Which one your rebuild needs, what each costs, and where the $2,400 report earns its keep.
A drainage plan is a drawing set. It shows how stormwater moves across your lot (roof runoff, driveway flow, sheet flow paths) and where it exits. It gets submitted with your building permit and reviewed by LA County DPW plan check.
A hydrology report is the analysis behind the drawings. It calculates flow rates: how much water hits your lot pre-fire, how much leaves it after development. Rational method calcs, time of concentration, the engineering math plan checkers can verify.
Short version: the plan shows where water goes. The report proves how much.
Flat fees, covering plan check comment responses. Not hourly.
Most Altadena fire rebuilds need a drainage plan. LA County does not require a hydrology report as a standalone submittal. But here is where it matters:
Plan checkers use hydrology to justify sump pump requirements. A sump pump system adds $30,000-$50,000 to construction. The way to fight it is showing your post-development flow rate does not exceed pre-fire flow. That analysis has to live somewhere: sometimes inside the drainage plan, sometimes as a separate report when plan check wants it standalone.
We calculate pre-fire and post-development flow rates on every project either way. The question is only whether the analysis ends up in a bound report or on the sheets.
If plan check conditions your permit on a sump pump, a hydrology report is usually the cheapest path to removing it. $2,400 against $30,000-$50,000 is not a close call.
The analysis compares pre-fire conditions (what existed before the Eaton Fire) to your proposed development. If a similar roof and driveway existed pre-fire, your post-development flow often does not increase, and that finding, accepted by the reviewer, goes on the plans for permanent record.
We will tell you whether your lot needs a report, a plan, or both, before you're conditioned into a sump pump.
Get a Quote