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HomeMy WebLinkAboutCOW 2009-11-23 Item 4I.1 - Shoreline Master Program - Attachment A.07: Shoreline Environment Designations7. 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 Existinn Retulatory 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 1 commercial /industrial. See Annexation History Map, Map 32 for an identification of the areas where the City administers the County's SMP. CL 47 11/19/2009 12:55:00 PM W \Shoreline \Council Review \\Document \Council SMP 187 188 LOW IMPACT ZONE CL W \Shoreline \Council Review \\Document \Council SMP 1 1 RIVER 1 LOW ZONE I IMPACT f: ZONE I, ,I 1 1 200' MEAN HIGH WATER LINE Figure 1. Current Tukwila SMP Shoreline Management Zones (1974 SMP; TMC 18.44) 7.2 Key Findings 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 Man 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 aualitv (especially fine sediment capttue and filterina of contaminants in stormwater), local surface hvdroloav (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. That is,The transition 48 11/19/2009 12:55:00 PM zone there are not specific ecc:ions of Tukwila' c shorelines that—needs greater protection ef-and restoration focus than other sections of the shoreline in the city. In addition, ecosystem processes, are largely aentrelled by up river 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 nroiects in the transition zone. Policies should promote and regulations should enable the City to accomplish restoration goals and actions. 7.3 State Environment Designation System 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 resource; 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 49 11/19/2009 12:5500 PM W \Shoreline \Council Review\ \Document \Council SMP 189 190 Table 2. State Recommended Environment Designation System WAC 173 -26 -211 (5) ica x ytronme l Asi atio Aquatic Natural Rural Conservancy Urban Conservancy Shoreline Residential High Intensity The purpose of the "aquatic" environment is to protect, restore, and manage the unique characteristics and resources of the areas waterward of the ordinary high -water mark. The purpose of the "natural" environment is to protect those shoreline areas that are relatively free of human influence or that include intact or minimally degraded shoreline functions intolerant of human use. The purpose of the "rural conservancy" environment is to protect ecological functions, conserve existing natural resources and valuable historic and cultural areas in order to provide for sustained resource use, achieve natural flood plain processes, and provide recreational opportunities. The purpose of the "urban conservancy" environment is to protect and restore ecological functions of open space, flood plain and other sensitive lands where they exist in urban and developed settings, while allowing a variety of compatible uses. The purpose of the "shoreline residential" environment is to accommodate residential development and appurtenant structures that are consistent with this chapter. An additional purpose is to provide appropriate public access and recreational uses. The purpose of the "high- intensity" environment is to provide for high- intensity water- oriented commercial, transportation, and industrial uses while protecting existing ecological functions and restoring ecological functions in areas that have been previously degraded. The City does not currently utilize an Aquatic designation. Uses or activities waterward of OHWM are regulated 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. While the Green River shorelines in Tukwila provide some important ecological functions, the river and adjacent uplands throughout Tukwila have been significantly altered by dense urban development and are generally armored or otherwise modified. Not applicable to Tukwila. All of the City's shorelines are urbanized. Potential annexation areas are either urbanized or proposed for intensive development. This designation is applicable in that the Green River is an important natural resource. The most significant shoreline function provided in Tukwila is related to fish and wildlife habitat. Open space is limited by the existing development pattern and flood plains are largely disconnected by a series of levees, revetments, and other infrastructure. This designation is most applicable for those portions of Tukwila's shorelines where the existing and planned development pattern is for low density (i.e., predominantly single family) residential uses or public recreation uses. This designation is applicable along only part of Tukwila's shorelines, in the Manufacturing and Industrial Center (MIC) north of the Turning Basin. Water dependent uses are currently limited, as only a small portion of the river in Tukwila is navigable for commercial purposes, and much of the river has levees, thus restricting use immediately adjacent to the river. CL 50 11/19/2009 12:55:00 PM W \Shoreline \Council Review \\Document \Council SMP 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 Proposed Shoreline Environments, which are identified on Map 4J, are: Shoreline Residential Environment Urban Conservancy Environment, and High Intensity 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 51 11/19/2009 12:55:00 PM W \Shoreline \Council Review\ \Document \Council SMP 191 Area MIC/H MIC /L Zoned property from North City Limits to EMWS Bridge, and North Potential Annexation Area LDR Zoned property w/o levees from EMWS to 1 -405 Table 3. Summary of Buffer Widths for Land Use Zones and Shoreline Ecological Conditions Modificatltet. The Director may Yec1uce the standard buffer on a case -by- case basis by up to 5(1,°10; upon construction of the followinQpefeived cross section: 1. reslope bank from OHWM (not toe) to be no steeuer than at- -3:1, using bioengineering techniques 2. Minimum 20' buffer landward from op bank of of b ba a 3. Bank and remaining buffer to be planted species with high habitat value Continent: Maximum slope is reduced d ui the Trans r from OHWM and to recogniz e location Zone where pronounced tidal influence makes work below OHWM difficult. Any buffer reduction proposal must demonstrate to the satisfaction of the Director that it ai to the ruler. direct, ect, indirect or long -term adverse imp cases a buffer enhancement plan must also be approved and roved an lam must of native veg implemented as a condietationnthat i proves tion of the include using a variety provides additional protection the funcrion attributes for the shorelshoreline anao o °ical, wetemeurse-fluictionses. with native Removal of invasive s ecies and replanting triggered by p p Distance unless trigg required to species of high habitat value voluntary set back requirement for a Shoreline Substantial Development slope from permit toe at 2.5:1 plus 20' setback, Min. 50' width Characteristics Fresh/Salt water Transition Zone, Lower flooding risk, Less than 20' difference fi OHWM to top of bank, influence February, 2009 planning Commission Recommended Shoreline Master Program Moderate flooding risk, Less Shai' ime Residential than 25' d ffetek e=<frPm OHWM'to top of batilda influence,on northern section Environment High Intensity Buffer 100' 11/19/2009 12:5500 PM 52 CL �1lecommen9 Couneil Recommended SMP-C 1 P:\ShorelineV\Council Revie� +lDocumentc {�'t LDR Zoned property with levees from EMWS to 1 -405 Commercially zoned propel` from 4o 1 Ave S. Bridg e 405 West River bank from 1-405 ��w 1 City Limit, 205 Levee and South Annexation Area Moderate flooding risk, Less than 25' difference from 01-1W01-1W W t to p of bank., tidal influence on northern section Moderate flooding risk, Less than 25' difference from OHWM to top of bank Hi flooding risk, Federally certified and County levee, large water level fluctuations CL W\Shoteline \Council Review \\Document \Council SMP Shoreline Residential 125' Urban Conservancy Urban Conservancy 100' reconstruction of levee in accordance with app ed o Upon rec e minimum profile, t h e Director may reduce the buff aire owned property at Fort Dent. actual width is lies to City-owned buffer fer on a case -by' Comment: this agU Director may reduce the standard of the The basis to 50% upomco case basis by up followi cross section. nap�d toe to be no steewC1it anat reslope bank from ioengineering techn q es bank m 2 5 using um 20' buffer with Minimum buffer landward from b Bank and remaining buffer to be p habitat value native species with high Ally buffer reduction proposal must demonstrate to the faction of the Director that will not o shoreline direct, s advers p indirect or long-term In all cases a buffer ecological functions us Q'be approved and e The plan implemented condition of the m e reduction. co etation that implemented as a a variety of native veg must include using improves the functional bates of the buffer and l provides additional protectiecti on for the sly ica lme eCOlo functions rr} i�ldanc e of levee in accordance Upon tion or reconstxuC t��it�ck�, duce the 125' n unimum -p with CiIY P the Director may be actual width required. buffer to the 53 11/19(2009 12 :55.00 PM East River bank without levee from I- 405 south to City Limits East River bank with levee from I-405 to South City Limit Any shoreline environment where street or road runs parallel to the river through the buffer Moderate flooding risk, 20 to 25' difference from OHWM to top of bank, Moderate slumping risk, large water level fluctuations Moderate flooding risk, 20 to 25' difference from OHWM to top of bank, Moderate slumping risk, large water level fluctuations CL W \Shoreline \Council Review \\Document \Council SMP Urban Conservancy The Director may reduce the standard buffer on a case -by- 100' case basis by up to 50% upon construction of the followingpreferred cross section: 1._reslope bank from toe to be no steeper than at max 2.5:1, using bioengineering techniques 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 functionsthe -rte. 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 watercourse functions amend;;. Urban Conservancy 125' Upon reconstruction of levee in accordance with City approved minimum profile 10' acco: ::sement, the Director may reduce the buffer to the actual width required for the levee. End buffer on river side of existing improved street or roadway. 54 11/19/2009 12:55:00 PM February, 2009 Planning Commission Recommended Shoreline Master Program 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 nears due to the increase in stormwater entering the river from increasing impervious surfaces throughout the watershed and the regent 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 the freciuencv and intensity of flows during high rain events. These higher and more freouent 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, ensuririg°lhat new structures are not built too close to the river's edge is crucial to avoid loss of 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 :repairlreconstruction) existing land use patterns, and state and federal agency policies The following:<nfprmation suninarizes 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 CL 55 11/19/2009 12:5500 PM 1 P \Shoreline\- \Council Review Document �efion =RE' Rcc:. ,...andecICouncil Recommended SMP -Clean Copy 195 196 SMP must identify mechanisms for restoration of lost ecological functions. 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 steer and more stable (reauirinl7 less armoring) more natural 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 -1-250 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 Endanaered Species Act Section 7 Consultation. Final Bioloaical Opinion and Magnuson Stevens Fishery Conservation and Management Act Essential Fish Habitat Consultation. Implementation of the Flood Insurance Program in the State of Washington. Phase One Document.. Puget Sound Region, September. 2008. CL W \Shoreline \Council Review \\Document \Council SMP 56 11/19/2009 12:55:00 PM affect water temperature by providing shade to reduce exposure to the sun and regulate high ambient air temperatures. 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 C 57 11/19/2009 12:55.00 PM W \Shoreline \Council Review \\Document \Council SMP 197 198 nutrients for many species of aquatic insects which in turn provide forage for fish. 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 Lilv 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 anv costs of land acauisition for laving 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 CL 58 11/19/2009 12:55:00 PM W \Shoreline \Council Review\ \Document \Council SMP avoidine such high expenditures in the future and saving money in the long run. The profile discussed above is the Tukwila minimum profile for levee reconstruction as illustrated in Figure 2 below: —18'� —10'— 2 2. tf�'?r I —7 1 F fi r. r n Y r e- -J C Maintenance Easement Typical Shoreline Buffer in Leveed Areas -Width Will Vary Reconfigured Levee Minimum Levee Profile Reconfigured Slope averages 2.5:1 with bench Not To Scale Vegetated Bench Willows 1.5 Existing Levee Ordinary High Water Mark OHWM 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 I -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 Pueet Sound. For areas without levees, north of I -405 and those areas south of 1 -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 allele of repose for a more stable slope. Even though the above explanation for determining appropriate buffer distance used 2 The 125 foot distance includes a 2.5.1 overall ;lope with a amid -slope bench Incorporated. 20 feet at the toll of the levee and 10 feet on the back side of the levee for access and ins0ection. CL 59 11/19/2009 12:5500 PM W•\Shoreline \Council Review\ \Document \Council SMP 199 200 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 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. Appendix D is a chart that presents a Net Loss Analysis and identifies risks to ecosystem restore some ecosystem functions. 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, CL 60 11/19/2009 12:55:00 PM W \Shoreline \Council Review \\Document \Council SMP 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; 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 ZONE of parcels of vacant within 50 parcels feet of within 50 OHWM feet LDR I 135 12 Number of parcels with structures within 50 feet/% 67/49% Number Number of parcels of vacant within 100 parcels feet of within 100 OHWM feet Number of parcels with structures within 100 feet 201 25 1 165/82% 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 pr€- e?-istinenonconformin structures in the proposed SMP buffer would be governed by Section 14.56 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. CL 61 11/19/2009 12:5500 PM W \Shoreline \Council Review \\Document \Council SMP 201 202 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. Since the proposed minimum buffer is the maximum reduction b icy to achieve mitigation for the lower buffer width. 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 1 50' min Buffer 2O H Ordinary High Water Mark 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 1 natural bank failures that result in the natural angle of repose (2.5:1 or areater). CL 62 11/19/2009 12:55:00 PM W \Shoreline \Council Review \\Document \Council SMP 7.7 Urban Conservancy 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 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 This 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 CL 63 11/19/2009 12:55 00 PM W \Shoreline \Council Review \\Document \Council SMP 203 204 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 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 functionsthc river. 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 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. Allow room to reconfigure river bank to 2.5:1 slope 200' al Urban Conservancy Environment 100' Ordinary High Water Mark q Figure 4. Schematic of Shoreline Jurisdiction and Buffers for the Urban Conservancy Environment in Areas without Levees Buffer in Levee Areas: CL 64 11/19/2009 12:55:00 PM W \Shoreline \Council Review \\Document \Council SMP 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 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. As -meted earlier, Tthe ACOE has indicated the 2.5:1 levee profile with the mid -slope bench will be the template for future levee repairs. As an alternative to the 125 foot buffer for leveed areas, a property owner may construct levee or riverbank improvements that meet the Ailey Corps of Engineers, King County Flood Control District, and City of Tukwila minimum levee standards 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, 2018' 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, provided that minor variations of the profile may be allowed in order to A floodwall may also be used, and other minor variations made, where necessary to avoid encroachment on a railroad easement. In areas of the river where the this condition minimum levee profile currently exists or where the property owner or a government agency has constructed the minimum profile se improvements, the setbackbuffer 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 pre—existing floodwall, plus 10 feet. In the event that the owner provides the City and /or applicable CL W• \Shoreline \Council Review \\Document \Council SMP 65 11/19/2009 12:55:00 PM 205 206 agency with a 10 -foot levee maintenance easement measured landward from the landward toe of the levee or levee wall (which 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 that could Be Replaced by Easements New Ground Plane.. Figure 5. Slope Fill N 10') 2 nspe on 1 Buffer Reduction cZ /t_ Proposed Levee 18' Top Width l ccs 2 I1 =_i i= ,(t- _;11—i 1... �r= _lil_11T� iii- ifi- 71_.ur 1 hi-- .1.1 ni== iil -`>11- ji j =1� i_ f (11 1 1_ID__;T»l �ii_r d. =:Iii..:.1r_ c: Landward 'fit- i I i �',;T1il7. I Levee Toe Buffer Reduction with Backfill Option Not To Scale Schematic of Buffer Reduction Through Placing of Fill on Levee Back CL 66 11/19/2009 12:55:00 PM W \Shoreline \Council Review\ \Document \Council SMP 7.8 Hiih Intensity Environment 200' Urban Conservancy Environment l=evee_ 125' Ordinary High Water Mark J Figure 6. Schematic of Shoreline Jurisdiction and Buffers for the Urban Conservancy Environment in Areas with Levees 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 velocities decrease and estuarine mudflats begin to appear. Habitat associated with the transition zone is particularlycritically 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 an extremely important crucial habitat for sahnonids. 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. CL 67 11/19/2009 12:55 PM W \Shoreline \Council Review \\Document \Council SMP 207 208 The purposes of the High Intensity River Buffer 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 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. Allow room to reconfigure river bank to 3:1 slope 200' High Intensity Environment I 100' Ordinary High Water Mark 1 1 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 areas of the river where this condition currently exists or where the property CL 68 11/19/2009 12:55:00 PM W \Shoreline \Council Review \\Document \Council SMP 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. CL 69 11/19/2009 12:55.00 PM W• \Shoreline \Council Review\ \Document \Council SMP 209