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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 17, 2016
Delaware Living Shoreline Training Workshop Lewes, Delaware
Acknowledgments Thank You 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
• Review of basic considerations
• Explore design parameters
– Why they are important
– How to get site-specific information
• Project types & lessons learned
• Putting the pieces together for concept designs
Shoreline Management Decision Process Review
1. Risk assessment & decision to act
Erosion history & forecast not tolerable?
Can upland land use adjustments solve problem?
If not, TAKE SHORELINE ACTION
2. Basic location & land use suitability considerations
3. Can adverse environmental harm be avoided?
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
Non-Structural
Planted Marshes
Fiber Logs & Mats
Sand Fill
Slope Changes
Beach Nourishment
Hybrid
Rock Sills
Pre-Fabricated Concrete
Biogenic Reefs
Living Shoreline Project Categories
Is there a simple formula to know which approach to use?
Parameters Typically Used in the Design of Living Shorelines Source: Living Shorelines Engineering Guidelines 2015
System Parameters Erosion History
Tidal Range Sea Level Rise
Ecological Parameters Water Quality
Soil Type Sunlight Exposure
Hydrodynamic Parameters Wind Waves Boat Wakes
Currents Ice
Storm Surge
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 2015
Additional Parameters Permits/Regulatory
End Effects Constructability
Native/Invasive Species Debris Impact
Project Monitoring
Property Owner Interest
Multiple parameters are not equally weighted Just one alone might make a difference Some may be more critical than others
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
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?’
Living shoreline project submerged during Nor’easter
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
• Vertical banks & existing bulkheads tricky due to vertical lift, but not impossible to work with
• Wading surveys at low tide to determine existing slope & estimate desired slope changes
• Developed, urban estuaries may have distinct vertical elevation changes ‘vertical lift’ – 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
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
ADDITIONAL CONSIDERATIONS
Permits – Regulatory
End Effects
Constructability Native/Invasive Species Debris Impact
Project Monitoring
End Effects
1. From adjacent engineered structures on living shoreline site
2. From proposed living shoreline project on adjacent shorelines
• Reflected wave energy from hybrid structures • Sediment capture & interruption
Transitions into adjacent shorelines
may need to be considered
Constructability
J. Scalf B. Burton
• Construction access from land or water
• Hand placement &/or machine types & sizes
• Wetland crossings & weight distribution
• Project designers & contractors must communicate early in design process
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 harming wetlands like this
Project Monitoring & Maintenance
• Needs to be included with design
– Document baseline conditions, problem being solved to determine success, access for monitoring & maintenance
• Does not have to be complicated or scientifically intense
• Troubleshooting not uncommon based on monitoring
• Data from multiple projects helps inform entire community of practice
– Adaptive Management Feedback
Different Monitoring Interests to Answer Specific Questions
• Industry performance, economics, satisfaction
• Regulatory habitat trade-offs, compliance, policy effectiveness
• Other local government TMDL & FEMA credits
• Academic ecosystem & protection effects
• NGO & Citizen Scientists demo sites, volunteer opportunities
PROJECT TYPES & LESSONS LEARNED
PROJECT TYPE DETAILS
Bank Grading & Riparian Buffer Planting Beach Nourishment & Dune Planting Planted Tidal Marshes Fiber Logs & Mats Marsh Sills Living Reefs
Bank Grading Potential sites include:
• High, eroding banks without trees or development near shoreline
• Failing or failed bulkheads with lawns
• Mean high water near bank toe, narrow intertidal zone
• Very effective yet not very popular
Riparian Buffer Planting
• Convert lawns to more effective storm surge buffers
• Plant or seed vegetation that intercepts runoff and stabilizes bank face
• Native shoreline plants are best suited to local soil, salt and wind conditions; Non-native plants should be adapted to similar conditions
• Flood tolerant species may need to be included
• Planting times for woody trees & shrubs may be different than perennials & ground covers
• Temporary irrigation may be needed during dry spells until plants are established
Beach Nourishment & Dune Planting • Addition of sand to a beach to
raise its elevation and increase its width
• Reshaping and stabilizing with dune plants
• Mimic local beaches & dunes
– Planting zones based on wind removal & deposition areas
• Avoid creating sand beaches where they do not occur naturally
– For recreational purposes
Beach & Dune Vegetation
American beach grass
Ammophila breviligulata
Cool-season grass for
northern Mid-Atlantic
Winter planting
Saltmeadow hay
Spartina patens
Bitter panicum
Panicum amarum
Seek advice from USDA Cape May Plant Materials Center
Planting Tidal Marshes at Upland Banks
• Fringing marsh most common (parallel to shore)
• Plant selection & zones based on local tide range, salinity, look for biological benchmarks
• Overhanging trees may cast shade, but avoid removing healthy shoreline trees just to increase sunlight for new marsh
– Prune overhanging branches
– Consult with arborist on tree life expectancy & health
Biological Benchmarks – Target Elevations
• Elevation ranges of natural marshes & riparian buffers in vicinity
Regular Low Tides
Regular High Tides High Marsh
Low Marsh
Upland
Embayed or “Pocket” Marsh Upland excavation areas where elevation can be lowered
More complex planting zones
Mimic tidal ponds
Low marsh
High marsh
VIMS Teaching Marsh Gloucester Pt, VA
Tidal connection
Salt Bushes
I. Frutescens &
B. halimifolia
Birdsong Wetland Norfolk, VA
Regular
high tide
line
Planted marsh must be sloped so it is completely exposed at low tide; plant failure may be caused by standing water
Low marsh
S. alterniflora
High marsh
S. patens
Planting Tidal Marshes at Eroding Marsh Edges
• Fill in between more erosion resistant points
• Wave climate information very important
• In most cases, at least fiber logs are necessary to help raise elevation & provide toe protection
• Low crested stone sills if bottom type & water depth are suitable
Typical Grass Species Used for Salt Marsh
Saltmarsh cord grass Spartina alterniflora
Saltmeadow hay Spartina patens
Switch grass Panicum virgatum
Salt grass Distichlis spicata
Low Marsh High Marsh
Groundsel Bush Baccharis halimifolia
Marsh Elder Iva frutescens
Salt Marsh Bushes planted at landward side of high marsh
Bayberry M. pennsylvanica
Not as flood tolerant, use at
upland transition
Planted Freshwater Marsh
• Many more plant species possible in freshwater areas
• Mimic natural marshes in area
• Try to include plants that stay above ground during winter
– Or design for winter conditions with no aboveground stems & leaves for wave attenuation
– Backshore protection
DNREC
Blackbird Creek Preserve
Wetland Plant Sources
• Wild harvest from donor marshes nearby that can recover from harvest – for small projects
– Hard to dig out plants from natural marshes
– Eroded marsh edge clumps can be salvaged
• Nursery stock has greatest success
– Plants typically grown in freshwater, must be brought up to site salinity by grower before delivery
Planting Process
2. Slow-release fertilizer in hole 3. Insert
plant at least 4 inches
deep
Can’t plant too deep!
1. Dig hole
New Gosport Wetland, Portsmouth
4. Pack well to remove air
pockets
Plant Spacing & Growth Pattern
Closer spacing for more rapid cover
Wider spacing to cover large area with limited budget
Marsh grasses will spread underground by rhizomes
Eventually space between plants will fill in naturally
If it’s done correctly…..
Spring Planting Day End of the Summer
Successful establishment indicated by flowering grasses
Grazing Exclusion Devices
Mute Swans & Canada Geese can pull new plants out of the ground, but not established
well-rooted plants
Exclusion devices typically removed after 1st
growing season
J. Scalf
Planted Marsh TLC During 1st Growing Season
• Regular inspections
• Monitor ebb & flood tides
• Look for & re-plant washed out plugs
– Pack in deep
– Keep grazers out Washed out plant plugs can be collected & re-planted
Main Reasons Planted Marsh Does Not ‘Take’ • Planted too low - below mid-tide elevation or in
wrong zones
• Washed out plugs
• Incomplete drainage & ponding at low tide
• Rapid sediment accretion
Other Reasons • Flow stresses – bottlenecks, runoff, waves
• Foot traffic & recreational uses
• Soil contamination
• Undetermined
Need monitoring & analysis of results
Don’t re-plant until cause of failure determined
Planted Marsh Maintenance – After Establishment
• Remove excessive tidal debris & trash periodically as needed
• Prune overhanging branches if shading leads to reduced cover
• Remove nuisance, invasive species that limit project success
• Inspect & document storm effects, storm tide levels
• Do not mow, install landscape design features to control adjacent mowing, e.g. split rail, timbers
• Avoid using lawn chemicals nearby
Coir Fiber Logs & Mats The use of manufactured, bio-degradable fiber
products to provide temporary support for planted tidal marshes and/or riparian buffer restoration
May also be effective for trapping sediment
P. Menichino P. Menichino
Evolution of Practices Fiber Logs
No elevation or slope changes Sand fill to raise planted marsh elevation Stacking rows of logs
Simple staking below MHW
More aggressive staking Higher elevation placement
J. Rigger P. Menichino
Using both mats & logs
Monitoring & Maintenance
Fiber Logs
• Inspect frequently
• Pound loose stakes back into ground ASAP
• Add more logs or blankets to repair sand ‘leaks’
Fiber Logs – Lessons Learned
• 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
Fiber Logs – Lessons Learned (cont.)
• Premium logs are denser for higher energy sites
• The faster sediments fill in, the less likely installation will fail
– Include sand backfill if the local sediment supply is low or to increase likelihood for successful marsh establishment
Ecological Parameter – Turbidity may indicate local sediment supply
So does evidence of accretion against logs, beaches, sand overwash, sediment trapped at groins or jetties
Marsh with Sill
A low-profile revetment backfilled with sand to create & support a tidal marsh
where wave climate too extreme for fiber logs
Typical Marsh Sill Construction Sequence
1. Filter cloth placed
2. Sand fill & stone sill
3. Settling period – check grade & tides
4. Plant tidal marsh vegetation
Evolution of Practices
Wide straight gaps Erosion & loss of marsh
Narrow & offset gaps or few gaps at all for engineering certainty – not always good practice
Marsh toe revetments at existing marsh edges & accretion
Marsh sills with sand fill + planted marshes
Potentially Negative Effects of Marsh Sills
• Covering shallow water benthic fauna
• Hydrodynamic changes - altering tidal exchange,
wave height and wave direction
• Altering sediment transport along shoreline
• Altering habitat use along marsh edge
• Construction access & maintenance impacts
– Temporary road fill, compaction
Design Criteria to Maintain Coastal Processes & Do No Harm
• 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
Tidal Openings
When should they be included?
• Sill crest height > MHW
• Sill length > 100 Ft ??
– No definitive standard
– May need more or less
• Site-specific
– Tidal ponds
– Natural or created channels
– Open ends
– To allow for recreation access
More monitoring needed
Straight Tidal Openings Design Challenge – too much energy
• “Straight” tidal openings allow access for marine wildlife, but also introduce wave energy into the planted marsh
• Shoaling may occur just inside gaps that blocks access & tides
• Stable embayments eventually form & can be included in design
Source: Maryland Department of the Environment
to address erosion inside straight gaps
Offset Tidal Openings
Gapped offset sections at pocket marsh Taper ends toward wave energy
Source: Maryland Department of the Environment
Weir Opening or Vented Sill
Gap covered with stone at lower elevation
Sediment deposition evident
with some marsh dieback
Narrow or “Pinched” Tidal Opening
Narrow & curved
Reduces sand deposits
Pinches flow & access
Marsh Sill Troubleshooting
• Not enough tidal drainage leads to marsh dieoff – Add more openings
– Check marsh elevation & slope, add sand & re-grade
• Too much tidal exchange at openings leads to marsh or bank erosion – Reduce width or add inner structure
• Settling below target height in soft sediments – Add more stone to raise height
Tightly packed stone in gabions restricts water movement through sill Algae bloom in warmer, stagnant area indicates stressful conditions for fish & crabs
Potential Stone Sill Alternatives
• Mid-tide bulkheads – Narrow waterways
– Deep nearshore depths
– Not well studied, may or may not have same adverse effects as traditional bulkheads
• Bio-genic Reefs
Evolution of Practices Stone for sill material Oyster Reef Alternatives
Proprietary Concrete Products
Oyster Castles Reef Balls Ready Reef
Living Reefs
Important Considerations
1. Are there any natural reefs in vicinity to mimic?
2. What is the local tide range & extreme tide potential? Will the reef remain submerged or be exposed ?
3. Is the wave climate low enough for loose shell or is some type of containment needed?
4. Are there any navigation or public health concerns?
Loose Shell Good for habitat value
Not usually effective for wave attenuation
Bagged Shell
Incidental impacts of plastic mesh? e.g. entrapment, microplastic pollution Are biodegradable products available?
Similar structural integrity as stone sills, but easier to install
Long-term reef evolution still under investigation
Desirable 3-D growth splitting bag open
Reef Balls
Pre-cast concrete with embedded oyster shell Pre-soaked for spat settlement
Requires crane to lift on and off boats
Oyster Castles
Smaller, interlocking units with embedded oyster shell
‘Ready Reef’ just one of several new products on market
Source: http://readyreef.com/index.html
Living Reef Combined with Other Elements to increase habitat diversity & troubleshoot erosion problems
Loose shell & reef balls at wide sill gap
PUTTING THE PIECES TOGETHER (VERY BRIEFLY)
Planted Marsh Materials
• Low marsh & high marsh plants
– Nursery stock or salvaged plants
– Quantity based on desired spacing
• Dibble bars or power augers to drill holes
• Slow release fertilizer
• Buckets to carry plants & fertilizer to shoreline
• Grazing exclusion fencing, stakes, &/or strings
Fiber Log Materials
• 12”x 12” 16”x12” 20”x12” 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
Marsh Sill Materials
• Filter cloth
• Quarry stone sized for wave climate
• Sand fill from upland source
• Material transport equipment
• Material placement equipment
Living Reef Materials
• Oyster shell or reef products
• Material transport equipment
Concept Design
1. Describe the location & the problem
2. Project goals – Establish success criteria, how will you know if the project ‘works’
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
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
Living Shoreline Professional Service Opportunities
Design & Construction
• Scouting out suitable sites
• Site evaluations & alternatives analysis
• Concept drawings
• Permit applications & coordination
• Construction management
– Sub-contractors for heavy lifting
– Horticulture industry partners (nurseries & installers)
• Post-construction as-built surveys
– To confirm design standards, permit compliance
Living Shoreline Professional Service Opportunities
Long-Term
• Routine inspection & maintenance contracts
– Provide assurance, document performance
• Debris removal
• Planted area enhancements – gardening, pruning
• Invasive species management
• Storm damage assessment & recovery
Living Shoreline Concept Designs
Summary
• Engineers & ecologists can work together to design-build-monitor-maintain living shoreline projects
• Take advantage of lessons learned from previous work – read reports & stay engaged with community of practice
• Good references & data are available to determine site-specific parameters – some parameters still uncertain
• Include monitoring, maintenance, site prep, demolition, construction access & post-construction restoration in the concept design
Thanks for your interest
in Living Shorelines!
Contact Information
Karen Duhring karend@vims.edu 804-684-7159
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