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Living Shoreline Concept Designs What needs to be considered?

Karen Duhring Virginia Institute of Marine Science

College of William & Mary

March 2, 2017 Delaware Living Shoreline Training Workshop

Lewes, Delaware

Acknowledgments for contributions to this presentation

DNREC & CIB Staff Jon Miller et al., Stevens Institute

Partnership for the Delaware Estuary Joe Reiger, Elizabeth River Project, Virginia Jim Cahoon, Bay Environmental, Virginia

Molly Mitchell, VIMS Scott Hardaway, VIMS

Walter Priest, III VIMS-NOAA-Wetland Design Bobbie Burton, Longwood University

Pat Menichino, James City County Virginia Bhaskar Subramanian, Maryland DNR

David Burke, Burke Environmental Associates Rob Schnabel, Chesapeake Bay Foundation

Living Shoreline Concept Designs

• Concept Design Process Steps

• Explore design parameters – How to get site-specific information

• Project Type Considerations

• Putting the pieces together for concept designs

Concept Design Process 1. Describe the location & the problem

2. Project goals

3. Lay out existing site conditions

4. Determine project type & possible elements

5. Don’t underestimate site prep & demolition costs

6. Approximate structure sizes & locations

7. Depict planting zones & plant species

8. Show jurisdictional boundaries & tide range

9. Prepare plan view & profile (cross-section)

10. Talk to regulatory officials & other advisors


2. Project goals – Establish success criteria, how will you know if the project ‘works’









How to Get Started Review

1. Risk assessment & decision to act Is erosion risk present & not tolerable? Is erosion or flooding risk significantly high? Can upland land use adjustments solve problem?

2. Property owner factors

Is the property owner willing to pursue living shoreline approach? What are their perceptions of the problem & possible solutions?

3. Basic location & land use suitability considerations Any significant natural or cultural resources? Is there enough room to access and work on the shoreline? Can living habitats be created or enhanced?

Stabilization Alternatives Simplistic Order of Preference

from least to most environmental impact

Minor erosion with low risk Minor erosion with some risk

Major erosion with some risk,

natural buffers present or feasible to create

Major erosion with high risk, natural buffers absent or not feasible

→ Maintain / enhance vegetation

→ Non-Structural Living Shoreline

→ Hybrid Living Shoreline

→ Traditional Structures e.g. revetment, offshore breakwaters

Main Reasons Planted Marshes Do Not ‘Take’ • Planted too low below mid-tide elevation or in wrong zones

• Excessive wave action, washed out plugs • Incomplete drainage & ponding at low tide • Rapid sediment accretion

Other Reasons • Flow stresses – bottlenecks, runoff, currents • Foot traffic & recreational uses • Soil contamination • Undetermined

Are these factors present? Can they be managed?

Would coir logs-mats or sill help support vegetative stabilization?

Potentially Negative Effects of Marsh Sills

• Covering shallow water benthic fauna

• Hydrodynamic changes altering tidal exchange, wave height, wave direction

• Altering sediment transport along shoreline

• Altering habitat use along marsh edge

• Construction access & maintenance impacts

How can a sill be designed to minimize these impacts?

Sill Design Criteria to Maintain Coastal Processes

• Crest height in relation to Mean High Water • Tidal gaps – windows – openings • Stone size & interstitial spaces • Re-locate living resources in footprint

– e.g. horseshoe crabs, oysters

How deep is the water? How soft is the bottom type? Where should tidal openings be located?

Can important resources be moved out of the way?

Shellfish Reef Considerations

• Are there any natural reefs in vicinity for recruitment? – Successful oyster reefs are expanding in Delaware estuary

• Will the reef remain submerged or be exposed?

• What base structures might be used? – Shell bags, oyster castles, others

• Are there any navigation or public health concerns?

Can a shellfish reef substitute for a stone sill? Or can oyster habitat be added to increase habitat diversity?

Parameters Typically Used in the Design of Living Shorelines Source: Living Shorelines Engineering Guidelines 2016

System Parameters Erosion History

Tidal Range Sea Level Rise

Ecological Parameters Native Plant Community

Water Quality Soil Type

Sunlight Exposure

Hydrodynamic Parameters Wind Waves Boat Wakes

Currents Ice

Storm Surge Stormwater Runoff

Terrestrial Parameters Upland Slope

Shoreline Slope Width

Nearshore Slope Offshore Depth

Soil Bearing Capacity Forces acting on the shoreline

short-term Affect how shoreline

responds to forces

Large scale - long term Local scale for natural elements

Parameters Typically Used in the Design of Living Shorelines Source: Living Shorelines Engineering Guidelines 2016

Additional Parameters Permits/Regulatory

End Effects Constructability

Native/Invasive Species Shellfish Recruitment

Debris Impact Project Monitoring

Property Owner Interest

Multiple parameters are not equally weighted Some may be more critical than others Just one alone might make a difference

Site Evaluation Parameters

Desktop - Map Parameters

• Existing information available from maps or Internet resources

• Not readily visible or measurable at ground level

• Data availability may be limited for some parameters

Site Visit Parameters

• Not easily captured by remote sensing

• Site-specific characteristics

• Local setting

• Local knowledge

SYSTEM & HYDRODYNAMIC PARAMETERS

Erosion History

• Have shoreline erosion trends been measured for Delaware?

• If not, look for physical evidence & local knowledge – Slumped marsh edges, fallen trees, decreasing width of

land between shoreline & permanent features, etc. – Property owner experience & documentation – Third party observations

• Try to determine if erosion has been chronic or episodic, i.e. slow & gradual or major events

Important for determining success criteria

Local Tide Range & Extreme Tide Levels

• NOAA Tides and Currents – Benchmark Sheets • Variable by region

~ 5.5 ft. at Delaware City ~ 4.1 ft. at Lewes

• Mean tide range and spring tide range • May want to supplement with real time

measurements made over 30 days

Important for any ‘living’ component e.g. planting zones, living reef

Also for submerged & low-crested hybrid structures

http://tidesandcurrents.noaa.gov/

Tidal Datums for Lewes, DE Tidal Epoch 1983 - 2001

Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS: HIGHEST OBSERVED WATER LEVEL (03/06/1962) = 2.810 MEAN HIGHER HIGH WATER MHHW = 1.418 MEAN HIGH WATER MHW = 1.290 North American Vertical Datum NAVD88 = 0.801 MEAN SEA LEVEL MSL = 0.680 MEAN TIDE LEVEL MTL = 0.669 MEAN LOW WATER MLW = 0.048 MEAN LOWER LOW WATER MLLW = 0.000 LOWEST OBSERVED WATER LEVEL (01/10/1978) = -1.284

1.24 meters (4.07 ft.)

Supplement with local knowledge of storm events & other extreme tides

Sea Level Rise • Living elements sensitive to rising sea level • Uncertainty for appropriate LS designs • Consider short term need vs. long term project lifespan

Stay Tuned!

Hours of inundation > MHHW have increased greatly

since 1990

Living shoreline projects should incorporate inundation areas

where possible

Traditional tide chart applications not always accurate

e.g. timing construction with low tide

Sea Level Rise & Inundation Frequency

Source: NOAA, M. Mitchell, VIMS 2015

Wind Waves

• Frequently encountered condition based on average & longest fetch

• Maximum expected or extreme wave may not matter as much if project will be submerged

• Refer to Living Shoreline Design Guidelines & US Army Corps of Engineers estimating methods for shallow water

• In situ wave data collection using simple low cost approaches – Recording water level oscillations on a graduated staff – Plaster cast approach

Longest Fetch black lines

Average Fetch

measure 5 green arrow vectors and

take an average

Measure Fetch Distances

Boat Wakes

• May be significant source of wave energy in sheltered waterways

• Large slow moving barges vs. smaller faster boats have different wakes

• No good archived data on wakes

• Look for presence or absence of docks, marinas, marked channels

• Simple observation techniques have been developed for the Hudson River

• Local knowledge and judgment calls are required to weigh this parameter

Currents

• Important consideration @ tidal inlets, meandering riverbanks, freshwater inflows

• Currents can uproot vegetation, dislodge fiber logs, scour the bank, transport debris & ice

• Little data available

• Measuring currents in sheltered estuaries tricky

Ice • Vegetation & structure uplift • Floating ice like debris with impact forces • Rely on local records, additional monitoring of living

shorelines needed to aid design factors

Storm Surge • Less significant for living shorelines compared to

bulkheads & revetments • Important for riparian buffer vegetation zones • FEMA flood maps provide estimates • Local knowledge from storm events (winter & summer)

e.g. ‘How high did the water get here in Sandy?’

• Debris impact potential

Living shoreline project submerged during Nor’easter

Stormwater Runoff - Precipitation • Recognize runoff patterns in vicinity, creek channels • Can upland stormwater management practices be

installed? • Does upland drainage need to flow through project

site?

TERRESTRIAL PARAMETERS

Shore Morphology

Pocket or embayed shorelines tend to cause waves to diverge and spread wave energy out Straight and headland shorelines receive the full impact of the wave climate Irregular shorelines tend to break up wave crests

Nearshore Slope & Offshore Depth distance to 2m contour

2m (6 ft.) contour lines

Broad shallow nearshore has different wave

attenuation than narrow deep water

with same fetch

Bathymetric maps are usually too coarse for design purpose May need to supplement with bathymetric survey

Upland & Shoreline-Intertidal Slope

Graphic courtesy Burke Environmental Associates

Upland Slope

Level to Spring Tide

Shoreline Slope

Spring Tide to MLLW

Upland & Shoreline Slopes

• Vegetation grows best on gradual slopes

• Wave run-up with less erosion & scarps

• Wading surveys at low tide to determine existing slope & estimate desired slope changes

• Developed, urban estuaries may have distinct vertical elevation changes ‘vertical lift’ – Is it possible to overcome for ‘greening’ existing bulkheads &

revetment shorelines ?

Width Horizontal space between upland & water’s edge

What to do if there is not enough space with natural slopes?

1. Landward design where possible gradual slopes & vegetation zones landward from MLW, including bank grading & upland-wetland integration

2. Channelward design may need to overcome low elevations, more frequent wave energy, navigation conflicts, submerged lands regulatory issues

• Design width for new tidal marshes depends on the energy

regime at project site, the erosion problem & available space – Protective fringe marshes with stable upland banks generally are 10-20

ft. wide from marsh edge to base of bank in Chesapeake Bay region

• Include both low marsh & high marsh zones

Soil Bearing Capacity

Important consideration for hybrid structures & sand fill

How much settling will occur?

Start with simple 200-lb man test walking the project site

Geotechnical investigations may be advisable

Firm vs. soft

ECOLOGICAL PARAMETERS

Native Plant Community • Evaluate natural upland & shoreline plant species in

vicinity – Indicators of high water tables, salinity

• Obtain biological benchmark elevations – natural plant zones & elevations related to tide range &

storm surge

• Consider recruitment potential – Plants growing nearby that readily re-seed may not need to

be planted

• Consider grazing pressure – Will any animals be attracted to new plantings?

• Seek advice from local native plant experts & guidelines

Biological Benchmarks – Target Elevations

• Elevation ranges of natural marshes & riparian buffers in vicinity

Regular Low Tides

Regular High Tides High Marsh

Low Marsh

Upland

Water Quality • Dissolved oxygen • Water temperature • Salinity • Turbidity

• Site-specific conditions determine plant choices for upland &

wetland areas – especially salinity (freshwater or brackish)

• More local WQ data now available

• These factors might explain why living components fail to thrive

• Engineers unfamiliar with these parameters encouraged to seek assistance from water quality monitors & ecologists for LS habitat choices & designs

Soil Type • Important for vegetation growth & strong root system Essential

for erosion resistance

• Most living shoreline marshes are planted in coarse sand fill or accretion material settled from water column

• Always take soil borings or dig test pits where fill is going to be removed, be ready for surprises & be flexible during excavation even with test results in hand – Legacy contamination, solid waste, etc.

Shoreline Orientation – Sunlight Exposure

Good lighting More shade

South North

• Important for upland bank erosion projects with shoreline trees not as important for wide open marsh edges except for piers

• South & east vs. north & west is rule of thumb, not always a determining factor











Work Through Design Considerations by Project Type

Riparian Buffer Protection, Planting & Enhancement

• Existing tree protection

• Locate equipment staging & stockpile areas, fueling stations, vehicle parking areas

• Generate desired plant species list & estimate quantity, container stock & seeding

• Investigate plant sources, availability

• Determine ideal planting times woody trees & shrubs may be different than perennials & ground covers

• Can temporary irrigation be provided during dry spells until plants are established

Bank Grading • Determine tree & other vegetation removal needs • Look for groundwater indicators, springs & seeps • Look at soil type at planting elevation

– Clay or confining layers may preclude vegetation growth – Over excavate and backfill with sand for planting

• Equipment access requirements • Temporary land disturbance, erosion & sediment controls • Riparian buffer planting plan for vegetation cover

Upland Excavation – Landfill Removal

• Soil testing expenses & logistics

• Excavated material handling & disposal plan

• Over-excavating & backfilling plan, sediment source

• Estimate areas for non-linear planting zones

Low marsh

High marsh

Planting Tidal Marshes at Upland Banks

• Estimate planting areas length & width

• Estimate sand fill quantity & potential source(s)

• Pruning overhanging trees & shrubs – Avoid removing healthy shoreline trees just to increase

sunlight for new marsh – Consult with arborist on tree life expectancy & health

Planting Tidal Marshes at Eroding Marsh Edges • Fill in between more erosion resistant points, estimate

size of planting areas • Marsh edge access paths for equipment & foot traffic • Estimate number of fiber logs, mats & stakes needed • Additional considerations if low-crested stone sills

needed

Wetland Plant Species List • Rough estimates of each area size (square feet)

– Low salt marsh – High salt marsh – Freshwater marsh – Upland transitional area

• Estimate quantity for clumps or row planting • Include plants that stay above ground during winter

– Or compensate design for winter conditions if no aboveground stems & leaves will be present, backshore protection

Wetland Plant Sources • Wild harvest from donor marshes nearby that can recover

from harvest for small projects if permittable – Hard to dig out plants from natural marshes – Eroded marsh edge clumps can be salvaged

• Nursery stock – Plants for high salinity planting must be brought up to site

salinity by grower before delivery

Planting Labor

• Professional services – In-house or sub-contractor

• Volunteer opportunity – Recruitment, coordination,

oversight, rewards – Follow up quality control OR

Other Planted Marsh Materials

• Grid device or flags to designate planting zones

• Dibble bars or power augers to drill holes

• Slow release fertilizer (optional)

• Buckets to carry plants & fertilizer to shoreline

• Grazing exclusion fencing, stakes, &/or strings

Grazing Exclusion Devices Mute Swans & Canada Geese can pull new plants out of the ground, but not established well-rooted plants

Other grazers include deer, wild horses, nutria, muskrats

Are any of these known to be around the project site? Plan for installation & then removal of exclusion devices after marsh establishment

Planted Marsh Care During 1st Growing Season

• Identify responsible party

• Access required for regular inspections

• Monitor ebb & flood tides

• Look for & re-plant washed out plugs – Pack in deep – Keep grazers out

Fiber Log & Mat Design Considerations

• Premium logs are denser for higher energy sites

• Staking & anchoring essential if they are in the water

• Full contact with ground should be maintained – Install logs end-to-end, tying them tightly together &

reinforcing the break – Place stakes in X across top of log – Use cotton based twine with breaking strength >800 lbs

with every turn around the stake knotted

– Logs should not be tucked against vertical erosion scarps where waves are abruptly reflected

• Plan for regular inspections & corrections

Fiber Log & Mat Design Considerations • Sand fill or natural accretion

– The faster sediments fill in, the less likely installation will fail

– Include sand backfill if the local sediment supply is limited or to increase likelihood for successful marsh establishment

– Indicators of local sediment supply are accretion against large woody debris, overwash ‘fans’ in marshes, sediment trapped at groins or jetties

– Jumpstarting with sand fill will require construction access to place sand

Fiber Log & Mat Design Considerations

• Planting into logs has mixed results – Saturation is important for wetland plants – Marsh plants easily grow into them

• Seeding with ribbed mussels possible – Especially where adjacent marsh not already colonized

with mussels

Fiber Log & Mat Materials

• Different lengths & diameter sizes available

• Wood stakes 7-20 per log depending on site energy

• Cotton based twine with breaking strength >800 lbs.

• Mallets

• Possibly sand fill from upland source

• Seek advice from material supplier

Marsh Sill Design Considerations • Availability of quarry stone & how to deliver to site • Rock size based on expected waves, water depth,

target crest elevation • Stones should be interlocking, haphazard dumping not

effective • Broken concrete should be used only for core material • Supposed to be low-crested 0 to 1 ft above MHW • Generally placed in shallow water < 6 ft • Sea level rise will gradually reduce freeboard &

structure effectiveness • Soil bearing capacity determines foundation layer

geotextile, gravel base, flexible gabion mattress, gradual sinking may occur

Marsh Sill Design Considerations (continued)

• Windows or gaps along the structure for circulation & access for marine fauna

• End effect erosion on adjacent shorelines can occur – Note location in relation to property lines

– Taper down at ends for transitions

• Construction access requirements – Temporary earth ‘roads’ and ‘bridges’ – Sufficient water depth for loaded barge access approx. 4 ft

Tidal Openings Where & when should they be included?

• Site-specific – Tidal ponds – Natural or created channels – Open ends – Recreation access

• Sill crest height > MHW

• Sill length > 100 Ft

– Not a definitive standard – May need more or less

Tidal openings are needed but they introduce wave energy into the planted marsh. Stable embayments eventually form at straight gaps.

Offset Tidal Openings

Gapped offset sections at pocket marsh Placed offshore or inshore of main sill structure

Weir & Cobblestone Tidal Openings

Weir Opening or Vented Sill

Gap covered with stone at lower elevation

Straight gap with cobblestone

Reduces sand deposits

How is biological activity altered?

Narrow or “Pinched” Tidal Opening

Narrow & curved

Reduces sand deposits

Pinches flow & access

Turn orientation away from shore before the gap

Marsh Sill Materials

• Foundation material • Quarry stone sized for wave climate • Sand fill from upland source • Material transport equipment • Material placement equipment

Shellfish Reef Design Considerations

• Public health restrictions in waters not approved for shellfish harvesting

• Navigation hazards

• Solo placement or combined with other elements

• Shell bags &/or pre-cast concrete structures

• Tide range & water depths at extreme low tide – Intertidal reefs are exposed to wave action

• Remote spat setting time needed

• Labor required for filling bags & moving structure units to shoreline

Shellfish Reef Materials

• Geotextile foundation material

• Oyster shell or reef products

• Shell bag filling station

• Material transport equipment

PUTTING ALL THE PIECES TOGETHER











Construction access & restoration plan &

Construction sequence

Sill locations & general shapes with dimensions labeled

No planting & sill gap for canoe-kayak launch

Survey Notes & Legend Sills turned away from shoreline at gaps & ends

Minimize & restore construction access impacts • For upland access, minimize vegetation removal &

protect large trees • Limit number of access paths to shoreline • Use construction mats to distribute weight of machinery

crossing through forest buffers and tidal marshes • Plan for access restoration as needed (e.g. re-seeding)

Try to avoid wetland impacts like this







7. Depict all planting zones & plant species (planting plan)




Show existing vegetation areas to be preserved or impacted

Concept Plan Example Avoided marsh labeled separately from planted marsh areas Other existing marsh outside of project area shown with symbols Different colors & patterns for low & high marsh elevation zones Transition zone plantings on sideslopes Approximate locations of proposed structure elements Other site features shown for reference Existing chain link fence Existing trees Existing signs

Lewes Ballpark Site Conceptual Plan with location & arrangement of

elements

Source: Partnership for the Delaware Estuary

Lewes Ballpark Site Conceptual Plan - Profile

With Existing & Proposed Slope relationship of different elements

Source: Partnership for the Delaware Estuary










10. Talk to regulatory officials & other advisors Back to the Drawing Board for Final Design

Living Shoreline Concept Designs Summary

• Take time to work through process steps & multiple project parameters for higher success potential

• Start with clear goals & realistic expectations

• Take advantage of lessons learned from previous work – read reports & stay engaged with community of practice

• Some good references & data are readily available – some parameters still uncertain

• Include site prep, demolition, labor, construction access & restoration in the concept design – Also keep in mind monitoring & maintenance needs

Concept Design Questions?

Contact Information Karen Duhring [email protected] 804-684-7159

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