Drainage & Detention in New Orleans, LA

What does drainage and detention work cover in New Orleans?

Drainage and detention work includes the full concrete scope of a site's stormwater system. A typical commercial project involves catch basin installation, trench drain placement at building entries and loading docks, subsurface pipe runs from collection points to outfall, and detention pond construction or lining where the site cannot discharge directly. New Orleans Concrete Contractors handles earthwork coordination, concrete forming and placement, and pipe bedding. Civil engineering, drainage design, and permit drawings are the client's or GC's responsibility and are not included in a concrete contract.

A first visit covers grade verification, existing outfall identification, and subgrade assessment. Most Greater New Orleans sites require a soil probe before any drainage scope is priced, because soft alluvial clay changes both the excavation method and the pipe bedding specification.

What does drainage and detention work cost in New Orleans in 2026?

Concrete drainage work in Greater New Orleans prices vary by system type. Trench drain installation runs $55 to $110 per linear foot, depending on channel width, grate specification, and whether existing concrete must be saw-cut and removed. Catch basin installation runs $1,800 to $4,500 per basin, depending on depth and barrel diameter. Detention pond excavation with concrete lining starts at $18,000 for sites under 5,000 square feet and rises with pond volume, liner thickness, and inlet and outlet structure complexity. Subsurface pipe runs add $22 to $48 per linear foot for materials and bedding.

Four variables move the number on any drainage job: depth to stable bearing soil, volume of demolition and spoil removal, pipe diameter and material, and the number of inlet and outlet structures requiring formed concrete work. Sites with a water table shallower than 4 feet below grade add cost for dewatering during excavation.

How is a concrete drainage job done, step by step?

A concrete drainage installation follows a fixed sequence because each stage depends on the one before it.

1. Site assessment and layout: Grade elevations are shot with a level to confirm the drainage fall. A minimum 1 percent slope, or 1 inch of fall per 8 linear feet, is required for gravity-flow trench drains and subsurface pipe. Catch basin rim elevations are marked to hold 4 inches below surrounding slab.
2. Demolition and excavation: Existing concrete is saw-cut 2 inches deep before breaking to produce clean edges. Excavation for subsurface pipe and detention ponds is taken to design depth plus 6 inches for bedding.
3. Subgrade preparation: Pipe trenches receive 6 inches of compacted crushed stone at 95 percent Proctor density. Detention pond floors are compacted and proof-rolled before any concrete is placed.
4. Forming and reinforcement: Catch basins are formed with 3/8-inch plywood on 2-by-4 frames. Walls are reinforced with #4 rebar on 12-inch centers. Pond liners use #4 rebar on 18-inch centers in both directions.
5. Pour and finish: Structural drainage concrete is 4,000 PSI with a 4 to 5 inch slump. Trench drain channels are poured monolithically with the surrounding slab where possible. Pond liners are placed in lifts no thicker than 6 inches and consolidated with a pencil vibrator.
6. Cure: All concrete drainage structures are cured for a minimum of 7 days under wet burlap or curing compound before backfill or loading.

What do New Orleans ground conditions change about drainage work?

Greater New Orleans sits on soft alluvial clay and organic silt over a water table that sits within 2 to 5 feet of the surface across most of Orleans and Jefferson Parish. That soil profile changes three things about concrete drainage work. First, pipe bedding cannot rely on native soil for support. Every subsurface pipe run requires a minimum 6-inch crushed stone bed and 6-inch crushed stone cover before native backfill begins. Second, detention pond excavation in soft clay requires sloped walls or sheet sheeting at depths beyond 4 feet to prevent sloughing. Third, catch basin walls in expansive clay are poured at 8 inches minimum thickness rather than the 6-inch minimum used in stable soil, because lateral soil pressure increases significantly during wet seasons. On the north shore in St. Tammany Parish, sandy loam allows thinner bedding in some locations, but high rainfall rates and pine flat topography make detention volume calculations more critical, not less.

How long does drainage and detention work take, and when can the system be used?

A single catch basin with a short trench drain run takes 2 to 3 days from excavation to backfill. A full detention pond with inlet and outlet structures runs 2 to 4 weeks depending on pond volume and access. Cure and use timelines for all concrete drainage structures are fixed by chemistry, not schedule pressure. Foot traffic around new structures is safe after 24 to 48 hours. Vehicle loading over trench drain slabs requires 7 days. Detention ponds must not be filled with water or backfilled against walls until concrete reaches 28-day full design strength. Compressing these timelines risks cracking and joint failure that will require full replacement within 3 to 5 years.

How do you tell good drainage and detention work from bad?

A property manager or GC can verify quality on a concrete drainage installation with a few direct checks.

• Drainage fall: Hold a 4-foot level on the trench drain channel or surrounding slab. A properly graded surface shows at least 1/4 inch of fall per foot toward the drain.
• Catch basin rim elevation: The basin rim should sit 3 to 4 inches below the surrounding finished grade so sheet flow enters the basin rather than bypassing it.
• Joint spacing: Control joints in concrete slabs surrounding drainage structures are cut no more than 10 feet apart and to a depth of 1/4 of the slab thickness within 12 hours of the pour.
• Pipe bedding: Request the inspection photo or compaction test report for pipe trench backfill. A 95 percent Proctor density reading on crushed stone bedding is the standard.
• Wall thickness: At any exposed edge of a catch basin or pond wall, the concrete should measure at least 8 inches. A wall thinner than 6 inches in Greater New Orleans soil is undersized.

Contact New Orleans Concrete Contractors for a free on-site estimate. Drainage scope is priced after a grade survey and soil assessment, so a site visit is the first step on any project.