SKM C45820100612260

CAPE COD CANAL SECTION 111MITIGATION OF STORM DAMAGE ATTRIBUTABLE TO NAVIGATION WORKS FEASIBILITY STUDY

SELECTMEN’S MEETINGMichael RiccioStudy ManagerNew England DistrictOctober 8, 2020

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STUDY AREA

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PROBLEMS/OPPORTUNITIES

Jetties at the mouth of the Canal interrupt natural longshore sediment transport resulting in significant erosion to the downdrift shoreline. The continued erosion now presents an imminent threat to both public and private, property and infrastructure.

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Problems

• Structures along the shoreline are vulnerable to undermining

• 600+ acre natural salt marsh habitat vulnerable to future catastrophic damages

• Downtown public infrastructure increasingly vulnerable to storm risk and flooding

• Town Hall• Fire Department• Police Department• Local commercial activity• Route 6A (evacuation route)

• Loss of recreational beach

• Negative impacts to local tourism/economy

• Lack of trust between public and USACE

Opportunities

• Reduce coastal storm risk to public and private property and infrastructure

• Reduce the risk of catastrophic failure of 600+ acres of salt marsh habitat

• Restore and preserve recreational use of the town beach

• Reduce the coastal storm risk to local tourism and economy

• Improve a strained relationship between the public and USACE

• Pave the way for long term sediment management strategies associated with operations and maintenance of the Canal

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Barrier beach absorbs and redistributes wave energy thereby protecting backshore resources

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- Fire Department- Police Department - Town Hall- Route 6A Evacuation Route- Historic District

If barrier beach erodes then the backshore area, including critical public infrastructure, becomes exposed to direct wave energy…

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600+ Acres of Salt Marsh

…as well as the marsh system itself

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STUDY OBJECTIVES

1. Determine extent of the problem. To what extent can erosion be directly attributed to the Cape Cod Canal Federal Navigation Project?

2. Identify and evaluate alternatives for mitigating the impact of the Cape Cod Canal FNP as it relates to future damages caused by continued erosion along Town Neck Beach/Springhill Beach.

3. Recommend a readily implementable solution. What can realistically be accomplished through this authority?

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STUDY APPROACH

1. Evaluate Cause-and-Effect Relationship• Shoreline Change Analysis

» Historical Change in Shoreline Position (Local)» Historical Change in Shoreline Position (Regional)» Projected Future Shoreline Position» Volumetric Shoreline Change

• Sediment Transport Analysis» Sediment Transport Modeling» Sediment Budget

2. Evaluate Alternatives• Initial Screening of Measures• Initial Array of Alternatives• Focused Array of Alternatives• Recommended Plan

3. Recommend and Implementable Plan

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CAUSE-AND-EFFECT RELATIONSHIP

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SHORELINE CHANGE ANALYSIS

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Long-Term Shoreline Change Rates (1952-2018)

HISTORICAL CHANGE IN SHORELINE POSITION (LOCAL)

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Short-Term Shoreline Change Rates (2000-2018)


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Long-Term and Short-Term Shoreline Change Rates (2000-2018)

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Massachusetts CZM Shoreline Change Maps depict pre- and post- Canal shorelines.

HISTORICAL CHANGE IN SHORELINE POSITION (REGIONAL)

Presenter

Presentation Notes

Eyeball/qualitative test

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Massachusetts CZM Shoreline Change Maps depict updrift accretion (yellow arrow)


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Massachusetts CZM Shoreline Change Maps depict stable updrift shoreline


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Massachusetts CZM Shoreline Change Maps depict downdrift erosion (Red Arrow).


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Massachusetts CZM Shoreline Change Maps depict downdrift stable shoreline


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Regional shoreline change area from Stage Point, Plymouth to Sandy Neck, Barnstable (1860-2014)

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Significantly more erosion/accretion in the vicinity of the Canal compared to the region

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PROJECTED FUTURE SHORELINE POSITION

Existing (2018) and projected (2068) MHW shoreline positions, west end of Town Neck Beach (WHG, 2020)

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Existing (2018) and projected (2068) MHW shoreline positions, east end of Town Neck Beach

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Existing (2018) and projected (2068) MHW shoreline positions, Springhill Beach (WHG, 2020)

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Projected (2068) areas of MHW inundation (WHG, 2020)

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VOLUMETRIC SHORELINE CHANGE

Volume loss transect locations (WHG, 2020)

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VOLUMETRIC SHORELINE CHANGE

Transect Profile Translation for Estimated Past and Projected Conditions

782,000 cubic yards lost

900,000 cubic yards lost

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SEDIMENT TRANSPORT ANALYSIS

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SEDIMENT TRANSPORT MODELING

Sediment Transport Modeling demonstrate how much material is capable of moving through the study area and in which direction

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SEDIMENT BUDGET

A sediment budget developed that applied real time sediment inputs/outputs to the sediment transport modeling in order to determine how much material actually goes where

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Shoreline Change Analysis• Long Term Shoreline Change

- Region: - 0.29 ft/yr- Scusset Beach: 1.16 ft/yr- Town Neck/Springhill - 1.33 ft/yr

• The Canal directly impacts erosion for approximately 10,800 linear feet • Town Neck Beach has been relatively stable between the Canal and Transect 31• Erosion is worst between Transect 31 and Old Harbor Inlet• Erosion along Springhill Beach is more consistent with background erosion• 782,000 cy of material estimated to have been lost over the past 50 years (1.45 cy/yr)• 900,000 cy of material projected to be lost over the next 50 years (1.66 cy/yr)

Sediment Transport Analysis• 95,000 cy/yr can come through the system from updrift of the Canal• 54,700 cy/yr of material are impounded updrift of the Canal by the jetties• 28,100 cy/yr of material shoals within the Canal channel• 9,800 cy/yr of material are lost offshore • 11,200 cy/yr of material from the Canal wind up on Town Neck Beach• 81,400 cy/yr of the 95,000 cy/yr of material that can migrate through the system do not actually reach the downdrift

shoreline

Summary• Shoreline Change Analysis suggests that the Canal contributes to approximately 78% of the erosion• Sediment Transport Analysis suggests that jetties interrupt approximately 85% of sediment transport

CAUSE-AND-EFFECT SUMMARY

The Canal directly and significantly contributes to erosion of the Sandwich shoreline

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ALTERNATIVES ANALYSIS

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INITIAL SCREENING OF MEASURES

A suite of coastal storm risk management measures were screened for effectiveness, constructability and environmental impacts

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INITIAL ARRAY OF ALTERNATIVES

Six primary alternatives were evaluated for cost comparison, along with 4 sub alternatives for beach nourishment (sediment source) during the first iteration of analysis

Measures1 Beach Nourishment Only 388,000 cubic yards of beach compatable material placed on Town Neck Beach

1A Beach Nourishment 388,000 cy of material dredged from Scusset Beach

1B Beach Nourishment 224,000 cy dredged from Scusset and 164,000 cy trucked from upland

1C Beach Nourishment 100,000 cy of material dredged from Canal O&M, 224,000 cy dredged from Scusset Beach and 64,000 cy trucked from an upland source

1D Beach Nourishment 388,000 cubic yards of material trucked from upland source

2Beach Nourishment w/ Dune Core Stabilization

388,000 cubic yards of beach compatable material placed on Town Neck Beach that will include sand envelopes built into the core of the dune using fiber matting

2A Beach Nourishment w/Dune Core Stabil ization 388,000 cy of material dredged from Scusset Beach

2B Beach Nourishment w/ Dune Core Stabil ization 224,000 cy dredged from Scusset and 164,000 cy trucked from upland

2C Beach Nourishment w/Dune Core Stabil ization 100,000 cy of material dredged from Canal O&M, 224,000 cy dredged from Scusset Beach and 64,000 cy trucked from an upland source2D Beach Nourishment w/ Dune Core Stabil ization 388,000 cubic yards of material trucked from upland source

3Beach Nourishment w/

Groin Modifications388,000 cubic yards of beach compatable material placed on Town Neck Beach as well as the construction of

four (4) 250 linear foot groins perpendicular to Town Neck Beach intended to retain material

3A Beach Nourishment w/Groin Modifications 388,000 cy of material dredged from Scusset Beach

3D Beach Nourishment w/Groin Modifications 224,000 cy dredged from Scusset and 164,000 cy trucked from upland

3C Beach Nourishment w/Groin Modifications 100,000 cy of material dredged from Canal O&M, 224,000 cy dredged from Scusset Beach and 64,000 cy trucked from an upland source

3D Beach Nourishment w/Groin Modifications 388,000 cubic yards of material trucked from upland source

4 North Jetty ModificationsReduce total length of jetty by 500' in order to allow for additional sediment flow around the Canal and onto Town Neck Beach

5 South Jetty Modifications Extend South Jetty by 500' in order to prevent sediment that does bypass the Canal from flowing back into it

6 Sediment BypassInstall a permanent bypass system that would continually pump material from Scusset Beach, under the Canal and onto Town Neck Beach

6A Sediment Bypass Only 150,000 cy of material pumped onto the downdrift shoreline annually

6B Sediment Bypass w/ Engineered Beach 150,000 cy of material pumped onto the downdrift shoreline annually, plus construction of a 224,000 cy beach

Cape Cod Canal 111 Initial Array of AlternativesAlternative

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ALTERNATIVE 1

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ALTERNATIVE 2

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ALTERNATIVE 3

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ALTERNATIVE 4

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ALTERNATIVE 5

Lengthen the southern jetty by 900’ in order to retain material that does reach Town Neck Beach, by preventing it from flowing back into the Canal

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ALTERNATIVE 6

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POTENTIAL SEDIMENT SOURCES

Scusset Borrow Area

Cape Cod Canal Borrow Area

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INITIAL ARRAY OF ALTERNATIVES SUMMARY

No plan under $12.5 million, even for initial construction (numbers can be refined)- More site-specific details, PED Phase, S&A, Contingencies

Alternative 1 was the most viable option- Initial construction costs potentially fit within the Section 111 federal expenditure limit of $12.5 million- Total volume could potentially be modified

Alternative 2, 3, 4 and 5 not feasible- Costs exceed the Section 111 Federal expenditure limit and/or do not effectively accomplish the project purpose

Additional iteration of alternatives analysis warranted for Alternative 1- Refine beach footprints/volumes- Refine sediment sources- Refine cost estimates

Reframe the duration of the project to one-time placement- Mattituck most recently completed Section 111 project was approved as a one-time placement project- Does not NEED to be evaluated for a 50-year project life and doing so would render the project unfeasible

Sand VolumeInitial Construction

CostRenourishme

nt RateRenourishement

Cycles Renourishment Costs Repair Frequency Repair CyclesRepair/O&M

CostsTotal Project

Cost 1A Beach Nourishment (Scusset) 388,000 14,337,000$ 9 years 6 182,614,000$ N/A N/A N/A 196,951,000$ 1B Beach Nourishment (Scusset, Upland) 388,000 26,701,000$ 9 years 6 240,618,000$ N/A N/A N/A 267,319,000$ 1C Beach Nourishment (Scusset, O&M, Upland) 388,000 18,977,000$ 9 years 6 176,429,000$ N/A N/A N/A 195,406,000$ 1D Beach Nourishment (Upland) 388,000 40,064,000$ 9 years 6 468,857,000$ N/A N/A N/A 508,921,000$

2A Beach Nourishment w/ Core Envelopes (Scusset) 388,000 23,304,000$ 11 years 5 231,466,000$ 5.5 years 8 306,891,000$ 561,661,000$ 2B Beach Nourishment w/ Core Envelopes (Scusset, Upland) 388,000 35,668,000$ 11 years 5 278,364,000$ 5.5 years 8 306,891,000$ 620,923,000$ 2C Beach Nourishment w/ Core Envelopes (Scusset, O&M, Upland) 388,000 27,944,000$ 11 years 5 226,071,000$ 5.5 years 8 306,891,000$ 560,906,000$ 2D Beach Nourishment w/ Core Envelopes (Upland) 388,000 49,032,000$ 11 years 5 472,079,000$ 5.5 Years 8 306,891,000$ 828,002,000$

3A Beach Nourishment w/ Groin Modifications (Scusset) 388,000 18,803,000$ 13.5 years 4 128,988,000$ N/A N/A N/A 147,791,000$ 3B Beach Nourishment w/ Groin Modifications (Scusset, Upland) 388,000 31,166,000$ 13.5 years 4 163,035,000$ N/A N/A N/A 194,201,000$ 3C Beach Nourishment w/ Groin Modifications (Scusset, O&M, Upland) 388,000 23,443,000$ 13.5 years 4 125,939,000$ N/A N/A N/A 149,382,000$ 3D Beach Nourishment w/ Groin Modifications (Upland) 388,000 44,529,000$ 13.5 years 4 333,824,000$ N/A N/A N/A 378,353,000$

4 Reduce Length of North Jetty 0 16,388,000$ N/A N/A N/A N/A N/A N/A 16,388,000$

5 Increase Length of South Jetty 0 43,182,000$ N/A N/A N/A N/A N/A N/A 43,182,000$

6A Permanent Bypass System 0 9,870,000$ continual N/A N/A varies varies 127,515,000$ 137,385,000$ 6B Permanent Bypass System (with beach nourishement) 224,000 17,795,000$ continual N/A N/A varies varies 127,515,000$ 145,310,000$

Cape Cod Canal 111 Alternatives Analysis (Initial Array of Alternatives)

Alternative Sand VolumeInitial Construction

CostRenourishme

nt RateRenourishement

Cycles Renourishment Costs Repair Frequency Repair CyclesRepair/O&M

CostsTotal Project

Cost 1A Beach Nourishment (Scusset) 388,000 14,337,000$ 9 years 6 182,614,000$ N/A N/A N/A 196,951,000$ 1B Beach Nourishment (Scusset, Upland) 388,000 26,701,000$ 9 years 6 240,618,000$ N/A N/A N/A 267,319,000$ 1C Beach Nourishment (Scusset, O&M, Upland) 388,000 18,977,000$ 9 years 6 176,429,000$ N/A N/A N/A 195,406,000$ 1D Beach Nourishment (Upland) 388,000 40,064,000$ 9 years 6 468,857,000$ N/A N/A N/A 508,921,000$

2A Beach Nourishment w/ Core Envelopes (Scusset) 388,000 23,304,000$ 11 years 5 231,466,000$ 5.5 years 8 306,891,000$ 561,661,000$ 2B Beach Nourishment w/ Core Envelopes (Scusset, Upland) 388,000 35,668,000$ 11 years 5 278,364,000$ 5.5 years 8 306,891,000$ 620,923,000$ 2C Beach Nourishment w/ Core Envelopes (Scusset, O&M, Upland) 388,000 27,944,000$ 11 years 5 226,071,000$ 5.5 years 8 306,891,000$ 560,906,000$ 2D Beach Nourishment w/ Core Envelopes (Upland) 388,000 49,032,000$ 11 years 5 472,079,000$ 5.5 Years 8 306,891,000$ 828,002,000$

3A Beach Nourishment w/ Groin Modifications (Scusset) 388,000 18,803,000$ 13.5 years 4 128,988,000$ N/A N/A N/A 147,791,000$ 3B Beach Nourishment w/ Groin Modifications (Scusset, Upland) 388,000 31,166,000$ 13.5 years 4 163,035,000$ N/A N/A N/A 194,201,000$ 3C Beach Nourishment w/ Groin Modifications (Scusset, O&M, Upland) 388,000 23,443,000$ 13.5 years 4 125,939,000$ N/A N/A N/A 149,382,000$ 3D Beach Nourishment w/ Groin Modifications (Upland) 388,000 44,529,000$ 13.5 years 4 333,824,000$ N/A N/A N/A 378,353,000$

4 Reduce Length of North Jetty 0 16,388,000$ N/A N/A N/A N/A N/A N/A 16,388,000$

5 Increase Length of South Jetty 0 43,182,000$ N/A N/A N/A N/A N/A N/A 43,182,000$

6A Permanent Bypass System 0 9,870,000$ continual N/A N/A varies varies 127,515,000$ 137,385,000$ 6B Permanent Bypass System (with beach nourishement) 224,000 17,795,000$ continual N/A N/A varies varies 127,515,000$ 145,310,000$

Cape Cod Canal 111 Alternatives Analysis (Initial Array of Alternatives)

Alternative

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FOCUSED ARRAY OF ALTERNATIVES

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Sand Volume Dredge Type Performance Period Total Project Cost1A Beach Nourishment (Scusset) 388,000 Hydraulic 9 years 11,656,000$ 1E Beach Nourishment (Scusset) 388,000 Mechanical 9 years 11,669,000$ 1F Beach Nourishment (Scusset) 388,000 Hopper 9 years 16,737,000$ 1G Beach Nourishment (Scusset) 224,000 Hydraulic 1 year 7,925,000$ 1H Beach Nourishment (Scusset) 224,000 Mechanical 1 year 8,136,000$ 1I Beach Nourishment (Scusset) 224,000 Hopper 1 year 11,201,000$ 1J Beach Nourishment (Scusset/Canal) 324,000 Hydraulic/Hopper 6 years 13,427,000$ 1K Beach Nourishment (Scusset/Canal) 324,000 Mechanical/Hopper 6 years 14,029,000$ 1L Beach Nourishment (Scusset/Canal) 324,000 Hopper/Hopper 6 years 14,577,000$ 1M Beach Nourishment (Scusset/Canal (O&M delta)) 324,000 Hydraulic/Hopper 6 years 10,094,000$ 1N Beach Nourishment (Scusset/Canal (O&M delta)) 324,000 Mechanical/Hopper 6 years 10,435,000$ 1O Beach Nourishment (Scusset/Canal (O&M delta)) 324,000 Hopper/Hopper 6 years 10,625,000$

Focused Array of Alternatives (performance/cost comparison)Alternative

FOCUSED ARRAY OF ALTERNATIVES

Beach Nourishment Only alternatives are feasible- Alternatives 1G, 1H and 1I can be constructed for under $12.5 million but would need to be renourished every year- Alternatives 1F, 1J, 1K and 1L could not be constructed for under $12.5 million- Alternatives 1M, 1N and 1O could be constructed for under $12.5 million but are reliant on O&M dredging of the Canal to align with

construction of Section 111 project- Alternatives 1A and 1E could be constructed for under $12.5 million

Recommended Alternative- Alternatives 1A, 1E, 1M, 1N and 1O were technically considered feasible- Alternatives 1M, 1N and 1O carry too much implementation risk and were not recommended accordingly- Alternative 1A was nominally less expensive than Alternative 1E and was therefore was the recommended alternative- Alternative 1A was the recommended alternative: One-time construction of a 388,000 cubic yard beach along Town Neck Beach

using material dredged from the nearshore at Scusset Beach using a mechanical dredge

Sand Volume Dredge Type Performance Period Total Project Cost1A Beach Nourishment (Scusset) 388,000 Hydraulic 9 years 11,656,000$ 1E Beach Nourishment (Scusset) 388,000 Mechanical 9 years 11,669,000$ 1F Beach Nourishment (Scusset) 388,000 Hopper 9 years 16,737,000$ 1G Beach Nourishment (Scusset) 224,000 Hydraulic 1 year 7,925,000$ 1H Beach Nourishment (Scusset) 224,000 Mechanical 1 year 8,136,000$ 1I Beach Nourishment (Scusset) 224,000 Hopper 1 year 11,201,000$ 1J Beach Nourishment (Scusset/Canal) 324,000 Hydraulic/Hopper 6 years 13,427,000$ 1K Beach Nourishment (Scusset/Canal) 324,000 Mechanical/Hopper 6 years 14,029,000$ 1L Beach Nourishment (Scusset/Canal) 324,000 Hopper/Hopper 6 years 14,577,000$ 1M Beach Nourishment (Scusset/Canal (O&M delta)) 324,000 Hydraulic/Hopper 6 years 10,094,000$ 1N Beach Nourishment (Scusset/Canal (O&M delta)) 324,000 Mechanical/Hopper 6 years 10,435,000$ 1O Beach Nourishment (Scusset/Canal (O&M delta)) 324,000 Hopper/Hopper 6 years 10,625,000$

Focused Array of Alternatives (performance/cost comparison)Alternative

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WHAT ABOUT THE LONG TERM?

Can Operations and Maintenance of the Canal be used to supplement beach nourishment?- Long term nourishment is not feasible under Section 111 - Canal is dredged every 7 years or so- Sand is a highly valuable and limited resource (why waste?)- Federal Interest exists due to the cause and effect relationship between the Canal and downdrift erosion- Can the additional cost of beneficially reusing the material on the downdrift shoreline be justified?

Alternative Sand Volume Dredge TypeInitial Construction

Cost (thousand) Renourishment RateRenourishment Costs

(thousand)Total Project Cost

(thousand)O&M Base Plan 90,000 Hydraulic 5,443$ 7 years 117,458$ 122,901$

Additional Costs for Beach disposal 90,000 Hydraulic 2,547$ 7 years 54,976$ 57,523$ Revised O&M Base Plan 90,000 Hydraulic 7,990$ 7 years 172,434$ 180,424$

$180 mil vs.$120 mil

Cost Justification- Costs for dredging the Canal over a 50-year period were estimated; both with ocean disposal and beneficial reuse- The additional cost of reusing the material would be significant (approximately 50% increase)- Cannot assume that the benefits exist to justify the increase in cost- Section 204 study from 2015 preliminarily justified the additional cost of beneficially reusing the material

Summary- This study did not fully explore the costs, benefits and statutory constraints associated with beneficially reusing material removed from the

Canal during future O&M dredging efforts- This study did establish a cause-and-effect relationship between the canal and downdrift impacts- This study did underscore the perpetual nature of the problem - This study did acknowledge the potential long-term availability of material via future Canal dredging efforts- Therefore this study recommends that the Corps consider opportunities to develop a more sustainable and mutually beneficial sediment

management strategy for future operations and maintenance of the Canal.

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1. All alternatives far exceed the $12.5 million Federal expenditure limit when considering long-term renourishment needs but several alternatives can at least be constructed for under that limit. Therefore the Recommended Plan will call for ‘one-time placement’.

2. Using material from the next O&M dredging of the Canal is still a possibility but due to uncertainty associated with the timing of that effort, Alternatives 1M, 1N and 1O could not be recommended for implementation in this study.

3. Alternative 1A maximizes the opportunity to significantly mitigate impacts through Section 111.

4. Recommended Plan includes the one-time construction of a 388,000 cubic yard engineered dune and berm beach along Town Neck Beach using material dredged from the Scusset Beach nearshore area using a mechanical dredge.

5. The recommended plan will be further developed and refined during the Design and Implementation phase of the project, with respect to sediment source and dredge type.

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1. Beneficially reusing the O&M dredging material makes sense intuitively but evaluating and recommending such measures was beyond the scope of this study.

2. This study acknowledges the opportunity to beneficially reuse material dredged from the Canal and recommends that additional consideration be given to developing a more sustainable and mutually beneficial sediment management strategy for operations and maintenance of the Canal

ALTERNATIVES ANALYSIS SUMMARY

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RECOMMENDED PLAN

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RECOMMENDED PLAN

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RECOMMENDED PLAN

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REAL ESTATE PLANS

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REAL ESTATE PLANS

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REAL ESTATE PLANS

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REAL ESTATE PLANS

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RISKS UNCERTAINTIES

Environmental

- Recommended Plan requires an expanded borrow area footprint

- Additional environmental coordination is needed to get concurrence from resource agencies

Real Estate

- Non-standard easements have been developed and preliminarily approved to allow for the project to be constructed on private property without requiring public access

- Final approval would coincide with the final approval of the study

Long Term Maintenance

- The recommended one-time construction of an engineered beach is the only work that would be guaranteed to be constructed through this study

- Beneficially reusing material from future O&M dredging of the Canal makes sense in concept but no specific process has been established by which that would be accomplished, thus there is still a risk that no long-term nourishment is provided by the Corps.

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SCHEDULE

Action Current

MDM 27-MAY-2020

Draft Report 30- SEP-2020

Draft Report Release for Public Comment 31-OCT-2020

Public Comment Period Closes 30-NOV-2020

Incorporate Public Comments 31-DEC-2020

Final Report Submitted to MSC 8-JAN-2021

Final Report Approval 31-JAN-2021

Documents

SKM C45820100612260