Although the California drought has been declared over in early 2017, state regulators continue to impose restrictions on landscape watering. These new restrictions may cause confusion on the part of landscapers and homeowners. UC Davis has created an irrigation scheduling worksheet that can help. The worksheet generates an annual calendar to irrigate an irrigation zone based on several factors. The user enters information about their site to find out how much to water their landscape.
Before using the irrigation scheduling worksheet, the user will need to first conduct an irrigation assessment to determine the distribution uniformity of the irrigation system. If needed, download instructions at Landscape Irrigation System Evaluation and Management.
This spreadsheet will generate an annual calendar to irrigate a single hydrozone based on local historical evapotranspiration (ET), distribution uniformity (DU) assessment information, soil type, and desired soil wetting depth. The worksheet will accommodate irrigation that is restricted to specific days of the week (designated irrigation days).
This tool will calculate and determine an irrigation schedule for one irrigation zone for a calendar year. The user enters information about the site location including: CIMIS ETo zone (using the included map), soil type (use the Soil Web application available online if needed), DU assessment information, the year of the desired irrigation schedule, and the desired depth to wet the soil. Some water providers restrict the days of the week when irrigation can occur and those days can be accommodated.
An irrigation assessment needs to be conducted and the catch can values from the assessment is entered into the spreadsheet. If runoff occurred from the site or significant puddling or pooling appeared, the duration of the irrigation when that occurred is also entered. From those values, irrigation information is calculated including DU, precipitation rate, minimum irrigation duration (lower boundary), and recommended duration (upper boundary). If runoff occurred, valve cycling will be calculated to determine the length of the cycle (duration) and number of cycles per irrigation event. This information can be used for programming an irrigation controller. Because of rounding, cycling may deliver less water than the upper boundary amount and that amount is determined.
The irrigation calendar shows the days that irrigation should occur based on historical ET and days of the week when irrigation is allowed. If there are restrictions when irrigation occurs and ET rates are high, sometimes the irrigation cannot “keep up” with water demand. So this spreadsheet will “look ahead” to see if and irrigation may be required in the next day or so (depending on the number of days when the next irrigation is allowed) and may schedule an irrigation on an earlier allowed day if necessary.
David A. Shaw & Dennis R. Pittenger, UC Cooperative Extension
This publication presents practical information and field procedures for evaluating landscape irrigation hardware performance and determining irrigation schedules. These guidelines will enable the user to develop a superior irrigation management program that will optimize plant growth and health without wasting water. Emphasis is given to water conservation strategies that are effective during periods of restricted water use.