Slope in landscaping is also known as grade. It shows how much change in elevation there is over a given distance. It is important to keep both of these measurements in the same unit; for example, feet. If you imagine the lawn as a right triangle, the slope is the hypotenuse. The change in elevation then is the base of the triangle and the distance is the third side. As such, the distance must be flat and does not take into account any slope.
Measure the elevation at one point in the lawn. Measure the elevation at a second point in the lawn. Subtract the results to find the change in elevation. For example, assume at point one you are at an elevation of 1000 feet and at point two you are at an elevation of 1010 feet. So, 1100 feet minus 1000 feet equals 10 feet.
Measure the distance between the two points. In the example, assume the distance is 50 feet.
Divide the change in elevation by the distance to find slope. In the example, 10 feet divided by 50 feet equals 0.2 or 20 percent slope.
Lay out the area for the border with a garden hose, rope or landscape paint.
Measure a few of the stones to determine the average height of your stones.
Dig out a trench for the edging area; the trench depth should be half the average height of the stones.
Place the larger stones at the base of the slope and progress to smaller stones as you work your way up.
Lay each stone on the broadest side to ensure that it will sit properly.
Dig out the area for a specific stone as needed for stones that are taller than the average figure you used to dig the trench. Add fill dirt to compensate for shorter stones.
Fill in the spaces around each stone with dirt as you fill in the edging so that at least half of the stone is covered. Pack the dirt well to ensure that the stone is anchored in the ground.
Pack smaller stones to fill in the gaps between larger stones.
Use a Sharpie to make hash marks on two identical stakes, spacing the markings 6 inches apart. Examine the dowels side by side to confirm that the marks line up with one another.
Locate the highest point within the scope of the drainage design and insert a dowel or stake into the ground. Affix a 10-foot-long piece of string (or cord) to the initial stake, running it along the decline.
Hold the string (or cord) taut to the corresponding stripe on the second dowel, which you have placed in the ground at a depth equivalent to the first.
Use the line level to ascertain the level location on the stake and mark it off. Measure the span from the mark at which the string was first held to the position at which it is level.
Use a calculator to divide this figure by the distance between the dowels, in this case 120 inches, and multiply by 100 to get the slope percentage. Repeat where needed throughout the drainage design.
Till the garden area horizontally with a rake or rototiller. Dig the tines into the soil, working to a depth of 8 inches. Add an inch of compost to the top of the soil. Re-till the area to mix in the compost.
Place wood planks, large stones or bricks around 4 foot by 4 foot sections, setting each raised bed below the next, building down the slope to create terraced raised beds. Make enough raised beds to cover the entire tiered garden area.
Plant vegetable plants and seeds in rows running across the slope. Place moisture-loving plants near the bottom of the slope as water naturally collects at the bottom. Follow the spacing requirements as printed on seed packets and plant labels.
Water the soil daily until moist. Skip watering on days when the soil looks moist. As the bottom of the slope retains moisture, refrain from watering that particular area if it appears moist, but water the rest of the garden if needed.