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Geographic variation in San Francisco Bay beach forms, sediments, and processes: an overview State of the Sediment Workshop April 19-20, 2010 San Francisco.

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Presentation on theme: "Geographic variation in San Francisco Bay beach forms, sediments, and processes: an overview State of the Sediment Workshop April 19-20, 2010 San Francisco."— Presentation transcript:

1 Geographic variation in San Francisco Bay beach forms, sediments, and processes: an overview State of the Sediment Workshop April 19-20, 2010 San Francisco Bay Conservation and Development Commission U.S. Geological Survey Menlo Park, California Peter Baye, Coastal Ecologist, Annapolis, California

2 Geographic variation in San Francisco Bay beach forms, sediments, and processes: an overview Summarize geographic distribution and variability of modern San Francisco Bay beach landforms and beach sediment Original purpose: classification of habitat suitability and restoration feasibility for rare/endangered estuarine beach plants Identify provisional subregional “provinces” of beaches with similar sediments, local wave energy climates, backshore settings, profiles, dynamics

3 Classification tools available for documenting geographic variation in San Francisco Bay Beaches Recent fetch-limited beach geomorphology literature: Pilkey, O.H., J. A.G. Cooper, D.A. Lewis Global Distribution of fetch-limited barrier islands. Journal of Coastal Research 25: Jackson, N.L. Nordstrom, K.F. Eliot, I. And Masselink, G “Low energy” sandy beaches in marine and estuarine environments: a review. Geomorphology 48: classic beach profile and planform typologies (Bird 1964, Johnson 1919) qualitative sediment typing Approximate historic distribution and planform of beaches delineated on T-sheets: EcoAtlas synthesis (Robin Grossinger, SFEI) Herbarium and flora records of beach & dune (strand) plant species (locality data on presence of estuarine beach, dune habitat)

4 Bay beach types: simplified planform-based classification Fringing beaches: mainland-attached beaches, extensive; limited headland influence Pocket beaches: mainland-attached beaches, narrowly confined by headlands or resistant shoreline indentations Barrier beaches: beach ridges, tombolos, or spits sheltering enclosing lagoons, intertidal flats, or marshes Marsh berms, marsh barriers - “marsh fringe barriers”, perched or fringing beaches along storm-eroded marsh scarps or peat outcrops (cf. chenier), usually vegetated Cuspate forelands – salient prograded or multiple beach ridges or recurved spits (rare)

5 Base map credit: Mike Perlmutter, BAEDN Beach shorelines ▬▬ historic ▬▬ modern Excluded: swell- influenced Golden Gate beaches Pinole mixed beaches (sand, shell gravel) San Rafael pocket sand beaches Richardson Bay pocket beaches West Berkeley sand beaches SE SF pocket sand beaches South Bay oyster shell hash beaches San Leandro- Hayward shoreline sand beaches SF Bay beach provinces provisional classification prevalent sediment type (sand, shell, gravel, mixed) geomorphic setting (headland, marsh fringe) Richmond pocket beaches

6 Point Pinole marsh barrier chains Mixed beach sediment (erosion of sedimentary headlands, small stream deltas = sand and gravel; nearshore erosion of shell) associated with prehistoric (Whittell) and modern salt marshes boat wake (Vallejo Ferry) and long NW fetch of San Pablo Bay – episodic high wave energy Transverse bar? Ebb deltas of tidal creeks WHITTELL MARSH 1948 BARRIER BEACH

7 2007 Point Pinole marsh barrier Ebb tidal delta BARRIER BEACH

8 Point Pinole – prehistoric Whittell Marsh sheltered by barrier beach (crest <0.75 m above marsh plain)

9 Point Pinole (west of Point) – salt marsh peat outcrops, proximal end

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12 Point Pinole cuspate sand & gravel barrier foreland gravel and coarse sand west-facing shore backbarrier tidal marsh Bluff erosion sediment source cobble lag- armored foreshore updrift

13 Point Pinole – west shore gravel beach and cobble lag foreshore

14 Pinole Creek mouth Marsh berm (“Marsh Bar” of Johnson 1919; marsh fringe barrier of Pilkey et al. 2009) Thin perched sand beach ridge deposit above salt marsh scarp vegetated: high salt marsh marsh peat outcrop

15 Active barrier beach (long fetch) Active barrier beach (short fetch) Multiple relict stabilized beach ridges? (past progradation) Nontidal salt marsh Central San Francisco Bay sand/shell hash beaches: Brooks Island, Richmond (tombolo and barriers)

16 Central San Francisco Bay sand/shell hash beaches: Brooks Island, Richmond (tombolo and barriers) Photo: Mike Perlmutter, BAEDN East Bay Regional Parks District – protected tern colonies

17 Marina Bay, Richmond South-facing barrier tombolo, mixed gravel-sand-shell

18 Radio Beach, Oakland (Bay Bridge Toll Plaza) West-facing barrier beach (tombolo) Rip-rap headland 1 m high foredune ridge

19 Radio Beach, Oakland (Emeryville Crescent) North-facing sand spit (seasonal tern roost)

20 Swash-aligned and drift-aligned bay beaches (Davies 1978) Swash-aligned pocket beach: facing dominant waves, confined by (artificial) headland Potential stable beach planform; symmetric Dominant local waves (NW) Longshore drift RADIO BEACH COMPLEX – Oakland Bay Bridge Toll Plaza Riprap headland Drift-aligned sand spit: oblique approach of dominant waves, unconfined longshore transport unstable beach planform, proximal narrowing, distal progradation

21 “West Berkeley” - Eastshore State Park (University Ave – Powell St) fringing beaches

22 San Leandro-Hayward shoreline Robert’s Landing “Long Beach” Salt marsh peat outcrops, foreshore, proximal (N) end

23 San Leandro-Hayward shoreline Robert’s Landing “Long Beach” – overwash transgression of backbarrier salt marsh

24 San Leandro-Hayward shoreline Robert’s Landing “Long Beach” – active washover fans

25 San Leandro-Hayward shoreline Robert’s Landing “Long Beach” ridge and runnel (multibarred) foreshore profile (sand, mud)

26 San Leandro-Hayward shoreline Robert’s Landing “Long Beach” updrift shoreline (N)

27 WESTERN SNOWY PLOVER – Pacific population, federally listed as threatened Roberts Landing sand spit – March 2006

28 Erosion of artificial shore fill nourishes SF beaches: Brisbane Bayshore gravel spit Heron’s Head (Pier 98) San Francisco gravel beach Brisbane spit, south of Candlestick Pt Pier 98 (Heron’s Head), San Francisco

29 SE San Francisco, Pier 94 constructed gravel-shell beach

30 SE San Francisco, India Basin Low foredunes, west-facing beach

31 Native (fossil) Olympia oyster (Ostrea lurida, syn. O. conchaphila) shell hash Central, South SF Bay nearshore sources: wave erosion, transport of shell hash eroded from marsh scarps, shelly mudflats swash bar welding? (onshore migration of shell hash swash bars)

32 SE Bair Island – Oyster shell hash beach accretion (2007)

33 SE Bair Island – prograded multiple spit recurves over salt marsh Oyster shell hash – recent beach ridge deposition

34 SE Bair Island – prograded oyster shell hash beach ridges

35 Recent swash bar formed by boat wakes

36 SE Bair Island – vertical scarp (boat wake erosion) in oyster shell beach ridge

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38 SE Bair Island – transgressive oyster shell hash beach ridges dam tidal creeks

39 SE Bair Island – transgressive oyster shell hash beach: perched beach ridge above marsh scarp; beach face below scarp

40 SE Bair Island – perched beach profile and infilled relict tidal creek in marsh peat scarp – oyster shell hash

41 2007 Foster City 1998 Foster City MARSH BERMS Vegetative stabilization of relict beach ridges – high salt marsh Analogous with chenier beach ridges (Gulf of Mexico)

42 Stabilization impacts of invasive non- native hybrid smooth cordgrass (Spartina alterniflora x foliosa) stabilization of nearshore shell-rich muds (marsh conversion) Wave damping Seal Slough, NE Foster City shoreline SOUTH SAN FRANCISCO BAY OYSTER SHELL HASH BEACHES

43 Conclusions Quartz-rich medium grain sand fringing beaches are prevalent from West Berkeley to Hayward, vicinity of Merritt Sands – regenerate in urban shoreline. Oyster shell hash (fossil sediment) marsh fringing barrier beaches are prevalent from Foster City to Ravenswood – esp. Bair Island (among largest in SF Bay) – regenerate in marsh and urban shorelines Mixed sediment (gravel-sand-shell) marsh fringing barrier beaches are prevalent in North Richmond to Point Pinole – likely headland and stream mouth sources? – near original marsh and bluff shoreline Small pocket and fringing beaches of quartz-rich sand occur in urban San Francisco shore (vicinity of Colma formation) – urban shoreline Drift-aligned sand spits occur in Central East Bay (Radio Beach, Roberts Landing) – among largest natural beaches in SF Bay

44 QUESTIONS Relative importance of nearshore erosion, onshore transport, versus headland/bluff erosion, longshore transport of beach sediment? Shoreline armoring, flood channel stabilization effect on bay beach sediment supply? Oyster shell hash (20 th c industrial mining and ongoing commercial mining of fossil sediment) Beach sediment budgets and sea level rise? Artificial barrier beaches and tidal marsh restoration – engineering alternatives to levee maintenance during sea level rise?


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