Marsh Vegetation and Substrate Interactions with Wind-wave Energy in San Francisco Bay:

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1 Whole Marsh Restoration: Wind Wave Energy Management in Context II (Baye) March 18, 2008 Wind-wave and Tidal Marsh Restoration Workshop BCDC, San Francisco Marsh Vegetation and Substrate Interactions with Wind-wave Energy in San Francisco Bay: Patterns, Processes of Erosion and Deposition in Natural Settings and Breached Diked Baylands

2 Wind-wave energy in natural and restored tidal marsh settings Pethick (1992) conceptual model: Natural tidal marsh and marsh and mudflat systems are parts of continuous dynamic shoreline profile, like beach and dune Wave erosion of marsh episodic = short-term storm profile response to excess wave energy. CYCLIC. Recovery (accretion, progradation) low energy phase long term, gradual Vegetated marsh = sediment reservoir, wave buffer

3 Tidal marsh edge = response to prevailing wave energy regime and sediment Episodic, infrequent events (storm waves) Prevalent annual or seasonal windwave climate Emeryville Crescent: prograding Hayward: retreating Marsh erosional and depositional landforms respond to local wave energy climate and sediment supply.

4 Vegetation succession in tidal restoration sites basic patterns Direct establishment on constructed emergent fill (levee or berm benches, slopes) Lateral spread (progradation) of shoreline fringing marsh Radial spread of discrete tidal flat colonies (eventual coalescence) Diffuse, frequent seedling colonization of tidal flats

5 Modes of marsh development in SF Bay tidal restoration sites colonization Pioneer seedling or juvenile (vegetative fragment) germination, emergence, initial survival sensitive stage for mechanical disturbance such as wind-wave energy) establishment threshold of individual plant survivorship; growth or clonal spread to size-class or life-history stage with high survivorship clonal spread

6 MARSH PROGRADATION BAYWARD SPREAD of marsh over open flats Spreads into bay tidal flats Fringing cordgrass marsh

7 EXAMPLES OF MARSH PROGRADATION CHINA CAMP - open bay fetch (NE) storm erosion / post-storm recovery and progradation Cordgrass marsh progradation Relict erosion scarp (Pickleweed edge)

8 CHINA CAMP Tidal marsh progradation OPEN BAY FETCH (NE)

9 TRIANGLE MARSH, CORTE MADERA Marin County open bay fetch (NE) and boat wakes storm erosion / post-storm recovery and net progradation Relict marsh scarps Cordgrass marsh progradation

10 MARE ISLAND fringing salt marsh progradation 3 5 m / yr ( ); > 20 miles W fetch Annual displacement of cordgrass zones by pickleweed zones

11 MARE ISLAND fringing salt marsh progradation EROSIONAL RILLS CORDGRASS COLONIZATION OF ERODED FIRM MUDS

12 Atwater, B.F., S.G. Conard, J.N. Dowden, C.H. Hedel, R.L. MacDonald, and W. Savage History, landforms and vegetation of the estuary s tidal marshes. Progradation of marsh terrace Despite highenergy wave erosion (rills 0.3 m deep)

13 HAMILTON (Novato) fringing marsh marsh vegetation and storm events mediate erosion cycle on highenergy transgressive marsh shore Drift-line (wrack) Relict wavecut erosion scarp Post-storm regeneration of vegetation (low marsh)

14 1998 Foster City Sediment types with different responses: mud, sand, shell hash, peat Sand, shell: high wave energy is constructive; builds beach ridges Foster City Some stabilize with high marsh vegetation and persist as natural MARSH BERMS

15 Whittell Marsh, Point Pinole Richmond (EBRPD) Shoreline profile response to high wind-wave energy with local SAND OR SHELL SEDIMENT SOURCES: DEPOSITION v. EROSION coarse sediment BARRIER BEACH OR MARSH BERM (cf. chenier )

16 Bay barrier beaches mobile (transgressive) self-construct if sand/shell supply suffices natural wave energy buffer at marsh edge high tide roost ecotone

17 Tidally restored diked baylands mostly sheltered from open bay wave energy perimeter levees = wave barriers eroded perimeter levee = wave buffer internal wind-wave energy initial post-breach flooding Steep, sparsely vegetated or bare interior levee slopes Reflective v. dissipative shore profile, smooth bed: water depth, bottom friction, and wave propagation in absence of bed roughness from submerged or intertidal vegetation;

18 Sedimentary processes contrasted Tidal breach subsided diked bayland (conventional 1970s-1990s) Basin (lagoon) infill: Vertical accretion of BARE MUD to threshold of emergence for SUBSEQUENT vegetation DEPOSITIONAL PROCESS AND VEGETATION ARE DECOUPLED IN TIME. Marsh vegetation is secondary, subsequent process following physical sedimentation and emergence of mid-intertidal flats Natural tidal marsh (Holocene) Vertical accretion of vegetated marsh (peat) with rising Holocene sea level Vegetation-sediment interactions are primary, contemporaneous mode of vertical marsh accretion

19 Cooper, N.J Wave dissipation across intertidal surfaces in the Wash tidal inlet, Eastern England. Journal of Coastal Research 21: high storm wave energy coastline (Wash, East Anglia, UK) Wave height and energy dissipation greatest along upper intertidal profile (marsh) Vegetation is principal factor in wave energy dissipation (friction) Marsh vegetation dissipates most incident wave energy, height (91-97%) on high energy coast Most critical parameters intertidal level, width of marsh/mudflat, vegetation type

20 Cooper N.J TABLE 2 Findings from previous wave dissipation field measurement studies (adapted) authors location cover type wave height reduction/distance wave energy reduction/distance Wayne 1976 Florida Spartina alterniflora seagrass (SAV) 71% over 20 m 42% over 20 m 92% over 20 m 67% over 20 m Knutson et al Chesapeake Bay Spartina alterniflora 94% over 30 m 100% over 30 m Moller et al North Norfolk, East Anglia UK (Stiffkey) salt marsh forbs sandflats 54% over 180 m 14% over 197 m 79% over 180 m 26% over 197 m

21 Cooper 2005 KEY VARIABLES INFLUENCING INCIDENT WAVE DISSIPATION PROCESSES (adapted) applicable to tidal restoration design Intertidal morphology (mounds, channels) Intertidal elevation (depth) Intertidal zone width, gradient Intertidal vegetation Presence / absence (marsh v. flats/open water) vegetation height surface roughness component vegetation density surface roughness component vegetation cover surface roughness component vegetation type, structure surface roughness component

22 Moeller, I., T. Spencer, and J.R. French Wind wave attenuation over saltmarsh surfaces: preliminary results from Norfolk, England. Journal of Coastal Research 12: % of European salt marshes are exposed to significant wind-wave energy (citing Dijkema 1987) (Dijkema, K.S Geography of salt marshes in Europe. Zeitschrift fur Geomorphologie, NF, 31: ). Chesapeake Bay tidal marshes are exposed very low wave energy (relative to European salt marsh) Vegetation roughness effects most wave attenuation in salt marshes WIDTH of salt marsh may be more important in determining effectiveness of wave energy buffering compared with marsh elevation

23 Roland, R.M. and S.L. Douglass Estimating wave tolerance of Spartina alterniflora in coastal Alabama. Journal of Coastal Research 21: Determine critical range of wave climate exposure (highest tolerable amount of wave energy) for wetland establishment and survival Spartina alterniflora Results used to minimize size of breakwaters used in constructed wetlands FIRST STUDY TO QUANTIFY CRITICAL WAVE ENERGY, HEIGHT FOR MARSH VEGETATION.

24 Roland, R.M. and S.L. Douglass Estimating wave tolerance of Spartina alterniflora in coastal Alabama. Journal of Coastal Research 21: CONCLUSIONS: Fetch per se is not always an adequate indicator of wave climate for wetland establishment (NEARSHORE PROFILE) Knutson et al. (1982) methodology confirmed skill at predicting wave climate-marsh vegetation and erosion relationships qualitative comparison among sites. Previous methods insufficient as basis for engineering structure designs for modification of wave climate (breakwater) Potential effect of water depth not accounted for in previous methods (fetch only) Hindcast wave energy and height model applied

25 Roland, R.M. and S.L. Douglass Estimating wave tolerance of Spartina alterniflora in coastal Alabama. Journal of Coastal Research 21: CRITICAL WAVE HEIGHT: rule of thumb CWH (incident at shoreline) = 1 ft in study area (Alabama); infrequent storm waves Spartina alterniflora (microtidal) did not exist where critical wave height exceeded 0.2 m in study area. CONCLUSION: USE OF MINIMAL PROTECTION (as opposed to large breakwaters) MIGHT INCREASE THE FUNCTIONALITY OF THE MARSH AS WELL AS REDUCE CONSTRUCTION COSTS. Critical wave height, energy hindcast method could be calibrated for other marsh species and settings.

26 Knutson, P.L., H.A. Allen, J.W. Webb Guidelines for vegetative erosion control on wave-impacted coastal dredged material sites. U.S. Army Corps of Engineers Technical Report Important first step in stabilizing shorelines: creation of broad, gradual, sloping beach dissipate wave energy. 1V:15H recommended minimum. Planting width recommended minimum 6.0 m; conservative 10.0 m recommended (follows 1:15 slope) Failure likely in moderate wave environments (ave. fetch km), justify wave protection devices lowcost, temporary (fiber mats, rolls, or plant armoring/anchorage) Spartina alterniflora BREAKWATER IS ONLY NECESSARY FOR THE FIRST 2-3 YEARS AFTER PLANTING

27 Newcombe, C.L., J.H. Morris, P.L. Knutson, and C.S. Gorbics Bank erosion control with vegetation, San Francisco Bay, California. U.S. Army Corps of Engineers Technical Report Planting method tested: plugs (sod fragments; peat), Spartina foliosa with attached mussels Alameda Creek Area 5 vegetative stabilization success with 7 km fetch Pacific cordgrass transplant plugs can be successfully established in areas with up to 7 km fetch in SF Bay Pacific cordgrass plugs extremely tolerant of wave action 2-3 YEARS needed for Pacific cordgrass to achieve density of natural stands

28 CONCLUSIONS Diked baylands are enclosed lagoons Lagoons are relatively low wave energy environments compared with marsh shores exposed to open bay waves Critical wave height for Spartina alterniflora is about 0.2 m in Alabama. Critical wave fetch for Spartina foliosa transplants in exposed shorelines of San Francisco Bay is over 7 km Highly wave-exposed salt marsh shorelines in San Francisco Bay undergo cyclic erosion and progradation San Francisco Bay marsh progradation occurs where wave energy is extremely high, but nearshore slopes are gentle

29 CONCLUSIONS Coarse sediment (sand, shell) can be used to buffer wave energy Native perennial terrestrial vegetation can be used to stabilize levees Planted marsh vegetation on gentle slopes is among the most cost-effective engineering tools for wave energy attentuation, shoreline stabilization, and marsh creation