Site Grading and Drainage
Grading questions test whether you can read and set elevations, slopes, and flow. Know the difference between spot elevations, contour lines, and slope expressed as percent, ratio, and degrees. Convert confidently: percent slope = rise/run × 100; a 2% slope over 50 ft is 1 ft of fall. Understand that contour lines close together mean steep; widely spaced mean gentle; contours crossing a stream form a V pointing upstream.
Traps: confusing cut and fill; forgetting that water flows perpendicular to contours; specifying slopes too steep for use or too flat to drain. Know typical rules: minimum 1-2% slope on paved surfaces and turf for drainage; 2% maximum on accessible routes (5% running max with landings); swales with side slopes typically 3:1 or flatter for mowing. Understand positive drainage away from structures (commonly 6 in fall in the first 10 ft, per code) and the role of swales, French drains, dry wells, and retention/detention basins.
Distinguish retention (holds water) from detention (temporarily stores and releases). Know why infiltration matters for stormwater and when soils (clay) limit it. Understand grading for walls, steps, and terraces, and how to balance cut and fill to minimize hauling.
Worked example: a 40-ft-wide lawn needs 2% slope to a swale. Fall = 40 × 0.02 = 0.8 ft (about 9.6 in) across the width. If the swale centerline is at elevation 100.0 and the lawn edge at 100.8, contours run parallel to the swale and water flows downhill toward it.
Review how to spot a grading error: water ponding against a foundation, a swale that slopes the wrong way, or contours that contradict spot elevations.