Chapter 18.86 ENVIRONMENTALLY CRITICAL AREAS

Chapter 18.86
ENVIRONMENTALLY CRITICAL AREAS¹

Sections

18.86.010 Adoption by reference.

18.86.020 City council findings.

18.86.030 Purpose.

18.86.040 Applicability.

18.86.050 Special studies required.

18.86.060 Maps and inventories.

18.86.070 Best management practices required.

18.86.080 Development restrictions.

18.86.090 Development standards – Compliance – Requirements.

18.86.100 Wetlands – Development standards.

18.86.110 Wetlands – Reasonable use exceptions.

18.86.120 Wetlands – Limited exemptions.

18.86.130 Wetlands – Mitigation requirements.

18.86.140 Streams – Development standards.

18.86.150 Streams – Reasonable use exceptions.

18.86.160 Streams – Limited exemptions.

18.86.170 Streams – Mitigation requirements.

18.86.180 Geologically hazardous areas – Development standards.

18.86.190 Ravine sidewalls and bluffs – Development standards.

18.86.200 Hillsides of 15 percent slope and greater – Development standards – Disturbance limitations.

18.86.210 Ravine sidewalls, bluffs, and hillsides of 15 percent slope and greater – Reasonable use exceptions.

18.86.220 Seismic hazard areas – Development standards.

18.86.230 Erosion and landslide hazard areas – Development standards.

18.86.240 Critical aquifer recharge areas – Development standards – Buffers and disturbance limitations.

18.86.250 Fish and wildlife habitat conservation areas – Development standards – Buffers and disturbance limitations.

18.86.260 Area of special flood hazard – Development standards – Buffers and disturbance limitations.

18.86.270 Limited density transfer.

18.86.280 Development exceptions.

18.86.290 Unauthorized critical area alterations and enforcement.

18.86.300 Tracts and easements.

18.86.310 Securities and enforcement.

18.86.320 Environmentally critical area mitigation fund.

18.86.330 Surface water design manual.

18.86.340 Surface water contamination – Determination.

18.86.350 Surface water contamination – Compliance required – Penalty.

18.86.360 Surface water contamination – Penalty not exclusive remedy.

18.86.370 Interpretation.

18.86.380 Appeals.

18.86.010 Adoption by reference.

The codes, standards, rules, and regulations adopted by this chapter are adopted by reference thereto as though fully set forth in this title. Not less than one copy of each such codes, standards, rules, and regulations, in the form in which it was adopted, and suitably marked to indicate amendments, additions, deletions and exceptions as provided in this chapter, shall be filed with the planning, building and public works department and be available for use and examination by the public. [Ord. 1400 § 11, 2007.]

18.86.020 City council findings.

The city council finds that:

(1) Development in wetlands results in:

(a) Increased soil erosion and sedimentation of downstream water bodies;

(b) Degraded water quality from increased sedimentation;

(c) Degraded water quality from loss of pollutant removal process of wetlands – sediment trapping, nutrient removal, and chemical detoxification;

(d) Elimination of wildlife and fisheries habitat. Wetland ecosystems support a diverse, unique, and rich group of flora and fauna. Habitat is especially productive at the interface between water and land ecosystems. Several wildlife species specifically require wetland habitats for breeding, nesting, rearing of young, and feeding;

(e) Loss of ground water discharge and recharge areas;

(f) Loss of storm water retention and detention capacity resulting in increased flooding, degraded water quality, and changes in the streamflow regimen of watersheds;

(g) Loss of slow-release detention resulting in loss of recharge to base flow of stream systems during low flow periods and increased peak flows and flooding during storm events; and

(h) Loss of fishery resources from water quality degradation, increased peak flow rates, decreased summer low flows, and changes in the streamflow regimen.

(2) Development in stream corridors results in:

(a) Siltation of streams, which destroys spawning beds, kills fish eggs and alevins, irritates fish gills, reduces aquatic insect populations, fills stream channels, and causes flooding;

(b) Loss of stream corridor vegetation, which raises stream temperatures, destabilizes stream banks, causes erosion, removes nutrients by removing source of fallen leaves and streamside insects, increases sedimentation, and reduces recruitment of large wood debris necessary for stream structure;

(c) Elimination of wildlife and fish habitat. The stream corridor is especially sensitive and is recognized as being among the most productive terrestrial and aquatic ecosystems. It usually provides all four of the basic habitat components: water, food, cover, and space. The stream corridor is usually richer in habitat diversity and, consequently, wildlife diversity and numbers of individuals are higher than in adjoining upland plant communities. Certain fish and wildlife species are totally dependent on the stream corridor and as uplands are developed, stream corridors become a place of refuge for many wildlife species;

(d) Increased peak flow rates and decreased summer low flow rates of streams, resulting in negative impacts to the physical and chemical requirements critical for sustained fish populations;

(e) Stream channelization, which increases current velocity and bank erosion, removes critical fish rearing and spawning habitat, and reduces habitat diversity and simplifies the biotic community;

(f) Piping of streamflow and crossing of streams by culverts, which increases potential for downstream flooding, reduces migratory fishery range and, therefore, fish populations, removes habitat, and eliminates the biotic community; and

(g) Construction near or within streams, which adversely impacts fish and wildlife by destroying habitat and degrading water quality and increases potential for flooding, property damage, and risk to public health, safety, and welfare.

(3) Development on hillsides results in:

(a) The loss of slope and soil stability as well as increased erosion. The removal of vegetation from hillsides deprives the soil of the stabilizing function of roots, and the moderating effects on wind and water erosion of leaves and branches. Loss of soil stability increases erosion and thus lowers downstream water quality as a result of siltation. Downstream wetlands can be injured in this way. Strong rains on unstable slopes can produce mass movements, such as landslides, slumps, and flaws, particularly in steeply sloping areas;

(b) Increased runoff. Development may alter the natural drainage pattern of a hillside, producing increased runoff and erosion. Removal of vegetative cover decreases percolation of precipitation into the soil, thereby reducing the amount of ground water recharge and adding water to runoff that would ordinarily be transpired by trees, shrubs, and ground covers. Construction of impervious surfaces, such as roads, parking lots, and buildings, decreases the amount of ground water percolation and thus increases the amount of runoff. Increased runoff, in addition to producing intensified erosion, also creates downstream flood hazards;

(c) Destruction of the community’s aesthetic resources. The hillsides of Des Moines mark the boundaries of several neighborhoods, lend natural character and distinctive features to the city, and provide open space and viewing points of remarkable vistas. They are also often associated with stream corridors and wetlands of the city. Degradation of hillsides resulting from erosion, mass movement, loss of vegetation, and damage to downstream areas deprives Des Moines of its attractive and distinctive setting, and decreases real estate values; and

(d) Major public expenditures to repair facility damages and protect against future damages due to instability created or exacerbated by development. [Ord. 1400 § 12, 2007.]

18.86.030 Purpose.

Geologically hazardous areas, hillsides, wetlands, areas of special flood hazard, fish and wildlife habitat conservation areas, aquifer recharge areas and streams, and the buffers of these areas as defined in chapter 18.04 DMMC, together constitute critical areas that are of special concern to the city. The purposes of this chapter are to protect the public health, safety, and welfare by preventing the adverse environmental impacts of development listed in DMMC 18.86.020, and by:

(1) Preserving, protecting, and restoring the functions and values of critical areas by regulating development within them and their buffers;

(2) Protecting the public from damage due to flooding, landslides, subsidence, and erosion;

(3) Preventing adverse impacts to ground and surface water quality, wetlands, tidelands, streams, stream corridors, and fish and wildlife habitat;

(4) Protecting the public against loss from:

(a) Unnecessary maintenance and replacement of public facilities;

(b) Publicly funded mitigation of avoidable impacts;

(d) Potential litigation from improper construction practices authorized for critical areas;

(5) Alerting appraisers, assessors, owners, and potential buyers or lessees to the development limitations of critical areas;

(6) Providing city officials with information to approve, condition, or deny public or private development proposals;

(7) Providing predictability and consistency to city environmental review procedures;

(8) Protecting sensitive, unique, fragile, and valuable features of the city’s environment;

(9) Adopting a goal of no overall net loss of wetland and stream functions and values; and the long-term goal to increase the quantity and quality of Washington’s wetlands and streams;

(10) Implementing the policies of the State Environmental Policy Act (chapter 43.21C RCW), Puget Sound Water Quality Management Plan, Washington State Executive Order 90-04, chapter 16.04 DMMC, the Des Moines Comprehensive Plan, shoreline master program, and all other present and future city functional and community plans and programs as presently constituted or as may be subsequently amended; [and]

(11) Provide for mitigation of potential impacts to critical areas using the following descending order of preference:

(a) Avoid the impact altogether by not taking a certain action or parts of an action;

(b) Minimize impact by limiting the degree or magnitude of the action and its implementation by using appropriate technology, or by taking affirmative steps to avoid or reduce impact;

(d) Reduce or eliminate the impact over time by prevention and maintenance operations during the life of the actions;

(e) Compensate for the impact by replacing, enhancing, or providing substitute environmentally critical areas and environments; and

(f) Monitor the impact and take appropriate corrective measures.

(12) Sources for attaining maps to determine where critical fish and wildlife habitats occur and the species that are present include:

•	Washington Department of Fish and Wildlife Priority Habitat and Species maps;

•	Washington State Department of Natural Resources official water type reference maps, as amended;

•	Washington State Department of Natural Resources Puget Sound Intertidal Habitat Inventory maps;

•	Washington State Department of Natural Resources Shorezone Inventory maps;

•	Anadromous and resident salmonid distribution maps contained in the Habitat Limiting Factors reports published by the Washington Conservation Commission;

•	Washington State Department of Health Annual Inventory of Shellfish Harvest Areas;

•	Washington State Department of Natural Resources State Natural Area Preserves and Natural Resource Conservation Area maps;

•	Washington State Department of Natural Resources Natural Heritage Program mapping data;

•	Any local city of Des Moines or King County maps available. [Ord. 1400 § 13, 2007.]

18.86.040 Applicability.

(1) All development proposals in critical areas, whether public or private, except city activities related to routine maintenance of public ways, shall comply with the requirements and purposes of this chapter. The city manager or designee is authorized to adopt written procedures for the purpose of carrying out the provisions of this chapter. Responsibility for enforcement of the provisions of this chapter shall rest with the city manager or designee.

(2) For the purposes of this chapter, development proposals include proposals that require any of the following: right-of-way permit; building permit; land clearing, grading, or filling permit; shoreline substantial development permit; shoreline variance; shoreline conditional use permit; shoreline environmental redesignation; conditional use permit; unclassified use permit; variance; zone reclassification; planned unit development; subdivision; short subdivision; any other land use approvals required by this code or the RCW.

(3) Prior to construction activity that would occur in, be adjacent to, or would likely affect critical areas, a review outlined by this chapter shall occur prior to the issuance of the necessary permit. [Ord. 1400 § 14, 2007.]

18.86.050 Special studies required.

When an applicant submits an application for any development proposal the application shall indicate whether any critical area is located on the site. The city manager or designee shall visit the subject property and review the information submitted by the applicant along with any other available information. If the city manager or designee determines that sufficient environmental information to evaluate a proposal is not available, the city manager or designee shall notify the applicant that special environmental studies are required. Special environmental studies shall include a comprehensive site inventory and analysis, a discussion of potential impacts from the proposed development, and specific measures designed to mitigate any potential adverse environmental impacts of the applicant’s proposal, on- and off-site. The city manager or designee shall develop and maintain a detailed list of required study contents. All special studies shall be funded by the applicant and conducted under the direct supervision of the planning, building and public works department. [Ord. 1400 § 15, 2007.]

18.86.060 Maps and inventories.

(1) The general distribution of critical areas in the city and its planning area is displayed by a series of maps within the conservation element of the Des Moines Comprehensive Plan. These maps shall be used to alert the public and city officials of the potential presence of critical areas on-site or off-site of a development proposal.

(2) Information provided by the maps of critical areas shall be used for general informational and illustrative purposes only. In cases of mapping error and recognizing that critical areas are dynamic environmental processes, the actual presence and location of critical areas, as determined by qualified professional and technical scientists, shall govern the treatment of a proposed development site. [Ord. 1400 § 16, 2007.]

18.86.070 Best management practices required.

All allowed activities under this chapter shall be conducted using the best management practices, adopted pursuant to the King County Surface Water Design Manual, that result in the least amount of impact to the critical areas. Best management practices shall be used for tree and vegetation protection, construction management, erosion and sedimentation control, water quality protection, and regulation of chemical applications. The city shall observe the use of best management practices to ensure that the activity does not result in degradation to the critical area. Any incidental damage to, or alteration of, a critical area shall be restored, rehabilitated, or replaced at the responsible party’s expense. [Ord. 1400 § 17, 2007.]

18.86.080 Development restrictions.

(1) Undevelopable Environmentally Critical Areas. The following environmentally critical areas shall remain undeveloped except as otherwise provided in DMMC 18.86.280.

(a) Wetlands and Their Buffers. The edge of the wetland and the outside edge of its buffer shall be determined and field marked by a professional wetland biologist or similarly qualified professional;

(b) Streams and Their Buffers. The top of the upper bank of the streams and the outside edge of its buffer shall be determined and field marked by a professional biologist, ecologist, or similarly qualified professional; and

(c) Ravine Sidewalls and Bluffs and Their Buffers. The top, toe, and edges of ravine sidewalls and bluffs, and the outside edge of their buffers, shall be determined and field marked by a qualified geotechnical engineer or similarly qualified professional.

(2) Developable Critical Areas. Critical aquifer recharge areas, areas of special flood hazard, fish and wildlife habitat conservation areas, and hillsides other than ravine sidewalls and bluffs are developable pursuant to the provisions of this chapter. The applicant shall clearly and convincingly demonstrate to the satisfaction of the city manager or designee that the proposal incorporates measures protecting the public health, safety, and welfare. [Ord. 1400 § 18, 2007.]

18.86.090 Development standards – Compliance – Requirements.

If a proposed project is within, adjacent to, or is likely to impact a critical area, all activities on the site shall be in compliance with the requirements and restrictions set forth in DMMC 18.86.100 through 18.86.260. [Ord. 1400 § 19, 2007.]

18.86.100 Wetlands – Development standards.

If a wetland is located on or contiguous to the site of a development proposal, all activities on the site shall be in compliance with the following requirements and restrictions:

(1) General Performance Requirements.

(a) Activities may only be permitted in a wetland or wetland buffer if the applicant can show that the proposed activity will not degrade the functions and functional performance of the wetland.

(b) Activities and uses shall be prohibited in wetlands and wetland buffers, except as provided for in this chapter.

(c) Category I Wetlands. Activities and uses shall be prohibited from Category I, except as provided for in the public agency and utility exception, reasonable use exception, and variance sections of this chapter.

(d) Category II and III Wetlands. With respect to activities proposed in Category II and III wetlands, the following standards shall apply:

(i) Where wetland fill is proposed, activities and uses shall be prohibited unless the applicant can demonstrate that:

(A) The basic project purpose cannot reasonably be accomplished on another site or sites in the general region while still successfully avoiding or resulting in less adverse impact on a wetland; and

(B) All on-site alternative designs that would avoid or result in less adverse impact on a wetland or its buffer, such as a reduction in the size, scope, configuration or density of the project, are not feasible. Compensation for the loss of acreage and functions of wetland and buffers shall be provided under the terms established under DMMC 18.86.130.

(e) Category IV Wetlands. Activities and uses that result in unavoidable and necessary impacts may be permitted in Category IV wetlands and associated buffers in accordance with an approved special environmental study and mitigation plan, and only if the proposed activity is the only reasonable alternative that will accomplish the applicant’s objectives. Compensation for the acreage and loss functions will be provided under the terms established under DMMC 18.86.130.

(2) Wetland Buffers. The following standard buffers shall be established from the wetland edge as delineated and marked in the field:


	Width of Buffer (feet)
Category I Wetlands
High habitat function (habitat score 29-36)	300
Moderate habitat function (habitat score 20-28)	150
High water quality function and low habitat function or none of the above characteristics (habitat score less than 20)	100
Category II Wetlands
High habitat function (habitat score 29-36 points)	300
Moderate habitat function (habitat score 20-28)	150
High water quality function and low habitat function or none of the above characteristics (habitat score less than 20)	100
Category III Wetlands
Moderate habitat function (habitat score 20-28)	150
Low habitat or not meeting above criteria (habitat score less than 20)	80
Category IV Wetlands
Low functions	50

Note: Removed information and buffers associated with the following wetlands that are not relevant to Des Moines: Category I – Natural Heritage, bogs, estuarine, and wetlands in coastal lagoons and Category II – Estuarine and Interdunal.

(a) Where a legally established and constructed street transects a wetland buffer, the city manager or designee may approve a modification of the standard buffer width to the edge of the right-of-way if the isolated part of the buffer does not provide additional protection of the wetland and provides insignificant biological, geological or hydrological buffer functions relating to the wetland. If the resulting buffer distance is less than 50 percent of the standard buffer for the applicable wetland category, no further reduction shall be allowed through wetland buffer reduction or averaging.

(b) Where a buffer has been previously established through city or county development review, and is permanently recorded on title or placed within a separate tract, the buffer shall be as previously established.

(3) Building Setback Lines. A building setback line of 10 feet is required from the edge of any wetland buffer. Minor structural intrusions into the area of the building setback line may be allowed if the city manager or designee determines that such intrusions will not negatively impact the critical area.

(4) Increased Wetland Buffers. The city manager or designee may require either additional native vegetation to achieve purposes of this chapter or increased buffer sizes when environmental information indicates the necessity for greater buffers to protect critical area functions, values, or hazards based on site-specific conditions. This determination shall be supported by appropriate documentation showing that additional buffer width is reasonably related to protection of critical area functions and values, or protection of public health, safety and welfare. Such determination shall be attached as permit conditions. The determination shall demonstrate that at least one of the following criteria are met:

(a) There is habitat for species listed as threatened or endangered by state or federal agencies present within the environmentally critical area and/or its buffer, and additional buffer is necessary to maintain a viable functional habitat; or

(b) There are conditions or features adjacent to the buffer, such as steep slopes or erosion hazard areas, which over time may pose an additional threat to the viability of the buffer or buffers, if any, associated with the conditions or feature posing the threat in addition to, or to a maximum, beyond the buffer required for the subject critical area.

(c) In cases where additional buffers are not feasible, the city manager or designee may require the applicant to undertake alternative on-site or off-site mitigation measures, including but not limited to a financial contribution to projects or programs which seek to improve environmental quality within the same watershed.

(5) Wetland Buffer Averaging. The city manager or designee may allow modification of the standard wetland buffer width in accordance with an approved special environmental study and the best available science on a case-by-case basis by averaging buffer widths. Averaging of buffer widths may only be allowed where a qualified professional wetland scientist demonstrates that:

(a) It will not reduce wetland functions or functional performance;

(b) The wetland contains variations in sensitivity due to existing physical characteristics or the character of the buffer varies in slope, soils, or vegetation, and the wetland would benefit from a wider buffer in places and would not be adversely impacted by a narrower buffer in other places;

(c) The total area contained within the buffer after averaging is no less than that which would be contained within the standard buffer; and

(d) The buffer width is not reduced to less than 75 percent of the standard width.

(6) Wetland Buffer Reduction. The city manager or designee may allow reduction of the required wetland buffer widths when accompanied by a special study that identifies appropriate mitigation strategies. Reduction of wetland buffer widths may be allowed where a qualified professional wetland scientist demonstrates that:

(a) The reduction in buffer width based on reducing the intensity of impacts from proposed land uses. Buffer widths required for proposed land uses with high-intensity impacts to wetlands may be reduced to those recommended for moderate-intensity impacts under the following conditions:

(i) For wetlands that score moderate or high for habitat (20 points or more for the habitat functions), the width of the buffer can be reduced if both of the following criteria are met:

(A) A relatively undisturbed, vegetated corridor at least 100 feet wide is protected between the wetland and any other priority habitats as defined by the Washington State Department of Fish and Wildlife. The corridor must be protected for the entire distance between the wetland and the priority habitat by some type of legal protection such as a conservation easement.

(B) Measures to minimize the impacts of different land uses on wetlands, such as the examples summarized in Table 8C-8 from “Wetlands in Washington State: Volume 2 – Protecting and Managing Wetlands” (Ecology, 2005), are applied.

(ii) For wetlands that score less than 20 points for habitat, the buffer width can be reduced to that required for moderate land-use impacts by applying measures to minimize the impacts of the proposed land uses. Measures include but are not limited to the following: direct light and noise away from wetlands, route untreated runoff away from wetlands, apply an integrated pest management program, use privacy fencing or vegetative buffer to delineate the wetland buffer edge and discourage disturbance, and use best management practices to control dust (see examples in Table 8C-8).

(b) Reductions in buffer widths where existing roads or structures lie within the buffer. Where a legally established, nonconforming use of the buffer exists (e.g., a road or structure that lies within the width of buffer recommended for that wetland), proposed actions in the buffer may be permitted as long as they do not increase the degree of nonconformity, or if no reasonable alternative exists. This means no increase in the impacts to the wetland from activities in the buffer. [Ord. 1400 § 20, 2007.]

18.86.110 Wetlands – Reasonable use exceptions.

(1) Adjustments to Dimensional Requirements.

(a) Yard Reductions for Building One Single-Family Dwelling. The city manager or designee may allow modification to the required front, rear, or side yard on the opposite of the wetland. The reductions must meet the following standards:

(i) The wetland, wetland buffer and required yard area opposite the wetland equals more than 50 percent of the property dimension of the development site.

(ii) A required side yard is reduced to five feet.

(iii) A required front or rear yard is reduced to 10 feet.

(2) Single-Family Dwelling. Development of one single-family dwelling within the buffer of a wetland on a development site shall be approved by the city manager or designee if the applicant demonstrates that:

(a) The extent of development within the buffer is limited to that which is necessary to create a developable area which is no larger than 4,000 square feet;

(b) The proposal utilizes to the maximum extent possible the best available construction, design, and development techniques which result in the least adverse impact on the critical area;

(c) The proposal incorporates the development standards of DMMC 18.86.100 through 18.86.130 and the surface water design manual to the maximum extent possible; and

(d) The proposal is consistent with the purpose and intent of this chapter. [Ord. 1400 § 21, 2007.]

18.86.120 Wetlands – Limited exemptions.

The city manager or designee may allow exemptions from the provisions of this chapter based on the following criteria:

(1) Wetlands larger than 4,000 square feet will be evaluated using standard procedures for wetland review.

(2) Wetlands between 1,000 and 4,000 square feet shall be evaluated using the Washington State Wetland Rating System for Western Washington (Hruby, 2004, or as revised) to establish category and evaluate functions. The following criteria and local knowledge of natural resources shall be used to determine whether to exempt wetlands between 1,000 and 4,000 square feet from the requirement to avoid impacts.

(a) The requirement to avoid impacts may be dropped for Category III and IV wetlands between 1,000 and 4,000 square feet that meet all of the following criteria:

(i) Wetland is not associated with a riparian corridor; and

(ii) Wetland is not part of a wetland mosaic; and

(iii) Wetland does not score 20 points or more for habitat in the wetland rating system; and

(iv) Wetland does not contain habitat identified as essential for local populations of priority species identified by [the] Washington Department of Fish and Wildlife.

(b) Impacts allowed under this provision to these wetlands will be fully mitigated as set forth in DMMC 18.86.130.

(c) All Category I and II Wetlands between 1,000 and 4,000 square feet should be evaluated with full mitigation sequencing and buffer establishment. Any approved impacts should be adequately compensated by mitigation as set forth in DMMC 18.86.130.

(3) Wetlands less than 1,000 square feet shall be exempt from regulation where the applicant has shown that they:

(a) Are not associated with a riparian corridor;

(b) Are not part of a wetland mosaic; and

(c) Do not contain habitat identified as essential for local populations of priority species identified by the Washington Department of Fish and Wildlife. [Ord. 1400 § 22, 2007.]

18.86.130 Wetlands – Mitigation requirements.

(1) Compensatory mitigation for alterations to wetlands shall achieve equivalent or greater biologic functions. Compensatory mitigation plans shall be consistent with the Guidance on Wetland Mitigation in Washington State – Part 2: Guidelines for Developing Wetland Mitigation Plans and Proposals, April 2004 (Washington State Department of Ecology, U.S. Army Corps of Engineers Seattle District, and U.S. Environmental Protection Agency Region 10; Ecology Publication No. 04-06-013b), or as revised.

(2) Mitigation shall be required in the following order of preference:

(a) Avoiding the impact altogether by not taking a certain action or parts of an action.

(b) Minimizing impacts by limiting the degree or magnitude of the action and its implementation, by using appropriate technology, or by taking affirmative steps such as project redesign, relocation, or timing, to avoid or reduce impacts.

(d) Reducing or eliminating the impact over time by preservation and maintenance operations.

(e) Compensating for the impact by replacing, enhancing, or providing substitute resources or environments.

(f) Monitoring the required compensation and taking remedial or corrective measures when necessary.

(3) Compensating for Lost or Affected Functions. Compensatory mitigation shall address the functions affected by the proposed project, with an intention to achieve functional equivalency or improvement of functions. The goal shall be for the compensatory mitigation to provide similar wetland functions as those lost, except when either:

(a) The lost wetland provides minimal functions as determined by a site-specific function assessment, and the proposed compensatory mitigation action(s) will provide equal or greater functions or will provide functions shown to be limiting within a watershed through a formal Washington State watershed assessment plan or protocol; or

(b) Out-of-kind replacement of wetland type or functions will best meet watershed goals formally identified by the city, such as replacement of historically diminished wetland types.

(4) Preference of Mitigation Actions. Methods to achieve compensation for wetland functions shall be approached in the following order of preference:

(a) Restoration (re-establishment and rehabilitation) of wetlands.

(b) Creation (establishment) of wetlands on disturbed upland sites such as those with vegetative cover consisting primarily of nonnative introduced species. This should only be attempted when there is an adequate source of water and it can be shown that the surface and subsurface hydrologic regime is conducive for the wetland community that is anticipated in the design.

(c) Enhancement of significantly degraded wetlands in combination with restoration or creation. Such enhancement should be part of a mitigation package that includes replacing the impacted area and meeting appropriate ratio requirements.

(5) Type and Location of Compensatory Mitigation. Unless it is demonstrated that a higher level of ecological functioning would result from an alternate approach, compensatory mitigation for ecological functions shall be either in-kind and on-site, or in-kind and within the same stream reach, sub-basin, or drift cell (if estuarine wetlands are impacted). Compensatory mitigation actions shall be conducted within the same sub-drainage basin and on the site of the alteration except when all of the following apply:

(a) There are no reasonable on-site or in sub-drainage basin opportunities (e.g., on-site options would require elimination of high-functioning upland habitat), or on-site and in sub-drainage basin opportunities do not have a high likelihood of success based on a determination of the capacity of the site to compensate for the impacts. Considerations should include: anticipated replacement ratios for wetland mitigation, buffer conditions and proposed widths, available water to maintain anticipated hydrogeomorphic classes of wetlands when restored, proposed flood storage capacity, and potential to mitigate riparian fish and wildlife impacts (such as connectivity);

(b) Off-site mitigation has a greater likelihood of providing equal or improved wetland functions than the impacted wetland; and

(i) Established watershed goals for water quality, flood storage or conveyance, habitat, or other wetland functions have been established by the city and strongly justify location of mitigation at another site; or

(ii) Credits from a state-certified wetland mitigation bank are used as compensation and the use of credits is consistent with the terms of the bank’s certification.

(d) The design for the compensatory mitigation project needs to be appropriate for its location (i.e., position in the landscape). Therefore, compensatory mitigation should not result in the creation, restoration, or enhancement of an atypical wetland. An atypical wetland refers to a compensation wetland (e.g., created or enhanced) that does not match the type of existing wetland that would be found in the geomorphic setting of the site (i.e., the water source(s) and hydroperiod proposed for the mitigation site are not typical for the geomorphic setting). Likewise, it should not provide exaggerated morphology or require a berm or other engineered structures to hold back water. For example, excavating a permanently inundated pond in an existing seasonally saturated or inundated wetland is one example of an enhancement project that could result in an atypical wetland. Another example would be excavating depressions in an existing wetland on a slope, which required the construction of berms to hold the water.

(6) Timing of Compensatory Mitigation. It is preferred that compensatory mitigation projects be completed prior to activities that will disturb the on-site wetlands. At the least, compensatory mitigation shall be completed immediately following disturbance and prior to use or occupancy of the action or development. Construction of mitigation projects shall be timed to reduce impacts to existing fisheries, wildlife, and flora. The city manager or designee may authorize a one-time temporary delay in completing construction or installation of the compensatory mitigation when the applicant provides a written explanation from a qualified wetland professional as to the rationale for the delay. An appropriate rationale would include identification of the environmental conditions that could produce a high probability of failure or significant construction difficulties (e.g., project delay lapses past a fisheries window; or installing plants should be delayed until the dormant season to ensure greater survival of installed materials). The delay shall not create or perpetuate hazardous conditions or environmental damage or degradation, and the delay shall not be injurious to the health, safety, and general welfare of the public. The request for the temporary delay must include a written justification that documents the environmental constraints that preclude implementation of the compensatory mitigation plan. The justification must be verified and approved by the city.

(7) Mitigation Ratios. The following ratios shall apply to creation or restoration that is in-kind, is on-site, is the same category, is timed prior to or concurrent with alteration, and has a high probability of success. The first number specifies the acreage of replacement wetlands and the second specifies the acreage of wetlands altered.

Wetland Mitigation Ratios


	Enhancement	Rehabilitation	Creation
Category I	6:1	4.5:1	3:1
Category II	3:1	2:1	1.5:1
Category III	2:1	1.5:1	1:1
Category IV	1.5:1	1:1	1:1

(a) The mitigation ratio is the acreage required for compensatory mitigation divided by the acreage of impact.

(b) The ratios are for a concurrent compensatory mitigation project. If the impacts to a wetland are to be mitigated by using an approved and established mitigation bank, the rules and ratios applicable to the bank should be used.

(c) The ratios are based on the assumption that the category, based on wetland ratings established in DMMC 18.04.663, and hydrogeomorphic (HGM) class/subclass of the wetland proposed as compensation are the same as the category and HGM class/subclass of the wetland impacts.

(d) Ratios for projects in which the category and HGM class/subclass of wetlands proposed as compensation is not the same as that of the wetland impacts will be determined on a case-by-case basis using the recommended ratios as a starting point. The ratios could be higher in such cases.

(e) Creation can be used in combination with rehabilitation or enhancement. For example, two acres of impact to a Category II wetland would require two acres of creation (i.e., replacing the lost acreage at a 1:1 ratio); the remaining one acre of creation necessary to compensate for impact could be substituted with one and one-half acres of rehabilitation or three acres of enhancement.

(f) Generally the use of enhancement alone as compensation is discouraged. Using enhancement in combination with some amount of creation is preferred.

(8) Preservation. Impacts to wetlands may be mitigated by preservation of wetland areas when used in combination with other forms of mitigation such as creation, restoration, or enhancement. Preservation may also be used by itself, but more restrictions apply as outlined below.

(a) Acceptable Uses of Preservation. The preservation of at-risk, high quality wetlands and habitat may be considered as part of an acceptable mitigation plan when the following criteria are met:

(i) Preservation is used as a form of compensation only after the standard sequencing of mitigation (avoid, minimize, and then compensate). See subsection (2) of this section;

(ii) Restoration (re-establishment and rehabilitation), creation, and enhancement opportunities have also been considered, and preservation is proposed by the applicant and approved by the permitting agencies as the best compensation option;

(iii) The preservation site is determined to be under imminent threat; that is, the site has the potential to experience a high rate of undesirable ecological change due to on-site or off-site activities that are not regulated (e.g., logging of forested wetlands). This potential includes permitted, planned, or likely actions;

(iv) The area proposed for preservation is of high quality or critical for the health of the watershed or basin due to its location. Some of the following features may be indicative of high quality sites:

(A) Category I or II wetland rating;

(B) Rare or irreplaceable wetland type (e.g., bogs, mature forested wetlands, estuaries) or aquatic habitat that is rare or a limited resource in the area;

(D) Provides biological and/or hydrological connectivity;

(E) High regional or watershed importance (e.g., listed as priority site in a watershed or basin plan);

(F) Large size with high species diversity (plants and/or animals) and/or high abundance of native species;

(G) A site that is continuous with the head of a watershed, or with a lake or pond in an upper watershed that significantly improves outflow hydrology and water quality.

(b) Preservation in Combination with Other Forms of Compensation. Using preservation as compensation is acceptable when done in combination with restoration, creation, or enhancement; provided, that a minimum of 1:1 acreage replacement is provided by reestablishment or creation and the criteria below are met:

(i) All criteria listed in subsection (8)(a) of this section are met;

(ii) The impact area is small and/or impacts are occurring to a low functioning system (Category III or IV wetland);

(iii) Preservation of a high-quality system occurs in the same watershed or basin as the wetland impact;

(iv) Preservation sites include buffer areas adequate to protect the habitat and its functions from encroachment and degradation; and

(v) Mitigation ratios for preservation in combination with other forms of mitigation shall range from 10:1 to 20:1, as determined on a case-by-case basis, depending on the quality of the wetlands being impacted and the quality of the wetlands being preserved.

(c) Preservation as the Sole Means of Compensation for Wetland Impacts. Preservation alone shall only be used as compensatory mitigation in exceptional circumstances. Preservation alone shall not apply if impacts are occurring to functions that must be replaced on-site, such as flood storage or water quality treatment that need to be replicated by water quality measures implemented within the project limits. Preservation of at-risk, high-quality wetlands and habitat (as defined above) may be considered as the sole means of compensation for wetland impacts when the following criteria are met:

(i) All criteria listed in subsections (8)(a) and (8)(b) of this section are met;

(ii) There are no adverse impacts to habitat for fish and species listed as endangered and threatened;

(iii) There is no net loss of habitat functions within the watershed or basin;

(iv) Higher mitigation ratios are applied. Mitigation ratios for preservation as the sole means of mitigation shall generally start at 20:1. Specific ratios should depend upon the significance of the preservation project and the quality of the wetland resources lost.

(9) Wetland Mitigation Banks.

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

(i) The bank is certified under Chapter 173-700 WAC;

(ii) The city manager or designee determines that the wetland mitigation bank provides appropriate compensation for the authorized impacts; and

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

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

(c) 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, the service area of the bank may include portions of more than one adjacent drainage basin for specific wetland functions.

(10) Substitute Fees. In cases where the applicant demonstrates to the satisfaction of the city manager or designee that a suitable compensation site does not exist, the city manager or designee may allow the applicant to make a financial contribution to a water quality project or program performing critical areas enhancement, restoration, or mitigation. The project or program must improve environmental quality within the same watershed as the altered wetland. The amount of the fee shall be determined by the city manager or designee and shall be equal to the cost of mitigating the impact of the wetland alteration.

(11) Mitigation Plan Requirements. When mitigation is required, the applicant shall submit for approval a mitigation plan prepared by a qualified scientist(s) following procedures set forth in the state Department of Ecology Guidelines for Developing Freshwater Wetlands Mitigation Plans and Proposals, 2004, or as revised.

(12) Final Approval. The city manager or designee shall grant final approval of a completed compensation project if the final report of the project mitigation plan satisfactorily documents that the area has achieved all requirements of this section and DMMC 18.86.290. [Ord. 1400 § 23, 2007.]

18.86.140 Streams – Development standards.

If a stream is located on or contiguous to the site of a development proposal, all activities on the site shall be in compliance with the following requirements and restrictions:

(1) Stream Buffers. The following standard buffers shall be measured from the ordinary high water mark or from the top of the bank if the ordinary high water mark cannot be identified:


Water Type	Buffer Width (feet)
Types S or F	115
Types Np or Ns	65

Type S: streams inventoried as “shorelines of the state” under the city’s shoreline master program.

Type F: streams that are salmonid-bearing or have the potential to support salmonids.

Type Np: streams that are perennial during a year of normal rainfall and do not have the potential to support salmonids use.

Type Ns: streams that are seasonal or ephemeral during a year of normal rainfall and do not have the potential to support salmonids use.

(a) Where a legally established and constructed street transects a stream buffer, the city manager or designee may approve a modification of the standard buffer width to the edge of the street if the isolated part of the buffer does not provide additional protection of the stream and provides insignificant biological, geological or hydrological buffer functions relating to the stream. If the resulting buffer distance is less than 50 percent of the standard buffer, no further reduction shall be allowed.

(c) Any stream relocated or altered as part of approved mitigation measures shall have at least the minimum buffer required for the type of stream involved.

(d) If the stream buffer includes a steep slope hazard area or landslide hazard area, the stream buffer width is the greater of either the stream buffer in this section or 25 feet beyond the top of the hazard area.

(e) Any stream adjoined by a riparian wetland or other contiguous critical area shall have the buffer required for the stream type involved or the buffer that applies to the wetland or other critical area, whichever is greater.

(2) Increased Stream Buffer. The city manager or designee shall require increased buffer widths in accordance with the recommendations of a qualified biologist and the best available science on a case-by-case basis when a larger buffer is necessary to protect stream functions and values based on site-specific characteristics.

This determination shall be based on one or more of the following criteria:

(a) A larger buffer is needed to protect other critical areas;

(b) The buffer or adjacent upland has a slope greater than 30 percent or is susceptible to erosion and standard erosion-control measures will not prevent adverse impacts to the wetland.

(3) Pursuant to RCW 35.21.180, the King County, Washington “Surface Water Design Manual,” including all subsequent revisions, is adopted by reference as the “Surface Water Design Manual for the City of Des Moines” in DMMC 18.86.330.

(4) Building Setback Lines. A building setback line of 10 feet is required from the edge of any stream buffer. Minor structural intrusions into the area of the building setback line may be allowed if the city manager or designee determines that such intrusions will not negatively impact the critical area. [Ord. 1400 § 24, 2007.]

18.86.150 Streams – Reasonable use exceptions.

(1) Adjustments to Dimensional Requirements.

(a) Yard Reductions for Building One Single-Family Dwelling. The city manager or designee may allow modification to the required front, rear, or side yard on the opposite of the stream. The reductions must meet the following standards:

(i) The stream, stream buffer and required yard area opposite the stream equals more than 50 percent of the property dimension of the development site.

(ii) A required side yard is reduced to five feet.

(iii) A required front or rear yard is reduced to 10 feet.

(2) Single-Family Dwelling. Development of one single-family dwelling within the buffer of a stream on a development site shall be approved by the city manager or designee if the applicant demonstrates that:

(a) The extent of development within the buffer is limited to that which is necessary to create a developable area which is no larger than 4,000 square feet;

(b) The proposal utilizes to the maximum extent possible the best available construction, design, and development techniques which result in the least adverse impact on the environmentally critical area;

(c) The proposal incorporates the development standards of DMMC 18.86.140 and the surface water design manual to the maximum extent possible; and

(d) The proposal is consistent with the purpose and intent of this chapter. [Ord. 1400 § 25, 2007.]

18.86.160 Streams – Limited exemptions.

The city manager or designee may allow exemptions from the provisions of this chapter based on the following provisions:

(1) Stream Crossings. Stream crossings, whether for access or utility purposes, shall be avoided to the extent possible. The city manager or designee may approve stream crossings only when he/she determines that there are no practicable or reasonable alternatives, and when the proposal complies with all of the following criteria:

(a) Bridges are required for streams which support salmonids; and

(b) All crossings using culverts shall use superspan or oversize culverts; and

(c) All construction and installation crossings shall comply with timing restrictions set by federal and state permit processes, generally during summer low flow; and

(d) Crossings shall not occur in salmonid spawning areas unless no other feasible crossing site exists; and

(e) Bridge piers or abutments shall not be placed in either the floodway or between the ordinary high water marks unless no other feasible alternative placement exists; and

(f) Crossings shall not diminish flood-carrying capacity; and

(g) Crossings shall provide for maintenance of culverts, bridges, and utilities; and

(h) Crossings shall serve multiple properties whenever possible; and

(i) Crossings shall comply with all applicable local, state, and federal laws.

(2) Stream Relocation and Dredging. Stream relocation and dredging are strongly discouraged and shall only occur to improve hydrologic, hydraulic, and fish and wildlife habitat functions. The city manager or designee may approve stream relocation and dredging only when he/she determines that there are no practicable or reasonable alternatives, and when the proposal complies with all of the following criteria:

(a) Relocation and dredging shall follow all applicable local, state, and federal laws and receive approvals from the agencies administering such laws;

(b) Dredging of any stream shall follow the standards for dredging set forth in the shoreline master program;

(c) A mitigation plan with a contingency plan shall be prepared by a licensed professional pursuant to DMMC 18.86.170 and shall include the following provisions:

(i) Identification of long-term goals (25 years) and objectives for restoration of the stream channel and riparian areas;

(ii) A three-year to five-year monitoring program to measure success of the restoration;

(iii) Mitigation shall be designed to accommodate a 100-year storm event.

(3) Stream Channel, Stream Bank, Bluff, or Shore Stabilization. The city manager or designee may approve stabilization of stream channels, stream banks, bluffs, or shorelines when he/she determines that the proposed stabilization complies with the Washington Department of Fish and Wildlife Integrated Streambank Protection Guidelines (2003) and the following criteria as applicable:

(a) Naturally occurring movement threatens existing structures, public improvements, unique natural resources, or the only feasible access to property.

(b) In the case of streams, stabilization results in improved fish and wildlife habitat, flood control, and improved water quality.

(c) The preferred methodology for stream channel and bank stabilization is bioengineering or some combination of bioengineering and more traditional structural solutions. Bioengineering involves use of plant materials to stabilize eroding stream channels and banks.

(d) The preferred methodology for bluff and shore stabilization is naturalistic shoreline protection measures such as creation of beaches that absorb and dissipate wave energy. Bluff and shore stabilization shall follow the standards of the shoreline master program for the construction of any stabilization device.

(e) Relocation and dredging shall follow all applicable local, state, and federal laws and receive approvals from the agencies administering such laws. [Ord. 1400 § 26, 2007.]

18.86.170 Streams – Mitigation requirements.

(1) Compensatory mitigation for alterations to streams shall achieve equivalent or greater biologic functions.

(a) On-Site and In-Kind for Streams. For streams, the applicant shall maintain or improve stream channel dimensions, including depth, length, and gradient; restore or improve native vegetation and fish and wildlife habitat; and create an equivalent or improved channel bed, biofiltration, and meandering. Unless otherwise specified by the city manager or designee, such mitigation to replace and enhance stream elements such as pools, riffles, and spawning gravel shall be provided on a relative 2:1 basis.

(b) Off-Site and In-Kind for Streams. When environmental information demonstrates that greater functions and values will be achieved, off-site compensation of greater size, functions, and values may be approved if the compensation project is within the same subwatershed as the wetland or stream to be altered. Unless otherwise specified by the city manager or designee, such mitigation shall be provided pursuant to the ratios specified in this section.

(c) Conditions Preceding Stream Alteration. In the case of the exceptions of DMMC 18.86.140, the following conditions shall precede any stream alteration approved pursuant to this section:

(i) A mitigation plan for the compensation project shall be submitted by the applicant and approved by the city manager or designee;

(ii) The compensation project shall be fully implemented following the requirements of the approved mitigation plan; and

(iii) A final report shall be submitted following the specified growing seasons documenting that all requirements of a mitigation plan have been fully achieved. The city may postpone or limit development, require bonds pursuant to DMMC 18.86.310, or use other appropriate techniques to ensure the success of the mitigation plan.

(d) The city manager or designee may postpone the issuance of development permits for one or more growing seasons until the success or viability of the approved mitigation measures can be demonstrated by the applicant.

(e) Substitute Fees. In cases where the applicant demonstrates to the satisfaction of the city manager or designee that a suitable compensation site does not exist, the city manager or designee may allow the applicant to make a financial contribution to a water quality project or program performing critical areas enhancement, restoration, or mitigation. The project or program must improve environmental quality within the same watershed as the altered stream. The amount of the fee shall be determined by the city manager or designee and shall be equal to the cost of mitigating the impact of the stream alteration.

(2) Mitigation Plans. All restoration and compensation projects shall follow a mitigation plan prepared by qualified scientists containing the following components:

(a) Baseline Information. Quantitative data shall be collected and synthesized for both the impacted critical area and the proposed mitigation site, if different from the impacted critical area, following procedures set forth by the city manager or designee.

(b) Environmental Goals and Objectives. Goals and objectives describing the purposes of the mitigation measures shall be provided, including a description of site selection criteria, identification of target evaluation species and resource functions.

(c) Performance Standards. Specific criteria for fulfilling environmental goals and objectives, and for beginning remedial action or contingency measures shall be provided, including water quality standards, species richness and diversity targets, habitat diversity indices, or other ecological, geological, or hydrological criteria.

(d) Detailed Construction Plan. Written specifications and descriptions of mitigation techniques shall be provided, including the proposed construction sequence, accompanied by detailed site diagrams and blueprints that are an integral requirement of any development proposal.

(e) Monitoring Program. A program outlining the approach for assessing a completed project shall be provided, including descriptions of proposed experimental and control site survey or sampling techniques. A protocol shall be included outlining how the monitoring data will be evaluated by agencies that are tracking the progress of the mitigation project. A report shall be submitted at least twice yearly documenting milestones, successes, problems, and contingency actions of the restoration or compensation project. The city manager or designee shall require that the applicant monitor the compensation or restoration project for a minimum of five years.

(f) Contingency Plan. A plan shall be provided fully identifying potential courses of action, and any corrective measures to be taken when monitoring or evaluation indicates project performance standards are not being met.

(g) Performance and Maintenance Securities. Securities ensuring fulfillment of the mitigation project, monitoring program, and any contingency measures shall be posted pursuant to DMMC 18.86.310.

(3) Final Approval. The city manager or designee shall grant final approval of a completed restoration or compensation project if the final report of the project mitigation plan satisfactorily documents that the area has achieved all requirements of DMMC 18.86.280. [Ord. 1400 § 27, 2007.]

18.86.180 Geologically hazardous areas – Development standards.

Development within all geologically hazardous areas shall comply with the following general performance requirements:

(1) Alterations of geologically hazardous areas or associated buffers may only occur for activities that:

(a) Will not increase the threat of the geological hazard to adjacent properties beyond pre-development conditions;

(b) Will not adversely impact other critical areas;

(c) Are designed so that the hazard to the project is eliminated or mitigated to a level equal to or less than pre-development conditions;

(d) Are designed and constructed in accordance with the surface water design manual; and

(e) Are certified as safe as designed and under anticipated conditions by a qualified engineer or geologist, licensed in the state of Washington.

(2) Critical Facilities Prohibited. Critical facilities shall not be sited within geologically hazardous areas unless there is no other practical alternative. [Ord. 1400 § 28, 2007.]

18.86.190 Ravine sidewalls and bluffs – Development standards.

Activities on ravine sidewalls and bluffs shall meet the general performance requirements of DMMC 18.86.180 and the specific following requirements:

(1) Buffers. A 50-foot undisturbed buffer of native vegetation shall be established from the top, toe, and sides of all ravine sidewalls and bluffs.

(2) Buffer Reduction. The city manager or designee may approve a reduction in the width of the required buffer, to a minimum width of 10 feet, when special environmental studies are provided that demonstrate all of the following:

(a) A licensed engineer specializing in geotechnical analysis or a licensed engineering geologist, after review of the geologic conditions of the site, the proposed development plans, and all mitigation measures proposed or required, concludes in a written statement that the development proposal will result in minimal risk of soil instability; and

(b) Special mitigation measures regarding design, construction, and maintenance can reasonably be employed to minimize adverse environmental impacts associated with the proposal; and

(3) Additional Buffers. The city manager or designee may require increased buffers if environmental studies indicate such increases are necessary to mitigate landslide, seismic and erosion hazards, or as otherwise necessary to protect the public health, safety, and welfare.

(4) Building Setback Lines. A building setback line of 10 feet is required from the edge of any buffer of a ravine sidewall or bluff. Minor structural intrusions into the area of the building setback line may be allowed if the city manager or designee determines that such intrusions will not negatively impact the critical area.

(5) All buffers shall be measured from the top, toe, and sides of all ravine sidewalls or bluffs. [Ord. 1400 § 29, 2007.]

18.86.200 Hillsides of 15 percent slope and greater – Development standards – Disturbance limitations.

Development on hillsides shall comply with the general performance requirements of DMMC 18.86.180 and the following requirements regarding disturbance limitations, development location, development design, construction techniques, and landscaping.

(1) Amount of Disturbance Allowed. The following chart sets forth the maximum slope disturbance allowed on a development site:


Slope	Amount of Slope Which Can Be Disturbed	Factor
0 – 15%	100%	1.00
15 – 25%	60%	.60
25 – 40%	45%	.45
40%+	30%	.30

The overall amount of disturbance allowed on development sites which have any combination of the above slope categories shall be determined by the following formula:

(Square Footage of Site having 0 – 15% slopes) X 1.00 + (Square Footage of Site having 15 – 25% slopes) X 0.60 + (Square Footage of Site having 25 – 40% slopes) X 0.45 + (Square Footage of Site having 40%+ slopes) X 0.30 = Total Amount of Allowable Site Disturbance.

(2) Development Location.

(a) Structures and improvements shall be clustered to retain as much open space as possible and the natural topographic character of the slope; and

(b) Structures and improvements shall conform to the natural contour of the slope, foundations must be tiered to generally conform to the existing topography of the site; and

(c) Structures and improvements shall be located to preserve the most sensitive portion of the site and its natural landforms and vegetation.

(3) Development Design.

(a) The footprint of buildings and other disturbed areas shall be minimized. The least number of buildings is desirable in order to consolidate the development; and

(b) Standard prepared building pads (slab on grade) resulting in grading more than 10 feet outside the building footprint area are prohibited; and

(d) Impervious lot coverage shall be minimized. With the exception of detached single-family structures, understructure parking and multilevel structures shall be incorporated where feasible; and

(e) Roads, walkways, and parking areas shall be designed to parallel the natural contours of the steep slope hazard areas while maintaining consolidated areas of natural topography and vegetation. Access shall be located in the least environmentally critical area feasible; and

(f) Use of retaining walls which allow the maintenance of existing natural slope areas is preferred over graded artificial slopes.

(4) Construction Techniques.

(a) Use of foundation walls as retaining walls is preferable to rock or concrete walls built separately and away from the building. Freestanding retaining devices are only permitted when they cannot be designed as structural elements of the building foundation; and

(b) Use of pole-type construction which conforms to the existing topography is desirable where feasible; and

(c) Structures shall be tiered to conform to existing topography and to minimize topographic modification. Piled deck support structures are preferred for parking or garages over fill-based construction types.

(5) Landscaping. The disturbed area of a development site not used for buildings and other improvements shall be landscaped according to a landscape design which will achieve a minimum 40 percent coverage by the canopy of trees and shrubs within 10 years to provide habitat desirable to native western Washington birds. The trees and shrubs shall be a mix of shade, flowering, and coniferous and broad-leaf evergreens that are either native to the Puget Sound region or are valuable to western Washington birds. The Department of Wildlife “Plants for Wildlife in Western Washington” shall be used as a general guide.

(a) Trees shall be the following size at time of planting and shall conform to the “American Standard for Nursery Stock”:

(i) Single-stem shade and flowering trees shall be a minimum one-inch caliper trunk as measured six inches above the ground.

(ii) Multistem shade and flowering trees shall be a minimum height of eight feet as measured from the ground level to the average uppermost point of growth of the plant.

(iii) Coniferous evergreen trees (Types 4, 5, and 6) shall be a minimum height of six feet as measured from the ground to the midpoint between the uppermost whorl and the tip of the leader. For species of trees without whorls, minimum height shall be measured to the uppermost side growth. The ratio of height to spread shall not be less than 5:3.

(iv) Broad-leaf evergreen trees (Types 4 and 5) shall be a minimum height of four feet as measured from the ground level to where the main part of the plant ends, not to the tip of a thin shoot.

(b) Shrubs shall be of the following size at time of planting and shall conform to the “American Standard for Nursery Stock”:

(i) Dwarf and semi-dwarf deciduous shrubs shall be a minimum height of two to two and one-half feet above grade, and either a No. 3 container size for container-grown plants, 10-inch diameter root ball for balled and burlapped plants, or 11-inch root spread for bare-root plants.

(ii) Strong-growing deciduous shrubs shall be a minimum height of two to three feet above grade, and either a No. 3 container size for container-grown plants, 10-inch diameter root ball for balled and burlapped plants, or 11-inch root spread for bare-root plants.

(iii) Coniferous and broad-leaf evergreen shrubs (Types 1, 2, and 3) shall be a minimum height of two to two and one-half feet spread or height, and either a minimum No. 3 container size for container-grown plants or 12-inch diameter root ball for balled and burlapped plants. [Ord. 1400 § 30, 2007.]

18.86.210 Ravine sidewalls, bluffs, and hillsides of 15 percent slope and greater – Reasonable use exceptions.

(1) Limited Waiver of Hillside Disturbance Limitations. Any one or all of the disturbance limitation requirements of DMMC 18.86.200 may be waived if the city manager or designee determines that the application of such requirements is not feasible for developing one single-family dwelling on a development site and the proposal is consistent with the purpose and intent of this chapter. [Ord. 1400 § 31, 2007.]

18.86.220 Seismic hazard areas – Development standards.

Development in seismic hazard areas shall be in accordance with the standards for earthquake design and seismic motion as established in the Des Moines Building and Construction Code (Title 14 DMMC). Seismic hazard areas shall be altered only when the city manager or designee concludes, based on environmental information, the following:

(1) There is no actual hazard based on a lack of seismic activity in the past in the area of the development proposal, and a quantitative analysis of potential for seismic activity indicates no significant risk to the development proposal; or

(2) The development proposal can be designed so that it will be as safe from any earthquake damage as a similar development not located in a seismic hazard area. [Ord. 1400 § 32, 2007.]

18.86.230 Erosion and landslide hazard areas – Development standards.

Development on hillsides containing or adjacent to erosion or landslide hazard areas shall meet the general performance requirements of DMMC 18.86.180 and the following:

(1) Buffer Requirement. A buffer shall be established from all edges of landslide hazard areas. The size of the buffer shall be determined by the city manager or designee to eliminate or minimize the risk of property damage, death, or injury resulting from landslides caused in whole or part by the development, based upon review of and concurrence with a special environmental study prepared by a qualified professional.

(a) Minimum Buffer. The minimum buffer shall be equal to the height of the slope or 50 feet, whichever is greater;

(b) Increased Buffer. The buffer may be increased where the city manager or designee determines a larger buffer is necessary to prevent risk of damage to proposed and existing development;

(c) Buffer Reduction. The buffer may be reduced to a minimum of 10 feet when a qualified professional demonstrates to the city manager or designee’s satisfaction that the reduction will adequately protect the proposed development, adjacent developm