What Are Grading and Drainage Plans?

Grading and drainage plans document the site's finished elevations and the complete surface and subsurface drainage system. They show existing and proposed contours, building pad and finished floor elevations, drainage swales and flow paths, storm drain pipes and structures, retaining walls, and construction-phase erosion control. The design ensures water drains away from buildings, doesn't pond, doesn't flood neighbors, and reaches the approved discharge point — proven by the calculations behind the plan. I think of the grading plan as the site's contract with gravity. Every elevation on that sheet is a promise about where water will go, and the contractor builds those promises into dirt and concrete. The precision matters because water doesn't negotiate — a tenth of a foot in the wrong direction is a ponding problem for the life of the project.

The core sheet is the grading plan itself: existing contours shown dashed or screened, proposed contours solid, spot elevations at every critical point — building corners, high and low points, inlet rims, wall tops and bottoms — and flow arrows tracing every drainage path to its outlet. Cross-sections through swales, berms, and retaining walls prove the shapes are buildable. The storm drain plan and profiles show the piped system: pipe sizes, slopes, invert elevations, and structure locations, designed so the hydraulic calculations behind them actually work. Supporting sheets complete the package: the erosion and sediment control plan for the construction phase (silt fence, inlet protection, stabilized entrances), retaining wall details where grade changes need structure, and the earthwork quantities — cut and fill volumes, import or export — that the contractor prices from. On larger projects the geotechnical report's grading recommendations get incorporated directly: compaction standards, slope ratios, and subgrade preparation that the plan references and the inspector enforces.

Pad elevation comes first, because everything ties to it — finished floor, driveway slopes, sewer depths, and the drainage fall away from the building. I set it from the constraints: flood elevation requirements where they apply, street grades at the driveway, utility invert depths, and the need for positive drainage in every direction. Then the drainage patterns: I lay out swales and collection points so no water ponds against the building and every drop has a designed path to the outlet. Retaining walls enter where the grade change exceeds what a slope can handle — and the wall design, including drainage behind it, is part of the grading package, not an afterthought. Throughout, I'm checking the constructability: can the contractor actually build these slopes with their equipment, do the quantities balance reasonably, and does the phasing work with the building construction? A grading plan that looks elegant on screen but can't be built is just an expensive drawing.

• Existing and proposed grades with spot elevations at every critical point
• Drainage patterns proving positive flow away from buildings to approved outlets
• Storm drain piping, inlets, and structures with hydraulic design behind them
• Erosion and sediment control for the construction phase
• Earthwork quantities and geotechnical grading recommendations incorporated