What Is a Forensic Hydrology Audit? A New Orleans Guide

A forensic hydrology audit is a paid diagnostic that measures how water moves across and through a property and finds the point where the site fails. Garden Picasso, a forensic landscaping firm in New Orleans, builds every audit around GPH, Gallons Absorbed Per Hour: the rate at which the soil column accepts water, measured through the full 36 inches rather than at the surface. The audit replaces guessing with a number.

What Does a Forensic Hydrology Audit Measure?

A forensic hydrology audit reads the whole site, not one spot on it. The 36-Inch Soil Column is the full depth of ground Garden Picasso reads, because compaction, clay layers and saturated soil sit below the reach of a surface test. Garden Picasso's Forensic Hydrology Audit (FHA) has four parts:

• Visual forensic scope: inspection of catch basins and underground lines for silt, collapse and blockage.

• Peak-load simulation: a 100-year rain event run against the site to find the GPH rate at which the system fails.

• Laser-level mapping: identification of the zones where gravity sends water toward the foundation.

• Certified Infrastructure Risk Report: the written diagnosis, which names the cause of the water problem and the order in which to fix it.

The 100-year rain simulation matters because a system that works in light rain tells you nothing about the storm that hurts you. The simulation loads the site until it fails, and the GPH rate at that point is the number the design has to beat.

How Is a Forensic Hydrology Audit Different From Soil or Perc Testing?

A soil test reports the make-up of a sample taken at one location. A perc test reports how fast water drains at one hole, and it is typically required for septic permitting. Each answers a narrow question. A forensic hydrology audit answers the question a property owner is actually asking: why is my water going where it is going?

The gap matters because of Surface-Level Trauma, the damage that traditional landscaping, paving and soil compaction do to a site's ability to absorb water. A single test at one spot can pass while the rest of the yard stays compacted and the catch basin next door stays blocked. A forensic hydrology audit does not replace a perc test that a permit requires. It explains the surface and subsurface water that the permit test cannot see. Soil and perc tests remain the right tool when a lender, building official or permit requires a lab-certified report.

What Does a Low GPH Rate Mean for Your Foundation?

A low GPH rate means the ground holds the storm at the surface. Water that cannot sink in moves sideways toward the lowest point, which is often the edge of the foundation. In New Orleans, saturated clay and failed drainage are the usual suspects behind foundation movement, which is why the audit comes before any structural repair.

When Does a New Orleans Property Need a Forensic Hydrology Audit?

• Standing water: after rain, in a yard, courtyard or lot.

• Foundation movement or slab cracks: where drainage failure and saturated clay are the suspects.

• A drainage fix that failed: a French drain or regrade that did not hold.

• Before a build or regrade: so the design starts from a measurement.

Each of these is a symptom. The audit is how you find the cause before you pay to treat the symptom.

What Does a Forensic Hydrology Audit Cost in New Orleans?

The Forensic Hydrology Audit costs $1,500. If you hire Garden Picasso for the design solution within 30 days, the full $1,500 is credited to your bill. If you know something is wrong with the ground but not what, the Basic Site Audit costs $250 and is credited the same way toward Basic Site Design or Basic Asset Stewardship. If a fix has already failed or the structure is moving, the Forensic Infrastructure Audit costs $1,500 and has a 7-business-day turnaround.

For context, the $1,500 audit sits against $15,000 to $40,000 for a foundation repair. Diagnosing first is the cheaper order of operations. Each price is fixed by scope, so you know the number before you book.

Is a Forensic Hydrology Audit the Same as a Drainage Inspection?

No. A drainage inspection looks at visible hardware. A forensic hydrology audit adds a peak-load simulation and laser-level mapping to show where the system fails and why. The inspection tells you what is broken. The audit tells you what the ground can and cannot absorb, which decides what should be built.

What Happens After the Audit?

The Certified Infrastructure Risk Report becomes the brief for the design. A Sponge Node, a designed, planted basin that absorbs and holds stormwater on site, may be part of that design. The Ripple Effect is how one property's water handling changes conditions for its neighbors and the drainage network downstream: a yard that sheds its storm to the street adds to the load on every property below it. Measuring first keeps your fix from becoming your neighbor's flood.

How Does an Audit Connect to Pathway First?

Reading a soil column, scoping a drain line and mapping a grade are skilled trades. Pathway First is Garden Picasso's social-enterprise hiring model, designed to open high-skill, high-wage green-infrastructure careers to justice-involved neighbors. Every audit is the kind of work that model is built around.

Ready to measure your ground? Start with a Forensic Hydrology Audit ($1,500) for drainage, or a Basic Site Audit ($250) for a first look. Book at gardenpicasso.com or call 504-575-8199.