Nicole T. Carter and Eva Lipiec authored this CRS report (27 April 2020): 'Flood Risk Reduction from Natural and Nature-Based Features: Army Corps of Engineers Authorities'.
Be sure to check out the USACE's Engineering With Nature (EWN) Initiative site: click here (this may take time to load - here is the URL to paste in your browser: https://ewn.el.erdc.dren.mil/nnbf.html).
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Download CRS_Report_Flood_Risk_Reduct_Natural_USACE_27April2020
Summary
The U.S. Army Corps of Engineers (USACE) is the primary federal agency involved in federal construction to help reduce community flood risk. Congressional direction on USACE flood risk reduction activities has evolved from primarily supporting levees, dams, and engineered dunes and beaches. Since 1974, Congress has required that USACE evaluate nonstructural alternatives, such as elevation of structures and acquisition of floodplain lands, during its planning of projects. Since the mid-2010s, Congress also has directed the consideration of natural and nature-based features(NNBFs). Examples of potential NNBFs for reducing flood risk include wetlands; oyster, mussel, and coral reefs; and the combination of these natural features with hard components, such as rock and concrete. Various actors are shaping how USACE is incorporating NNBFs into its flood risk reduction projects and post-flood repair activities.
NNBFs in Flood Risk Reduction Projects
Congress specifically included NNBFs as a planning requirement for USACE flood risk reduction projects in 2016. In 2018, Congress required that USACE feasibility reports for flood risk reduction projects consider using traditional and natural infrastructure, alone or in conjunction with each other. In recent feasibility reports, USACE primarily has proposed using NNBFs (other than engineered dunes and beaches) in combination with traditional structural measures rather than having the NNBFs as the primary means for reducing flood risk. To be recommended for congressional construction authorization, a USACE flood risk reduction project generally must have national flood risk reduction benefits that exceed the project’s costs. Under current Administration guidance, USACE’s evaluation of NNBFs is tailored to each project (i.e., it is case-by- case rather than standardized).
NNBFs in Program to Repair Damaged Nonfederal Flood Control Works
In 1996, Congress amended USACE’s program to repair damage to certain nonfederal flood control works. Congress allowed for the program to fund nonstructural alternatives in lieu of USACE making repairs if a nonfederal entity requests and assumes responsibility for the nonstructural alternative. In 2016, Congress defined the program’s nonstructural alternatives to include restoring and protecting natural resources (e.g., floodplains, wetlands, and coasts), if those alternatives reduce flood risk. In practice, the program continues to predominantly repair the damaged flood control works. That is, there remain a limited number of nonfederal entities pursuing nonstructural alternatives under this program.
Identifying Challenges and Opportunities for NNBFs as Flood Risk Reduction Measures
Quantifying the effectiveness and reliability of NNBFs as flood risk reduction measures in different environmental conditions and for different floods and storms is an area of ongoing research. In some circumstances, NNBFs may provide flood risk reduction and a suite of environmental and social benefits. In other applications, NNBFs may be unable to replicate the level of flood risk reduction provided by traditional structural and nonstructural measures. Congress may consider the following issues for NNBFs in USACE flood risk reduction activities: knowledge gaps in measuring the benefits and limitations of NNBFs and the research to fill these gaps; how USACE processes account for NNBFs’ benefits, costs, and performance; and effects of agency practice, Administration guidance, and statutory authority on the consideration and adoption of NNBFs for flood risk reduction. Congress has requested two reports related to NNBFs from USACE. These reports, when available, may inform congressional deliberations on whether—and, if so, how—to support the use of NNBFs as part of USACE flood risk reduction efforts.
Cutting to the chase...
Conclusion
In 2010, USACE ramped up its efforts to identify opportunities to incorporate natural processes into its flood risk reduction activities with its Engineering With Nature initiative. Starting in the mid-2010s, Congress has authorized the consideration of NNBF alternatives in circumstances where NNBFs can reduce flood risk. The reliance on natural processes in NNBFs may provide flood resilience advantages compared with traditional structural measures or when used in combination with traditional structural measures. However, various challenges to the adoption of NNBFs as part of USACE projects remain.
Among recently completed feasibility reports, USACE has recommended a few flood risk reduction projects that use NNBFs. Typically, the recommendation is to use the NNBFs in combination with structural measures if the combined alternative can be economically justified.
The limited use of NNBFs in USACE flood risk reduction activities to date is shaped by various factors ranging from what is known about NNBF performance to how NNBFs are evaluated. In some circumstances, NNBFs may not be able to provide levels of flood risk reduction similar to traditional structural and nonstructural measures. In other circumstances, NNBFs may be able to reduce flood risks, but the ability to quantify the effectiveness and reliability of NNBFs as flood risk reduction measures in different environmental conditions and for different flood and storm conditions remains limited. In circumstances where NNBFs may be effective alone or in combination with traditional flood risk reduction measures, they can provide a suite of environmental and social benefits. The extent to which USACE considers NNBFs’ environmental and social benefits, as well as their flood risk reduction potential, in agency feasibility reports and their recommendations and in decisions on repairing damaged flood control works remains unclear. USACE’s evaluations and recent applications of NNBFs have raised questions about how environmental and social benefits are considered in USACE planning and the potential opportunities and limitations for USACE’s use of NNBFs.
Some questions related to NNBFs relevant to decisions about USACE authorities and policies include the following:
What are the remaining knowledge gaps regarding the benefits and limitations of NNBFs in flood risk reduction? What are the options for decisionmakers to direct USACE or other federal agencies to address these gaps or otherwise support research that addresses these gaps?
What is the impact of current decisionmaking processes on the accounting of NNBFs’ benefits, costs, and performance over time?
How do statutes, Administration guidance, and agency practice create disincentives and incentives for NNBF adoption for USACE and nonfederal project sponsors?
The congressionally directed reports discussed in the previous section may inform USACE decisionmakers’ and planners’ understanding of the circumstances in which use of NNBFs may be beneficial. They also may inform congressional deliberations on whether—and, if so, how—to support use of NNBFs as part of USACE flood risk reduction and resilience efforts.
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