Drainage, Stormwater & Flood

Stormwater Management Plan

Engineered stormwater plan and report showing how a project controls runoff volume, peak flow and water quality. Typical US fees run $3,000 to $40,000, and most projects take 2 to 8 weeks. Our drawings, calculations and reports are sealed by a Professional Engineer (PE) licensed in the state where your project is located, ready for permit submission.

Typical US fee$3,000 to $40,000

Typical timeline2 to 8 weeks

Permit drawingsSealed by a PE

What the work involves

When a project adds impervious surface or disturbs land above local thresholds, a civil engineer prepares a stormwater management plan with hydrologic calculations, detention or retention design, water quality treatment and maintenance requirements. Design storms are typically based on NOAA Atlas 14 precipitation data. Municipal separate storm sewer (MS4) permits push many cities to require these plans for development and redevelopment.

When you need it

New development or redevelopment above the local impervious or disturbance threshold
Planning board requires stormwater report
Downstream flooding concerns
Water quality treatment required (for example, impaired waters)
Expanding a parking lot or building

What you receive

Stormwater management report with calculations
Detention or retention facility design
Water quality treatment design
Operation and maintenance plan
Plan sheets

What drives the cost

Estimate. Small residential reports cost a few thousand dollars; commercial projects with detention and treatment cost more. Municipal stormwater review fees are separate and often tiered by acreage.

Related calculators

Detention Pond Volume Calculator (Modified Rational)Estimate required stormwater detention storage with the modified rational method from inflow, storm duration and allowable release rate.NRCS Curve Number Runoff CalculatorCalculate direct runoff depth and volume from rainfall and NRCS (SCS) curve number using the TR-55 runoff equation.Rational Method Runoff Calculator (Q = CiA)Estimate peak stormwater runoff in cfs with the rational method Q = CiA from runoff coefficient, rainfall intensity and drainage area.Time of Concentration Calculator (Kirpich)Estimate a watershed's time of concentration in minutes with the Kirpich formula from flow length and average slope.

Frequently asked questions

How much does stormwater Management Plan cost?

Across the US, stormwater Management Plan usually costs $3,000 to $40,000. Estimate. Small residential reports cost a few thousand dollars; commercial projects with detention and treatment cost more. Municipal stormwater review fees are separate and often tiered by acreage.

How long does stormwater Management Plan take?

Plan on 2 to 8 weeks from signed proposal to stamped deliverables, longer if a site visit, soil testing or a permit review cycle is involved.

Do I need a licensed PE for stormwater Management Plan?

In most US jurisdictions, yes. When the work needs a permit, the plans, calculations or report usually must be sealed by a Professional Engineer licensed in the state where the project is located. Every deliverable we issue for permit is sealed that way.

Will I also need a land surveyor?

Sometimes. Depending on the site, stormwater Management Plan can also involve a land surveyor, geotechnical engineer or landscape architect. We tell you up front which other professionals your project needs and coordinate with them so the drawings agree.

Who do you provide stormwater Management Plan for?

Most of our clients for this service are developers, contractors, business owners and municipalitys. Describe your project and one of our engineers will reply with scope, fee and schedule.

What triggers a stormwater management plan?

Local codes set thresholds by disturbed area or added impervious surface. Many tie to the 1 acre federal construction permit threshold, and some cities use much smaller ones.

Is this the same as a SWPPP?

No. A SWPPP manages pollution during construction. A stormwater management plan addresses permanent runoff after construction.

What rainfall data do engineers use?

Most use NOAA Atlas 14 precipitation frequency estimates unless a local standard applies. NOAA's Precipitation Frequency Data Server provides point estimates for most of the US.

Who maintains the stormwater facility?

Usually the property owner, under a recorded maintenance agreement with the jurisdiction. Neglected facilities can be cited by the jurisdiction during inspections.