International Guidelines on Natural and Nature-Based Features for Flood Risk Management

Figure 1.3. Spectrum of Sustainable FRM Systems Natural flood or erosion risk management

(Semi-) natural ecosystem Natural floodplain/ coastal zone (minimal intervention)

Soft engineering

Mitigated hard engineering

More natural

Managed realignment, upland grip blocking, remeandering

Floodplain connected with channel/sea with high degree of freedom. Erosion ongoing.

Less natural

Wet washlands, balancing ponds, regulated tidal exchange, swales

Floodplain connected with channel/sea with high degree of control. Erosion restricted.

Green roofs, permeable paving

Hard engineering

Heavily modified river or coastline Floodwalls, pump drainage, dry washlands

Floodplain disconnected from channel/sea, except in exceptional circumstances. Erosion prevented.

Source: Modified from Environment Agency 2010

The flexibility and adaptability of NNBF are useful for achieving flood resilience. All engineered FRM interventions and measures are dynamic—they change over time. Conventional structural measures deteriorate with age and can be damaged by storms. The same or similar processes affect NNBF. Consequently, all FRM measures require investments in monitoring and periodic maintenance. NNBF are predominantly made up of natural materials such as sediment, biomass (e.g., plants), and, to a lesser degree, rock. Therefore, it can be argued that NNBF are more dynamic than structural measures made of concrete, rock, and steel. However, the dynamism of NNBF also offers benefits. NNBF have the capacity for natural recovery and are inherently adaptable systems. Because the building blocks of NNBF are natural (e.g., sediments and plants), the environment itself is a source of natural resupply and repair. For example, existing or restored sediment transport processes could be sufficient to sustain a natural island or wetland that is providing FRM value. When a nature-based feature is designed and constructed in synchrony with local biophysical processes, its maintenance can be supported by ”mother nature.” At the risk of stating the obvious, human intervention is always required—usually at considerable cost—to repair levees and floodwalls.

01 | The Need and Opportunity for NNBF: An Introduction to the Guidelines

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International Guidelines on Natural and Nature-Based Features for Flood Risk Management

Published on Sep 16, 2021

US Army Engineer Research and Development Center

International Guidelines on Natural and Nature-Based Features for Flood Risk Management (NNBF Guidelines) is the product of a large-scale collaboration that included 5 years of working-level meetings and knowledge sharing involving key practice leaders from around the world. The project was initiated and led by the U.S. Army Corps of Engineers (USACE) as a part of its Engineering With Nature Initiative. USACE in the United States, the Rijkswaterstaat Ministry of Infrastructure and Water Management in the Netherlands, and the Environment Agency in the United Kingdom were the three primary government institutions that organized and led the effort. Many other organizations also provided critical leadership and participation, including the National Oceanic and Atmospheric Administration, World Bank, National Institute of Standards and Technology, The Nature Conservancy, and the World Wildlife Fund.