LID vs. WQMP: Which Stormwater Report Does Your Project Need?

Why there are two different names for the same idea

California requires new development and major redevelopment to treat stormwater on-site. Every region of the state implements this through its Regional Water Quality Control Board's municipal permit. But each region developed its own terminology and framework.

San Diego Region: LID Report (Low Impact Development). Orange County and LA County: WQMP (Water Quality Management Plan). Bay Area: Stormwater Control Plan (SCP). Same requirement, different acronyms.

If you're working across Southern California — and plenty of clients do — you need to know which you're dealing with, because the submittal requirements, forms, and review processes are different even if the underlying engineering is similar.

LID Report — San Diego Region

The City and County of San Diego, plus most municipalities in the San Diego region, use the LID framework under the San Diego Regional Water Quality Control Board's municipal permit.

When you need it: Projects creating or replacing more than 500 SF of impervious surface (residential) or meeting Priority Development Project criteria (commercial).

What it covers: Drainage Management Area (DMA) delineation, BMP selection and sizing, infiltration testing if using infiltration-based BMPs, maintenance plan, and compliance documentation.

Key difference from WQMP: San Diego's LID framework places a strong emphasis on infiltration as the preferred treatment method. If your soil can infiltrate water at an acceptable rate (confirmed by perc testing), you're expected to use infiltration BMPs first. Only if infiltration isn't feasible can you use biofiltration or other alternatives.

San Diego also has specific city-developed LID forms and templates — the submittal package looks different from an OC or LA WQMP.

Working on a project in Southern California? We can handle the engineering.

WQMP — Orange County and LA County

Orange County operates under the Orange County MS4 permit, and LA County under its own permit. Both use the WQMP framework, though they have different templates and some different technical requirements.

When you need it: Priority Development Projects (PDPs) — which include single-family hillside homes, multi-family residential (10+ units), commercial development, restaurants, parking lots, and redevelopment that adds/replaces 5,000+ SF of impervious area.

What it covers: Project description, pollutant source identification, BMP selection (Site Design, Source Control, Treatment Control), sizing calculations using the 85th percentile 24-hour storm, maintenance plan, and engineer's certification.

Key difference from LID: WQMP has a more structured priority order: Site Design BMPs first, Source Control BMPs second, Treatment Control BMPs last. The hydromodification analysis (limiting post-development runoff to pre-development rates) is also more prominent in some OC and LA jurisdictions than in San Diego.

So which one does your project need?

Simple answer: look at your project address.

• City or County of San Diego, Chula Vista, Carlsbad, Oceanside, Escondido, El Cajon, or most other San Diego County cities → LID Report
• Irvine, Anaheim, Santa Ana, Huntington Beach, Newport Beach, or most other Orange County cities → WQMP
• Los Angeles, Long Beach, Pasadena, Glendale, Torrance, or most LA County cities → WQMP
• Riverside or San Bernardino counties → Their own versions; most use WQMP-style frameworks under their respective Regional Board permits.

The one exception: some projects in San Diego County might reference WQMP terminology in older documents or from contractors who work primarily in OC/LA. If you're confused about which applies to your project, just tell us the address — we'll know immediately.

What both have in common (and why it matters)

Regardless of whether you need an LID report or WQMP, the underlying engineering is similar: you're sizing a stormwater treatment system — whether infiltration basin, bioretention planter, permeable pavement, or underground vault — to handle the runoff from your project's impervious areas.

The design has to work. You can't pick a BMP that looks nice in the plans but won't actually treat the water. For infiltration BMPs, that means perc testing. For biofiltration, that means sizing calculations. The plan reviewer will check both.

And once it's built, you're responsible for maintaining it — in perpetuity. That's true for both LID BMPs and WQMP BMPs. The maintenance plan becomes part of your property's recorded documents.

Related Service

Stormwater LID & WQMP

We handle this for projects across Southern California.