Surf’s Up! Engineering Design and Construction of an Estuarine Bay Beach at Aramburu Island,

Marin County, CA

Roger Leventhal, PE, CFM Senior Engineer, Marin County Flood Control Dan Gillenwater, ESA Environmental Scientist/GIS Analyst ESA, San Francisco, CA

2014 FMA Santa Clara, Ca

Point Isabel, Richmond Marina Bay tombolo, Richmond

Increased 21st c Wave Erosion at SF Bay Shorelines

• As sea level rises → deeper bay (deep water fetch↑, wave

energy ↑)

• potential increase in urban route ferry traffic (wakes)

Typical Bay Levee Rip-Rap Armoring (rip-rap, rubble, boulder revetments)

Roberts Landing, San Leandro

Powell St Emeryville

Bel Marin Keys, Novato

bay levee

bay levee armor

Peninsula fill (slag, rubble)

Bay mud levee scarp

Underlying tidal marsh peat outcrop platform

Typical Unarmored Erosional SF Bay shorelines (cohesive bay mud levee, salt marsh peat scarps)

Muzzi Marsh, Corte Madera

Bel Marin Keys, Novato

• wave attack at base of scarp (undermining) • slump block failure, cantilever failure • progressive rapid retreat of wave-cut scarps • elevation loss (no marsh berm deposition)

Legacy of former shoreline armoring: ineffective “stabilization” of shoreline and continued erosion of

unconsolidated cliff and beach

Wave erosion of fill behind concrete blocks

Paradise Beach, Marin County

The shoreline future? rock and walls

San Rafael shoreline

SF Bay Beaches – dynamic v. static armor shorelines:

Coarse sediment beach crest elevation responds to variable wave runup and water level given sufficient

supply of suitable sediment size; rises with sea level

Freshly deposited swash bar (boat wakes)

Storm berm crest elevation ≈ 1 m > salt marsh plain

Relict neap berms

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 • prevalent sediment type (sand, shell, gravel, mixed) • geomorphic setting (headland, marsh fringe)

Richmond pocket beaches

San Francisco Bay natural coarse sediments vary with local sources and shoreline setting

• headland, stream mouths, nearshore erosion sources • local wave climate (fetch, offshore water depth gradient)

MEDIUM SAND SHELL HASH

GRAVEL

Unique SF Bay Olympia oyster shell hash

relict Holocene deposits – shell shoals and shell muds comparable to Gulf of Mexico shell beaches, cheniers

Imbricate coarse structure, low density, high permeability

Marsh-fringing shell barrier beach (outer Bair Island) - natural levee; STORM RIDGE deposited by high waves

Boat wake wave series

Aramburu Island Beach Demonstration Project – Built 2011/2012

Wind-Wave Climate Fetch = 8 miles Significant wave height = 2-3 feet Wave period = 2-3 seconds

2007 Cosco Busan Oil Spill

Aramburu Island, Richardson Bay 45+ yr shoreline retreat > 130 ft; boulder-cobble lag

0.5-1.0 m wave erosion scarp

Degraded Island Features

Cobble-boulder lag field

Erosional scarp

How to Design a Bay Beach…

Historical Ecology

Review the literature (not Corps manuals)

Empirical Data - measure reference sites (bay and beyond)

Design Cues from local beaches

Analytical data – do the math

Look at Historical Ecology artificial fill – 1960s - adjacent to historical gravel beach (spit)

Graphic: Dan Gillenwater, WWR

Bay Beach Reference Sites • Sanctuary beach

• Radio Beach

• Pier 94

• Brisbane

• Foster City

Pier 94, San Francisco

0

2

4

6

8

10

12

0 10 20 30 40 50 60 70 80 90

Ele

vati

on

(ft

NA

VD

88

)

Distance from Start of Transect (ft)

Pier 94 Beach-Transect 3

P94-T3-1 P94-T3-2

P94-T3-3

P94-T3-4

Lag Field

Start of Rip-Rap

Berm

Gravel Berm Slope = 15% D50 = 6 -13 mm Fetch = 5 miles

data: Dan Gillenwater, WWR

Beyond the bay… constructed sites

HMSC site, Oregon

- 3 m wind-wave

Cape Lookout SP, Oregon

- 10 m ocean swell

Flathead Lake, Montana

- 2 m wind-wave

Design from Nature - Urban Beach Design Cues from

Natural Shoreline Examples:

Coarse sediment supply-limited natural gravel & oyster shell hash form beaches over boulder revetments

Pinole bayshore railroad Foster City beach park

Design from Nature - Urban Beach Design Cues from Natural Shoreline Examples:

Wave erosion and transport of landfill debris (glass,

concrete, asphalt, rock, metal) forms beaches

Eastshore State Park, Berkeley – Schoolhouse Creek mouth

Urban beach design cues from natural processes: partially embedded large driftwood in cohesive bay mud

Potential longshore sediment transport resistance, sediment trap “micro-groins”

Pinole bayshore

Roberts Landing 2010

Salt marsh peat outcrop in beach with embedded log

Roberts Landing 2007

Lorang Formula Max Mobile Particle

Largest Particle Entrained Function of 2% Wave Runup (Ru2%)

Work done for a boulder beach

Significant Wave

Height(ft)

Estimated

Fetch

Length

(miles)

Wave

Period (sec)

Calculated

Mobile Rock

Mass (kg)

Calculated

Maximum

Mobile Rock

Size (assume

spherical

rock)

4.25 feet (South

Cell) – deep water

fetch limited

8 miles 4 9 – 30 kg 14 to 21 cm

2.70 feet (South

Cell) – deep water

fetch limited

8 miles 3.3 3.4 – 12 kg 10 to 16 cm

2.1 feet

(North/Central

Cells)

2 miles 2.5 1.5-5.5 kg 8 to 12 cm

1.8 feet

(North/Central

Cells)

2 miles 2.3 1.1 – 4 kg 7 to 11 cm

Shoreline Plan Coarser sediments at south facing slopes

Mixed gravels and oyster shell – central cell

Oyster shell at north end

Wood micro-groins and “complexity”

Lowest wave

energy

Highest wave

energy

Mixed Sand-Gravel

• Mix of ¾” to 6” (15 cm) rounded rock

Oyster Shell

Waste Graves In-Bay Operations (9 to 16 mm D50)

On to construction…

Grading back vertical wave-cut scarp; creating ramp-like platform for gradual beach retreat with rising sea level

Initial Placement of Oyster Shell Hash, Prior to Wave-Reworking

Placement of oyster shell hash at N end, lowest wave energy gradient

Placing larger wood groins – eucalyptus logs

Multiple large (back, upper beach profile) and small (lower beach profile) wood pieces combined for artificial driftwood

groin

Wood groin at terminus of N cell, base of large log deep in bay mud

Finished wood-boulder groins, with brace wood on downdrift side, cobble updrift

Waves begin to rework oyster shell hash into small berms

under low wind-wave energy, prior to groin placement N cell

Sandy Foreshore Construction 2012

Monitoring Photos 2012-2013

Dec 5, 2012 post-construction Feb 2, 2013 post storm Apr 16, 2013 post significant

southern storms

Sept 19, 2013

High-energy, wave-

exposed

HEADLAND gravel-

cobble beach

Stable beachface –

cobble lag with

interstitial fines

Beach crest elevation:

mobile coarse

sediment accretion to

EHW

Beach Profile Changes

Mixed sand –

gravel shell

beach

Rapid recovery

from winter

erosion

No rapid net

erosion; net

accretion

Beach crest

elevation: above

approx. High Tide

Line each year

Beach Profile Changes (2012)

Oyster catchers

Elegant terns

Aramburu Island Birds 2013

More Pilots - IWRMP Proposal

• Design, permit and construct at 2-3 sites

• Demonstrate engineered beaches as a viable approach to shoreline erosion

• Determine limits of applicability

3

2

1

2000 ft

N

4?

Mill Valley

shoreline

Outer Bothin

Marsh scarp

Seminary Drive

Blackies

Pasture?

Design Solution MV shoreline

eucalyptus knoll

pocket beaches

…extent of project to be

determined – partner is

City of Mill Valley