Chapter 16C.07


16C.07.01    Purpose and Intent.

16C.07.02    Designating and Mapping.

16C.07.03    Protection Approach.

16C.07.04    Wetland Functions and Rating.

16C.07.05    Compensatory Mitigation Requirements.

16C.07.06    Wetland Mitigation Banks.

16C.07.01 Purpose and Intent.

The purpose and intent of the provisions protecting wetland critical areas is equivalent to the purpose and intent for Chapter 16C.06.01 (Purpose and Intent).

(Ord. 5-2017 § 2(C) (Exh. 1) (part), 2017: Ord. 13-2007 §1 (Exh. A)(16C.07.01), 2007).

16C.07.02 Designating and Mapping.

(1)    Wetlands are those areas that meet the definition found in Section 16C.02.425 as provided in RCW 36.70A.030(21). All areas within Yakima County meeting the wetland definition are hereby designated critical areas and are subject to the provisions of this title. The following clarifications guide the application of the wetland definition:

(a)    Due to the inherent design of most irrigation systems, such systems are reasonably and foreseeably expected to result in some leakage or seepage. Such leakage or seepage is a normal result of utilization of irrigation systems and is deemed for the purposes of this title to be a nonregulated, artificial wetland.

(2)    The approximate location and extent of wetlands are shown on maps maintained by Yakima County, which may include information from the National Wetlands Inventory produced by the U.S. Fish and Wildlife Service and soil maps produced by United States Department of Agriculture National Resources Conservation Service that are useful in helping to identify potential wetland areas. These maps are to be used as a guide for Yakima County, project applicants and/or property owners, and may be continuously updated as wetlands are more accurately identified, located and delineated.

(Ord. 5-2017 § 2(C) (Exh. 1) (part), 2017: Ord. 13-2007 §1 (Exh. A)(16C.07.02), 2007).

16C.07.03 Protection Approach.

(1)    Wetlands will be protected using the protection approach for Hydrologically Related Critical Areas found in Section 16C.06.02 (Protection Approach), which accommodates issues affecting wetlands.

(2)    Wetlands and their functions will be protected using the standards found in the Stream Corridor Chapter (16C.06), which includes provisions to:

(a)    Follow mitigation sequencing as outlined in Section 16C.03.10 (Mitigation Requirements);

(b)    Avoid degrading the functions and values of the wetland and other critical areas;

(c)    Provide a zero net loss of wetland functions and values together with, if reasonably possible through voluntary agreements or government incentives, a gain in functions and values through the long term.

(Ord. 5-2017 § 2(C) (Exh. 1) (part), 2017: Ord. 13-2007 §1 (Exh. A)(16C.07.03), 2007).

16C.07.04 Wetland Functions and Rating.

(1)    Wetlands are unique landscape features that are the interface between the aquatic and terrestrial environments. Wetlands provide the following functions:

(a)    Biogeochemical functions, which are related to trapping and transforming chemicals and include functions that improve water quality in the watershed such as: nutrient retention and transformation, sediment retention, metals and toxics retention, and transformation;

(b)    Hydrologic functions, which are related to maintaining the water regime in a watershed, such as: flood flow attenuation, decreasing erosion, groundwater recharge;

(c)    Food web and habitat functions, which includes habitat for: invertebrates, amphibians, anadromous fish, resident fish, birds, mammals.

(2)    Wetlands shall be rated based on categories that reflect the functions and values of each wetland. Wetland categories shall be based on the criteria provided in the Washington State Wetland Rating System for Eastern Washington, 2014 Update (Ecology Publication #14-06-030 - as determined using the appropriate rating forms contained in that publication. These categories are summarized as follows:

(a)    Category I wetlands are those that represent a unique or rare wetland type, are more sensitive to disturbance than most wetlands, are relatively undisturbed and contain ecological attributes that are impossible or too difficult to replace within a human lifetime, and provide a high level of functions. Generally, these wetlands are not common and make up a small percentage of the wetlands within Yakima County. The following types of wetlands are Category I:

(i)    Alkali wetlands are characterized by the presence of shallow saline water with a high pH and provide the primary habitat for several species of migrant shorebirds and are also heavily used by migrant waterfowl and small alkali bee that is used to pollinate alfalfa and onion for seed production;

(ii)    Wetlands of High Conservation Value (formerly called Natural Heritage Wetlands) - Wetlands that are identified by scientists of the Washington Department of Natural Resources Natural Heritage Program as important ecosystems for maintaining plant diversity that represent rare plant communities or provide habitat for rare plants are uncommon in eastern Washington;

(iii)    Bogs and Calcareous Fens are peat wetlands sensitive to disturbance and have not been successfully re-created through compensatory mitigation. Bogs are wetlands with peat soils and a low pH, usually a pH <5. Calcareous fens are a type of alkaline, rather than acidic wetland, maintained by groundwater that have a neutral or high pH and high concentrations of calcium and other alkaline minerals;

(iv)    Mature and old-growth forested wetlands with native slow growing trees, which include Western Red Cedar (Thuja plicata), Alaska Yellow Cedar (Chamaecyparis nootkatensis), pine spp. (mostly White pine - Pinus monticola), Western Hemlock (Tsuga heterophylla), Oregon White Oak (Quercus garryana) and Englemann Spruce (Picea engelmannii);

(v)    Forested wetlands with stands of Aspen contribution as a priority habitat far exceeds the small acreage of these stands and relatively small number of stems (Hadfield & Magelssen, 2004). Furthermore, mature stand of aspen and its underground root system may be difficult to reproduce. Regeneration of aspen stands by sexually produced seeds is an unusual phenomenon (Romme et al., 1997);

(vi)    Wetlands scoring 22 points or more (out of 27) from the rating of functions are Category I wetlands in the Eastern Washington Wetland Rating System.

(b)    Category II wetlands are difficult, though not impossible, to replace, and provide high levels of some functions. These wetlands occur more commonly than Category I wetlands, but still need a relatively high level of protection. Category II wetlands include:

(i)    Forested wetlands in the floodplains of rivers are an important resource in the floodplains of rivers, especially in the areas through which the river may flow regularly (often called the channel migration zone). Trees in the Floodplains are critical to the proper functioning and the dynamic processes of rivers. They influence channel form, create pools, riffles, and side channels that are essential habitat for many fish and other aquatic species. These trees also create localized rearing and flood refuge areas, and contribute to the stabilization of the main river channel (NRC, 2002);

(ii)    Mature and old-growth forested wetlands with fast growing native trees, which include Alders (Red - Alnus rubra, Thin-leaf - A. incana ssp. tenuifolia), Cottonwoods (Narrow-leaf - Populus angustifolia, Black - P. balsamifera), Willows (Peach-leaf - Salix amygdaloides, Sitka - S. sitchensis, Pacific - S.lasiandra); Quaking Aspen (Populus tremuloides), or Water Birch (Betula occidentalis);

(iii)    Vernal pools, also called rainpools, are ecosystems located in a landscape with other wetlands that retain water until the late spring when they dry out to allow some strictly aquatic organisms to flourish, and provide areas where migrating waterfowl can find food and pair bonding;

(iv)    Wetlands scoring between 19-21 points (out of 27) on the questions related to the functions present are Category II wetlands in the Eastern Washington Wetland Rating System.

(c)    Category III wetlands are often smaller, less diverse or more isolated from other natural resources in the landscape than Category II wetlands. Category III wetlands include:

(i)    Vernal pools that are isolated; and

(ii)    Wetlands with a moderate level of functions (scoring between 16 - 18 points) in the Eastern Washington Wetland Rating System and can often be adequately replaced with a well-planned mitigation project.

(d)    Category IV wetlands have the lowest levels of functions, (scoring less than 16 points) in the Eastern Washington Wetland Rating System, and are often heavily disturbed. These are wetlands that should be able to be replaced, and in some cases be improved. These wetlands may provide some important functions, and also need to be protected.

(3)    The wetland rating categories as described in section (2), above, shall be applied to projects which are submitted on or after the date of adoption of these provisions. The wetlands shall be rated as they exist on the day of project application submission, as the wetland naturally changes thereafter, or as the wetland changes in accordance with permitted activities. However, illegal modifications to wetlands which have been made since the amended Critical Areas Ordinance (YCC Title 16A 1995) shall not be considered when rating the wetland. Information regarding the original condition of illegally modified wetlands that cannot be discerned from aerial photographs or other reliable information sources, which is needed to complete the Eastern Washington Wetland Rating System data sheets, shall use the highest appropriate points value within each missing data field of the rating sheet to complete the rating.

(Ord. 10-2019 (Exh. 1) (part), 2019; Ord. 5-2017 § 2(C) (Exh. 1) (part), 2017: Ord. 13-2007 §1 (Exh. A)(16C.07.04), 2007).

16C.07.05 Compensatory Mitigation Requirements.

Projects that propose to compensate for wetland acreage and/or functions are subject to State and Federal regulations. Compensatory mitigation for alterations to wetlands shall provide no net loss of wetland functions and values, and must be consistent with the Mitigation Plan Requirements in Section 16C.03.17(13) (Compensatory Mitigation Plans). The following guidance documents were developed to assist applicants in meeting the regulations and requirements.

(1)    Compensatory mitigation plans must be consistent with Wetland Mitigation in Washington State Part 1: Agency Policies and Guidance and Wetland Mitigation in Washington State Part 2: Developing Mitigation Plans or as revised (see latest update at

(2)    Compensatory mitigation application and ratios for mitigation of wetlands shall be consistent with “Wetlands in Washington State - Volume 2: Guidance for Protecting and Managing Wetlands – Appendix 8-D- Section 8D.3” or as revised (Washington State Department of Ecology. Publication No. 05-06-008 -

(Ord. 5-2017 § 2(C) (Exh. 1) (part), 2017: Ord. 13-2007 §1 (Exh. A)(16C.07.05), 2007).

16C.07.06 Wetland Mitigation Banks.

(1)    Credits from a wetland mitigation bank may be approved for use as compensation for unavoidable impacts to wetlands when:

(a)    The bank is certified under RCW 90.84 and its administrative rules, WAC 173-700;

(b)    The Administrative Official determines that the wetland mitigation bank provides appropriate compensation for the authorized impacts; and

(c)    The proposed use of credits is consistent with the terms and conditions of the bank’s certification.

(2)    Replacement ratios for projects using bank credits shall be consistent with replacement ratios specified in the bank’s certification.

(3)    Credits from a certified wetland mitigation bank may be used to compensate for impacts located within the service area specified in the bank’s certification. In some cases, bank service areas may include portions of more than one adjacent drainage basin for specific wetland functions.

(Ord. 5-2017 § 2(C) (Exh. 1) (part), 2017: Ord. 13-2007 §1 (Exh. A)(16C.07.06), 2007).