Home / Services / Drainage Plans
Drainage Plans
Water has to go somewhere. On an undeveloped lot, it soaks into the ground or runs off naturally across open terrain. The moment you add a house, a driveway, a patio or any hardscape, that natural pattern breaks. The water still has to go somewhere the only question is whether that path was engineered on purpose or left to chance. A drainage plan is how we make sure it’s the former.
Trusted By:
At its core, a drainage plan is a technical drawing that shows existing and proposed contours, pad and finish floor elevations, flow direction across the site, and exactly how stormwater moves from your roof, yard and hardscape to the street, a storm drain, or another approved discharge point. It has to do this without flooding a neighbor’s property, pooling against your own foundation, or violating the standards of whichever agency is reviewing the project.
Why drainage problems are rarely obvious upfront
Most drainage issues don’t reveal themselves until the first real storm hits. A driveway that sheets water onto the sidewalk. A low corner of the backyard that stays soggy for a week after every rain. Water creeping toward a foundation instead of away from it. These aren’t random bad luck they’re almost always the direct result of grading that was never actually engineered, just assumed to work because the lot “looked flat enough.”
A proper drainage plan avoids this by starting from the opposite direction: instead of grading first and hoping the water finds a reasonable path, we design the water’s path first, then shape the grading to support it. Pad elevations, slope percentages, swale placement and cut-and-fill quantities are all derived from the same site model that produces the drainage pattern. That’s exactly why grading and drainage are almost never treated as separate problems in our process our grading plans and drainage plans are typically developed together, since one without the other tends to produce a design that looks fine on paper and fails on-site.
What's actually included in a drainage plan
A complete drainage plan generally includes existing and proposed contours across the parcel, pad and finish floor elevations, clearly marked drainage direction arrows and swale locations, storm drain, area drain and catch basin placement where needed, and the specific connection point to the public storm system or another approved discharge location. We also include erosion control notes covering the construction phase, since a site is often at its most vulnerable to runoff damage before landscaping and permanent surfaces are in place.
For sites with more complicated offsite flow, detention requirements, or a documented history of drainage complaints from neighbors or the city, we pair the drainage plan with a full hydrology and hydraulics study. This ensures the numbers behind the design not just the drawing itself hold up under agency scrutiny, particularly on infill lots where upstream and downstream conditions are already tight.
How this fits into the broader approval process
Every jurisdiction in California reviews drainage a little differently, and site conditions vary just as much. A hillside parcel in the Inland Empire behaves nothing like a flat infill lot in Irvine, and a coastal site in Orange County has different discharge constraints than a valley lot further inland. What stays consistent across all of them is the underlying standard: the reviewing agency needs to see clear evidence that water is controlled, that it won’t damage adjacent property, and that the design is consistent with your broader stormwater management strategy if the project triggers a Water Quality Management Plan or SWPPP.
We prepare the drainage plan as part of the same coordinated submittal package as your grading and encroachment permit documents, rather than as an isolated deliverable. That matters more than it might seem agency reviewers are far more likely to raise redlines and delay approval when the grading, drainage and stormwater documents don’t quite agree with each other. A single coordinated package, prepared by the same engineer of record, moves through review with far fewer round trips.
When you actually need a drainage plan
You’ll need one when building a new home or ADU, when adding a room, converting a garage, or installing significant new hardscape, when regrading a lot that already has drainage complaints on record, when responding directly to a neighbor or agency notice about runoff, and when subdividing a parcel where each new lot needs its own independent, approvable drainage solution.
- Common Questions
Frequently asked questions
They're closely related but not identical. A grading plan shows how the land itself is shaped pad elevations, slopes and cut-and-fill quantities. A drainage plan shows what happens to water once that shape exists where it flows, where it's collected, and where it discharges. We typically prepare both together, since a grading design that ignores drainage almost always creates problems later.
In most California jurisdictions, yes even a modest addition changes roof area, hardscape and grading enough to affect how water moves across the lot. Some smaller projects qualify for a simplified drainage exhibit rather than a full engineered plan, but that depends on your specific city or county's requirements.
This is one of the more common reasons people come to us. We start with a site evaluation to understand where the water is actually coming from often it's a grading issue upstream, not on your property at all then design a drainage solution that addresses the real source rather than just moving the symptom somewhere else.
Not if it's done correctly the first time. Most delays come from drainage and grading documents that don't match each other, or that leave out details the specific reviewing agency expects. A coordinated, jurisdiction-specific plan tends to move through review faster, not slower.
Only if your project triggers it typically larger sites, sites with significant offsite flow, or lots with a documented drainage complaint history. For a straightforward single-family lot, a standard drainage plan is usually sufficient on its own.
Where we start
Whether your project is a single lot in Orange County or a full subdivision spanning dozens of parcels across California, the process starts the same way: send us the address and the scope of work. We’ll review it, tell you exactly what the drainage plan needs to show for your jurisdiction, and give you a fee and schedule in writing or tell you directly if the project falls outside what we should take on.