Updating the Washington Irrigation Guide

Over the last 40 years, Ecology has collaborated with Washington State University and various state and federal agricultural agencies to produce guidance documents that estimate crop irrigation requirements. This information was used for many different purposes, including:

By farmers for design and operation of irrigation systems.
By the Department of Ecology and Courts in estimating the amount of water needed for water rights for irrigation purposes.
By planners estimating how much water was being used by crops.

The first such document, published in 1969, was called “Circular 512” and provided crop irrigation requirements for 38 locations throughout Washington for 18 different crops. These data were compiled using the modified Blaney-Criddle procedure from 30 years of weather records.

The second guidance document, Irrigation Requirements for Washington—Estimates and Methodology, was published in 1982 and is still in print today. This guidance document estimates crop irrigation requirements for 40 locations throughout Washington for 39 different crops. These data were compiled using the Doorenbos and Pruitt Blaney-Criddle method based on 26 years of NOAA weather data.

The most recent guidance document, the State of Washington Irrigation Guide (WIG), was published in 1985 and supplemented in 1992. It remains the definitive irrigation guidance document in use today. This guidance document estimates crop irrigation requirements for 90 locations throughout Washington for 60 different crops. These data were compiled using the Doorenbos and Pruitt Blaney-Criddle and SCS Blaney-Criddle Modified methods based on up to 29 years of NOAA weather data.

Why Update the Washington Irrigation Guide?

Good data is required to manage Washington’s water resources. Updating the WIG is important because:

The Washington Irrigation Guide is used extensively throughout the state for irrigation system design and planning, irrigation scheduling and management, water rights evaluations and transfers, and hydrologic studies.
The crop-water-use estimates currently being used were created in the early 1980’s and 1990’s using old data and out-dated estimation techniques.
Data from the last 20 years is available which will provide more accurate estimates of crop water demand.
Additional monitoring stations are available which will allow users to more closely match their geographic location.
The American Society of Civil Engineers recently completed a study evaluating over 50 methods of calculating evapotranspiration (ET) and concluded that the Penman Monteith equation is the preferred ET estimation method.
The current guide lacks information on new or emerging crops, such as wine grapes, terraced orchards and biofuels, and on traditional crops grown in new areas.
The current WIG data is not available in electronic format and is therefore difficult for the public to access and use.

Public Comment on Scope

Ecology, WSU and NRCS have developed a Scope of Work to update the Washington Irrigation Guide. However, because of the widespread use of this document by Washington State stakeholders, Ecology asked for comments on the proposed scope before funding the work. Ecology received comments from the public on the scope of work between January 22 to February 22, 2008. Those comments may be incorporated into the scope of work.

Scope of Work to Update the Washington Irrigation Guide - 1st DRAFT

Contacts

Daniel R. Haller, P.E.
Columbia River Unit Supervisor
Department of Ecology, Central Region Office
Phone: (509) 454-4255
E-mail: wig@ecy.wa.gov

Troy Peters, P.E.
Irrigation Engineer, Extension Specialist
WSU Prosser
Phone: (509) 786-9247
E-mail: troy_peters@wsu.edu