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HomeMy WebLinkAboutCAP 2010-07-12 Item 2B - Attachment A - Addendum to SAO Departures Memo for Wetland & Watercourse Buffer WidthsCity of Tukwila 9.12922=- -1111192M48- Department of Community Development Jack Pace, Director ADDENDUM TO SAO DEPARTURES MEMO FOR WETLAND WATERCOURSE BUFFER WIDTHS BACKGROUND AND PURPOSE June 17, 2010 Attachment A Jim Haggerton, Mayor The City of Tukwila adopted its Sensitive Areas Ordinance (SAO, codified in TMC 18.45) in 2004, as required by the State Growth Management Act. As part of the development of the regulations three technical documents were prepared in 2003 by the City's consultant, ESA Adolfson. 1) Best Available Science (BAS) Report for Wetlands, 2) Best Available Science Report for Watercourses; and 3) a memo explaining the reasons for departures from BAS "BAS Departures Memo The original departures analysis identified three areas where the City's proposed ordinance deviated from BAS for wetlands: the wetland classification system, wetland buffer widths, and wetland mitigation ratios. The City is in the process of updating its Sensitive Areas Ordinance and this addendum has been prepared to document remaining departures from BAS One of the proposed modifications to the Sensitive Areas Ordinance is to adopt the Washington State Wetland Rating System for Western Washington. Another proposed modifications it to adopt the recommended wetland mitigation ratios in the "Wetland Mitigation in Washington State, Agency Policies and Guidance thus meeting BAS for these two areas. The continuing departure from BAS in the Sensitive Areas Ordinance is related to the establishment of wetland and watercourse buffers. BEST AVAILABLE SCIENCE FOR WETLAND BUFFERS Best Available Science for establishing wetland buffers is documented in "Wetlands in Washington State, Volume 1: A Synthesis of the Science (March 2005) and in Volume 2, Protecting and Managing Wetlands April 2005. These are jointly issued documents prepared by the Washington Department of Ecology, the Seattle District Corps of Engineers, and the US Environmental Protection Agency Volume II provides three alternatives for establishing buffers, based on BAS: 1) width based on wetland category, 2) width based on wetland category and the intensity of impacts from proposed changes in land use; and 3) buffer width based on wetland category, intensity of impacts and wetland functions or special characteristics. SW Page 1 of 21 07/07/2010 W. \Lon Ran e Proiects \2010 SAO Revisions \Planning Commission \6 -24 Mtg\Addendum to SAO Departures Memo FINAL 6300 Southcenter Boulevard, Suite #100 0 Tukwila, Washington 98188 0 Phone 206 431 -3670 0 Fax: 206-431-3665 4 Addendum to SAO Departures Memo for Wetland and Watercourse Buffer Widths June 17, 2010 For the first alternative (based on wetland category alone), the wetland buffer widths would be as follows: Category I 300 feet Category II 300 feet Category III 150 feet Category IV 50 feet For the second alternative (based on wetland category and extent of impact) the following buffer widths would apply: Wetland Category 1 Low land use impact .1 Moderate land use impact High land use impact I 1 150ft 225ft 300 ft. II 150 ft I 225ft 300 ft III 75ft 1 110ft 150ft IV 25 ft I 40 ft 50 ft For the third category (wetland category, impact from land use and wetland functions) the buffer ranges would vary as follows: Category I ranging from 50 feet to 250 feet depending on level of functions and forested wetlands buffers are determined on a case by case basis) Category II ranging from 50 to 300 feet depending on level of functions Category III ranging from 40 to 150 feet, depending on level of functions Category IV ranging from 25 to 50 feet, depending on level of functions Tukwila is not proposing to modify its wetland buffers from those that are already in the draft SMP and which reflect the widths in the current Sensitive Areas Ordinance. Current required buffer widths are: Category I 100 feet (there are no wetlands in Tukwila that currently score highly enough to qualify for this category) Category II 100 feet (roughly equivalent to current Type I wetland) Category III 80 feet (roughly equivalent to current Type II) Category IV 50 feet (roughly equivalent to current Type III) No Category I wetlands exist in Tukwila The City's Category II wetland buffer width, currently in the Sensitive Areas Ordinance would fall within the low range of BAS -based buffer widths, as defined in "Wetlands in Washington State, Volume 2, Protecting and Managing Wetlands" if alternative 3 were used, depending on proposed land uses and wetland functions. The City's Category III wetland buffers 1 Where wetlands have already been assessed using the Washington State Wetland Rating System, the state system classifications will be so shown on revisions to the SAO map. Where this classification system has not been applied to wetlands, they will be provisionally classified as indicated in the text. This approach is based on experience applying both Tukwila's and the state classification systems. For example where the wetland was rated a Type 2 under Tukwila's existing system, it is scored as a Category III under the state system. SW Page 2 of 21 07/07/2010 W \Long Range Projects \2010 SAO Amdts \Planning Commission \6 -24 Mtg \Addendum to SAO Departures Memo -FINAL Addendum to SAO Departures Memo for Wetland and Watercourse Buffer Widths June 17, 2010 would fall within the low end of the range if alternatives 2 or 3 were used to set buffer widths, depending on proposed land use impacts and wetland functions. Finally, the current SAO buffer widths for Category IV wetlands are consistent with the recommended buffer widths based on BAS. Another alternative approach for establishing wetland buffer widths was adopted by the City of Renton and approved by the Department of Ecology, and is based on wildlife habitat functions. Buffer widths would be 50 feet for all Category IV wetlands, no matter what the habitat score and would range from 75 150 feet for Category III Wetlands, 100 to 225 feet for Category II wetlands, and 125 225 feet for Category I wetlands, all depending on habitat scores. In general Tukwila wetlands would score very low for habitat function due to the urbanized nature of the city and the fact that most of the wetlands are isolated and surrounded by dense development. If that is assumed to be true, Tukwila buffer widths already comply with the low end of the buffer widths adopted by Renton (Category IV 50 feet, Category III 75 feet [Tukwila specifies 80 feet], and Category II 100 feet). Tukwila's SAO further deviates from BAS by allowing buffer reductions of up to 50 percent for degraded buffers, in exchange for buffer enhancement (enhancement generally involves removal of invasive plants, soil amendments; installation of native plants, including trees; and mulching). Although this provision allows for reduction of the buffer to less than BAS based widths, buffer reduction is intended to improve buffer function over what currently exists in the mostly degraded wetland buffers in Tukwila. The code does not allow buffer reductions for buffers that are not degraded. BEST AVAILABLE SCIENCE FOR WATERCOURSE BUFFERS The Washington Department of Natural Resources under the Forest Practices Rules (WAC 222 -16 -030) designates water types for watercourses and also specifies buffer widths for each watercourse type These prescribed buffer widths are considered to be based on Best Available Science, but it should be noted that they were developed for forest practices and don't necessarily make sense for urbanized areas, where little if any forested buffers remain along watercourses. Under the DNR system, the following buffers (Riparian Management Zones RMZ) would apply to watercourses in Western Washington: Watercourse Type Buffer Width (RMZ) (feet) Type S (Tukwila Type 1) 200 Type F (Tukwila Type 2) 140 -170 Type Np (Tukwila Type 3) 110 Type Ns (Tukwila Type 4) 90 The Washington Department of Fish and Wildlife (WDFW) in its report entitled "Management Recommendations for Washington Priority Habitats. Riparian provides standard recommended Riparian SW Page 3 of 21 W \Long Range Projects \2010 SAO Amdts \Planning Commission \6 -24 Mtg \Addendum to SAO Departures Memo -FINAL 07/07/2010 5 6 Addendum to SAO Departures Memo for Wetland and Watercourse Buffer Widths June 17, 2010 Habitat Area (RHA) widths, based on BAS as shown in the following table (stream typing adapted to current WDNR typing system). Watercourse Type 1 Recommended RHA widths (feet) 1 Type S and F streams 1 250 Type Np streams, or other perennial or fish bearing streams 200 1 5 -6 1 m (5 -20 ft) wide Type Np streams; or other perennial or fish bearing streams 150 <1.5 m (5 ft) wide Type Ns streams; or intermittent streams and washes with low 150 mass wasting* potential Type Ns streams; or intermittent streams and washes with 225 high mass wasting potential ANALYSIS OF EXISTING SENSITIVE AREA BUFFERS IN THE SHORELINE JURISDICTION The development pattern in Tukwila is typical of an urban area with many sections of watercourses channelized or piped, wetlands isolated and disconnected from habitat corridors and both watercourses and wetlands with narrow degraded buffers that have significant invasive vegetation and low buffer function. This development primarily occurred over a period of years prior to the passage of the Growth Management Act and the adoption of sensitive area regulations m Tukwila. As a result, development has encroached in most areas of the city to the point where applying buffer widths complying with those based on BAS would make many existing sites partially or completely nonconforming and vegetating the buffer would be unachievable due to existing development. In order to justify the deviation from BAS for buffer widths, the City has analyzed existing buffer conditions and effective widths for many sensitive areas. The results of the analysis are provided below. Watercourses Tukwila has analyzed the existing buffer conditions for watercourses and evaluated the opportunities for achieving wider buffers and unproved buffer functions. Our findings are presented below for each major watercourse. The reaches of the major watercourses which are in the Shoreline Jurisdiction are not addressed in this analysis There are other short fragments of watercourses (mostly seasonal and not fish bearing) that drain wetlands or carry seeps from slopes, which generally have minimal and very disturbed buffers and are not included in this analysis In general, most watercourses have been channelized and left with significantly reduced buffers over years of development prior to adoption of critical areas legislation. In many cases watercourse segments flow through roadside ditches that have virtually no buffers except for narrow strips of mowed grass /weeds. Many stream segments flow through residential properties, where buffers have been reduced or eliminated for lawn and non- native landscaping. Riverton Creek. This watercourse flows through residential and commercial/industrial areas and, prior to the establishment of sensitive area protections, was rerouted, channelized, straightened, and culverted SW Page 4 of 21 07/07/2010 W \Long Range Projects \2010 SAO Amdts \Planning Commission \6 -24 Mtg \Addendum to SAO Departures Memo FINAL Addendum to SAO Departures Memo for Wetland and Watercourse Buffer Widths June 17, 2010 throughout its length. Many sections of the watercourse have steepened and hardened banks (rip rap, concrete walls) and little buffer vegetation. The upper reaches of both the east and west tributaries of Riverton Creek flow mostly through residentially developed properties, and are characterized by narrow (ranging from 2 to 30 feet on average), disturbed buffers. Some narrow portions of the buffer are vegetated with native trees, others are in residential lawn areas and are mowed to the edge of the bank. Others are largely vegetated by invasive and/or ornamental shrubs. In the west tributary, the watercourse is mostly open, except where it is culverted to pass underneath SR 599 and associated ramps, under local streets and across existing paved areas of commercial and industrial development. In this area, the watercourse has been moved to the edges of industrially developed land between parking lots and the highway. Actual vegetated buffers in these reaches range from about 90 feet for about 1500 feet of its length on the west, narrowing to 15 -30 feet; and 5 -30 feet on the east. Across one developed property the watercourse is confined to a concrete walled channel, with some meanders and vegetated buffers (trees, shrubs, recently planted small trees in some parts) varying from 5 to 10 feet wide. Due to the constraints presented by existing development and road infrastructure, minimal to no opportunity is available for increasing the vegetated buffer. The lower reach of the east tributary is piped for over 2,600 feet, where it then flows in an open ditch in the right of way of SR 599. In this location it has periodically mowed narrow buffers. It then flows through a culvert and is united with the west tributary in an open ditch as previously described. Due to the constraints presented by existing development, there is little opportunity for achieving wider effective buffers on this watercourse. Recent riparian restoration work done by property owners on a small segment of this watercourse illustrate how buffer reduction tends to work in Tukwila. The watercourse reach in question is classified as a Type 2 watercourse (F) and required a buffer of 100 feet. In the first case, the existing buffer was already impacted by a single family residence, lawn and a driveway. The buffer was vegetated by invasive plants with some overstory of small native trees and ranged from 10 to 50 feet in width between the existing house and the driveway. The property owner applied to short-plat the property, which would require respecting the regulatory buffer of 100 feet. A buffer reduction was granted and the buffer was enhanced by removing invasive species and planting a variety of native trees, groundcover and shrubs. The buffer remains the same width as it was prior to the short-plat, but has much higher function than the previous situation. The other case is directly across the watercourse from the buffer restoration site described above. The buffer on the property was already degraded by existing residential development and was about 15 to 20 feet wide and characterized by significant invasive vegetation Because the owner proposed to change the use, a buffer reduction was granted, and the buffer was enhanced by removing invasive vegetation and planting a variety of native trees, shrubs and groundcover and mulching As a result of the granted buffer reduction, the buffer has been widened to between 25 and 40 feet, resulting in a wider effective buffer than existed previously and a buffer with improved function. Southgate Creek. This watercourse has three main tributaries, most of which are open channels, that are culverted where the tributaries cross streets SW Page s of 21 07/07/2010 W \Long Range Projects \2010 SAO Amdts \Planning Commission \6 -24 Mtg \Addendum to SAO Departures Memo -FINAL 7 8 Addendum to SAO Departures Memo for Wetland and Watercourse Buffer Widths June 17, 2010 The northern tributary, which has three main branches (classified as Types 3 and 4 (Np and Ns), flows mostly through residential areas and has vegetated buffers that vary in width from property to property (generally from a few feet to 25 feet). The south branch of this tributary, classified as a Type 3 watercourse (Np) flows through Southgate Park, where buffers are disturbed but have a native tree canopy with an understory of mostly invasive species. Buffers are about 100 feet wide in part of this reach (the section on publicly owned property), but are much narrower downstream, where the watercourse passes through residential properties. In these areas the vegetated buffers (not including lawn) range from 15 to 40 feet wide The middle branch of this tributary, classified as a Type 4 watercourse (Ns) is open in its upper reach and has wide forested buffers (generally 160 feet on either side, except for one residential development that encroaches on the buffer). From there, the branch is piped through a residential area, opening up again into additional residential areas where buffers are generally vegetated but range from 5 to 40 feet wide. The north branch of this tributary, classified as a Type 4 watercourse (Ns), is mostly open with two sections of piping and flows through residential properties. It has disturbed buffers with some vegetation that range from 0 to 20 feet wide. These three branches meet where they then enter a pipe that runs along a street for about 450 feet before opening up again in roadside ditches with poorly vegetated and very narrow buffers (5 -10 feet wide). The middle tributary (classified as Type 4 [Ns] in its upper reach and Type 3 [Np] in the lower reach) also flows through residential areas, where its effective vegetated buffer varies from 15 to 50 feet on either side The lower reach flows through a channel between a commercially /industrially development and a major street. Buffers here are vegetated but range from 10 to 20 feet wide. In its lower reach the tributary is piped for over 300 feet, discharging into the open channel of the southern tributary. Widening of buffers in this tributary would be constricted by existing development except in the upper reach. Buffer reductions in the upper reach would be unlikely due to steep slopes. The southern tributary of Southgate Creek is mostly open. The upper reach, classified as a Type 3 watercourse (Np), flows in a narrow channel between I -5 and a city street (Macadam). It has disturbed narrow buffers (5 to 10 feet wide) with mostly invasive vegetation. Some of this reach has recently been planted as mitigation for impacts from the Sound Transit Light Rail construction. The middle reach of this watercourse flows along the base of steep slopes just to the west of I -5 and the Light Rail line. Buffers are variable and are impacted on the west by existing residential development. They are mostly less than 20 feet wide in this reach. The lower, northern reach of this watercourse is classified as Type 2 (F) and is open except for street crossings (culverts) It flows through a series of roadside ditches with buffers ranging from a few feet to 20 feet. Buffers are mostly vegetated with invasive species and mowed grasses in this reach. At the lowest part of the reach, the other tributaries join this one and the watercourse passes through a recently restored wetland, which forms the watercourse buffer ranging from 25 to 200 feet. It is vegetated (currently with shrubby vegetation, but eventually will be partly forested as the plants grow). Upon exiting the wetland, the watercourse is piped underneath SR 599 and all the way to where it discharges into the Duwamish River, except for a short open channel segment in the shoreline jurisdiction. Because of existing development, there is little to no opportunity for achieving wider buffers except in the upper reaches, where no development has occurred due to steep slopes or being located on public property. SW Page 6 of 21 07/07/2010 W \Long Range Projects \2010 SAO Amdts \Planning Commission \6 -24 Mtg \Addendum to SAO Departures Memo -FINAL Addendum to SAO Departures Memo for Wetland and Watercourse Buffer Widths June 17, 2010 Gilliam Creek. This watercourse originates on the slopes west of 1 -5 and north and south of I -518, eventually flowing eastward in between 1 -405 and Tukwila Parkway, discharging into the Green River. The upper reaches of the watercourse tributaries are generally classified as Type 3 (Np). The southwest tributary of the watercourse was recently partially relocated and restored as mitigation for work on SR 518. It is considered to be fish bearing or have the potential for fish. It has degraded buffers with invasive vegetation (about 200 feet wide on the west and 20 on the east) for most of its length except for the recent restoration of buffers along the relocated segment. Buffers in the restored areas are around 25 feet wide and are bordered by the highway on the north and existing development on the other sides Other tributaries on the south side of SR 518 have well vegetated buffers in excess of 200 feet wide (located on WSDOT right of way on steep slopes), except where they are impacted by residential development. One tributary has recently restored buffers, which do not yet have much areal cover. The northwest tributary of Gilliam Creek in its upper reaches is open channel in some areas and piped in others. Where open, buffers generally range from 10 to 25 feet and are surrounded by existing residential development and paved parking areas. A segment of the watercourse flows along the north side of SR518 with Southcenter Blvd on the other side. Buffers in this reach range from abut 75 to 100 feet and are vegetated but disturbed (significant presence of invasive vegetation. A north tributary of the watercourse consists of a segment with seasonal flow that flows through a residentially developed area. Buffers are degraded and range from zero to 20 feet. The seasonal watercourse then flows through a steep ravine (now part of a regional stormwater detention facility) that has forested buffers ranging from 150 to 250 feet wide. Some enhancement of the buffers and riparian edges has been done to remove invasive plants and install native shrubs and trees under the existing tree canopy. These buffers are in public ownership. From this area, the stream is piped, flowing easterly to and beneath I -5 until it is again open in a channel on the east side of 1 -5. This channel, which is mostly open with some culverted segments, is classified as a Type 2 watercourse (F) and flows between 1 -405 and Tukwila Parkway. Buffers are forested, where the channel is open, but are narrow, generally 25 feet wide on either side of the watercourse, with some areas up to 150 feet in width. Few opportunities exist for achieving wider buffers for Gilliam Creek. Johnson Creek. This watercourse, located in the recently annexed Tukwila South project area, is a ditched watercourse surrounded by previously mowed agricultural fields. It is classified as a Type 2 watercourse (DNR Type F). The open portion of the stream has a partially vegetated buffer (native and invasive plants) that ranges from about 5 to 15 feet wide on both sides in the lower reach. In the middle reach of this stream, it flows in a roadside ditch with narrow, mowed buffers about 5 feet wide on the south and well over 200 feet wide on the north into an agricultural field/wetland where cattle grazing used to take place. There is no upper story vegetation along this stretch of the watercourse The upper part of the stream is ditched through an emergent wetland (located in unincorporated King County) that is mowed for hay production. There is no shrub or tree canopy along the watercourse in this location. A development proposal called the Tukwila South Project plans to relocate and rehabilitate the lower reach of Johnson Creek. The work will include installation of a fish passable flap gate. The proposed buffer, which will be planted with native trees and shrubs, will extend from 5 to 50 feet on the south side (bordering S. 204 Street) and 40 to 75 feet on the north side (bordering a new cross valley levee) Part SW Page 7 of 21 07/07/2010 W \Long Range Projects \2010 SAO Amdts \Planning Commission \6 -24 Mtg \Addendum to SAO Departures Memo -FINAL 9 10 Addendum to SAO Departures Memo for Wetland and Watercourse Buffer Widths June 17, 2010 of the buffer will be on levee, and the proposal is to plant the levee slope with native shrubs, but it is uncertain if the Corps of Engineers will allow planting with anything other than grass. The conceptual design of this watercourse relocation (and accompanying expanded buffer widths) was approved through the Hydraulics Permit Approval issued by the Washington Department of Fish and Wildlife (WDFW) and the Department of Ecology 401 Water Quality Certification. Wetlands Tukwila has analyzed a representative sample of its wetlands (different categories, relatively disturbed and non disturbed, varying sizes and locations) to determine actual vegetated buffer widths and evaluate the potential for providing wider buffers. There are only 2 wetlands mapped in the urban center of Tukwila (south of I -405 and east of I -5). Both are analyzed below. The newly annexed area of Tukwila, south of S. 180 has numerous wetlands that are subject to an existing 401 Water Quality Certification, a pending Section 404 permit and a pending Special Permission from the City for filling of many of the wetlands and permitting of mitigation in the southern end of the site. The remaining wetlands in the City are found north of I -405 and west of 1 -5. The vast majority of the wetlands falls into the lowest category of wetland (currently Tukwila Type 3 and most likely Category IV under the state system) and are mostly isolated and surrounded by development. Not including the newly created wetlands in salmon habitat restoration projects in the shoreline of the Green/Duwamish River, Tukwila has only 3 highly rated wetlands (under the current SAO rating system they are Type 1 and would likely be Category II or III under the state system), two of which are in City ownership. There are just over 20 wetlands that are classified as Type 2 under the current SAO and would likely be Category III or IV under the state system. Tukwila Pond Wetland. This wetland (see Figure 1) is currently classified as a Type 1 wetland under Tukwila's existing SAO, with prescribed buffers of 100 feet. It likely would be classified as a Category II or III wetland under the state classification system. Tukwila has designated the wetland complex as a Fish and Wildlife Habitat Conservation Area, due to its importance for migratory waterfowl, which provides the wetland with additional protection. The revisions to the SAO include a proposed buffer of 100 feet for Fish and Wildlife Habitat Conservation Areas to be consistent with the adopted Shoreline Master Program. It is a 19 acre open water wetland with an emergent and scrub shrub wetland associated with it. The associated wetland is being enhanced to increase wildlife habitat function and eventually will have 4 wetland classes. The entire site is owned by the City as a park and is, therefore protected. The wetland is surrounded by commercial development and has very narrow vegetated buffers. The vegetated buffer on the east varies from 20 to 100 feet and is adjacent to a 5 lane street with a sidewalk. The southern 3 /4 of this buffer has been recently enhanced by removal of blackberries and planting of native shrubs and trees The vegetated southern buffer is only a few feet wide for its entire length and is adjacent to an underground electrical cable, a railroad track, and a warehouse operation on the west side. The northern buffer is about 15 feet wide and is adjacent to a retaining wall with commercial development and paved parking beyond the retaining walland a retail building on the northwest end of the buffer. The western buffer is a developed park with gravel trails, viewing platforms overlooking the wetland, some native and non- native vegetation and a large gravel area, with a building and picnic tables. It is about 300 feet in width and is bordered on the west by commercial buildings and paved parking SW Page 8 of 21 07/07/2010 W \Long Range Projects \2010 SAO Amdts \Planning Commission \6 -24 Mtg \Addendum to SAO Departures Memo -FINAL Addendum to SAO Departures Memo for Wetland and Watercourse Buffer Widths June 17, 2010 areas. There is no opportunity of achieving a wider buffer for this wetland due to the existing development on all sides. There is opportunity for improving buffer function, however. Military Road Wetland. This wetland (see Figure 2), is currently classified as Type 1 under Tukwila's existing system with prescribed 100 foot buffers, and would likely be a Category II or III wetland under the state system. It is a relatively undisturbed wetland on steep slopes. It has not been delineated, so the boundaries are approximate. It forms the headwaters for Riverton Creek. The buffers on the north, west and south sides are also relatively undisturbed and vary from 250 to 350 feet wide. There is no functional buffer on the east, as the wetland is adjacent to a street that is entirely developed for residential use. Therefore, no buffer widening would be possible on the east side of the wetland. Wider buffers on the north, east and south would be possible and could be required by the Director under the existing code due the steep slopes. No buffer reduction would be allowed, as the proposed buffers are relatively undisturbed. Interurban Trail Wetland Complex. This wetland complex (Figure 3), classified as Type 1 under Tukwila's current SAO (with a required buffer of 100 feet) and likely to be classified as Category II or III under the state system, consists of linear wetlands along the Interurban Trail, running over 5,000 linear feet, and between two sets of railroad tracks. There is an additional depressional wetland adjacent to the wetlands on the north that was created as mitigation for wetland impacts elsewhere. The buffer on the west side of the westernmost wetland has been reduced by industrial development along West Valley Highway to an average of 0 to 5 or 10 feet. The southern wetland buffer extends into an existing street and has very little vegetation between the street and the wetland edge. The buffers along the east and west sides of the wetlands are also minimal, with the wetland edges running up to the base of the elevated railroad track and trail beans. The slopes of the berms are mowed grass and rocks. Buffers on the north of the wetlands average about 50 feet in width. They are bordered by an existing industrial gravel storage yard with no structures. Due to the presence of existing infrastructure on three sides of the wetland complex, no increases in buffer width are possible. The northern buffer could possibly be widened. Wetland East of 32 Avenue South. South of S. 135 This wetland (Figure 4) is classified as Type 2, with prescribed buffers of 80 feet. It would likely be classified as a Category III or IV wetland under the state system. As can be seen on the aerial photo, the wetland is surrounded by residential development and the partially vegetated buffers are part of residential back yards, with some areas of lawn. Buildings are encountered within 25 feet of the wetland edge in some areas of the buffer. The width of shrub and tree canopy in the buffers generally range from 0 to about 20 feet in width, with the remaining buffer in lawn. Due to the existing development pattern, increases in buffer width are not possible, unless through development, buffer reductions of up to 50% could be granted, resulting in an enhanced, vegetated buffer that is at least 25 feet or possibly 40 feet, depending on the wetland classification under the state system. Wetland Complex off 65 Avenue. There are two wetlands in the wetland complex (see Figure 5) One is classified as a Type 2 and the other as a Type 3 under Tukwila's current SAO It is likely that both wetlands would be classified as Category III under the state system. The buffer between the wetlands is about 200 feet and is forested and relatively undisturbed, with minimal invasive vegetation in the understory. The southern effective buffer for both wetlands is very narrow, with the western wetland buffer consisting of residential multi- family buildings and paved parking areas up to the edge of the wetland and the eastern wetland fonned by single family residential back yards. The western wetland SW Page 9 of 21 07/07/2010 W \Long Range Projects \2010 SAO Amdts \Planning Commission \6-24 Mtg \Addendum to SAO Departures Memo -FINAL 11 12 Addendum to SAO Departures Memo for Wetland and Watercourse Buffer Widths June 17, 2010 also has disturbed buffer on the north and northwest, where single family developments encroach almost to the edge of the wetland. The western buffer for the western wetland ranges from about 50 to 200 feet in one location and has a dirt trail through it. The eastern wetland's northern vegetated buffer is about 200 feet in width, with the closest structure within about 150 feet. The eastern buffer is approximately 150 to 200 feet wide and is disturbed on its outer edge from existing residential uses. Because the buffers on the west and east sides of the wetland complex are on steep slopes and are relatively well vegetated, buffer reductions would not be allowed. Fire Station 53 Wetland. This wetland (Figure 6) is classified as a Type 3 under the current SAO with prescribed buffers of 50 feet, and would likely be a Category IV under the state system. The buffers on the east, south and west sides are degraded due to the presence of railroad tracks and an existing fire station, with associated paved parking and landscaping. Effective buffer widths on the east and west sides are about 25 feet or less. The buffer on the northwest side of the wetland is forested and extends up a steep slope and across an unused public right -of -way on to platted, undeveloped lots for about 175 feet before encountering residential structures. The buffer on the south end of the wetland extends about 80 feet before encountering residential structures. Thus, except for the northwestern side of the wetland, wider buffers are not possible due to existing development. Wetland North of S. 152 (off 58 Avenue SW). This wetland (Figure 7) is classified as a Type 3 wetland under Tukwila's current SAO (with required 50 foot buffers) and would likely be a Category IV wetland under the state system. Buffers around the western, eastern and southern sides are vegetated and are about 50 feet wide. They are bordered by existing residential development. On the northwest the vegetated portion of the buffer extends another 50 feet to the edge of a mowed area that is part of a school ground. The northern buffer is vegetated for between 15 and 20 feet in width, has a structure within it and is bordered by a cleared and graveled area. Buffer increases would not likely be possible on the west or south sides of the wetland due to existing development. Increased buffers are possible on the north, as the site is not fully developed. Wetland South of I -405. This is a Type 3 wetland (see Figure 8) under the existing SAO ordinance and would probably be classified as a Category TV wetland under the state system. The wetland is adjacent to a watercourse, Gilliam Creek. It has a vegetated buffer about 20 feet wide on the north, where it lies next to I -405. To the south the buffer extends about 100 feet to Southcenter Blvd. In this area, the buffer is partially vegetated with native trees and shrubs, as well as invasive plants, and partially mowed grass and ornamental trees. The east buffer is about 30 feet wide and extends to a street that crosses over I -405). The buffer on the west extends about 100 feet (except where I -405 intersects the buffer) to another wetland that is also adjacent to Gilliam Creek. These wetlands may have been created in the past as mitigation for work on I -405. Due to the constraints presented by the existing transportation infrastructure, no buffer expansion is possible. Wetlands near Crystal Snrinas Park (formerly called Five Rivers site). This site (Figure 9) contains 5 small, isolated wetlands that are classified under the existing SAO as Type 3 (with required 50 foot buffers) and would likely be categorized under the state system as Category IV. Buffers are forested but have been disturbed, as the understory is mostly vegetated with invasive plants. The easternmost wetland and part of the buffer lies across a public utility right -of way that is periodically mowed. The buffer SW Page 10 of 21 07/07/2010 W \Long Range Projects \2010 SAO Amdts \Planning Commission \6 -24 Mtg \Addendum to SAO Departures Memo -FINAL Addendum to SAO Departures Memo for Wetland and Watercourse Buffer Widths June 17, 2010 extends some 150 feet, before encountering a street. The buffer along the west side of the western wetland is nearly nonexistent, as the wetland borders an existing street. The buffers to the north are forested and extend over 200 feet. Wider regulatory buffers on three sides could be required for these low function wetlands, but some use of the property would still need to be allowed. CONCLUSION As explained in the above analysis, virtually none of the existing buffer areas for the sensitive areas in the City currently comply with the buffer widths called for by BAS, nor is there much opportunity for widening the buffers to meet regulatory requirements. Also, all but a few sensitive area buffers are disturbed. In some cases wider areas of buffer plantings can be achieved when buffer reductions are granted where existing vegetated areas are already narrower than half of the regulatory buffer In all cases if a buffer reduction were granted, buffer enhancement would be required that would help to improve buffer function for water quality (soil amendments, dense plantings, shade from trees), hydrology (dense plantings) and wildlife (plantings, habitat features such as logs or snags). For the reasons cited above, the City of Tukwila does not believe it makes sense to adopt buffers that are recommended by the Department of Ecology, WDFW or DNR. SW Page 11 of 21 W \Long Range Projects \2010 SAO Amdts \Planning Commission \6 -24 Mtg \Addendum to SAO Departures Memo -FINAL 07/07/2010 13 14 Addendum to SAO Departures Memo for Wetland and Watercourse Buffer Widths June 17, 2010 SW Page 12 of 21 07/07/2010 W \Long Range Projects \2010 SAO Amdts \Planning Commission \6 -24 Mtg \Addendum to SAO Departures Memo -FINAL Addendum to SAO Departures Memo for Wetland and Watercourse Buffer Widths June 17, 2010 FIGURE 1 SW Page 13 of 21 W \Long Range Projects \2010 SAO Amdts \Planning Commission \6 24 Mtg \Addendum to SAO Departures Memo -FINAL 07/07/2010 15 16 Addendum to SAO Departures Memo for Wetland and Watercourse Buffer Widths June 17, 2010 FIGURE 2 SW Page 14 of 21 07/07/2010 W \Long Range Projects \2010 SAO Amdts \Planning Commission \6 -24 Mtg \Addenda n to SAO Departures Memo FINAL 17 18 Addendum to SAO Departures Memo for Wetland and Watercourse Buffer Widths June 17, 2010 FIGURE 3 SW Page 15 of 21 07/07/2010 W \Long Range Projects \2010 SAO Amdts \Planning Commission \6 -24 Mtg \Addendum to SAO Departures Memo FINAL 19 20 Addendum to SAO Departures Memo for Wetland and Watercourse Buffer Widths June 17, 2010 FIGURE 4 SW Page 16 of 21 W \Long Range Projects \2010 SAO Amdts \Planning Commission \6 -24 Mtg \Addendum to SAO Departures Memo -FINAL 07/07/2010 21 22 Addendum to SAO Departures Memo for Wetland and Watercourse Buffer Widths June 17, 2010 FIGURE 5 SW Page 17 of 21 W \Long Range Projects \2010 SAO Amdts \Planning Commission \6 -24 Mtg \Addendum to SAO Departures Memo -FINAL 07/07/2010 23 24 Addendum to SAO Departures Memo for Wetland and Watercourse Buffer Widths June 17, 2010 FIGURE 6 SW Page 18 of 21 W \Long Range Projects \2010 SAO Amdts \Planning Commission \6 -24 Mtg \Addendum to SAO Departures Memo -FINAL 07/07/2010 25 26 Addendum to SAO Departures Memo for Wetland and Watercourse Buffer Widths June 17, 2010 FIGURE 7 SW Page 19 of 21 W \Long Range Projects \2010 SAO Amdts \Planning Commission \6 24 Mtg \Addendum to SAO Departures Memo FINAL 07/07/2010 27 28 Addendum to SAO Departures Memo for Wetland and Watercourse Buffer Widths June 17, 2010 FIGURE 8 SW Page 20 of 21 07/07/2010 W \Long Range Projects \2010 SAO Amdts \Planning Commission \6 -24 Mtg \Addendum to SAO Departures Memo FINAL 29 30 Addendum to SAO Departures Memo for Wetland and Watercourse Buffer Widths June 17, 2010 FIGURE 9 SW Page 21 of 21 07/07/2010 W \Long Range Projects \2010 SAO Amdts \Planning Commission \6 -24 Mtg \Addendum to SAO Departures Memo -FINAL 31