Drainage swales are the most common grading feature inspected at residential grading permit closeout. They carry stormwater between lots, along property lines, and to street inlets — and if the grade is wrong, water ends up against foundations. Getting the grade documentation right the first time prevents re-inspection, schedule delays, and future drainage complaints.
What drainage swale grade documentation is required for residential grading permits?
Residential drainage swale documentation requires: flowline elevation shots at every grade change and at maximum 25-foot intervals, calculated grade percentage for each segment compared to the minimum 1.0% IRC requirement, swale cross-section dimensions at each station, a benchmark reference tying all elevations to a recognized datum, and comparison to the permitted grading plan. The documentation package must demonstrate positive drainage away from all structures and no reverse grade in any swale segment. Most building departments require this as part of the final grading inspection or pad certification submittal.
The International Residential Code (IRC) Section R401.3 establishes the minimum drainage requirements for residential sites. Swales and drainage courses must maintain a minimum 1.0% grade (1 foot of fall per 100 feet of horizontal run) to ensure positive flow to a drainage outlet.
Local jurisdictions frequently adopt stricter requirements. California commonly specifies 2.0% minimum for side yard swales. Many planned developments have project-specific grading plan requirements that supersede the IRC minimums. Always verify the applicable grade requirement before field documentation.
| Swale Type | Minimum Grade | Code Reference |
|---|---|---|
| Side and rear yard swale | 1.0% minimum | IRC R401.3 |
| Swale adjacent to foundation | 5.0% min first 10 ft | IRC R401.3 (ground surface slope) |
| Concrete-lined drainage channel | 0.5% acceptable | Project specification |
| California side yard swale | 2.0% typical | California CBC Title 24 / local grading codes |
| Common-area drainage swale | 1.0% minimum | IRC / local municipal ordinance |
Swale grade documentation starts with accurate flowline elevation shots. The flowline is the lowest point of the swale cross-section — where water actually flows. Shooting the side slope or the top of the swale bank instead of the flowline is the most common documentation error on residential grading projects.
A complete swale grade documentation submittal for grading permit closeout includes:
Benchmark ID, published elevation, datum, and method used to establish height of instrument.
Plan view showing swale centerline, lot numbers or addresses served, and the outlet location. Red-lined on the permitted grading plan is acceptable.
Station, rod reading, computed flowline elevation, and cumulative distance for every shot. Match station designations to the plan view.
Each segment: start station, end station, length, upstream flowline, downstream flowline, computed grade %, specified minimum grade, and pass/fail.
Swale bottom width, side slope (H:V), and depth. Verify against the permitted grading plan dimensions.
Side-by-side comparison of as-built flowline elevations versus design elevations from the permitted grading plan. Flag deviations exceeding ±0.10 ft.
These are the most frequent reasons swale documentation is rejected at residential grading permit closeout:
Rod placed on the swale side slope or top bank instead of the lowest point. Calculated grade appears correct but does not represent actual flow path.
Documentation covers the swale run but omits the elevation at the outlet — typically a curb inlet, storm drain inlet, or daylight point. The outlet elevation is required to confirm the swale actually drains.
Elevations are relative only — cannot be independently verified or compared to design. Building departments reject unbenchmarked elevation data.
One or more segments compute below 1.0%. The fix is to re-grade and re-shoot — not to adjust the data. Re-inspection is required.
Swales that cross property lines require documented flowline elevations at the property line. Missing these shots leaves the inspector unable to verify drainage across the lot line.
Sitemark generates swale grade documentation with flowline elevation tables, grade calculations, and plan comparisons formatted for building department submittal.
Start Free Trial →Rotating lasers and grade rods for residential drainage swale documentation.
Shop at Express Tools →IRC Section R401.3 requires a minimum 1.0% grade (1 foot of fall per 100 feet) for drainage swales on residential lots. Some jurisdictions are stricter — California commonly requires 2.0% for side yard swales. Always check the permitted grading plan for project-specific requirements.
Required documentation includes flowline elevation shots at 25-foot intervals tied to a benchmark, grade percentage calculations for each segment, swale cross-section dimensions, comparison to the permitted grading plan, and a pass/fail determination for each segment against the minimum grade requirement.
The swale must be re-graded to achieve the minimum slope. Documentation of the corrective re-grade is required, and re-inspection by the building department is typically needed before the grading permit can be closed. Adjusting the documentation data without re-grading is not acceptable.