Water Resources Program guidance and policy

Ecology’s Water Resources Program is updating its irrigation efficiency guidance and related documents to reflect best available science.

Two documents are available for review. We are accepting comments and hosting an informational webinar.

Program guidance: Determining Irrigation Efficiency and Consumptive Use

Read the draft guidance.

Program policy: Evaluation of Changes to Enable Irrigation of Additional Acreage or the Addition of New Purposes of Use to Existing Water Rights

Read the draft policy. The document is available showing tracked changes on page 5.

Background

These documents will guide Ecology's work. The updates do not change the formula used to calculate annual consumptive quantity (ACQ) or irrigation efficiency nor will these impact existing water rights. The new irrigation efficiency tool, developed by Washington State University, gives Ecology staff and others access to best available science and current data.

Irrigation efficiency, consumptive use, or the amount of water available for change will depend on the facts of a project. For example, Ecology determines ACQ when a proposed project adds irrigated acres — sometimes called “spreading” — or changes the purpose of use. State law requires that the changes do not increase consumptive water use. This helps protect senior water rights and instream flows.