memorandum date March 6, 2012 Clallam County SMP Advisory Committee Basis of proposed shoreline buffer width recommendations

Transcription

1 5309 Shilshole Avenue NW Suite 200 Seattle, WA phone fax memorandum date March 6, 2012 to subject Clallam County SMP Advisory Committee Basis of proposed shoreline buffer width recommendations The Preliminary Draft Shoreline Master Program update contains consultant recommendations for increases in shoreline buffer widths to: 1) protect ecological functions and processes and 2) protect people and property from hazards such as flooding, channel migration, and landslides. The recommended buffer widths were developed in consideration of the specific conditions along Clallam County shorelines as well as pertinent scientific literature regarding stream, nearshore and riparian functions. This memo briefly summarizes buffer recommendations contained in the literature that were used as the basis for the Clallam County buffer recommendations. Background Most studies that have examined stream, lake and marine buffers and their role in protecting ecological functions have acknowledged that there is no single buffer width that will protect a particular function or group of functions. Instead, buffer recommendations are generally stated as a range of widths or minimum width required to achieve a certain level of functionality. For example the Washington Department of Fish and Wildlife document Protecting Nearshore Habitat and Functions in Puget Sound (2009) reports buffer width recommendations in terms of what is needed to achieve 80 to 100% effectiveness of various functions. Other documents also recommend a range of buffer widths to protect different marine riparian functions. Levings and Jamieson (2001) recommend buffers of 300 to 450 feet to protect marine shorelines. Depending on the type of shore, wind conditions, and the specific resources being protected by the buffer, recommended widths may differ. Studies of freshwater environments have also yielded a range of buffer width recommendations for different functions. For example Knutson and Naef (1997) report buffer recommendations of between 13 and 600 feet for different stream functions. In all cases the buffer width needed to adequately protect streams, lakes and marine waters will depend on geographic specific factors such a slope, soils, vegetation, aspect, exposure, and vulnerability to impact. Where there uncertainty, most scientists recommend adopting a precautionary approach to ensure buffer are adequate to protect the full spectrum of functions. Most jurisdictions have adopted buffer widths that Tables 1 and 2 summarize recommended marine and stream buffer widths (or ranges of widths) reported in the literature for several functions. Table 3 depicts buffer requirements in other counties in western Washington for comparison. A more detailed summary of the buffer literature is included following the tables.

2 Table 1. Marine buffer width recommendations, by ecological function Function Buffer Range (ft) Source(s) Comments Fine Sediment Removal 92 to 299 Desbonnet et al. (1994) [92 ft] and Pentec (2001) [299 ft] 197 ft buffer needed to remove 80% of sediment load Nitrogen Removal Phosphorus Removal Pollution Filtration (At Estuaries) Large Woody Debris Recruitment 4 to 350 Desbonnet et al. (1994) 197 ft buffer needed to remove 80% of nitrogen load 5 to 550 Desbonnet et al. (1994) 279 ft buffer needed to remove 80% of phosphorus load 175 Phillips (1989) 20 to 240 FEMAT (1993) 131 ft buffer needed for 80% effectiveness (as compared to predevelopment conditions) Shade (Water Temperature) General Wildlife Habitat 56 to 125 Belt et al. (1992) [56 ft] and Christensen (2000) [125 ft] 240 to 902 Goates (2006) [240 ft] and Burke and Gibbons (1995) [902 ft] 121 ft buffer needed for 80% effectiveness (as compared to predevelopment conditions) Literature average is 571 ft. Knutson and Naef (1997) recommend a buffer width of at least 200 feet to maintain deer and forest bird populations. Table 2. Stream riparian buffer width recommendations, by ecological function Function Buffer Range (ft) Source(s) Comments Sediment Removal 100 Johnson and Ryba (1992) 90% sediment removal at 2% grade Erosion Control 100 to 125 Knutson and Naef (1997) Pollutant Removal 13 to 600 Knutson and Naef (1997) Schultz et al. (1995) recommend a minimum buffer of 66 feet Large Woody Debris Recruitment 33 to 328 May (2000) 150 ft buffer needed for 80% effectiveness (as compared to pre-development conditions) 2

3 Function Buffer Range (ft) Source(s) Comments Shade (Water Temperature) Organic Matter Input Chinook salmon habitat General Wildlife Habitat 35 to 151 Knutson and Naef (1997) 120 ft buffer needed for 80% effectiveness (as compared to pre-development conditions) 100 FEMAT (1993) 100 Raleigh et al. (1986) 200 Zeigler (1992) Channel Migration 50 1 NOAA (2008) Recommended width to comply with the Biological Opinion concerning the Federal Flood Insurance Program 1 As measured from the outside edge of a channel migration zone Table 3. Example buffer requirements in other western Washington jurisdictions Habitat/Geologic Hazard Type(s) Marine shores Streams Lakes Jurisdiction Clallam County (proposed) Clallam County (proposed) Clallam County (proposed) Buffer Range (ft) , depending on designation , depending on designation Marine Shorelines and SMP Streams Jefferson County 150 SMP Lakes Jefferson County 100 Marine Shorelines Whatcom County 150 SMP Streams Whatcom County 150 Marine Shorelines Kitsap County

4 Habitat/Geologic Hazard Type(s) Jurisdiction Buffer Range (ft) Shoreline Streams Kitsap County 200 Landslide Hazards Pierce County Variable. Geotechnical study required; structure must be sited to ensure 120 years of useful life. Marine Bluffs 1 City of Port Angeles Variable. Geotechnical study required; setback equal to the annual erosion rate times 75 years plus 20 feet. 2 1 From July 2011 SMP, not yet adopted. 2 For example, setback for bluff eroding 2 feet a year: (2 ft/yr *75 years) + 20 ft = 170 ft Discussion The effectiveness of riparian buffers for protecting water quality depends on a number of factors including soil type/stability, vegetation type, slope, annual rainfall, type and amount of pollution, surrounding land uses, and buffer width. Soil stability and sediment control are directly related to the amount of impervious surface. In areas where riparian vegetation has been removed and soils have been compacted, soils are less capable of intercepting and absorbing rainfall (May, 2003). Water that is not absorbed / intercepted by vegetation runs off the surface leading to erosion, siltation, burial of aquatic environs, and introduction of contaminants into water and can increase potential for landslides. Pollutants such as excess nutrients, metals, and organic chemicals are commonly found in stormwater and agricultural runoff, usually in particulate form. Sediment control therefore is essential for removing a large percentage of the pollutant load (May, 2000). In general, a 50-foot buffer is estimated to be approximately 60 percent effective at removing sediments, while an 82- to 300-foot buffer would remove approximately 80 percent of sediment load (Brennan and Culverwell, 2004; Pentec 2001). Although sediment carried into nearshore marine environments will seldom be of a magnitude to significantly compromise water clarity, the minimum recommended buffer width for sediment control and pollutant removal is 98 feet (30 meters) (May, 2003). According to the literature, buffer widths as small as 27 feet could reduce nitrogen by as much as 60 percent, while widths up to 200 feet would be required to reduce nitrogen by 80 percent (Desbonnet et al., 1994, in Pentec, 2001). Minimum buffer recommendations for controlling agricultural runoff are 79 feet for 20 percent slopes with slight erosion, and 160 feet for 30 percent slopes with severe erosion (Brennan and Culverwell, 2004). Control of fecal coliform inputs from agriculture or septic systems to acceptable levels for primary contact recreational use could be achieved by a 115 feet buffer (Young et al., 1980, in Pentec, 2001). For wildlife, the principal functions of riparian buffers are to provide habitat and travel corridors, microclimate regulation, organic input, and to ameliorate the impacts of human disturbance such as light and noise. Bald eagles, kingfishers, and other birds use logs on beaches, tideflats, and estuarine channels as perches (which provide visibility for foraging, resting areas), and to reduce flight times (energy conservation) between foraging areas and nesting sites. Herons and egrets will use drifted trees that are partially out of the water, as well as floating logs and log rafts for foraging and resting. Cormorants, pelicans, small shorebirds, and some waterfowl also require perches and platforms for rest between periods of foraging to spread their wings to dry their feathers and for preening themselves. As rotting trees on land near the water become limiting, purple martins and other cavity-nesting birds will use rotting snags on beaches for nesting. Gulls use log beaches and estuarine 4

5 meadows for breeding. Logs function to visually isolate adjacent nests, provide thermoregulatory benefits for egg development, and cover for newly hatched chicks. Logs enable gulls to spend less time protecting the nest and more time foraging, resulting in increased survival of chicks. LWD is suspected to serve similar functions for other ground nesting wildlife. In addition, LWD and beach wrack provide habitat structure for species that are prey for fish and wildlife (Brennan and Culverwell, 2004). For Washington State, the average width reported to retain riparian function for wildlife habitat is 288 feet (Knutson and Naef, 1997). No requirements for riparian corridor connectivity have been established in scientific literature; however Booth et al. (2002, in King County, 2004) recommend riparian buffer zones that minimize road and utility crossings as well as overall clearing. Microclimatic influences on air that passes through riparian vegetation include humidity, temperature, and wind speed. This in turn affects plant growth, therefore influencing ecosystem processes such as decomposition, nutrient cycling, plant succession, and plant productivity. The minimum recommended buffer for microclimate protection is 328 feet (May, 2003). Recent studies have shown that riparian vegetation on open marine shorelines may play an important role in producing terrestrial insect prey for juvenile salmon. Eelgrass beds are known to provide habitat for numerous fish and invertebrates, abundant fish prey production, as well as spawning habitat for herring. Buffer recommendations have not been made for protection of fish prey production function. Shade provided by riparian vegetation along marine shorelines is not likely to influence marine water temperatures due to mixing and tidal fluctuations, but may be an important factor in moderating water temperature in pocket estuaries. Solar radiation is also an important factor determining distribution, abundance, and species composition of upper intertidal organisms (Brennan and Culverwell, 2004). Moisture and direct solar radiation also influence egg viability of intertidal-spawning forage fish such as surf smelt and sand lance (Penttila, 2001). Buffer recommendations range from 98 to 262 feet for natural temperature regulation and shading, or providing equivalent shading as a mature forest (May, 2003). Large woody debris provides a multitude of functions in aquatic ecosystems including habitat structure. In the marine riparian zone, vegetation and large woody debris trap and stabilize sediments in salt marshes and on beaches, creating back beaches, berms, and spits. Beach logs retain moisture that becomes important to the establishment and survival of dune plants, which further stabilize sediments, provide wildlife habitat, and contribute nutrients to the system. In the lower intertidal and subtidal areas, LWD may become immobilized and become colonized by sessile invertebrates, algae, and mobile invertebrates for feeding opportunities, refuge, and spawning substrate, thereby increasing habitat complexity and attracting other species in search of prey, refuge, or spawning substrate. In riverine environments, more than half of all large woody debris is recruited from within 15 feet of streams. About 90 percent of all large woody debris comes from trees growing within about 50 feet of streams (Herrera, 2005). Appropriate widths for natural levels of recruitment and retention have been reported as one Site Potential Tree Height (SPTH) (May, 2003). The minimum buffer width recommended for LWD recruitment is 1 SPTH, or approximately 165 meters (May, 2003). Because most buffer recommendations have been developed for riverine systems, marine buffer requirements may need to be adjusted to account for the effects of wind, salt spray, desiccation, and general microclimatic effects (Brennan and Culverwell, 2004). References 5

6 Belt, G.H., J. O Laughlin, and T. Merrill Design of forest riparian buffer strips for the protection of water quality: Analysis of scientific literature. Idaho Forest, Wildlife and Range Policy Analysis Group, Report No. 8. Brennan, J.S., and H. Culverwell Marine Riparian: An Assessment of Riparian Functions in Marine Ecosystems. Published by Washington Sea Grant Program, UW Board of Regents Seattle, WA. 34 pp. Burke, V.J. and J. W. Gibbons Terrestrial buffer zones and wetland conservation: A case study of freshwater turtles in a Caroline Bay. Conservation Biology: 9(6), Christensen, D Protection of riparian ecosystems: A review of best available science. Jefferson County Environmental Health Division, WA. Desbonnet, A., P. Pogue, V, Lee, and N. Wolff Vegetated buffers in the coastal Zone: A summary review and bibliography. Coastal Resources Center Technical Report No University of Rhode Island Graduate School of Oceanography. Narragansett, RI. Desbonnet, A., V. Lee, P. Pogue, D. Reis, J. Boyd, J. Willis, and M. Imperial Development of coastal vegetated buffer programs. Coastal Management 23: FEMAT (Forest Ecosystem Management Assessment Team) Forest ecosystem management: An ecological, economic, and social assessment. U.S. Departments of Agriculture, Commerce, and Interior. Portland, OR. Goates, M.C The dogma of the 30 meter riparian buffer: The case of the Boreal Toad (Bufo boreas boreas). M.S. Thesis, Brigham Young University. Provo, UT. Johnson, A.W., and D.M. Ryba A literature review of recommended buffer widths to maintain various functions of stream riparian areas. Prepared for the King Co. Surface Water Manage Div., Seattle, WA. Knutson, K.L. and V.L. Naef Management recommendations for Washington s priority habitats: Riparian. Washington Department of Fish and Wildlife, Olympia, WA. May, C.W Stream-riparian ecosystems in Puget Sound lowland eco-region: A review of best available science. Watershed Ecology LLC. May, C.W., R.R. Horner, J.R. Karr, B.W. Mar, and E.B. Welch Effects of urbanization on small streams in the Puget Sound lowland ecoregion. Watershed Protection Techniques 2(4). (NOAA) National Marine Fisheries Service Endangered Species Act Section 7 Consultation Final Biological Opinion and Magnuson-Stevens Fishery Conservation and Management Act Essential Fish Habitat Consultation for Implementation of the National Flood Insurance Program in the State of Washington, Phase One Document Puget Sound Region. Consultation conducted by the National Marine Fisheries Service, Northwest Region. Pentec Environmental Use of Best Available Science in City of Everett Buffer Regulations. Prepared for: City of Everett Planning and Community Development, Edmonds, WA. Phillips, J.D Effect of buffer zones on estuarine and riparian land use in eastern North Caroline. Southeastern Geographer 29:

7 Raleigh, R.F., W.J. Miller, and P.C. Nelson Habitat suitability index models: Chinook salmon. U.S. Fish and Wildlife Service. Schultz, R.C., J.P. Colletti, T.M. Isenhart, W.W. Simpkins, C.W. Mize, and M.L. Thompson Design and placement of a multi-species riparian buffer strip system. Agrofor. Sys. 29: Zeigler, B.C Buffer needs of wetland wildlife. Washington Department of Fish and Wildlife. Olympia, WA. 7