Drainage, Stormwater & Flood

Detention and Retention Pond Design

Design of detention basins, retention ponds, underground storage and outlet structures to control runoff. Typical US fees run $5,000 to $50,000, and most projects take 3 to 10 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$5,000 to $50,000

Typical timeline3 to 10 weeks

Permit drawingsSealed by a PE

What the work involves

Detention basins temporarily store runoff and release it slowly; retention ponds hold a permanent pool. The engineer sizes storage, designs outlet structures and emergency spillways, checks soils for infiltration or liners, and provides maintenance guidance. Underground chambers are used where land is costly. Failing or silted ponds may need a redesign or retrofit.

When you need it

Development requires peak flow control
Limited space requiring underground detention
Existing pond is silted, eroding or overflowing
HOA or owner needs pond maintenance or retrofit plan
Pond embankment shows seepage or slumping

What you receive

Pond grading and outlet design
Hydrologic and hydraulic calculations
Spillway design
Maintenance plan
Retrofit or repair plans

What drives the cost

Estimate. Underground systems and dam-safety-regulated embankments cost more.

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.

Frequently asked questions

How much does detention and Retention Pond Design cost?

Across the US, detention and Retention Pond Design usually costs $5,000 to $50,000. Estimate. Underground systems and dam-safety-regulated embankments cost more.

How long does detention and Retention Pond Design take?

Plan on 3 to 10 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 detention and Retention Pond Design?

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 geotechnical engineer?

Sometimes. Depending on the site, detention and Retention Pond Design can also involve a geotechnical engineer or land surveyor. We tell you up front which other professionals your project needs and coordinate with them so the drawings agree.

Who do you provide detention and Retention Pond Design for?

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

What is the difference between detention and retention?

Detention empties after storms; retention keeps a permanent water level. Both control peak flows; retention ponds can also provide water quality treatment through settling.

Who is responsible for HOA ponds?

Usually the HOA under a maintenance agreement. Neglected ponds can lose capacity and fail inspection.

Can a pond embankment be a dam?

Yes. Larger embankments may fall under state dam safety rules depending on height and storage.

Why use underground detention?

It saves surface land on tight sites, though it costs more to build. Underground systems still need access for inspection and cleaning.