HomeMy WebLinkAboutPC 9.17.25_CAO PC Public HearingDOCKET #235
CRITICAL AREAS ORDINANCE (CAO) UPDATE
Planning Commission Public Hearing
September 17, 2025
Presented by: Mariah Kerrihard, Associate Planner
425-430-7238
mkerrihard@rentonwa.gov
Issue:
1.The Growth Management Act (GMA) requires all cities and counties in Washington to adopt
regulations protecting “critical areas” to preserve the natural environment, wildlife habitats, and
sources of fresh drinking water. Critical areas regulation also encourage public safety by limiting
development in areas prone to natural hazards like floods and landslides.
2.Every ten years, counties and cities are required to take legislative action to review and, if needed,
revise their comprehensive land use plans and development regulations to ensure the plans and
regulations comply with the requirements of the GMA. This update is due by December 31, 2025.
3.The level of review depends on several factors.
•If the jurisdiction contains significant, extensive, and/or inadequately protected critical areas, a
more detailed review of its policies and development regulations may be necessary.
•If new sources of best available science (BAS) are identified (including any management
recommendations associated with the new science), the jurisdiction should review those updates
for applicability to its critical areas regulations.
SUMMARY OF D-235
PROPOSED AMENDMENTS TO THE CAO
1.Code Update:
•Updating terminology, clarifying document references, and ensuring
current standards use best available science
2.Channel Migration Zones (CMZs):
•The CMZ identifies river or stream corridors at risk for channel movement
over time due to erosion, flooding, or natural stream processes. The CMZ
for the Cedar River is specifically mapped by King County’s 2015 study
and adopted into the city’s regulatory framework (2015)
•The City or a property owner may request a site-specific reassessment of
CMZ boundaries using a geomorphic assessment. Updates are allowed if
conditions have changed and must be documented
3.Wetland Buffers:
•Wetland buffer requirements have been revised to apply the best
available science consistent with Wetland Mitigation in Washington State,
Part 1: Agency Policies and Guidance, Version 2 (Ecology Publication No.
21-06-003, April 2021)
•Detailed tables for buffer widths and mitigation ratios are integrated for
various wetland categories and mitigation scenarios, aligned with state
best practices
•Administrative buffer reductions and averaging have clear minimum
reduction standards by critical area type and strong criteria for when
reductions are allowed, especially requiring functionally equivalent or
improved ecological outcomes.Cedar River 2025
Category I
•Represent a unique or rare wetland type; or
•Are more sensitive to disturbance than most
wetlands; or
•Are relatively undisturbed and contain ecological
attributes that are impossible to replace within a
human lifetime; or
•Provide a very high level of functions
Category II
•Difficult, though not impossible, to replace, and
provide high levels of some functions.
•Occur more commonly than Category I wetlands,
yet still need a relatively high level of protection
City of Renton (COR) Maps – Wetland Layer
WETLAND CATEGORIZATION
City of Renton
Category III
•Wetlands with a moderate level of functions
•Can often be adequately replaced with a well-
planned mitigation project
Category IV
•The lowest levels of functions and are often heavily
disturbed.
•These are wetlands that we should be able to
replace, and in some cases be able to improve.
•May provide some important functions and also
need to be protected.
Renton Wetland 2025
WETLAND CATEGORIZATION
PROPOSED WETLAND BUFFER WIDTHS
Wetland Category Wetland
Characteristic
Intensity of Impact of Adjacent Land Use
Low Moderate High
I and II
Bogs and wetlands of high
conservation value 125 feet 190 feet 250 feet
Habitat score of 8 to 9 150 feet 225 feet 300 feet
Habitat score of 6 to 7 75 feet 110 feet 150 feet
Habitat score of less than 6
and water quality score of 8
to 9
50 feet 75 feet 100 feet
Not meeting any of the
above characteristics 50 feet 75 feet 100 feet
III
Habitat score of 8 to 9 150 feet 225 feet 300 feet
Habitat score of 6 to 7 75 feet 110 feet 150 feet
Habitat score of 3 to 5 40 feet 60 feet 80 feet
IV Any habitat score 25 feet 40 feet 50 feet
COMPARISON OF EXISTING VS. PROPOSED WETLAND BUFFER WIDTH
Wetland Category Habitat Function
Existing Requirement
(Low Impact / All Other
Land Uses)
Proposed
Requirement
(Low / Moderate /
High Impact)
Difference
(Proposed - Existing)
(Low / Moderate /
High)
I – Bogs & Heritage
Wetlands 175 ft / 200 ft 125 / 190 / 250 ft –50 / –10 / +50 ft (vs.
Low / All Other Uses)
I Habitat score 8–9 175 ft / 200 ft 150 / 225 / 300 ft –25 / +25 / +100 ft
I or II Habitat score 6–7 125 ft / 150 ft 75 / 110 / 150 ft –50 / –40 / 0 ft
I or II Habitat <6 & Water
Quality 8–9 75 ft / 115 ft 50 / 75 / 100 ft –25 / –40 / –15 ft
I or II Not meeting any above
characteristics 75 ft / 115 ft 50 / 75 / 100 ft –25 / –40 / –15 ft
II Habitat score 8–9 150 ft / 175 ft 150 / 225 / 300 ft 0 / +50 / +125 ft
III Habitat score 8–9 100 ft / 125 ft 150 / 225 / 300 ft +50 / +100 / +175 ft
III Habitat score 6–7 75 ft / 100 ft 75 / 110 / 150 ft 0 / +10 / +50 ft
III Habitat score 3–5 50 ft / 75 ft 40 / 60 / 80 ft –10 / –15 / +5 ft
IV Any habitat score 40 ft / 50 ft 25 / 40 / 50 ft –15 / –10 / 0 ft
PROPOSED TYPES OF LAND USE IMPACTS
Level of Impact
From Proposed
Land Use
Types of Land Use
High
•Commercial
•Urban
•Industrial
•Institutional
•Mixed-use developments
•Residential (more than 1 unit/acre)
•Roads: federal and state highways, including on-ramps and exits, state routes, and other roads associated
with high-impact land uses
•Railroads
•Agriculture with high-intensity activities (dairies, nurseries, greenhouses, growing and harvesting crops
requiring annual tilling, raising and maintaining animals, etc.)
•Open/recreational space with high-intensity uses (golf courses, ball fields, etc.)
•Solar farms (utility scale)
Moderate
•Residential (1 unit/acre or less)
•Roads: Forest Service roads and roads associated with moderate-impact land uses
•Open/recreational space with moderate-intensity uses (parks with paved trails or playgrounds, biking, jogging,
etc.)
•Agriculture with moderate-intensity uses (orchards, hay fields, light or rotational grazing, etc.)
•Utility corridor or right-of-way used by one or more utilities and
•including access/maintenance road
•Wind farm
Low
•Natural resource lands (forestry/silviculture–cutting of trees only, not land clearing and removing stumps)
•Open/recreational space with low-intensity uses (unpaved trails, hiking, birdwatching, etc.)
•Utility corridor without a maintenance road and little or no vegetation management
•Cell tower
Mitigation Ratios for Wetland Impacts
•Compensatory mitigation for wetland alterations shall be based on the wetland category and the type
of mitigation activity proposed.
•The replacement ratio shall be determined according to the ratios provided in the table.
•The created, re-established, rehabilitated, preserved, or enhanced wetland area shall at a minimum
provide a level of functions equivalent to the wetland being altered
•Compensation for wetland buffer impacts shall occur at a minimum one to one (1:1) ratio.
Compensatory mitigation for buffer impacts shall include enhancement of degraded buffers by planting
native species, removing structures and impervious surfaces within buffers, and other measures.
REPLACEMENT RATIOS
Wetland Mitigation Type and Replacement Ratio*
Wetland
Category**
Creation or Re-
establishment Rehabilitation Preservation Enhancement
Only
Category IV 1.5:1***3:1 6:1 6:1
Category III 2:1 4:1 8:1 8:1
Category II 3:1 6:1 12:1 12:1
Category I 4:1 8:1 16:1 16:1
General Purpose
•The typically required critical area buffers may be
reduced to no net loss of functions or values as
documented in a study prepared by a qualified
professional. Greater buffer width reductions
require review as a variance
Mitigation to Reduce Buffers
•Criteria for Reduction of Wetland Buffer Width
with Enhancement
•Criteria for Averaging of Wetland Buffer Width
Reasonable Use Variance
•No proposal shall result in a loss of critical area
functions or values. If the application of these
provisions would deny all reasonable use of the
property, the applicant may apply for a variance as
identified in RMC 4-9-250
Black River 2025
ALTERATIONS TO CRITICAL AREAS AND/OR BUFFERS
Example A – Vuecrest II Short Plat
•Category II wetland
•The site was 106,680 square feet (2.45 acres)
•The site includes a 0.19 acre of onsite critical
area (Category 2 wetland), in the northwest
corner of the property
•As proposed the short plat subdivided the parcel
into eight (8) residential lots, and one (1) critical
area tract (Tract A)
Example B – Valley Vue Short Plat
•Category III wetland
•The site was 100,188 square feet (2.3 acres)
•The eastern portion of the site is comprised of
established forest with a Category III wetland that
extends off-site to the east and south.
•As proposed the short plat subdivided the parcel
into two (2) residential lots, leaving both existing
houses undisturbed, and one (1) Native Growth
Protection Tract (Tract A). City of Renton
EXAMPLES WITHIN RENTON
Example A
Example B
Wetland Mitigation - Category II
•As compensatory mitigation for the permanent buffer impacts, a total of 4,907 square feet of
relatively undisturbed forested area, located adjacent to the buffer of wetland were designated as
buffer
•This represents a mitigation to impact ratio of 1.1:1, providing an increase in total buffer area of 458
square feet
•The additional buffer areas will be permanently protected as part of the NGPA on the project site
City of Renton – COR Maps
EXAMPLE A
Wetland Mitigation - Category III
•No impacts to the critical areas onsite were proposed
•In order to preserve and protect the wetland and its associated buffer, the applicant established a
Native Growth Protection Easement for the Category III wetland and its associated 100-foot buffer
area within Tract A
•The additional buffer areas will be permanently protected as part of the NGPA on the project site
City of Renton – COR Maps
EXAMPLE B
General Purpose
•RMC 4-10-090, Critical Areas Regulations – Nonconforming
Activities and Structures
Existing Development
•Normal and routine maintenance and repair of any existing
public or private uses and facilities where no alteration of
the critical area and required buffer or additional fill
materials will be placed.
•In every case, critical area and required buffer impacts shall
be minimized and disturbed areas shall be restored during
and immediately after the use of construction equipment.
Proposed Development
•Prior to any development or alteration of a property
containing a critical area the owner or designee must obtain
a development permit, critical area permit, and/or letter of
exemption.
•No separate critical area permit is required for a
development proposal for which development permits are
required or that has received a letter of exemption.May Creek 2025
LEGALLY NON-CONFORMING
WHAT IS A CHANNEL MIGRATION ZONE?
The area that a stream or river could be
expected to occupy in the future due to
lateral migration or channel avulsion.
Often delineated into hazard areas
with regulations applied differently
Moderate
Severe
Regulation is for the purpose of
prevention of loss of life and damage
to property or infrastructure
Cedar River – King County derived CMZ
LATERAL CHANNEL MIGRATION
Occurs when a stream or river moves laterally through bank and floodplain erosion
2015 2024
Skagit River
CHANNEL AVULSION
Occurs when a stream or river moves or cuts a new mainstem channel across the
floodplain. It can happen quickly, or it can develop over time.
1990 2006
Cedar River – Near Ron Regis Park
DIFFERENCE BETWEEN MIGRATION AND FLOODING
Flooding involves the inundation of the floodplain, areas that are typically dry, with
excess water. It is a short-term, temporary condition.
Channel migration is the sudden or gradual movement of a channel across it’s
floodplain. It can be described as the stream or river modifying or changing course.
It is a long-term change.
THREE MAIN AREAS OF CHANGE
Area Update Rationale
Code Updates Up to date terms and
references Ensures scientific accuracy
Channel Migration Zone
(CMZ) Mapping
Mapping expands river
protections; includes
procedures for boundary
challenges
Safer development for areas
near rivers; aligns with state
policy
Wetland Buffers &
Replacement Ratios
Some buffer sizes and
replacement ratios
increased under the
Department of Ecology
guidance
Greater environmental
protection and updating to
Best Available Science
Next Steps:
•Planning Commission Deliberations & Recommendations (10/01)
•Planning & Development Committee Recommendations (10/13)
Presented by: Mariah Kerrihard, Associate Planner
425-430-7238
mkerrihard@rentonwa.gov