idealized marsh geometry. One hundred seventy-one hydrodynamic simulations were conducted by varying wetland features under variable hydrodynamic forcing. Increased tidal channel area enhances water flow across marshes by reducing the capacity of vegetated platforms to resist propagation of a storm surge. The level of surge attenuation and channel area shows a non-linear relationship. Storm scales also affect surge attenuation for a given channel geometry. Higher amplitudes and lower surge durations provide greater attenuation of peak water levels. The level of attenuation and surge scales also show a non-linear correlation. A multivariate scaling relationship was developed that successfully integrates the combined effects of channel geometry and surge scales on water level attenuation by salt marsh. This research provides guidance to engineers and coastal managers on salt marsh’s flood hazard reduction benefits.
Engineering Coastal Structures to Centrally Embrace Biodiversity
B.C. Suedel, A.S. Tritinger, J. Calabria, M.V. Bilskie, J.E. Byers, K. Broich, S.K. McKay, C.B. Woodson (2022), Journal of Environmental Management, 323. doi:10.1016/j.jenvman.2022.116138.
Global environmental factors (e.g., extreme weather, climate action failure, natural disasters, human environmental damage) increasingly threaten coastal communities. Shorelines are often hardened (seawalls, bulkheads) to prevent flooding and erosion and protect coastal communities. However, hardened shorelines lead to environmental degradation and biodiversity loss. Developmental pressures that are growing in scale, scope, and complexity necessitate the development of sustainable solutions to work with, rather than against, nature. Such nature-based solutions (NBS) provide protection and improve environmental quality and enhance biodiversity. To further this pressing need into action, the US Army Corps of Engineers (USACE) began the Engineering With Nature (EWN) initiative to balance economic, environmental, and social benefits through collaboration with partners and stakeholders. This work shows how engineering practice can be advanced through structured decision-making and landscape architecture renderings that include ecological sciences and NBS into an integrated approach for enhancing biodiversity in coastal marine environments. This integrated approach can be applied when designing new infrastructure projects or modifying or repairing existing infrastructure. To help communicate designs incorporating NBS, drawings, and renderings showcasing EWN concepts can aid decision-making. Our experiences with implementing EWN in practice have revealed that involving landscape architects can play a crucial role in successful collaboration and lead to solutions that protect coastal communities while preserving or enhancing biodiversity.
Meet the Team
This project is a collaborative effort through the Network for Engineering With Nature. UGA’s Institute for Resilient Infrastructure Systems and the U.S. Army Corps of Engineers established N-EWN in 2020 to work together to address the major infrastructure challenges facing our society while creating opportunities that align ecological, social and engineering processes to achieve multiple societal benefits. Funding from this work is provided by the US Department of Army (Sponsor Award #W912HZ2020031).


Matt Bilskie, Ph.D. Associate Professor, College of Engineering

Brian Bledsoe, Ph.D. Director, IRIS

Brock Woodson, Ph.D. Associate Director of Engineering and Natural Sciences, IRIS

Rhett Jackson, Ph.D., P.E. Professor of Water Resources, Warnell School of Forestry and Natural Resources

Aditya Gupta, Ph.D. Research Scientist, IRIS

Matt Chambers, Ph.D. Research Professional, College of Engineering

Rebecca Stanley PhD Student, College of Engineering
Several IRIS alumni also contributed to this project:
Rod Lammers, Ph.D.
Daniel Buhr, Ph.D.
Hithaishi Wewageegana, Ph.D.
Sheppard Medlin


Amanda Tritinger, Ph.D., P.E. Deputy Program Manager, USACE Engineering With Nature Program

Candice Piercy, Ph.D. Research Environmental Engineer, USACE ERDC

Dave Smith, Ph.D. Research Ecologist, USACE ERDC