Irrigation water that runs off a sloped lawn is inefficient, costs extra money in watering costs and can cause damage to lower areas of the lawn. Wet areas of a lawn on the bottom of a slope lead to pests, mold and mildew lawn diseases and lessen the drought tolerance of those areas. Calibration of your sprinkler system by taking into consideration the amount of water it produces in a given time period helps determine the frequency and amount of water needed for irrigation without runoff.
Place baking pans or other shallow containers at the bottom of your sloped lawn.
Manually turn on your hose-end timer for a garden hose and sprinkler system, or the irrigation control for an in-ground irrigation system.
Write down the time you turn the system on.
Allow the lawn to receive water, and as soon as it starts to run off the bottom of the slope, manually turn off the timer.
Write down how many minutes you irrigated the lawn until the point of runoff at the bottom of the slope. Set your hose-end timer or irrigation controller so that it only turns on in cycles for the same amount of minutes until runoff occurs.
Measure the water depth in each container with a measuring tape. Each container should have about the same amount of water.
Determine how many irrigation cycles you need to run per week to administer about 1 inch of water per week to your lawn. For example, if the containers have about 1/8 inch of water in them, set your hose-end timer or irrigation controller to 8 cycles per week for the amount of time determined until runoff occurs.