--- title: a feature is not the floodplain canonical_url: https://ensurance.app/guide/a-feature-is-not-the-floodplain markdown_url: https://ensurance.app/guide/a-feature-is-not-the-floodplain.md subtitle: natural and nature-based features are line items. the floodplain is the living hold category: nature-finance --- # a feature is not the floodplain *natural and nature-based features are line items. the floodplain is the living hold* People type **natural and nature-based features** and get a line item. A flood-risk study scores a dune, a reef, a floodplain reconnection, a riparian buffer — and files them as **NNBF**. The word that does the damage is **feature**. The floodplain was already taking the river. The U.S. Army Corps of Engineers uses that phrase as civil-works feature language: landscape features used to provide engineering functions relevant to flood risk management, while producing additional economic, environmental, and social benefits. Those features may occur naturally, or be engineered, constructed, or restored to mimic natural conditions. That is the right door. A door on a sheet is still not the living hold behind it. :::johnson **a feature is a line item. the floodplain is the living hold.** Natural and nature-based features are how a civil-works sheet names a dune, a reef, a floodplain, or a riparian corridor. Naming it does not create it, and constructing a copy does not retire the living one. [what wetlands actually are →](/guide/what-wetlands-actually-are?from=guide) ::: ## what natural and nature-based features are **Natural and nature-based features** put a living landscape onto an alternative array. A **natural feature** is formed by natural processes. An existing dune ridge. A biogenic reef. A connected floodplain. A vegetated riparian corridor. Nobody poured it. It grew, migrated, and failed on its own terms, and it was already doing flood, water, or shoreline work before a planner scored it. A **nature-based feature** is engineered to mimic those processes. A constructed dune. A restored or modular reef. A living shoreline that combines vegetation with a low structure. A setback levee that reconnects overbank storage. Someone designed it, permitted it, and will one day close the construction account. Both sit on the same sheet as **features**. That is useful for a district that needs a scored option next to a levee. It is also the trap. A naturally occurring floodplain and a constructed wetland that mimics flood storage can share a heading. One is a living system with a history. The other is a project. Both can do flood work. Only one was already doing it before the alternative was drawn. An engineer should hear this as a scope cut, not a slight on NNBF. The Corps wrote the category so a living process could compete with gray on a study. A feature is still a planning object. The floodplain is still the living hold. ## what nnbf is on the sheet **NNBF** is the acronym. It means **natural and nature-based features**. It is how the method shows up as a row. **Engineering With Nature** is how a civil-works team designs *with* a living system. That method is [ewn is a method not a marsh](/guide/ewn-is-a-method-not-a-marsh?from=guide). This page stays on the feature language the method uses. **Natural infrastructure**, in the Corps dialect, is a procurement name for the living system already doing the work. That definition is [what natural infrastructure actually is](/guide/what-natural-infrastructure-actually-is?from=guide). A feature is one way that name appears on a sheet. The sheet is not the system. The 2015 Corps report on NNBF for coastal resilience is the engineering framework a lot of post-Sandy practice still cites — beaches, dunes, wetlands, islands, reefs, floodplains, riparian systems, living shorelines. The April 2024 civil-works memo put that family of measures on the planning array. A memo does not put a payroll on a marsh. Filing an existing floodplain as an NNBF alternative can be the right planning move. Treating the filing as if it *were* the floodplain is how a district selects a "natural" option and still loses the acre that was doing the work. ## dune, reef, floodplain, riparian Four objects. Each can appear as a natural feature, a nature-based feature, or both. A **dune** is a ridge of sand and vegetation that takes wave energy before a road or a levee has to. Wind and tide built it. It moves, and that movement is part of the work. A constructed dune is a nature-based feature: sand placed to a template, planted, sometimes fenced. The living dune field is the hold — sediment supply, vegetation, room to migrate. Starve any of those and the feature on the sheet is a pile that will not be there for the next storm. A **reef** breaks a wave, holds a shore, and grows habitat in the same water. An oyster reef or a coral reef accretes and changes roughness with the organisms that built it. An engineered reef module or a restored shell bed is a nature-based feature. It can mimic wave attenuation. It is still a project with a completion date. The biogenic reef is the hold — water quality, larval supply, the living matrix after the barge leaves. If the water you care about is a tidal basin, start with [what estuaries actually are](/guide/what-estuaries-actually-are?from=guide). A **floodplain** is the land a river still uses when it leaves the channel. It stores water, drops sediment, and gives the peak somewhere to go that is not a living room. A reconnection — a setback levee, a lowered berm, a controlled overflow — is a nature-based feature. It can be the right alternative. The floodplain is the living hold: the connected acre that stores the water this year, not the line that says "reconnect." [What wetlands actually are](/guide/what-wetlands-actually-are?from=guide) already defines that hydrologic object — a wetland is the floodplain that still works. A reconnection feature is not the wet acre. A **riparian corridor** is the vegetated strip along a bank — roots, shade, roughness, overbank storage. It holds soil, cools water, and slows what would otherwise scour a road or an intake. A bioengineered revetment or a specified buffer is a nature-based feature. The corridor is the living hold: continuity, age of the stand, connection to the floodplain. A utility should hear that as operating capacity, not a planting ceremony. | living hold | natural feature | nature-based feature | what the sheet still is not | |---|---|---|---| | **dune** | existing ridge taking wave energy | constructed, planted, or fenced dune | sediment supply and room to migrate | | **reef** | biogenic reef already breaking a wave | engineered module, restored shell bed | the living matrix after the barge leaves | | **floodplain** | connected overbank land storing a river | setback levee, floodplain lowering | the wet acre that still works | | **riparian** | vegetated corridor holding a bank | bioengineered revetment, specified buffer | continuity and condition along the reach | Four objects. One error: treating the right-hand columns as if they retired the left. Some of what these systems do is infrastructural. That does not make a living ridge a cheaper wall, and it does not make a floodplain's worth the capex of the gray thing beside it. ## how a feature is different from the floodplain The distinction is not poetry. It is what you can close out. | | feature on the sheet | living hold | |---|---|---| | **what it is** | a scored NNBF alternative — natural or nature-based | the dune, reef, floodplain, or riparian corridor already doing the work | | **where it lives** | on the alternative array, then the project sheet | on the landscape, named or not | | **if you stop** | the line item drops, or the project is marked complete | condition thins before anyone decommissions it | | **what success looks like** | selected, constructed, closed | still storing, breaking, holding, filtering this year | A gray project sits in a third column: levee, seawall, pump, hardened bank. Hybrid is ordinary Corps practice. The argument is narrower. Selecting an NNBF alternative is not the same as funding the living hold. Copying the floodplain in a design is not owning the floodplain. A constructed feature can become a living system if sediment keeps arriving, the connection stays open, and someone pays the condition after the ribbon. That second ticket is not automatic because the first said NNBF. A living shoreline stamped on a permit can still be a seawall with plants — [a living shoreline is not a seawall with plants](/guide/a-living-shoreline-is-not-a-seawall-with-plants?from=guide). The floodplain, dune, reef, and riparian corridor exist whether or not a civil-works alternative calls them natural infrastructure. **[*ensurance*](https://ensurance.app/?from=guide)** funds that living hold. It is not the USACE line item. ## who gets the bill when the sheet replaces the hold A government that funds the feature and not the hold has bought a completion date. The living system does not have one. Underfund the condition and the "natural" line item becomes a liability — a failed planting, a thinning marsh, a dune that no longer takes the wave. An insurer that treats a selected NNBF alternative as coastal protection already on the books is reading a study, not a shore. For a tidal edge, the claim is often a receipt for acres that used to hold the tide — [you don't have a surge problem. you have a missing marsh](/guide/you-dont-have-a-surge-problem-you-have-a-missing-marsh?from=guide). A utility that books a constructed wetland or a specified riparian buffer as source-watershed capacity still needs the living corridor and the connected floodplain. A CIP feature can be the right first move. It is not the operating system. Green, natural, nature-based, and living are procurement dialects for overlapping parts of one unpaid system — mapped in [four names, one unpaid system](/guide/green-natural-living-infrastructure?from=guide). This series enters through the Corps' feature language and stays on the object. Ownership, payors, and stewardship already live in [how to implement natural infrastructure](/guide/how-to-implement-natural-infrastructure?from=guide), which owns the head term. ## the unpaid job is still the living hold A civil-works ticket can mention nature and still hold concrete. The unpaid job is holding living condition after the alternative is selected. Insurance pays after a defined loss. Ensurance is built to fund present condition before the loss, on a named place. A **certificate** funds that living condition; a **coin** funds protection more broadly. Neither *is* the floodplain, and neither *is* the NNBF line item. Our stage, stated plainly: the instruments are live; the volumes are small. Districts that need a Corps-aligned project today should use the Corps. Nothing here asks you to wait for a substitute feature catalog. ## frequently asked questions ### what are natural and nature-based features? Natural and nature-based features are landscape features used to provide engineering functions — especially flood risk management — while also producing economic, environmental, or social benefits. A **natural feature** is formed by natural processes. A **nature-based feature** is engineered to mimic those processes. Both are civil-works feature language. Neither is, by itself, the living hold. ### what is nnbf? **NNBF** means **natural and nature-based features**. It is the acronym a Corps study uses when a dune, reef, floodplain, wetland, or riparian corridor appears as an alternative. Engineering With Nature is the method. NNBF is the line item. The floodplain is the living hold. ### is a dune a feature or a living system? Both, if you let the sheet collapse them. An existing dune field is a living system already taking wave energy. A constructed dune is a nature-based feature that mimics that work. Filing either as NNBF is a planning move. Treating the filing as the living ridge is the error. The same cut applies to a reef, a floodplain, and a riparian corridor. ### how is a feature different from the floodplain? A feature is a scored object on a civil-works sheet — selected, constructed, closed. A floodplain is the connected land a river still uses when it leaves the channel. Reconnecting a floodplain can be a nature-based feature. The wet acre that stores the water is the living hold. One can point at the other. They are not the same object. ## next Inland object: [what wetlands actually are](/guide/what-wetlands-actually-are?from=guide). Tidal room: [what estuaries actually are](/guide/what-estuaries-actually-are?from=guide). Surge receipt: [you don't have a surge problem. you have a missing marsh](/guide/you-dont-have-a-surge-problem-you-have-a-missing-marsh?from=guide). Corps name on the living system: [what natural infrastructure actually is](/guide/what-natural-infrastructure-actually-is?from=guide). ## the series Five posts. One spine: USACE says natural infrastructure / NNBF. That is a procurement name for a living system already doing flood, water, and shoreline work. A feature on a civil-works sheet is not the marsh. 1. [what natural infrastructure actually is](/guide/what-natural-infrastructure-actually-is?from=guide) — the living system, not a civil-works nickname 2. [ewn is a method not a marsh](/guide/ewn-is-a-method-not-a-marsh?from=guide) — Engineering With Nature is how you design with a living system 3. [a feature is not the floodplain](/guide/a-feature-is-not-the-floodplain?from=guide) — you are here 4. [natural infrastructure investment holds the living part](/guide/natural-infrastructure-investment-holds-the-living-part?from=guide) — a ticket can mention nature and still hold concrete 5. [who pays to keep natural infrastructure working](/guide/who-pays-to-keep-natural-infrastructure-working?from=guide) — a living system that does flood work still needs a payor after the ribbon Adjacent: [four names, one unpaid system](/guide/green-natural-living-infrastructure?from=guide), [how to implement natural infrastructure](/guide/how-to-implement-natural-infrastructure?from=guide). ## sources [Natural and Nature-Based Features — Engineering With Nature](https://ewn.erdc.dren.mil/natural-nature-based-features/) — NNBF as landscape features used for flood-risk functions; natural features versus constructed nature-based features [Bridges et al., Use of Natural and Nature-Based Features for Coastal Resilience (2015)](https://ewn.erdc.dren.mil/publications/archive/use-of-natural-and-nature-based-features-nnbf-for-coastal-resilience/) — coastal NNBF framework [USACE Engineering With Nature](https://ewn.erdc.dren.mil/) — Corps practice; public description of natural infrastructure and NNBF [Incorporation of Nature-Based Solutions in Civil Works Projects](https://api.army.mil/e2/c/downloads/2024/04/22/628c20e7/incorporation-of-nature-based-solutions-in-civil-works-projects.pdf) — Assistant Secretary of the Army for Civil Works, April 2024