Stormwater management is the engineering and permitting that controls how rain leaves a site. It covers how fast the water leaves (peak flow), how much leaves (volume), and how clean it is (quality). On the Gulf Coast it also means designing against high groundwater, flat grades and tailwater from tide or surge. That’s why a system that works on paper inland can back up here.
Cypress designs stormwater systems, writes the construction SWPPP, inspects for permit compliance where we offer that service, and supports counties and cities with stormwater programs and watershed plans. We work in Mississippi, Alabama, Florida and Louisiana, from Biloxi, Mobile and Pensacola.
Last reviewed: October 14, 2026. Technical review: Cindy Henderson, PE.
What is stormwater management?
Stormwater is rainwater (and snowmelt, for more northern climates) that runs off land instead of soaking in. Roofs, roads and parking lots turn rainfall that used to infiltrate into faster runoff, and that runoff typically carries more pollution: sediment, nutrients, oil and grease, metals and bacteria.
Managing it is two problems, solved together:
| Problem | What goes wrong | Typical controls |
|---|---|---|
| Quantity (peak and volume) | Flooding downstream, channel erosion, road and yard flooding | Grading, inlets and pipes, detention and retention ponds, outlet control structures |
| Quality | Sediment and pollutants reach creeks, bayous and the Sound | Construction BMPs, water-quality ponds, swales, filter strips, infiltration where the soils allow |
Two things are often confused. The SWPPP is the construction-phase plan and is not the drainage design. The drainage design is the permanent system that stays after the contractor leaves. A project usually needs both, and the two have to agree. See What Is a SWPPP?.
Why Gulf Coast sites are different
- High groundwater: a seasonal high water table close to the surface limits infiltration and pond depth. A retention pond designed to soak water in may simply sit full.
- Flat grades: little fall from the site to the outfall means larger pipes, shallow ponds and careful outlet design.
- Tailwater: where the outfall is tidal, or drains to a bayou that rises in storms, the downstream water level controls the system. Design checks the outfall at the tide and storm conditions the local reviewer requires.
- Rainfall: design storms come from NOAA Atlas 14, Volume 9, which covers MS, AL, FL and LA.
- Floodplains and wetlands next to the site: grading in a mapped floodplain may need a floodplain development permit and a No-Rise analysis. An outfall into a wetland or tidal water can bring in Section 404/10 permitting.
The permits: federal, state and local
The federal basis is the Clean Water Act. Section 402 created the NPDES permit program (33 U.S.C. 1342), and EPA’s stormwater rules are at 40 CFR 122.26. All four states run their own NPDES programs, so the permit a site actually needs comes from the state agency.
Construction sites. Coverage is generally required for land disturbance of 1 acre or more, or less if the site is part of a larger common plan of development (40 CFR 122.26(b)(14)(x) and (b)(15)).
| State | Agency | Construction general permit | Notes |
|---|---|---|---|
| Mississippi | MDEQ | MSR10 (large construction, 5+ acres); MSR15 (1 to under 5 acres) | MSR10 reissued 2022-02-04, expires 2027-01-31; MSR15 administratively continued |
| Alabama | ADEM | ALR100000 | Reissued effective 2026-04-01; a Construction Best Management Practices Plan (CBMPP) is required before the NOI; the definition of Qualified Credentialed Professional (QCP) includes PE and CPESC |
| Florida | FDEP | Generic Permit for Stormwater Discharge from Large and Small Construction Activities (Rule 62-621.300(4), F.A.C.) | NOI at least two days before construction; records kept 3 years |
| Louisiana | LDEQ | LAR100000 (large); LAR200000 (small) | LAR100000 10/01/2024–09/30/2029; LAR200000 08/25/2023–08/24/2028, no NOI |
ADEM Schedule F construction stormwater fees
Beginning Thursday, October 15, 2026, Alabama Department of Environmental Management (ADEM) construction stormwater application fees under Fee Schedule F replace the prior flat Notice of Intent (NOI) fee. Sites under 5 acres pay a $1,000 base fee. Sites of 5 acres or more pay that base plus $100 per acre. Priority construction sites add $100, and if the site is 5 acres or more they also add $10 per acre. The total for each permit action is capped at $10,000. Modification of coverage uses the same Schedule F base and additive rules when acreage increases; it is no longer a flat $800 fee. Confirm the live Schedule F and the ADEM Construction General Permit page before filing. Cypress prepares the NOI and the SWPPP (or Alabama CBMPP) for Gulf Coast projects from Biloxi, Mississippi; Mobile, Alabama; and Pensacola, Florida.
Sources: ADEM Construction General Permit page (https://adem.alabama.gov/water/npdes-programs/construction-general-permit); CSWGP2026CGPPermitChanges.pdf (https://adem.alabama.gov/sites/default/files/2026-08/CSWGP2026CGPPermitChanges.pdf).
Permanent (post-construction) stormwater.
- This is mostly local: city and county drainage ordinances and design manuals set detention and water-quality requirements, and review the plans.
- Florida also regulates permanent stormwater at the state level through the Environmental Resource Permit (ERP, Chapter 62-330, F.A.C.), issued by FDEP or the water management district, which in the Panhandle is the Northwest Florida Water Management District.
Municipal programs (MS4). Cities and counties that operate a municipal separate storm sewer system hold an MS4 permit (Phase II rules at 40 CFR 122.34). It requires ongoing control measures: mapping, illicit discharge detection, construction and post-construction runoff control, public education, good housekeeping, and annual reporting. See MS4 permit compliance for Gulf Coast cities.
How a stormwater system is designed
- Site data:
- topographic survey
- soils and hydrologic soil group
- seasonal high groundwater
- FEMA flood zone and base flood elevation (BFE)
- wetlands
- the receiving water and its condition, including any TMDL or impairment listing
- Design basis: the governing local manual, the design storms (return periods and duration), the rainfall source, and the allowable release rate (often “post-development peak no greater than pre-development”).
- Hydrology:
- The Rational Method suits small, simple drainage areas.
- NRCS curve number / TR-55 suits small urban watersheds.
- HEC-HMS or SWMM suits larger or connected systems, and SWMM also handles tailwater and backwater in pipe networks.
- Hydraulics and sizing:
- pond storage
- outlet control structure
- pipes and inlets
- checks at the outfall’s tailwater
- freeboard to the pond’s top of bank and to finished floor elevations
- Water quality: treatment volume or BMP selection to meet the local or state requirement.
- Permits and review: the local drainage review; state construction general permit coverage; Florida ERP where it applies; and 404/10 permitting if the outfall or grading touches jurisdictional waters.
- Construction-phase controls: SWPPP or CBMPP, BMP installation and inspections.
- Close-out and maintenance: as-builts, a maintenance plan and the responsible party, and the Notice of Termination once the site is stabilized.
All design work is done under the responsible charge of a licensed Professional Engineer, who seals the drawings and calculations.
For pond selection, see Retention vs Detention Ponds.
Construction phase: SWPPP, BMPs and inspections
While a site is graded and bare, the risk is sediment. The SWPPP (CBMPP in Alabama) shows the controls and when they go in:
- silt fence
- inlet protection
- check dams
- sediment basins
- a stabilized construction exit
- temporary and permanent stabilization
Permits require inspections on a schedule and after qualifying rain, by a qualified person. Cypress provides construction stormwater compliance inspections in Baldwin and Mobile Counties, Alabama, and Escambia County, Florida only, led by Cathy Barnette, CPESC, Practice Lead. See Stormwater Compliance Inspections.
After construction: maintenance and MS4 programs
A pond nobody maintains stops working: sediment fills the storage, outlets clog and vegetation takes over. Local approvals usually assign maintenance responsibility (owner, HOA or the jurisdiction) and may require inspection and reporting.
At the community scale, cities and counties manage stormwater as a program. That means an MS4 permit, a system inventory and condition assessment, capital project priorities, and watershed plans that tie flooding and water quality together. See What Is a Watershed Management Plan? and Watershed Management Plans.
What drives the cost
We don’t publish prices because every site is different. These are the factors that move a stormwater design or program budget:
| Driver | Why it matters |
|---|---|
| Site size and how much of it becomes impervious | More runoff means more storage and conveyance to design |
| Groundwater and soils | Shallow groundwater or poor soils rule out infiltration and force larger detention |
| Outfall condition | Tidal or backwater tailwater requires more modeling and larger structures |
| Floodplain or wetlands on or next to the site | Adds No-Rise analysis, Section 404 permitting or mitigation |
| Local review requirements | Some manuals require continuous modeling, water-quality volumes or additional storms |
| Data available | Missing survey, as-builts or geotechnical data must be collected first |
| Construction duration and phasing | Longer sites mean more inspection visits and BMP maintenance |
Worked examples
Hancock County Stormwater Program Management (Hancock County, Mississippi). Stormwater program management for Hancock County, including writing three watershed management plans. Project started 2021.
Jackson County Watershed Management Plans (Jackson County, Mississippi). Four watershed management plans for Jackson County. Project started 2022.
Tantallon & Shamrock Drainage Improvements (U.S. Army Corps of Engineers, Mobile District). Drainage improvements for the USACE Mobile District. Phases 1 and 2, 2024.
Miramar Stormwater Infrastructure Condition Assessment (City of Biloxi, Mississippi). A condition assessment of the stormwater infrastructure in Biloxi’s Miramar area for the City of Biloxi.
East Pier Roadway and Stormwater Park (Port of Gulfport, Mississippi). Grading, stormwater and landscape design for the redesigned East Pier roadway, including a stormwater park, constructed wetlands, rain gardens and roadside green infrastructure that filter roadway runoff before it reaches the Mississippi Sound. See the project page.
What Cypress does, and what it does not
We do:
- stormwater and drainage design
- hydrology and hydraulics
- construction SWPPPs and CBMPPs
- permit coverage support
- construction stormwater inspections in Baldwin and Mobile Counties, AL and Escambia County, FL
- county and city stormwater program support
- watershed management plans
- coordination with wetland and floodplain permitting
We do not:
- provide construction stormwater inspections outside Baldwin, Mobile and Escambia Counties
- act as the local plan reviewer
- install or maintain BMPs (contractors do)
- give a legal opinion on permit obligations
FAQ
What is the difference between stormwater management and a SWPPP?
Stormwater management is the whole system: permanent drainage, storage, treatment and maintenance. A SWPPP covers only the construction period and controls erosion and sediment until the site is stabilized.
Does my project need a stormwater permit?
Usually, if it disturbs 1 acre or more, or is part of a larger common plan of development. The construction general permit comes from MDEQ, ADEM, FDEP or LDEQ depending on the state. Local drainage approval is separate and often applies to smaller sites too.
What is an MS4?
A municipal separate storm sewer system: the streets, ditches, pipes and outfalls a city or county operates to carry stormwater. Its operator holds an NPDES MS4 permit and runs an ongoing stormwater program.
Retention or detention pond?
A detention pond holds water and releases it slowly. A retention pond keeps a permanent pool or infiltrates the water. On the Gulf Coast, groundwater often decides. See Retention vs Detention Ponds.
Who can inspect my construction site?
It depends on the permit. Alabama’s ALR100000 recognizes CPESC among the QCP credentials. See Stormwater Compliance Inspections for Alabama and Florida requirements.
How does flooding fit in?
Drainage design controls what leaves the site. Floodplain rules control building and fill in mapped flood zones. Many Gulf Coast sites deal with both.
Talk to us about a site or program
Send the site location, acreage, the permit or review you’re facing, and your schedule. A stormwater engineer will reply with what the site needs and what information to gather first.
Contact Cypress. Offices in Biloxi, Mobile and Pensacola.
Sources
- Clean Water Act Section 402, 33 U.S.C. 1342
- 40 CFR 122.26 (stormwater discharges; construction thresholds) and 40 CFR 122.34 (small MS4 permits)
- MDEQ construction stormwater general permits MSR10 and MSR15
- ADEM NPDES general permit ALR100000, effective 2026-04-01
- FDEP Rule 62-621.300(4), F.A.C., construction generic permit; Chapter 62-330, F.A.C. (ERP)
- LDEQ LAR100000 and LAR200000
- NOAA Atlas 14, Volume 9