Reduce Flooding with Green

Community • Published on October 8

Mitigate Flooding with Green Infrastructure

The big picture

Downpours are getting heavier in much of the United States, which raises the odds of street flooding and rivers overtopping their banks. Observations show extreme single-day precipitation has risen notably since the 1980s, and heavy downpours have become more frequent and intense over roughly the last half-century. Environmental Protection Agency+1

As storms intensify, green infrastructure (GI)—the systems that capture, store, and soak in rain where it falls—helps communities handle water smarter, reduce damages, and stretch infrastructure dollars. The U.S. EPA highlights GI as a practical way to cut runoff, protect floodplains, and lower flood risk alongside conventional (“gray”) pipes and culverts.

What kinds of floods are we talking about?

  • Localized (urban) flooding: occurs when rainfall overwhelms streets and drains. GI slows and infiltrates water so pipes don’t surge and intersections don’t pond. 19january2017snapshot.epa.gov
  • Riverine flooding: occurs when rivers/streams exceed channel capacity. GI that protects and reconnects floodplains helps store water out of harm’s way and lower peaks downstream.

Looking toward the end of the century, more places are projected to be at risk, and annual U.S. flood damages are expected to rise—EPA’s summary points to an increase on the order of hundreds of millions of dollars per year (drawing on FEMA’s AECOM study and peer-reviewed work on future flood losses).


Using Green Infrastructure to Reduce Risk

1) Tackle localized flooding: absorb and detain

GI features that soak and store stormwater—such as rain gardens, bioswales, permeable pavements, and underground galleries—cut street ponding and reduce pollutant wash-off. Communities can quickly test “what-if” scenarios with EPA’s National Stormwater Calculator to estimate runoff and the benefit of different practices at a site or neighborhood scale. For deeper, program-level comparisons of cost and performance, use CLASIC (Community-enabled Lifecycle Analysis of Stormwater Infrastructure Costs). The Water Research Foundation+3Environmental Protection Agency+3swcweb.epa.gov+3

Real-world proof (St. Paul, MN):

The Arlington–Pascal project combined rain gardens, infiltration trenches, a large underground storage/infiltration facility, and a regional pond to solve chronic flooding near Como Lake. The green/hybrid solution eliminated the need for a $2.5M second storm pipe and delivered substantial water-quality and flood-reduction benefits at community scale. CRWD

EPA’s program page summarizes reported runoff reductions for the project’s components (e.g., high volume reductions from rain gardens, trenches, and underground storage), underscoring why GI can outperform an all-gray alternative in both function and cost.

2) Manage riverine flooding: protect floodplains

Pair GI with smart floodplain management. Conserving open space with water-absorbing soils in headwaters and along creeks reduces the volume/velocity of runoff that reaches rivers during storms—often at lower cost than expanding channels everywhere. GIS and hydraulic modeling help target the highest-value acres for conservation and quantify expected flood-damage reduction. Tools like CLASIC and the National Stormwater Calculator can incorporate future precipitation to stress-test plans. Environmental Protection Agency+1

Watershed-scale example (Milwaukee, WI):

The Greenseams® partnership has permanently protected ~5,000+ acres of flood-prone land since launch—now exceeding 5,800 acres by recent accounts—storing billions of gallons outside developed areas and reducing future flood peaks and pollutants. JSON Line+3The Conservation Fund+3MMSD+3

How to get started (practical steps)

  1. Screen sites: target parking lots, schools, and public parcels with good soils and limited utility conflicts for rain gardens, bioswales, and permeable retrofits; map repetitive nuisance flooding blocks first. 19january2017snapshot.epa.gov
  2. Model fast, then refine: use the National Stormwater Calculator for quick sizing; advance finalists into CLASIC to compare life-cycle cost, runoff reduction, and co-benefits against a gray baseline. Environmental Protection Agency+1
  3. Plan O&M up front: include media replacement, sediment forebays, vacuum-sweeping for permeable pavements, and seasonal vegetation care in budgets and maintenance contracts (state/municipal GI manuals provide frequencies). Environmental Protection Agency

Funding & policy snapshot (as of Oct 9, 2025)

  • FEMA Flood Mitigation Assistance (FMA): active; supports community-scale and property-level projects that reduce National Flood Insurance Program (NFIP) losses. Check your state hazard mitigation office for timelines. FEMA
  • FEMA BRIC (Building Resilient Infrastructure & Communities): FEMA announced termination in April 2025, but a federal court issued a preliminary injunction in August 2025 blocking diversion of BRIC funds while multistate litigation proceeds. Status remains unsettled; watch for court-driven updates before investing proposal effort. Congress.gov+2Reuters+2

Resources you can use today

  • EPA: Mitigate Flooding (GI hub)—overview, examples, and links to calculators and case studies. Environmental Protection Agency
  • National Stormwater Calculator (EPA)—estimate runoff & GI performance for a site. Environmental Protection Agency
  • CLASIC—compare green, gray, and hybrid options on cost, performance, and co-benefits; GIS-enabled. Environmental Protection Agency
  • Arlington–Pascal project (CRWD)—project overview, components, results, and avoided gray costs. CRWD
  • Greenseams® (Milwaukee/MMSD & The Conservation Fund)—watershed-scale land conservation for flood risk reduction. The Conservation Fund+1

References (selected)

  • Observed trends in heavy precipitation: EPA Climate Change Indicators — Heavy Precipitation (updated through 2023); NOAA Climate.gov explainers on intensifying downpours. Environmental Protection Agency+1
  • Projected flood risk & damages: FEMA/AECOM study on climate change & NFIP through 2100; Wobus et al., Journal of Flood Risk Management (national flood-damage projections under warming). scrcog.org+1
  • Case studies & tools: EPA GI Modeling Toolkit and calculators; CLASIC documentation and EPA feature; CRWD’s Arlington–Pascal project page. Environmental Protection Agency+2Environmental Protection Agency+2
  • Watershed land conservation: The Conservation Fund’s Greenseams summary; MMSD program metrics/updates. The Conservation Fund+1

What I verified or updated vs. your draft

  • The trend toward heavier downpours and the resulting flood risk increase is supported by EPA’s indicator set and NOAA’s reporting. Environmental Protection Agency+1
  • The $750 million figure for increased annual damages by 2100 is consistent with EPA’s page synthesizing FEMA/AECOM and peer-reviewed studies; I’ve cited the EPA page plus the underlying sources. Environmental Protection Agency+2scrcog.org+2
  • The Arlington–Pascal example and its avoided $2.5 M pipe are documented by the watershed district; EPA also summarizes performance outcomes for the component practices. CRWD+1
  • Greenseams acreage is verified across MMSD and Conservation Fund sources; figures have grown beyond 5,000 acres in recent reports. MMSD+1
  • Funding programs: FMA remains available; BRIC’s status changed in 2025 and is currently subject to an injunction—flagged so you don’t rely on an outdated assumption. FEMA+1