Water follows elevation before it follows a product
The most useful first sketch is a map of high points, low points, hard surfaces, concentrated roof discharge and the place water can safely leave or infiltrate.
Grade calculator
Measure horizontal run and elevation drop along the route you are considering.
Keep foundation water separate from yard convenience
Water next to a foundation has a higher consequence than a soft wet area at the back of a lawn. Prioritize roof discharge, grading near the building and obvious inflow paths before optimizing cosmetic puddles elsewhere.
Use broad surface solutions when possible
Surface grading and shallow vegetated conveyance are visible and inspectable. Buried systems can be appropriate, but they are harder to diagnose after installation.
How to measure fall without guessing
The calculator only needs horizontal run and vertical fall, but those two measurements should come from a repeatable method. A builder's level, rotary/laser level, water level or survey elevations can all be more reliable than judging the lawn by appearance. For a short low-consequence route, even a carefully set string line can reveal whether the endpoint is actually lower.
Measure the route you intend to build, not a diagonal line that avoids the real obstacles. If the path bends around trees, structures or utilities, check grade at the bends as well as the endpoints.
Example: what a 2% grade means
A route that drops 1 foot over 50 feet has a 2% end-to-end grade. The percentage is simply drop ÷ run × 100. The same 2% relationship can be expressed as 0.2 m of drop over 10 m of horizontal run.
Positive endpoint grade is not the same as continuous fall
A route can begin higher and end lower while still having a hump in the middle that traps water. Check intermediate grade breaks, especially where a proposed pipe crosses a driveway, root zone or existing utility corridor.
When regrading deserves the first look
If water is moving visibly across the surface and there is room to create a broad, continuous downhill path, surface grading or a shallow swale can be easier to inspect and maintain than a buried collector. See French drain vs swale for a source-based comparison.
When grade is not enough
Even a workable gravity slope does not answer whether the outlet is lawful, whether the route will erode, whether a pipe is large enough for peak flow or whether excavation conflicts with utilities. Carry the measurement into the 12-step drainage checklist before digging.
Do not mistake a sketch for a survey
Wrivel's high/low markers are qualitative notes. If the route is close to a building, property boundary or other sensitive area, verify elevations with a level, laser or survey rather than estimating by eye.