Loading...
HomeMy WebLinkAboutCOW 2011-06-27 Item 4A - Shoreline Master Program - Ordinance - Attachment A.07: Shoreline Environment Designations 7. SHORELINE ENVIRONMENT DESIGNATIONS The City of Tukwila's Shoreline Master Program (SMP) establishes a system to classify shoreline areas into specific "environment designations." This system of classifying shorelines is established by the Shoreline Management Act (RCW 90.58) and Master Program Guidelines (WAC 173 -26 -211). The purpose of shoreline environment designations is to provide a uniform basis for applying policies and use regulations within similar shoreline areas. Generally, shoreline designations should be based on existing and planned development patterns, biological and physical capabilities and limitations of the shoreline, and a community's vision or objectives for its future development. 7.1 Existing Ret?ulatory Framework Tukwila's current SMP, first adopted in 1974, designates all shorelines as "Urban." At the time the 1974 SMP was developed, all of the land in Tukwila's shoreline jurisdiction was either zoned commercial /industrial or was developed with urban uses. The SMP defines the Urban Environment as "areas to be managed in high intensive land uses, including residential, commercial, and industrial development and accessory uses, while providing for restoration and preservation to ensure long -term protection of natural and cultural resources within the shoreline" (Tukwila, 1974). The SMP further states that the management objectives for the shoreline "are directed at minimizing adverse impacts on the river and shoreline ecology, maximizing the aesthetic quality and recreational opportunities of the river shore, and recognizing the rights and privileges of property owners" (Tukwila, 1974). Within the Urban Environment, Tukwila's SMP employs a tiered system of regulations based on the distance from the Green/Duwamish River mean high water mark (MHWM). These tiered management zones are generally described below and illustrated on Figure 1: River Environment/Zone: a 40 -foot wide zone extending landward from MHWM and having the most environmentally protective regulations; Low Impact Environment /Zone: the area between the River Environment and 100 feet from the MHWM; and High- Impact Environment/Zone: the area between 100 and 200 feet from the MHWM. The City also administers the King County Shoreline Master Program for the areas which have been annexed since the adoption of the City's SMP in 1974. These areas are designated Urban and the setbacks from Ordinary High Water Mark vary from 20 feet to 50 feet depending on whether the use is water dependent, single family or commercial/industrial. See Annexation History, Map 1 for an identification of the areas where the City administers the County's SMP. CL 49 06/21/2011 9:49 AM W: \Shoreline \Council Review\ \Document \Council Adopted SMP- Revised per Ecology Required Changes 65 I 200' I 1 200' 1 URBAN ENVIRONMENT 11 URBAN ENVIRONMENT 100' 60' 40' I is 9 14 i i HIGH j LOW j RIVER I I RIVER j LOW j HIGH I IMPACT i IMPACT I ZONE ZONE I IMPACT I IMPACT I I ZONE ZONE i I i ZONE ZONE RIVER i MEAN HIGH WATER LINE Figure 1. Current Tukwila SMP Shoreline Management Zones (1974 SMP; TMC 18.44) 7.2 Kev Findines of the Shoreline Inventory Characterization Report and Restoration Plan This section summarizes findings from the Inventory and Characterization Report and Restoration Plan elements of the SMP update (Appendices A and B). These findings inform the goals, policies, regulations, and the development and application of environment designations. In this context, the key findings can be summarized as follows: The Green/Duwamish River throughout Tukwila is a critical resource, particularly in the Transition Zone portion of the river that extends from the East Marginal Way South bridge through the north City limits (see Map 2), where juvenile salmon adjust from fresh to salt water habitat. The river provides migratory habitat for numerous fish species, as well as riparian habitat for a variety of wildlife. The river is a critical resource for Muckleshoot Indian Tribe fishing. The river is a critical resource for some water dependent uses north of the Turning Basin. The river is an important recreational resource for sport fishing, small water craft and Green River Trail users. At an ecosystem scale, the habitat is largely homogenous throughout the city. In addition, many ecosystem processes are largely controlled by up -river characteristics, particularly the Howard Hanson Dam and are little affected by actions in the City, except for such functions as water quality (especially fine sediment capture and filtering of contaminants in stormwater), local surface hydrology (stormwater from increasing amounts of impervious surfaces and contribution to peak flows of the river), riparian habitat, and temperature control (shading from riparian habitat).With the exception of the functions provided by the transitional mixing zone from salt to fresh water, habitat conditions and functions are relatively similar throughout the shoreline. The transition zone CL 50 06/21/20119:49 AM W: \Shoreline \Council Review \\Document \Council Adopted SMP- Revised per Ecology Required Changes 66 needs greater protection and restoration focus than other sections of the shoreline in the city. Restoration opportunities are numerous and spatially distributed throughout Tukwila's shoreline. Activities that provide restoration of both floodplain functions and habitat functions should be prioritized, particularly those projects in the transition zone. Policies should promote and regulations should enable the City to accomplish restoration goals and actions. 7.3 State Environment Desiznation Svstem State Master Program Guidelines (WAC 173 -26 -211) establish the environment designation system for shorelines regulated by the Shoreline Management Act. The guidelines (WAC 173 -26 -150 and 176 -26 -160) give local jurisdictions the option to plan for shorelines in designated Urban Growth Areas (UGA) and Potential Annexation Areas (PAA) as well. The City can "pre- designate" shoreline environments in its designated PAA as part of this planning process. However, shorelines in the PAA would continue to be regulated under the provisions of the King County SMP until the City annexes those areas. King County's SMP designates the City's north PAA "Urban" and the south PAA as "Rural." King County is also in the process of updating its SMP, so these designations may change when the County adopts an updated SMP, expected sometime before December 2009. The County's Draft SMP designates the City's North PAA and the South PAA as High Intensity. The guidelines (WAC 173 -26 -211 (4) (b)) recommend six basic environment designations: high intensity; shoreline residential; urban conservancy; rural conservancy; natural Farc and aquatic. Local governments may establish a different designation system, retain their current environment designations and/or establish parallel environments provided the designations are consistent with the purposes and policies of the guidelines (WAC 173 -26 -211 (4)(c)). The guidelines also note that local shoreline environment designations should be consistent with the local comprehensive plan (WAC 173 -26 -211 (3)). For each environment designation, jurisdictions must provide a purpose statement, classification criteria, management policies and environment specific regulations. Table 2 describes the purpose for each of the recommended designations in the state guidelines. For each designation, the potential applicability to Tukwila is noted. CL 51 06/21/2011 9:49 AM W: \Shoreline \Council Review \\Document \Council Adopted SMP- Revised per Ecology Required Changes 67 Table 2. State Recommended Environment Designation System WAC 173 -26 -211 (5) Environment Purpose Applicability to Tukwila Designation Aquatic The purpose of the "aquatic" environment is to The City does not currently utilize an protect, restore, and manage the unique Aquatic designation. Uses or activities characteristics and resources of the areas waterward of OHWM are regulated waterward of the ordinary high -water mark. according to the provisions of the associated upland designation. The aquatic designation appears to have limited utility for Tukwila, as the management policies and objectives for aquatic areas can be met through the adjacent upland designation. Natural The purpose of the "natural" environment is to While the Green River shorelines in protect those shoreline areas that are relatively Tukwila provide some important free of human influence or that include intact or ecological functions, the river and adjacent minimally degraded shoreline functions uplands throughout Tukwila have been intolerant of human use. significantly altered by dense urban development and are generally armored or otherwise modified. Rural The purpose of the "rural conservancy" Not applicable to Tukwila. All of the Conservancy environment is to protect ecological functions, City's shorelines are urbanized. Potential conserve existing natural resources and annexation areas are either urbanized or valuable historic and cultural areas in order to proposed for intensive development. provide for sustained resource use, achieve natural flood plain processes, and provide recreational opportunities. Urban The purpose of the "urban conservancy" This designation is applicable in that the Conservancy environment is to protect and restore ecological Green River is an important natural functions of open space, flood plain and other resource. The most significant shoreline sensitive lands where they exist in urban and function provided in Tukwila is related to developed settings, while allowing a variety of fish and wildlife habitat. Open space is compatible uses. limited by the existing development pattern and flood plains are largely disconnected by a series of levees, revetments, and other infrastructure. Shoreline The purpose of the "shoreline residential" This designation is most applicable for Residential environment is to accommodate residential those portions of Tukwila's shorelines development and appurtenant structures that where the existing and planned are consistent with this chapter. An additional development pattern is for low density purpose is to provide appropriate public access (i.e., predominantly single family) and recreational uses. residential uses or public recreation uses. High- Intensity The purpose of the "high- intensity" This designation is applicable along only environment is to provide for high intensity part of Tukwila's shorelines, in the water oriented commercial, transportation, and Manufacturing and Industrial Center industrial uses while protecting existing (MIC) north of the Turning Basin. Water ecological functions and restoring ecological dependent uses are currently limited, as functions in areas that have been previously only a small portion of the river in Tukwila degraded. is navigable for commercial purposes, and much of the river has levees, thus restricting use immediately adjacent to the river. CL 52 06/21/2011 9:49 AM W: \Shoreline \Council Review\ \Document \Council Adopted SMP- Revised per Ecology Required Changes 68 7.4 Proposed Environment Designations The Aquatic, Natural and Rural Conservancy Environments are not well suited to a highly developed, urbanized river that is navigable for only a small portion of the system and is significantly constrained by levees for flood management, such as the Green/Duwamish River in Tukwila. The City's Shoreline Environments, which are identified on Map 3, are: Shoreline Residential Environment Urban Conservancy Environment, and High Intensity Environment Aquatic Environment The City proposes to designate a buffer to replace the current system of parallel shoreline management zones. Instead of the current River Environment, a minimum buffer will be established for each shoreline environment and allowed uses will be designated for the buffer area along the river and the remaining shoreline jurisdiction. This system is intended to facilitate the City's long -range objectives for land and shoreline management, including: Ensuring no net loss of ecological shoreline functions; Providing for habitat protection, enhancement, and restoration to improve degraded shoreline ecological functions over time and protection of already restored areas; Allowing continued and increased urban development in recognition of Tukwila's role as a regionally significant industrial and commercial center; and Providing for improved flood control in coordination with King County and the Army Corps of Engineers. Table 3, on the following page, provides a summary of the characteristics of the river shoreline in Tukwila to set the stage for the discussion in Section 7.5 on the determination of shoreline buffers. CL 53 06/21/2011 9:49 AM W: \Shoreline \Council Review \\Document \Council Adopted SMP- Revised per Ecology Required Changes 69 Table 3. Summary of Buffer Widths for Land Use Zones and Shoreline Ecological Conditions Area Characteristics Environment Buffer Modification MIC /H Fresh/Salt water High Intensity 100' The Director may reduce the standard MIC /L Transition Zone, buffer on a case -by -case basis by up Zoned Lower flooding to 50% upon construction of the property risk, Less than 20' following cross section: from North difference from 1. reslope bank from OHWM City Limits OHWM to top of (not toe) to be no steeper than 3:1, to EMWS bank, tidal using bioengineering techniques Bridge, and influence 2. Minimum 20' buffer North landward from top of bank Potential 3. Bank and remaining buffer to Annexation be planted with native species Area with high habitat value Comment: Maximum slope is reduced due to measurement from OHWM and to recognize location in the Transition Zone where pronounced tidal influence makes work below OHWM difficult. Any buffer reduction proposal must demonstrate to the satisfaction of the Director that it will not result in direct, indirect or long -term adverse impacts to the river. In all cases a buffer enhancement plan must also be approved and implemented as a condition of the reduction. The plan must include using a variety of native vegetation that improves the functional attributes of the buffer and provides additional protection for the shoreline ecological functions. LDR Zoned Moderate flooding Shoreline Distance Removal of invasive species and property w/o risk, Less than 25' Residential required replanting with native species of high levees from difference from to set habitat value voluntary unless EMWS to I- OHWM to top of back triggered by requirement for a 405 bank, tidal slope Shoreline Substantial Development influence on from toe permit northern section at 2.5:1 plus 20' setback, Min. 50' width CL 54 06/21/2011 9:49:00 AM P: \Shoreline \Council Review \Document\ Council Adopted SMP- Revised per Ecology Comments 70 LDR Zoned Moderate flooding Shoreline 125' Upon reconstruction of levee in property with risk, Less than 25' Residential accordance with minimum profile, the levees from difference from Director may reduce the buffer to actual EMWS to I- OHWM to top of width required. 405 bank, tidal Comment: this applies to City -owned influence on property at Fort Dent. northern section Commercially Moderate flooding Urban 100' The Director may reduce the standard zoned risk, Less than 25' Conservancy buffer on a case -by -case basis by up to property from difference from 50% upon -construction of the following 42 Ave S. OHWM to top of cross section: Bridge to I- bank reslope bank from toe to be 405 no steeper than 2.5:1 using bioengineering techniques Minimum 20' buffer landward from top of bank Bank and remaining buffer to be planted with native species with high habitat value Any buffer reduction proposal must demonstrate to the satisfaction of the Director that it will not result in direct, indirect or long -term adverse impacts to shoreline ecological functions. In all cases a buffer enhancement plan must also be approved and implemented as a condition of the reduction. The plan must include using a variety of native vegetation that improves the functional attributes of the buffer and provides additional protection for the shoreline ecological functions. West River High flooding risk, Urban 125' Upon construction or reconstruction of bank from I- Federally certified Conservancy levee in accordance with City minimum 405 to South and County levee, profile the Director may reduce the City Limit, large water level buffer to the actual width required. in Tukwila 205 fluctuations no case shall the buffer be less than 50 Levee and feet. South Annexation Area CL 55 06/21/2011 9:49 AM W: \Shoreline \Council Review \\Document \Council Adopted SMP- Revised per Ecology Required Changes 71 East River Moderate flooding Urban The Director may reduce the standard bank without risk, 20 to 25' Conservancy 100' buffer on a case -by -case basis by up to levee from I- difference from 50% upon construction of the following 405 south to OHWM to top of cross section: City Limits bank, Moderate 1. reslope bank from toe to be no slumping risk, steeper than 2.5:1, using large water level bioengineering techniques fluctuations 2. Minimum 20' buffer landward from top of bank 3. Bank and remaining buffer to be planted with native species with high habitat value Any buffer reduction proposal must demonstrate to the satisfaction of the Director that it will not result in direct, indirect or long -term adverse impacts to shoreline ecological functions. In all cases a buffer enhancement plan must also be approved and implemented as a condition of the reduction. The plan must include using a variety of native vegetation that improves the functional attributes of the buffer and provides additional protection for the shoreline ecological functions. East River Moderate flooding Urban 125' Upon reconstruction of levee in bank with risk, 20 to 25' Conservancy accordance with City minimum profile levee from I- difference from the Director may reduce the buffer to 405 to South OHWM to top of the actual width required for the levee. City Limit bank, Moderate In no case shall the buffer be less than slumping risk, 50 feet. large water level fluctuations Any shoreline End buffer on river side of existing environment improved street or roadway. where street or road runs parallel to the river through the buffer CL 56 06/21/20119:49 AM W: \Shoreline \Council Review \\Document \Council Adopted SNIP-Revised per Ecology Required Changes 72 Map 3 t, =w4 �"„t r=. MIL Shoreline Reach G2 9 i t Environments PAA rrrn Turning Basin t �t t Reach G2 ,A L I r z ill kL t Reach G1 jj Is s Legend Tukwila City Limits PAA Potential Annexation Areas Aquatic Environment wd.. Urban Conservancy Shoreline Environment (�!3= Reach G 1 PAA High Intensity Shoreline Environment aaoii f Shoreline Residential Environment �1 CM.TUWla Gl ,4 Cowry GIs CL 57 06/21/20119:49 AM W: \Shoreline \Council Review \\Document \Council Adopted SMP- Revised per Ecology Required Changes 73 CL 58 06/21/20119:49 AM W: \Shoreline \Council Review\ \Document \Council Adopted SMP- Revised per Ecology Required Changes 74 7.5 Determination of Shoreline Buffers The determination of the buffer distances for each shoreline environment was based on several factors including the analysis of buffer functions needed for protecting and restoring shoreline ecological function (as presented in the Shoreline Inventory and Characterization Report) and the need to allow space for bank stability and for protecting human life and structures from damage from high flows, erosion and bank failures. Safety of residents and people who work in buildings along the shoreline has become even more important in recent years due to the increase in stormwater entering the river from increasing impervious surfaces throughout the watershed and the recent problems with the Howard Hanson Dam, which preclude being able to store as much flood water behind the dam in the winter until the dam is repaired, and increasing the frequency and intensity of flows during high rain events. These higher and more frequent flows will put more stress on over steepened banks all along the river, increasing the possibility of bank erosion, levee failures, and bank failures. Thus, ensuring that new structures are not built too close to the river's edge is crucial to avoid loss of human life. Staff also reviewed the rationale for the buffer widths established for watercourses under TMC 18.45, the Sensitive Areas Ordinance, as well as buffer widths recommended by resource agencies, such as the State Department of Fish and Wildlife, Department of Natural Resources and the recent Biological Opinion issued by National Marine Fisheries Service in relation to FEMA's National Flood Insurance Program. The final buffer widths proposed by staff for each shoreline environment attempted to balance shoreline ecological function needs, human life and property protection needs (including future levee repair /reconstruction), existing land use patterns, and state and federal agency policies. The following information summarizes the analysis carried out and the rationale used for determining buffer widths. A. Buffer Functions Supporting Shoreline Ecological Resources, Especially Salmonids Buffers play an important role in the health of any watercourse and an even more important role when considering the health of salmonids in the Green/Duwamish River system. The key buffer functions for the river are summarized below. The Shoreline Management Act and the Department of Ecology regulations require evaluation of ecological functions and that local SMPs ensure that the policies and regulations do not cause any net loss of shoreline ecological function. In addition, the SMP must identify mechanisms for restoration of lost ecological functions. CL 59 06/21/20119:49 AM W: \Shoreline \Council Review \\Document \Council Adopted SMP- Revised per Ecology Required Changes 75 The crucial issue for the Green/Duwamish River is the presence of salmonids that are on the Endangered Species list. To protect and restore ecological functions related to these species it is important to provide for the installation of native vegetation along the shoreline. Such vegetation provides shade for improving temperature conditions in the river and habitat for insects on which fish prey. Trees along the shoreline also provide a source of large woody debris (tree trunks, root wads, limbs, etc. that fall into the water), which in turn provides pooling and areas of shelter for fish and other animals. In order to allow for planting of native vegetation, banks need to be set back to allow for less steep and more stable (requiring less armoring) slopes, so that they can be planted. The Corps of Engineers does not allow planting on levees unless they are set back to an average slope of 2.5:1 and constructed with a mid -slope bench. Plantings are allowed on the mid slope bench and this is crucial for improving shoreline ecological functions that are needed in the river. The buffer widths needed to achieve a particular buffer function vary widely by function type from as little as 16 feet for large woody debris recruitment (assuming the buffer has large trees) to over 400 feet for sediment removal. The Washington State Department of Fish and Wildlife (WDFW) recommends a riparian buffer width of 250 feet for shorelines of statewide significance (this applies to the Green/Duwamish River). The Washington Department of Natural Resources (WDNR) recommends a riparian buffer of 200 feet for Class 1 Waters (the Green/Duwamish River is a Class 1 Water under the WDNR classification scheme). The National Marine Fisheries Service (responsible at the federal level for overseeing protection of endangered salmonids under the Endangered Species Act) has recommended a buffer of 250 feet in mapped floodplain areas to allow for protection of shoreline functions that support salmonids. Tukwila's Sensitive Areas Ordinance (TMC 18.45) has established a 100 foot buffer for Type 2 watercourses in the city (those that bear salmonid species). The key buffer functions for the river are summarized below. 1. Maintenance of Water Quality Salmonid fish require water that is both colder and has lower nutrient levels than many other types of fish. Vegetated shoreline buffers contribute to improving water quality as described below. a. Water Temperature: The general range of temperatures required to support healthy salmonid populations is generally between 39 degrees and 63 degrees. Riparian vegetation, particularly forested areas can affect water temperature by providing shade to reduce exposure to the sun and regulate high ambient air temperatures. t Endaneered Species Act Section 7 Consultation. Final Bioloeical Opinion and Maenuson Stevens Fishery Conservation and Manaeement Act Essential Fish Habitat Consultation. Implementation of the Flood Insurance Proeram in the State of Washinaton. Phase One Document. Pueet Sound Rea_ ion. September. 2008. CL 60 06/21/20119:49 AM W: \Shoreline \Council Review \\Document \Council Adopted SMP- Revised per Ecology Required Changes 76 b. Dissolved Oxygen: dissolved oxygen is one of the most influential water quality parameters for aquatic life, including salmonid fish. The most significant factor affecting dissolved oxygen levels is water temperature cooler streams maintain higher levels of oxygen than warmer waters. c. Metals and pollutants: Common pollutants found in streams, particularly in urban areas, are excessive nutrients (such as phosphorous and nitrogen), pesticides, bacteria and miscellaneous contaminants such as PCBs and heavy metals. Impervious surfaces collect and concentrate pollutants from different sources and deliver these materials to streams during storm events. The concentration of pollutants increases in direct proportion to the total amount of impervious area. Undisturbed or well vegetated riparian buffer areas can retain sediment, nutrients, pesticides, pathogens and other pollutants, protecting water quality in streams. Elevated nitrogen and phosphorus levels in runoff are a typical problem in urban watersheds and can lead to increased in- stream plant growth, which results in excess decaying plant material that consumes oxygen in streams and reduces aquatic habitat quality. 2. Contributing to in- stream structural diversity a. Large woody debris (LWD) refers to limbs and tree trunks that naturally fall into the stream bed from a vegetated buffer. LWD serves many functions in watercourses. LWD adds roughness to stream channels, which in turn slows water velocities and traps sediments. Sources of LWD in urban settings are limited where stream corridors have been cleared of vegetation and developed and channel movement limited due to revetments and levees. Under natural conditions, the normal movement of the stream channel, undercutting of banks, wind throw, and flood events are all methods of LWD recruitment to a stream channel. b. LWD also contributes to the formation of pools in river channels that provide important habitat for salmonids. Adult salmonids require pools with sufficient depth and cover to protect them from predators during spawning migration. Adult salmon often hold to pools during daylight, moving upstream from pool to pool at night. 3. Providing Biotic Input of Insects and Organic Matter a. Vegetated buffers provide foods for salmonids and other fish, because insects fall into the water from overhanging vegetation. b. Leaves and other organic matter falling into stream provide food and nutrients for many species of aquatic insects which in turn provide forage for fish. CL 61 06/21/2011 9:49 AM W: \Shoreline \Council Review\ \Document \Council Adopted SMP- Revised per Ecology Required Changes 77 B. Bank Stability and Protection of Human Lives and Structures The main period of runoff and major flood events on the Green River is from November through February. The lower Green and Duwamish levees and revetments form a nearly continuous bank protection and flood containment system. Farmers originally constructed many of these levees and revetments as the protection to the agricultural lands of the area and this original material is still in place as the structural core. In particular, these protection facilities typically have over steepened banks, areas with inadequate rock buttressing at the toe, and lack habitat enhancing features such as overhanging vegetation or in -water large woody debris. Because of these design and construction shortcomings, the protection to river banks has not always performed as intended. Instead, there have been bank failures that have threatened structures and infrastructure; erosion of banks making them even steeper; and damage to levees that has required a series of repair projects. The damage to the levee system in recent storm events lead to discussions among the City, US Army Corps of Engineers and the King County Flood Control District to determine the best levee profile to use to prevent the recurring problem of continued levee repairs. The criteria used to determine the best profile were: Public Safety; Maintaining levee certification; Solutions that eliminate or correct factors that have caused or contributed to the need for the levee repair; Levee maintenance needs; and Environmental considerations. To overcome the existing problems and to reduce future maintenance and repair costs, the Corps chose to lessen the overall slope to a stable grade. This selected method is consistent with recommendations set forth in the Corps of Engineers' Manual for Design and Construction of Levees (EM 1110 -2 -1913) for slope stability. It also is consistent with the levee rehabilitation project constructed on the nearby Briscoe School levee that has proven to be a very effective solution to scour problems the design slows the river down, provides additional flood storage and allows a vegetated mid -slope bench for habitat improvements. The Corps indicated that this type of profile would become the template for future levee repair and construction projects. King County also plans to use the 2.5:1 overall slope with a mid -slope bench incorporated for planting vegetation for its future levee repairs. This profile was used to repair two areas of the federally certified levee in Tukwila the Lily Point project and the Segale project, which were about 2,000 linear feet of repairs. Costs of these repairs were around $7 million dollars, not including any costs of land acquisition for laying back the levees. It is expected that the use of this levee design will reduce the need to continually repair the levee in those areas, thus avoiding such high expenditures in the future and saving money in the long run. CL 62 06/21/20119:49 AM W: \Shoreline \Council Review \\Document \Council Adopted SMP- Revised per Ecology Required Changes 78 The profile discussed above is the Tukwila minimum profile for levee reconstruction as illustrated in Figure 2 below: Typical Shoreline Buffer in Leveed Areas -Width Will Vary Reconfigured Levee Vegetated Bench 18' =10' 6 Willows 2 2' 1.5 /Existing Levee Z. �1 r Maintenance Easement Ordinary High r 2' Water Mark OHWM Reconfigured Slope averages 2.5:1 with bench Minimum Levee Profile Not To Scale Figure 2. Minimum Levee Profile Because of the similarities in the soil conditions and taking into consideration the tidal influence, the Green/Duwamish River can be divided into three areas South of I -405; North of I -405; and areas around residential neighborhoods. Looking at the slope geometry and the difference in height between the ordinary high water mark and the 100 year flood elevation for these three areas, it was found that 125 -feet of setback distance (buffer) is needed to accommodate the "lay back" of the levee in the area south of 1 -405 and around Fort Dent Park. During high flow events, the water surface can be as much as 16 feet above the OHWM in these areas. At locations further downriver, the water surface elevation difference is much less pronounced due to the wider channel and proximity to Puget Sound. For areas without levees, north of I -405 and those areas south of I -405 on the east side of the river (right bank), a 100 -foot setback distance is required to accommodate the slopes needed for bank stability. Within residential neighborhoods, a minimum 50 -foot setback is justified because of the less intense land use associated with single family home construction and the estimated amount of space needed to achieve the natural angle of repose for a more stable slope. Even though the above explanation for determining appropriate buffer distance used levee design as the example, the same problems exist where there are no levees. The river makes no distinction between an over steepened slope associated with a levee or a riverbank. Scouring within the river will cause sloughing and slope stability will be 2 The 125 foot distance includes a2.5:1 overall slope with a mid -slope bench incomorated, 18 feet at the ton of the levee and 10 feet on the back side of the levee for access and inspection. CL 63 06/21/2011 9:49 AM W: \Shoreline \Council Review \\Document \Council Adopted SMP- Revised per Ecology Required Changes 79 weakened, potentially resulting in the loss of structures. In fact, the non leveed riverbank can be more prone to these problems since they tend to be steeper and consist mainly of sand and silt. This makes them susceptible to erosion. Because the non leveed riverbanks are for the most part privately owned, they are not actively monitored for damage by the City or County. C. Conclusions The determination of buffer widths was based on two important criteria: the need to achieve bank stability and protect structures along the shoreline from damage due to erosion and bank failures and to protect and enhance shoreline ecological function. Applying the 200 to 250 foot buffer widths recommended by WDFW and WDNR would not be practical given the developed nature of the shoreline. It was also felt that a buffer less than that already established for Type 2 Watercourses under the City's SAO would not be sufficiently protective of shoreline functions, unless those functions were enhanced through various restoration options. Therefore, 100 feet was established as the starting point for considering buffer widths from the standpoint of shoreline ecological function in each of the Shoreline Environments. Between 100 and 125 feet was the starting point for buffer widths from the standpoint of bank stability and property protection. Thus buffers were established taking into account (as explained in the following sections) the characteristics of each Shoreline Environment, needs for protection/restoration of shoreline ecological functions, and needs for stable banks and human life and property protection. 7.6 Shoreline Residential Environment A. Designation Criteria: All properties zoned for single family use from the ordinary high water mark landward two hundred (200) feet. In addition, those areas zoned for single family use but developed for public recreation or open space within 200 feet of the shoreline shall also be designated Shoreline Residential, except Fort Dent Park. B. Purpose of Environment and Establishment of River Buffer: The purpose of the Shoreline Residential Environment is to accommodate urban density residential development, appurtenant structures, public access and recreational activities. However, within the 200 foot shoreline jurisdiction in the Shoreline Residential Environment there will be a protective buffer along the river, where development will be limited to protect shoreline function. The purpose of the river buffer in the shoreline residential environment is to: Ensure no net loss to shoreline ecological functions; CL 64 06/21/20119:49 AM W: \Shoreline \Council Review\ \Document \Council Adopted SMP- Revised per Ecology Required Changes 80 Help protect water quality and habitat function by limiting allowed uses; Protect existing and new development from high river flows by ensuring sufficient setback of structures; Promote restoration of the natural character of the shoreline environment; and Allow room for reconstructing over steepened river banks to achieve a more stable slope and more natural shoreline bank conditions and avoid the need for shoreline armoring. C. Analysis of Development Character of Residential Shoreline: An analysis was prepared that looked at the residential properties along the shoreline and identified the number of parcels with structures within 50 feet and 100 feet of the OHWM. This analysis showed the following: Number Number Number of Number Number Number of ZONE of parcels of vacant parcels with of parcels of vacant parcels with within 50 parcels structures within 100 parcels structures feet of within 50 within 50 feet of within 100 within 100 OHWM feet feet OHWM feet feet LDR 135 12 67/49% 201 25 165/82% As can be seen from the chart above, almost half of the parcels in the residential neighborhoods have a structure within 50 feet of the OHWM a direct result of the current King County regulations. To apply a buffer width that is consistent with the City's Sensitive Areas Ordinance (SAO) of 100 feet would create a situation where 82% of the properties along the river would have nonconforming structures as they relate to the proposed shoreline buffer. Expansion of single family nonconforming structures in the proposed SMP buffer would be governed by Section 14.5 of the SMP, which permits an expansion of only 50% of the square footage of the current area that intrudes into the buffer and only along the ground floor of the structure. For example, if 250 square feet of a building extended into the proposed buffer, the ground floor could be expanded a maximum of 125 feet in total area along the existing building line. A buffer of 100 feet was considered for the shoreline residential properties, with the potential of a property owner applying for a buffer reduction of 50 however, under the Shoreline Management Act, this would have required an application for a shoreline variance for each requested buffer reduction, a process that requires review and approval both at the local and state level (Ecology must review and approve the variance in addition to the City of Tukwila). This did not seem a reasonable process to require of so many property owners. CL 65 06/21/20119:49 AM W: \Shoreline \Council Review \\Document \Council Adopted SMP- Revised per Ecology Required Changes 81 The river bank in the Shoreline Residential Environment is typically in a modified and degraded state but generally not stabilized with revetments, dikes or levees. Based on an analysis of the river elevations and existing banks, a 50 foot minimum buffer in the Shoreline Residential Environment would allow room to achieve a 2.5:1 bank slope with an additional 20 foot setback from the top of the slope a distance that will allow for bank stability and in -turn, protection of new structures from high flows, and bank failures. A schematic of the shoreline jurisdiction showing the buffer is provided in Figure 3. 200' Shoreline Residential Environment 50' min 20 feet frorA top of Buffer reconfigured riverbank 20' Ordinary High Water Mark w Figure 3. Schematic of Shoreline Residential Environment and Buffer The proposed buffer area for the Shoreline Residential Environment will allow for removal of invasive plants, planting of native vegetation in the riparian zone and inclusion of other features to improve shoreline habitat. It also will prevent the placement of any structures in an area that could potentially prove unstable. In the event of bank erosion or slope failures, the buffer will provide sufficient space for re- sloping the bank to a more stable 2.5:1 slope, either through bank stabilization projects or through natural bank failures that result in the natural angle of repose (2.5:1 or greater). 7.7 Urban Conservancv Environment A. Designation Criteria: This environment will be designated in the area between the Ordinary High Water Mark and 200 feet landward as regulated under the Shoreline Management Act and applied to all shorelines of the river except the Shoreline Residential Environment and the High Intensity Environment. The Urban Conservancy Environment areas are currently developed with dense urban multifamily, commercial, industrial and/or transportation uses or are designated for such uses in the proposed south annexation area. This environment begins at the southern end of the Turning Basin and includes portions of the river where levees and revetments generally have been constructed and where the river is not navigable to large water craft. Uses will be restricted immediately adjacent to the river by establishment of a minimum protective CL 66 06/21/20119:49 AM W: \Shoreline \Council Review\ \Document \Council Adopted SMP- Revised per Ecology Required Changes 82 buffer. B. Purpose of Environment: The purpose of the Urban Conservancy Environment is to protect ecological functions where they exist in urban and developed settings, and restore ecological functions where they have been previously degraded, while allowing a variety of compatible uses. C. Establishment of River Buffers: The Urban Conservancy environment will have two different buffers, depending on the location along the river and whether or not the shoreline has a flood control levee. The purpose of Urban Conservancy River Buffers is to: Protect existing and restore degraded ecological functions of the open space, flood plain and other sensitive lands in the developed urban settings; Ensure no net loss of shoreline function when new development or re- development is proposed; Provide opportunities for restoration and public access; Allow for adequate flood and channel management to ensure protection of property, while accommodating shoreline habitat enhancement and promoting restoration of the natural character of the shoreline environment, wherever possible; Avoid the need for new shoreline armoring; and Protect existing and new development from high river flows. Buffer in Non -Levee Areas: A buffer width of 100 feet is established for the Urban Conservancy Environment for all non residential areas without levees. This buffer width is consistent with that established by the City's Sensitive Areas Ordinance for Type 2 streams that support salmonid use, which is based on Best Available Science. In addition, as noted above, looking at the slope geometry and the difference in height between the ordinary high water mark and the 100 -year flood elevation for these areas, it was found that a 100 -foot setback distance is required to accommodate the slopes needed for bank stability. The buffer width of 100 feet allows enough room to reconfigure the river bank to achieve a slope of 2.5:1, the "angle of repose" or the maximum angle of a stable slope and allow for some restoration and improvement of shoreline function through the installation of native plants and other habitat features. The actual amount of area needed to achieve a 2.5:1 slope may be less than 100 feet, depending on the character of the river bank and can only be determined on a site -by -site basis. As an alternative to the 100 foot buffer, a property owner may re -slope the river bank to 2.5:1, provide a 20 foot setback from the top of the new slope and vegetate both the river bank and the 20 foot setback area in accordance with the standards in the Vegetation CL 67 06/21/20119:49 AM W: \Shoreline \Council Review\ \Document \Council Adopted SMP- Revised per Ecology Required Changes 83 Protection and Landscaping Section. Any buffer reduction proposal must demonstrate to the satisfaction of the Director that it will not result in direct, indirect or long -term adverse impacts to shoreline ecosystem functions. In all cases a buffer enhancement plan must also be approved and implemented as a condition of the reduction. The plan must include removal of invasive plants, and plantings using a variety of native vegetation that improves the functional attributes of the buffer and provides additional protection for the watercourse functions. In no case shall the buffer be less than 50 feet. In areas of the river where this condition currently exists or where the property owner has constructed these improvements, the buffer width will be the actual distance as measured from the ordinary high water mark to the top of the bank plus 20 feet. The shoreline jurisdiction and buffers for the Urban Conservancy Environment are depicted in the schematic in Figures 4 and 5 below. I I 200 :I 1 Urban Conservancy Environment I I 100 Allow room to reconfigure l I river bank to 1 i, i Buffer 2.5:1 slope l Ordinary High Water Mark k:>\R Figure 4. Schematic of Shoreline Jurisdiction and Buffers for the Urban Conservancy Environment in Areas without Levees Buffer in Levee Areas: For properties located behind the Army Corps of Engineers (ACOE) Certified 205 levee and County constructed levees, the buffer will extend 125 feet landward from the ordinary high water mark, determined at the time of development or redevelopment of the site or when levee replacement or repair is programmed. This buffer width is the maximum needed to reconfigure the river bank to the minimum levee profile and to achieve an overall slope of 2.5:1, the "angle of repose" or the maximum angle of a stable slope. The establishment of the 2.5:1 slope along the Corps certified 205 levee in the Tukwila Urban Center will allow for incorporating a mid -slope bench that can be planted with vegetation to improve river habitat. The mid -slope bench also will allow access for maintenance equipment, when needed. As the Corps of Engineers does not permit planting on the levee prism, the only way to improve habitat along the 205 levee portion of the river is to create a bench that can be vegetated that will not create a hazard for the CL 68 06/21/2011 9:49 AM W: \Shoreline \Council Review \\Document \Council Adopted SMP- Revised per Ecology Required Changes 84 stability of the levee. A ten foot easement necessary to allow access for levee inspection is required on the landward side of the levee at the toe. The ACOE has indicated the 2.5:1 levee profile with the mid -slope bench will be the template for future levee repairs. I I I 200' Urban Conservancy Environment I I I 1 125` t Allow room for Levee repair or 1 Buffer' I` replacement 1 >I Ordinary High Water Mark Figure 5. Schematic of Shoreline Jurisdiction and Buffers for the Urban Conservancy Environment in Areas with Levees As an alternative to the 125 foot buffer for leveed areas, a property owner may construct levee or riverbank improvements that meet the Army Corps of Engineers, King County Flood Control District, and City of Tukwila minimum levee profile. These standards at a minimum shall include an overall slope of 2.5:1 from the toe of the levee to the riverward edge of the crown, a 15 foot mid slope bench, 18' access across the top of the levee, a 2:1 back slope, and an additional 10 foot no -build area measured from the landward toe for inspection and repairs. In instances where an existing building that has not lost its nonconforming status prevents the complete construction of the minimum levee profile, achieving an overall slope of 2.5:1 may be difficult however, the slope should be as close to 2.5:1 as possible. A floodwall is not the preferred back slope profile for a levee and may be substituted for all or a portion of the back slope only where necessary to avoid encroachment or damage to a structure legally constructed prior to the date of adoption of this Master Program and which has not lost its nonconforming status and to preserve access needed for building functionality. The floodwall shall be designed to be the minimum necessary to provide 10' (ten foot) clearance between the levee and the building or the minimum necessary to preserve access needed for building functionality while meeting all engineering safety standards. A floodwall may also be used where necessary to avoid encroachment on a railroad easement. In areas of the river where the minimum levee profile currently exists or where the property owner or a government agency has constructed the minimum profile, the buffer will be reduced to the actual distance as measured from the ordinary high water mark to the landward toe of the levee or face of a floodwall, plus 10 feet. In the event that the owner provides the City and/or applicable agency with a 10 -foot levee maintenance easement measured landward from the landward toe of the levee or levee wall (which CL 69 06/21/2011 9:49 AM WAShoreline \Council Review\ \Document \Council Adopted SMP- Revised per Ecology Required Changes 85 easement prohibits the construction of any structures and allows the City and/or applicable agency to access the area to inspect the levee), then the buffer shall be reduced to the landward toe of the levee, or landward edge of the levee floodwall, as the case may be. In cases where fill is placed along the back slope of the levee, the shoreline buffer may be further reduced to the point where the ground plane intersects the back slope. The area between the landward edge of the buffer and a point ten (10) feet landward of the underground levee toe shall be covered by an easement prohibiting the construction of any structures and allowing the City and /or applicable agency to access the area to inspect the levee and /or floodwall and make any necessary repairs. See Figure 5 below. Buffer Reduction Buffer that could Proposed Levee Be Replaced 18' Top Width by Easements w New Ground Acce 2 Inspection 1 E 2 �il Fill ;�i����fj i� d 1 i au i i i I,IJ Landward!�,.''� Levee Toe Buffer Reduction with Backfill Option Not To Scale Figure 6. Schematic of Buffer Reduction Through Placing of Fill on Levee Back Slope 7.8 Hieh Intensitv Environment A. Designation Criteria: The High Intensity Shoreline Environment area is currently developed with high intensity urban commercial, industrial and/or transportation uses or is designated for such uses in the proposed north annexation area. This environment begins at the Ordinary High Water Mark and extends landward 200 feet and is located from the southern edge of the Turning Basin north to the City limits and includes the North PAA. This Environment is generally located along portions of the Duwamish River that are navigable to large watercraft. Uses will be restricted immediately adjacent to the river by establishment of a minimum protective buffer. The transition zone is located partly in the High Intensity Environment. The transition zone is the location where freshwater from a river and saltwater from the marine salt wedge mix creating brackish conditions. Often it is also where the river widens, stream CL 70 06/21/2011 9:49 AM W: \Shoreline \Council Review \\Document \Council Adopted SMP- Revised per Ecology Required Changes 86 velocities decrease and estuarine mudflats begin to appear. Habitat associated with the transition zone is critically important for juvenile Chinook and chum smolts making the transition to salt water. The transition zone moves upstream and downstream in response to the combination of stream flow and tidal elevations and as a result varies over a twenty -four hour period and seasonally. The transition zone is a crucial habitat for salmonids. B. Purpose of Environment and Establishment of River Buffer: The purpose of the Urban High Intensity Environment is to provide for high intensity, commercial, transportation and industrial uses and to promote water dependent and water oriented uses while protecting existing shoreline ecological functions and restoring ecological functions in areas that have been previously degraded. The purposes of the High Intensity River Buffer are to: Protect existing and restore degraded ecological functions of the open space, flood plain and other sensitive lands in the developed urban settings; Ensure no net loss of shoreline function when new development or re- development occurs; Provide opportunities for shoreline restoration and public access; Allow for adequate flood and channel management to ensure protection of property, while accommodating shoreline habitat enhancement and promoting restoration of the natural character of the shoreline environment, wherever possible; Avoid the need for new shoreline armoring; and Protect existing and new development from high river flows. A buffer of 100 feet is established, which allows enough room to reconfigure the river bank to achieve a slope of 3:1, (starting at the OHWM rather than the toe) the "angle of repose" or the maximum angle of a stable slope and allow for some restoration and improvement of shoreline function through the installation of native plants and other habitat features. The actual amount of area needed to achieve a 3:1 slope may be less than 100 feet, depending on the character of the river bank and can only be determined on a site -by -site basis. CL 71 06/21/2011 9:49 AM W: \Shoreline \Council Review \\Document \Council Adopted SMP- Revised per Ecology Required Changes 87 I I is 200' I I High Intensity Environment I I I I L_ 100' Allow room to reconfigure I I river bank to I Buffer 3:1 slope I j I Ordinary High Water Mark a Figure 7. Schematic Showing the Proposed Shoreline Jurisdiction and Buffer for the High Intensity Environment As an alternative to the 100 foot buffer, a property owner may re -slope the river bank to a maximum -3:1, provide a 20 foot setback from the top of the new slope and vegetate both the river bank and the 20 foot setback area in accordance with the standards in the Vegetation Protection and Landscaping Section. The property owner must also demonstrate that this approach will not result in a loss of ecological functions of the shoreline. In no case shall the buffer be less than 50 feet. In areas of the river where this condition currently exists or where the property owner has constructed these improvements, the buffer width will be the actual distance as measured from the Ordinary High Water Mark to the top of the bank plus 20 feet In any shoreline environment where an existing improved street or road runs parallel to the river through the buffer, the buffer would end on the river side of the street or road. 7.9 Aquatic Environment A. Designation Criteria: All water bodies within the Citv limits and its DOtential annexation area under the iurisdiction of the Shoreline Mana <aement Act waterward of the ordinary hich water mark. The aquatic environment includes the water surface together with the underlvint? lands and the water column. B. Purpose: The Durnose of this desicnation is to Drotect the uniaue characteristics and resources of the aauatic enviromnent by manaainc use activities to Drioritize preservation and restoration of natural resources, navi cation, recreation and commerce and by assuri.nL compatibility between sho.reland and aauatic uses. CL 72 06/21/2011 9:49 AM W: \Shoreline \Council Review\ \Document \Council Adopted SMP- Revised per Ecology Required Changes 88