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LARE Section 3 study materials
LARE Section 3 study resources

LARE Section 3: Grading, Drainage, and Construction Documentation

LARE Section 3 · Work through your exam, one topic at a time.

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Grading, Drainage, and Construction Documentation

Domain 4 - Grading, Drainage, and Construction Documentation. This section tests technical precision: turning design intent into spot elevations, contours, pipe inverts, and details a contractor can build from without calling you.

Grading fundamentals

  • Slope = vertical change ÷ horizontal run, as a percentage or ratio (1:12 = 8.33%).
  • Set spot elevations at corners, breaks, and grade changes; contours are smooth, never cross, and form upstream-pointing V shapes at drainageways.
  • Minimum grades: 1% for paved positive drainage with 2% as standard practice, 2% for turf, 1–4% for vegetated swales; accessible surfaces at 5% running and 2% cross slope maximum.

Drainage

  • Rational method: Q = CiA, where increased tributary area or runoff coefficient drives a larger peak flow.
  • Manning's equation sizes pipe: Q = (1.486/n) A R^(2/3) S^(1/2); minimum pipe slope is typically 0.5%.
  • Invert out = invert in − (slope × length). Rim = invert + structure depth.
  • Detention stores the post-development peak and releases it at or below the pre-development rate.

Cut and fill

Average end area: volume = (A₁ + A₂) ÷ 2 × distance. Balance on site where possible; export and import are expensive and regulated.

Worked example

An 8-in storm line runs 200 ft at 0.5% to an outlet invert of 102.40. Upstream invert = 102.40 + (0.005 × 200) = 103.40. With a 4-ft-deep structure, the rim must be at least 103.40 + 4.00 = 107.40. A rim proposed at 107.00 does not work - raise the rim to 107.40 or shorten the run so the pipe rises less.

Documentation

  • Plans, sections, details, and specifications must agree; conflicts get corrected by addendum or RFI, not resolved in the field.
  • Details show materials, connections, and tolerances; specifications govern quality and testing.
  • Disturbed sites need erosion and sediment control plans, sequencing, and temporary stabilization.

Traps

  • Contours that cross, or that run straight through a wall, curb, or headwall.
  • Sizing pipe before computing tributary area and runoff coefficients.
  • Designing a swale with no positive outfall, which turns it into a pond.
  • Mixing decimal feet and feet-inches on the same sheet.