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Stormwater Drainage Cost Calculator
Stormwater drainage protects sites from flooding, foundation damage, and erosion. Standard system components: french drains/channels for surface and subsurface water, catch basins to capture sheet flow, and outlet piping to a disposal point. EPA Phase II MS4 permits add cost on sites disturbing 1+ acre. This calculator builds the budget with industry costs and 15% contingency.
$45-100/LF
Total stormwater drainage cost
$29,555
Cost / SF site
$1.48
French drain / channel
$11,700
Catch basins
$6,000
Outlet piping
$4,500
Contingency 15%
$3,855
How the math works
Stormwater drainage = french drains, area drains/catch basins, and outlet piping to disposal point. EPA Phase II MS4 permits require post-construction stormwater management for sites disturbing 1+ acre — adds $1-3/SF to budget.
Detention/retention basin pricing varies wildly: $5-15/CY for excavation, $20-60/SF for vault systems. Get geotech and hydrology reports before sizing.
How to Use
- Enter site SF and french drain LF.
- Enter cost per LF (typical $45-100/LF).
- Enter catch basin count and cost.
- Enter outlet piping budget and engineering.
- Read total cost and per-SF cost.
Frequently Asked Questions
When is engineering required?
Most jurisdictions require sealed drainage plans for sites over 1/2 acre disturbed. EPA MS4 communities require Stormwater Pollution Prevention Plans (SWPPP) regardless.
Detention vs retention?
Detention temporarily stores then releases at controlled rate; retention permanently retains and infiltrates. Detention basins $5-15/CY; underground vault systems $20-60/SF.
Maintenance budget?
Catch basin clean-out $200-400/basin/yr; french drain clean $1-2/LF/2-3 years. Add to operating budget.
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