SJRWMD • SFWMD • SWFWMD Permit Requirements
& FL Drainage Contractor Guide
Permit assessment loading...
FL Water Management Districts regulate total impervious surface percentage on any developed parcel. If your project adds concrete, pavers, or other hardscape as part of a full stormwater system, the cumulative impervious percentage of your lot may trigger a formal stormwater permit — even if the drainage installation alone would not. Miami-Dade County limits residential lots to 35-50% impervious coverage; most WMDs use similar thresholds. Have a drainage engineer calculate your existing impervious percentage before adding hardscape.
Properties with documented, permitted stormwater management systems may qualify for NFIP (National Flood Insurance Program) premium reductions through FEMA's Community Rating System (CRS). Over 150 FL communities participate in CRS, offering flood insurance discounts of 5–45% to policyholders. A permitted French drain or stormwater system — when combined with your municipality's CRS score — can directly reduce your annual NFIP premium by hundreds of dollars. Ask your contractor to provide a letter of completion for your insurance file; some FL insurers also offer private flood policy discounts for documented stormwater improvements.
A soil percolation ("perc") test is strongly recommended before finalizing any drainage design in Florida. FL's soil variability is extreme — a single property in Miami-Dade can have sandy topsoil, hardpan 18" down, and oolitic limestone 36" down, each requiring a different drainage approach. Perc tests typically cost $150–$400 and take 2–4 hours. Results directly affect pipe sizing, aggregate depth, and dry well dimensions. Without a perc test, contractors may significantly under- or over-engineer your system — in FL's challenging soil environments, this mistake can cost $5,000–$20,000 in retrofit work. Always require a perc test for systems over $3,000.
Florida has five regional Water Management Districts (WMDs) that regulate stormwater management: SFWMD (South FL), SJRWMD (St. Johns River), SWFWMD (Southwest FL), NWFWMD (Northwest FL), and SRWMD (Suwannee River). Any project that disturbs more than 1 acre of land, creates more than a specified amount of new impervious surface (varies by WMD — often 1 acre), or involves construction in a floodplain requires an Environmental Resource Permit (ERP) from the applicable WMD. Residential drainage improvements under these thresholds typically fall under local county/municipal jurisdiction only. Always determine your WMD before planning a drainage project — violations can result in restoration orders and fines up to $10,000/day under Florida Statutes Chapter 373.
While the Florida Building Code doesn't specify French drain design standards directly, all grading and drainage work that directs water onto neighboring properties or into roads is regulated under FL common law nuisance doctrine (riparian rights) and local county ordinances. Most FL counties prohibit any grading that increases stormwater runoff onto adjacent properties — doing so can create civil liability regardless of whether permits were pulled. Drainage improvements must be designed to handle at minimum the 25-year, 24-hour storm event per most FL county land development regulations. Miami-Dade, Broward, and Palm Beach counties have particularly strict drainage requirements tied to their South FL Water Management District rules and the C-51 (West Palm Beach) / C-9 (Miami) basin management plans. Violation of local drainage codes can result in stop-work orders, mandatory demolition, and fines of $250–$1,000 per day in most FL jurisdictions.
Florida has more FEMA Special Flood Hazard Area (SFHA) properties than any other state — over 1.7 million insured properties under the National Flood Insurance Program (NFIP). Installing a permitted stormwater management system can qualify your property for FEMA Letter of Map Amendment (LOMA) or Letter of Map Revision (LOMR) review, potentially removing it from a high-risk flood zone and reducing mandatory NFIP flood insurance premiums, which average $1,000–$2,000 per year in FL. Communities enrolled in FEMA's Community Rating System (CRS) offer additional discounts of 5–45% on NFIP premiums for properties that document proper stormwater management practices. A drainage improvement with documented flood mitigation benefits — especially in Zones AE, VE, or X500 — can be one of the most financially impactful home improvements possible in Florida, with premium savings that pay back installation costs within 3–7 years.
Florida Statute 489 requires a licensed contractor for drainage work that involves plumbing connections, excavation over specified depths, or structural components. Connecting any drainage system to a storm sewer, public right-of-way drain, or ditch regulated by a local drainage district requires a licensed plumbing contractor (CFC license) and a public works permit from your county or municipality. Yard grading and French drain installation that doesn't connect to public infrastructure may be performed by a licensed general contractor (CGC) or landscape contractor (LSCAPER) in some FL counties — but requirements vary significantly. Unpermitted drainage work that requires a licensed contractor is considered unlicensed contracting in FL, which is a second-degree misdemeanor. Enforcement has increased significantly post-Hurricane Ian and Idalia as FL counties tighten drainage compliance — always verify contractor licensing at MyFloridaLicense.com before hiring.
Florida has extensive jurisdictional wetlands regulated by both the Florida Department of Environmental Protection (FDEP) and the Army Corps of Engineers under Section 404 of the Clean Water Act. Installing drainage systems near wetlands — even if the wetland appears to be a dry retention area during drought conditions — can require a separate wetland permit with mitigation requirements costing $5,000–$50,000+. A 25-foot minimum buffer from wetland edges is required by most FL WMDs for construction activities; Miami-Dade and Broward counties impose 25–50 foot buffers depending on wetland classification. FL DEP's Environmental Resource Permit (ERP) program reviews all drainage projects in or near wetlands, and unpermitted work can result in mandatory restoration orders — always conduct a wetland delineation survey ($500–$2,000) before beginning any grading work on properties adjacent to natural areas, canals, or retention ponds.
FL homeowners in HOA communities must obtain board approval for any grading, drainage, or landscaping changes that materially alter the property's exterior appearance or drainage pattern, as required under FL Statute 720 (Homeowners' Association Act). Many FL HOA architectural review committees (ARCs) require a drainage plan stamped by a licensed engineer (PE) before approving French drain or catch basin installations — even for entirely underground systems. Shared drainage easements, which are common in FL planned communities and PUDs, require written consent from all easement holders before any work — this can include neighbors, the HOA board, and local drainage districts. Violation of HOA drainage rules can result in daily fines of $100–$500, mandatory restoration at the homeowner's expense, and compounding legal fees — all while the original drainage problem persists. Get written HOA approval before signing any contractor agreement.
Following the unprecedented flooding from Hurricanes Ian (2022) and Idalia (2023), FEMA allocated over $3.5 billion in Florida for flood mitigation programs including HMGP (Hazard Mitigation Grant Program) and BRIC (Building Resilient Infrastructure and Communities). FL homeowners in declared disaster counties may qualify for HMGP grants covering up to 75% of eligible flood mitigation costs — including stormwater management improvements, elevation of utilities, and drainage infrastructure — with the remaining 25% covered by the homeowner. Applications are administered through FL Division of Emergency Management (FDEM) at floridadisaster.org and local county emergency management offices. Property owners in Tier 1 flood-risk zones who completed permitted drainage improvements post-disaster may also qualify for FEMA Increased Cost of Compliance (ICC) coverage up to $30,000. Contact your county emergency management office to determine if your property is in an active grant cycle — funding windows are limited and applications are competitive.
| System | Best For | FL Soil Compat. | Install Depth | Typical Life | Maintenance | Cost/Linear Ft | Permit Usually? |
|---|---|---|---|---|---|---|---|
| French Drain (perf pipe) | Subsurface water, foundation drainage, soggy yards | Sandy/loam (excellent); poor in muck | 18"–48" | 25–40 yrs | Low — flush every 3–5 yrs | $25–$65/ft | Rarely (small scale) |
| French Drain (fabric sock) | Fine-sand FL soils prone to pipe clogging | Best in fine FL sand; prevents migration | 18"–36" | 15–25 yrs | Low-Med — sock clogs faster | $28–$70/ft | Rarely (small scale) |
| Catch Basin / Area Drain | Low spots, pool decks, driveway ponding | All FL soils — surface collection only | 24"–48" (basin) | 30–50 yrs | Low — clean debris yearly | $800–$2,500/basin | If connecting to city storm |
| Channel / Trench Drain | Driveways, patios, garage aprons, pool areas | Works in any soil — surface only | 4"–12" (channel) | 20–40 yrs | Low — clear grates seasonally | $40–$100/ft installed | Sometimes (hardscape tie-in) |
| Dry Well / Soakage Pit | Downspout discharge, isolated ponding, limited space | Excellent in FL sandy; poor in muck/rock | 36"–84" | 20–30 yrs | Med — inspect for compaction | $1,500–$5,000/unit | Rarely if under volume threshold |
| Swale Regrading | Positive grade away from structures, neighborhood swales | All FL soils with proper seed/sod | Surface only | Indefinite (maintained) | Med — re-sod 2–3 yrs | $3–$12/sq ft | Rarely (unless near roads) |
| Retention Pond | Large lots, HOA common areas, commercial | All FL soils — engineered liner if needed | 4'–12' deep | 50+ yrs | High — aquatic vegetation control | $15–$50k+ | Yes — WMD ERP required |
| Rain Garden / Bioswale | Eco-friendly, utility-visible areas, front yards | Sandy to sandy-loam FL soils best | 12"–24" | 10–20 yrs | Med — planting management | $8–$25/sq ft | Rarely |
| Underground Cistern | Water reuse, irrigation storage, green building | Works in all FL soils with proper base | 36"–72" | 30–50 yrs | Low — inspect annually | $5–$20k/unit | Sometimes (water reuse permit) |
| Permeable Pavement | Driveways, parking, replacing impervious surface | Best over FL sandy soils; poor over hardpan | Pavement + 12"–24" base | 15–25 yrs | High — vacuum sweeping required | $8–$20/sq ft | Yes if large-scale |
| WMD / Agency | Counties Covered | ERP Threshold (Impervious) | Small-Scale Threshold | Processing Time | Contact | Post-Ian Update |
|---|---|---|---|---|---|---|
| SFWMD South FL WMD | Miami-Dade, Broward, Palm Beach, Martin, St. Lucie, Indian River, Okeechobee, Glades, Hendry, Collier, Lee, Charlotte, Sarasota | >1 acre impervious OR >1 acre land disturbance | General Permit for <1 acre residential; verify per basin | 90–120 days (ERP); 30 days (GP) | sfwmd.gov / (800) 432-2045 | C-43 reservoir basin projects expedited; Charlotte/Lee post-Ian streamlined GP processing |
| SJRWMD St. Johns River WMD | Duval, Clay, St. Johns, Flagler, Volusia, Brevard, Indian River, Okeechobee, Orange, Osceola, Polk, Lake, Putnam, Marion, Alachua, Levy, Columbia | >1 acre land disturbance or new impervious | General Permit available for most residential <1 acre | 60–90 days (ERP); 21 days (GP) | sjrwmd.com / (386) 329-4500 | Expanded BMAP (Basin Management Action Plan) compliance areas post-2023 flood events |
| SWFWMD Southwest FL WMD | Hillsborough, Pinellas, Pasco, Hernando, Citrus, Sumter, Lake (partial), Sarasota (partial), Manatee, Hardee, Highlands (partial), Polk (partial) | >1 acre impervious; lower thresholds near Outstanding Waters | Noticed General Permit for residential ≤1 acre | 60 days (ERP); 14–21 days (NGP) | watermatters.org / (352) 796-7211 | Tampa Bay post-Idalia surge — new swale and inlet requirements for coastal Pasco/Hernando |
| NWFWMD Northwest FL WMD | Escambia, Santa Rosa, Okaloosa, Walton, Holmes, Washington, Bay, Jackson, Calhoun, Gulf, Liberty, Gadsden, Franklin, Wakulla (partial) | >1 acre disturbance or >0.5 acre in Outstanding Florida Waters basin | Exemption available for residential single-family projects meeting volume criteria | 45–75 days (ERP); often exempt | nwfwater.org / (850) 539-5999 | Bay County post-Michael recovery projects still have expedited processing tracks |
| SRWMD Suwannee River WMD | Suwannee, Hamilton, Madison, Taylor, Lafayette, Dixie, Gilchrist, Levy (partial), Columbia (partial), Union, Bradford (partial) | >1 acre disturbance; spring protection areas have lower thresholds | Residential exemptions broadly available; check spring-shed overlays | 30–60 days (ERP); often exempt | srwmd.state.fl.us / (386) 362-1001 | Increased scrutiny on projects near first-magnitude springs following algae bloom events |
| Miami-Dade DERM Dept. of Env. Resources Mgmt | Miami-Dade County only (supplements SFWMD) | Any project requiring SFWMD ERP; plus local Class I/II criteria | Class I Permit for minor drainage modifications; Class II for larger | 45–90 days local; concurrent with SFWMD | miamidade.gov/derm / (305) 372-6700 | Updated Sea Level Rise impact criteria — all coastal projects must demonstrate 2050 resilience |
| Broward EPD Environmental Protection Dept. | Broward County only (supplements SFWMD) | Concurrent with SFWMD; local grading permits for any significant work | Local Drainage Permit for projects over 500 sq ft disturbed area | 30–60 days local | broward.org/epd / (954) 519-1483 | Updated C-9 Basin compliance requirements; increased enforcement in Pompano/Deerfield Beach flood areas |
| Palm Beach ERM Environmental Resources Mgmt | Palm Beach County only (supplements SFWMD) | Concurrent with SFWMD; local Right-of-Way permits separate | Local Environmental Control Permit for drainage impacts; admin review for residential | 30–45 days local | discover.pbcgov.org/erm / (561) 233-2400 | C-51 Western Basin Management updates affecting western communities (Wellington, Royal Palm Beach) |
| Orange County ENV Environmental Protection | Orange County (supplements SJRWMD) | Concurrent with SJRWMD; local Drainage Permit for projects >500 sq ft | Administrative exemption for single-family residential under 1 acre | 21–45 days local | ocfl.net/environment / (407) 836-7400 | Updated Shingle Creek / Butler Chain Basin stormwater requirements post-2024 flood events |
| Hillsborough EPC Environmental Protection Commission | Hillsborough County (supplements SWFWMD) | Concurrent with SWFWMD; local grading permit for >1/4 acre disturbance | Local Exemption for residential drainage not connecting to public systems | 14–30 days local | epchc.org / (813) 627-2600 | New Tampa Bay watershed protections — enhanced review for projects within 1,000 ft of tidal waters |
| Soil Type | FL Location | Percolation Rate | French Drain Effectiveness | Special Considerations | Avg Cost Modifier |
|---|---|---|---|---|---|
| Quartzite Sand (Panhandle) | Escambia, Santa Rosa, Okaloosa, Walton | Very Fast (>2"/hr) | Excellent — drainage usually natural | Pipe must be bedded in gravel to prevent sand migration into perforations; use geotextile fabric | ×0.85 |
| Fine Sand (Central/South FL) | Orange, Osceola, Polk, most of FL coastal plain | Fast (1–2"/hr) | Very Good — standard installation works well | Fine particles can migrate through standard geotextile; specify 3–4 oz non-woven fabric; HDPE pipe preferred | ×0.90 |
| Sandy Loam (North FL) | Alachua, Marion, Putnam, Columbia, Clay | Moderate (0.5–1"/hr) | Good — aggregate sizing important | Higher clay fraction slows drainage in wet season; may need more aggregate volume to compensate; verify with perc test | ×1.0 |
| Muck (Everglades Fringe) | Palm Beach western areas, Glades, Hendry, Okeechobee | Very Slow (<0.1"/hr) | Poor alone — needs pump or positive outlet | Highly compressible — pipe can shift and collapse; requires engineered design; pump systems often required; FDEP wetland jurisdiction likely | ×1.25 |
| Organic Peat (Lake Regions) | Lake County, Polk County lake districts, Brevard marsh edges | Variable (0.1–0.8"/hr) | Fair — depends on peat depth and saturation | Seasonal water table often at surface; French drains may require dewatering during installation; decomposing peat causes pipe settlement | ×1.20 |
| Clay-Sand Mix (Central FL) | Orange, Seminole, Volusia, I-4 Corridor | Slow-Moderate (0.2–0.6"/hr) | Moderate — larger aggregate required | Expansive clay component — pipe bedding must accommodate soil movement; HDPE preferred over rigid PVC for long runs; perc test essential | ×1.0 |
| Oolitic Limestone (Miami-Dade) | Miami-Dade (especially western and south), Monroe Keys | Very Fast when broken, but excavation is nightmare | Excellent percolation once installed — getting there is expensive | Requires core drilling or rock saw; equipment costs 3×–5× normal; but once in, drainage superior; check for voids and karst features | ×1.50 |
| Marl (SW FL) | Collier County (interior), Lee County (wetland margins), Monroe | Slow (<0.3"/hr) | Poor to Fair — often better to grade to positive outlet | Gray-blue calcareous mud — difficult to excavate, poor drainage capacity; swale grading often more cost-effective than French drain in marl areas; check for wetland jurisdiction | ×1.18 |
| Hardpan / Caliche (Marion) | Marion County, parts of Alachua, Levy, Hernando | Very Slow (<0.1"/hr) | Poor — hardpan acts as barrier; must be broken through | Dense calcium carbonate cemented layer at 18"–48" depth; acts as perched water table; French drain must penetrate hardpan to work; jackhammer or excavator with rock bucket required | ×1.35 |
| Fill (Coastal Developments) | All FL coastal barrier islands, most post-1950 developments | Highly Variable — depends on fill material | Variable — must test specific fill composition | Fill composition unknown without testing — may contain construction debris, concrete, sand, or clay in layers; always perc test; may encounter buried debris that requires removal; settlement ongoing in recent fill areas | ×1.10–1.25 |
| Storm Type | Typical Rainfall (24hr) | FL Flood Risk | Drainage System Sizing | Pre-Storm Checklist | Recovery Timeline | Insurance Relevance |
|---|---|---|---|---|---|---|
| Tropical Storm | 3–8 inches | Low-Moderate — localized flooding in poor-drainage areas | Standard 25-yr design (most FL county code) | Clear catch basin grates; confirm positive grade; check outlet points | 24–72 hrs drainage | Standard homeowners policy often covers if no exclusion; document with photos |
| Category 1 Hurricane | 6–12 inches | Moderate — yard flooding common, some street flooding | 25–50 yr design recommended | Sandbag low entries; clear downspout extensions; verify sump pump operation | 2–5 days drainage; debris 1–2 weeks | NFIP covers flood damage if separate policy; wind/rain combo claims contested — document carefully |
| Category 2 Hurricane | 8–15 inches | Moderate-High — widespread yard/street flooding, some structural | 50-yr design; consider pump-assisted systems | All above plus: elevate HVAC if possible; move outdoor equipment; check swale depth | 3–7 days drainage; 2–4 weeks for property | NFIP flood policy essential; ICC coverage important for repeat flooding; document all damage immediately |
| Category 3 Hurricane | 12–20 inches | High — most FL low-lying properties will flood regardless of drainage | Pump systems required; design for controlled flooding then rapid drainage | Evacuation may be required; ensure drainage system won't trap water against foundation | 1–3 weeks drainage; months for property | NFIP + federal disaster declaration likely; FEMA HMGP grants activated for future mitigation |
| Category 4 Hurricane | 15–30 inches (Ian delivered 18" in 6 hrs over Port Charlotte) | Very High — catastrophic flooding; storm surge compounds rainfall flooding | No drainage system eliminates risk; focus on flood resistance (elevation, barriers) | Mandatory evacuation in surge zones; all previous steps; document property condition before storm | Weeks to months; pumping required for low-lying properties | NFIP maxes at $250k structure / $100k contents; supplemental private flood essential; ICC up to $30k for mitigation post-claim |
| Category 5 Hurricane | 20–40+ inches over landfall track | Catastrophic — drainage irrelevant at peak; post-storm drainage critical | Post-storm retrofit focus: ensure water can exit, not pool against structure | If still present: highest floor/above flood line; protect from interior damage; ensure drainage paths clear for recession | Months to years; engineered dewatering may be needed for affected properties | Federal major disaster declaration certain; FEMA Individual Assistance, SBA loans, HMGP all available; mitigation grants prioritized |
| Atmospheric River (Non-Hurricane) | 8–20 inches over 2–5 days (FL sees these Nov–April) | High for developed areas — slow-moving rain saturates soil before drainage works | Storage capacity important — dry wells and retention more valuable than conveyance alone | Monitor NWS flood watches; pre-position dewatering equipment; verify catch basin capacity | 3–10 days for soil drainage; faster in sandy FL soils | Homeowners flood coverage often applies if flash flood designation; NFIP flood policy covers slow-rise flooding; keep documentation |
| King Tide Event | 0 inches rainfall — flooding from astronomical high tides | Moderate-High for coastal FL below +3 ft NAVD; worsening annually with sea level rise | Check valves on all storm drain outlets essential; tidal backflow prevention critical | Monitor NOAA tide predictions; ensure check valves functional; clear outlets of debris; do not rely on standard drainage during king tides | Tidal: 4–8 hrs per event; 3–4 events/yr getting longer; will require permanent pump stations in decade for some areas | NFIP covers tidal flooding; FL insurers increasingly excluding coastal flood risk; CRS discounts most valuable in tidal-risk communities |
FL's 5 water management districts have vastly different permit thresholds. A 1-acre project that qualifies for a simple exemption in NWFWMD may require a full Environmental Resource Permit with engineering plans in SFWMD. A 15-minute call to your WMD field office can save thousands in after-the-fact compliance costs. Most WMDs have regional offices with pre-application meetings — they're free and knowledgeable staff will tell you exactly what you need.
Florida law (FS Chapter 556) requires calling 811 (Sunshine State One Call) before any excavation — and "excavation" includes hand digging, probe rods, and any tool that penetrates the ground more than 12 inches. French drain trenching in FL residential neighborhoods routinely hits irrigation lines, fiber optic conduit, gas lines, and water mains that aren't shown on any map. Call 3 full business days before digging — it's free, takes 2 minutes, and is required by law. Violating this can result in $5,000 fines before you even pay for the utility repair.
In FL's acidic sandy soils and year-round high humidity, corrugated metal pipe (CMP) corrodes from the inside out — typically failing within 5–10 years. HDPE corrugated pipe (N-12 dual-wall) or smooth-wall PVC (SDR 35) lasts 50+ years in FL conditions and costs only $0.50–$2.00/linear foot more. If a contractor bids CMP for your FL drainage project, it's a red flag — either they're cutting corners or they're unfamiliar with FL soil conditions. Put the pipe specification in writing in your contract before signing.
Florida's nearly flat topography — many residential lots have less than 12 inches of total grade change — means even small grading errors trap water against foundations and in low spots indefinitely. Every French drain outlet point must have positive drainage to "daylight" — minimum 1% grade (1/8" per foot) from inlet to outlet. If no positive outlet to daylight exists on your property, a dry well, sump pump, or engineered retention area must be included in the design. Never let a contractor tell you "it'll drain on its own" in FL without confirming a verified outlet point.
Estimate the 10-year financial benefit of installing a drainage system — comparing installation cost against flood damage avoided, NFIP premium reductions, and FEMA grant potential.
Florida's prevalent slab-on-grade construction makes foundations uniquely vulnerable to drainage failures. Repeated flooding cycles — wetting and drying — cause differential settlement in FL's variable soils, leading to slab cracking and foundation movement. Documented drainage repairs in FL: French drain systems around perimeter foundations have prevented or arrested foundation movement in dozens of cases. Foundation repair in FL ranges from $10,000 for minor crack injection to $40,000–$80,000 for mudjacking, pier installation, or slab lifting. A $8,000 French drain installation that prevents even one foundation repair episode delivers 5–10× ROI on that protection alone.
Florida's year-round high humidity (averaging 74% RH) makes post-flood mold growth explosive — visible mold colonies can establish within 24–48 hours of flooding in FL conditions, versus 48–72 hours in drier climates. Professional mold remediation in FL averages $2,000–$8,000 for minor cases (single room) and $15,000–$30,000 for major structural infestations. Repeated flood events that are prevented by a drainage system avoid not just cleanup costs but also the FL homeowner's insurance mold claims that can trigger policy non-renewal. Many FL insurers now limit mold coverage to $10,000 or exclude it entirely for properties with repeated water claims.
According to Florida Realtors and licensed FL appraisers, documented water drainage problems reduce FL residential property values by 3–10% at the time of sale — significantly more than the national average — due to FL buyers' acute awareness of flood risk and the mandatory flood zone disclosure requirements (FL Statute 689.261). A $400,000 FL home with documented drainage issues may sell for $360,000–$388,000 (losing $12,000–$40,000 in value), while the same home with a permitted, documented drainage solution can recover full market value or even command a premium in flood-prone neighborhoods. Document your drainage system installation with permits, inspection certificates, and performance photos for maximum resale impact.
A FEMA Letter of Map Amendment (LOMA) or Letter of Map Revision Based on Fill (LOMR-F) can officially remove your property from a Special Flood Hazard Area (SFHA) designation — eliminating the mandatory purchase requirement for NFIP flood insurance. For FL coastal properties currently paying $1,500–$3,500/year in mandatory NFIP premiums, a successful LOMA (which typically costs $1,500–$4,000 in surveying and engineering fees) pays for itself within the first 1–2 years. A permitted stormwater management system with engineered documentation significantly strengthens a LOMA application. Over 40,000 FL properties have been removed from high-risk flood zones via LOMA/LOMR — the process is well-established and worth investigating for any SFHA-designated property with elevation data supporting the application.