Protecting Natural Functions through Open Space, Green Infrastructure & No Adverse Impact (NAI)

Protecting Natural Functions through Open Space, Green Infrastructure & No Adverse Impact (NAI)

Knowing that floodplains store water, support wetlands, and recharge aquifers is only half of a CFM's job. The other half is implementing tools that keep those functions working as communities grow. Three complementary approaches dominate modern practice: open space preservation, green infrastructure / low-impact development (LID), and the ASFPM-promoted No Adverse Impact (NAI) floodplain management philosophy. Together they connect Chapter 8 science to ordinances, capital projects, CRS, mitigation grants, and professional ethics.

Open Space Preservation as Mitigation

Open space in the floodplain context means land kept free of intensive development so it can flood without damaging buildings or trapping people. Mechanisms include:

• Fee-simple acquisition / buyouts (often post-disaster or for repetitive-loss properties)
• Conservation easements and deed restrictions prohibiting fill and structures
• Cluster subdivisions that keep buildings on high ground and dedicate floodable lots as common open space
• Transfer of development rights and land-use plan designations (parks, greenways, agriculture)
• Setbacks and stream buffers that function as linear open space

Why open space is high-value mitigation:

CFM scenario: After three floods, a community acquires a cluster of slab-on-grade homes in the flood fringe, demolishes them, and deed-restricts the land as a riverside park with floodable trails and native plantings. Residual risk drops, storage returns, habitat improves, and the CRS coordinator documents the parcels for open space preservation credit—linking natural functions, mitigation, and insurance premium discounts for the whole community.

Critical documentation details CFMs must get right: clear title or enforceable easements, restrictions that survive land transfer, maintenance plans that do not reintroduce fill or enclosed buildings, and GIS layers that match the SFHA for CRS verification.

Green Infrastructure and Low-Impact Development

Green infrastructure and LID manage rainfall close to where it falls using soils, vegetation, and distributed storage rather than relying only on curb-and-pipe systems that dump peaks into channels.

Common tools at the stormwater–floodplain interface:

• Bioretention cells and rain gardens
• Permeable pavement
• Green roofs and cisterns
• Constructed wetlands and wet ponds designed with water-quality and peak-shaving goals
• Disconnected downspouts and conserved natural drainageways
• Riparian reforestation on previously mowed floodplain turf

How these tools support natural floodplain functions:

1. Reduce runoff volume and peak delivered to SFHA channels from upland development.
2. Improve water quality of water that does enter the floodplain (sediment and nutrient reduction).
3. Enhance recharge where soils allow infiltration without contaminating groundwater.
4. Create habitat patches that complement larger open-space corridors.

CFMs should coordinate with municipal stormwater (MS4) programs so floodplain ordinances and stormwater manuals do not work at cross-purposes—for example, requiring detention that is sited in the floodway without hydraulic analysis, or allowing pipe outfalls that destroy wetlands the floodplain program is trying to protect.

Green infrastructure is not a substitute for elevating buildings in the SFHA, but it is a powerful partner for residual risk reduction, especially in urbanizing watersheds where upland imperviousness is the primary driver of nuisance flooding and flashy peaks.

No Adverse Impact (NAI): ASFPM's Guiding Philosophy

No Adverse Impact (NAI) is an ASFPM-promoted floodplain management philosophy. In plain language: the action of one property owner or community should not adversely affect the flood risk of other property owners or the community at large. Adverse impacts include increased flood stages, velocities, erosion, sedimentation, drainage problems, and loss of natural beneficial functions that previously protected others.

NAI matters because minimum NFIP standards are necessary but not always sufficient:

• A project can meet BFE + freeboard and still remove storage that raises a neighbor's flood depth.
• Floodway no-rise protects the designated floodway under a specific model, but fringe fill, cumulative small projects, and upland runoff changes can still shift risk.
• Mapping lag means residual risk and future-conditions hydrology may not appear on today's FIRM.
• Ecological and water-quality damage may fall outside traditional building-code checks.

NAI operational tools (local higher standards and programs):

• Compensatory storage requirements for fill
• Zero-rise or reduced allowable surcharge floodways
• Cumulative substantial improvement tracking
• Prohibition or severe restriction of floodplain fill
• Future-conditions hydrology / climate-informed freeboard
• Downstream impact analysis for major projects
• Protection of wetlands, buffers, and open space as explicit ordinance purposes
• Stormwater standards that limit post-development peaks and volumes to pre-development levels

NAI is not anti-development. It is accountable development: build in ways that keep risk on the site that benefits from the development, rather than exporting it. That framing is politically useful when CFMs face pressure to "just issue the permit."

Connecting to Unified National Program Goals and CFM Ethics

The Unified National Program for Floodplain Management articulates goals that include reducing loss of life and property and preserving natural and beneficial floodplain functions. NAI, open space, and green infrastructure are how local programs turn those national goals into enforceable practice.

The ASFPM Code of Ethics requires CFMs to hold paramount the health, safety, and welfare of the public. Transferring flood damage onto downstream neighborhoods, approving cumulative fill that slowly eliminates community storage, or ignoring wetland and habitat duties all conflict with that ethical core—even if a checklist says "BFE met." Ethical practice means:

• Disclosing residual and transferred risk to decision-makers
• Recommending multi-objective alternatives (open space, elevated structures on open foundations, LID)
• Coordinating across floodplain, stormwater, wetland, and emergency management silos
• Continuing education on NAI tools and natural functions science

Putting It Together: A CFM Decision Sequence

When reviewing a significant floodplain or near-floodplain proposal, a practical sequence is:

1. Map and function inventory — SFHA/floodway, storage areas, wetlands, buffers, conveyance paths.
2. Regulatory floor — NFIP minimums, state standards, local higher standards.
3. NAI screen — Who else is affected in stage, velocity, drainage, or function loss?
4. Alternatives — Avoidance, redesign, compensatory storage, open-space set-aside, LID.
5. Other permits — Section 404, endangered species, stormwater, local land use.
6. Long-term stewardship — Deed restrictions, maintenance, CRS documentation if open space results.

Communities that master this sequence do more than pass audits—they keep the floodplain working as infrastructure. That is the essence of Chapter 8: natural and beneficial functions are not soft topics on the CFM blueprint; they are the landscape-scale systems that make every other chapter's maps, permits, insurance products, and mitigation grants more effective.