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Large areas of eastern Washington have been converted to agriculture and are under irrigation. Additionally, some agricultural areas in western Washington are also irrigated. Many wetlands have formed adjacent to irrigation conveyance systems and in low-lying areas where irrigation occurs.
Ecology’s authority to regulate wetlands is based in two principal statutes: RCW 90.48, the Water Pollution Control Act (WPCA); and RCW 90.58, the Shoreline Management Act (SMA). Both laws define “wetlands” and “artificial” wetlands, such as irrigation ditches and canals. The definition in both laws states that an “artificial” wetland must be both “intentionally created” and created in an upland area.
A wetland that may be influenced by irrigation is considered a wetland under the state definition and regulated accordingly. However, this does not mean that irrigation-influenced wetlands cannot be filled; it means that one must obtain state approval to do so.
It is often difficult to differentiate between wetlands and artificial wetlands in the field because it is often not easy to determine whether the wetland is the result of an intentional act and whether it occurred in an upland or in an already existing wetland. With the issue of irrigation, it can be particularly difficult to make these distinctions because it is difficult to determine the relative influence of natural sources of water such as precipitation, snowmelt and groundwater as compared to both regional and site-specific irrigation practices.
Ecology's focus sheet on irrigation-influenced wetlands explains in more detail how Ecology addresses a wide range of situations where wetlands are influenced by human activities. Applicable provisions of federal or local laws are not addressed in the focus sheet. Consult with the U.S. Army Corps of Engineers for applicability of federal law and your local city or county planning department for applicability of local laws.
Copyright © Washington State Department of Ecology. See http://www.ecy.wa.gov/copyright.html.
