How to Prevent Runoff on a Sloped Lawn

Lay a 4-foot-long carpenter's level across the top of the slope at one far side, and adjust the level until it reads the ground as perfectly level. Place a marking flag at each end of the level in that location. Move the level laterally across the slope toward the top's other side, and place another flag to mark the same elevation 4 feet beyond the previous flag. Continue across the slope to mark the elevation contour in that way.

Dig a trench 6 inches deep along the row of flags. Pile the removed soil in a mound about 3 feet downhill from the trench.

Widen the trench to about 3 feet, and make its sides taper upward gradually from the trench's maximum depth of 6 inches in its center. Spread the excavated soil on the downhill side of the trench, forming a low berm.

Rake the excavated soil into a smooth mound that tapers gradually up and down in the inverse, or opposite, shape of the trench. The trench is the swale, and the mound is the berm.

Spread a 2- to 3-inch-deep layer of compost over the area of the swale and berm, and mix the compost into the soil by using a digging fork or tiller. Rake the soil to create a smooth surface.

Plant grass seed or sod on the swale and berm.

Repeat the process to create a swale and berm every 20 to 30 feet down the slope's length. The swales and berms will slow the flow of storm-water runoff and help the water infiltrate the ground.