MZB VOR MB Island Seawall Investigation_Report_Final.pdf

MZB VOR MISSION BAY ISLAND SEAWALL INVESTIGATION

Inspection Period: April 2022

Prepared for:

Amanda Edwards, Subcontract Administrator

Prepared by:

1660 Hotel Circle N. Ste 500 San Diego, CA 92108

(619) 220-6050

M&N JN:

May 18, 2022 i

Executive Summary Moffat and Nichol (M&N) performed a field investigation at MZB VOR Mission Bay on April 14, 2022. The investigation included a shoreline and seafloor assessment as presented in the M&N Proposal for Mission Bay VOR Island Seawall Investigation.

The inspection focused on collecting data from multiple shoreline failures located on the northern and southern extremity of MZB VOR Mission Bay Island. The data collected includes horizontal and vertical revetment measurements, mudline elevations, rock sizes, observed geotextile filter fabric, and site photos.

If the existing condition is not addressed immediately, the shoreline surrounding MZB VOR Mission Bay Island will continue to lose material into the bay. Moffatt & Nichol recommends that the subject areas be repaired to restore the original square footage and to enhance the durability of MZB VOR Mission Bay Island. The recommended repair alternatives consist of the following:

• Alternative 1 – Rock revetment repair o Backfill o Bedding material as needed o Geotextile filter fabric o Rebuild armor stone revetment

• Alternative 2 – Articulated concrete block o Backfill o Bedding material as needed o Geotextile filter fabric o Articulated concrete block

The recommendations provided in this report are evaluated at a preliminary and conceptual level and do not represent fully engineered designs. An additional site-specific analysis should be conducted to provide proper design guidance and should be pursued before any construction commences.

ii

TABLE OF CONTENTS

Executive Summary i

Introduction 1

Description of Shoreline 2

Inspection Procedures 5

Original Shoreline Construction 5

Site Observation 6

Compiled Data 6

Shoreline Sections 6

Wind and Wave Data 8

Alternative 1 Repair Concepts and Recommendations 8

Construction Concepts/Recommendations 11

ROM Cost Estimate 12

Permitting 13

Alternative 2 Repair Concepts and Recommendations 14

Construction Concepts/Recommendations 16

ROM Cost Estimate 17

Permitting 18

Data Tables 18

Inspection Photos: Shoreline Failure 1 21

Inspection Photos: Shoreline Failure 2 23

Inspection Photos: Shoreline Failure 3 25

Inspection Photos: Shoreline Failure 4 27

Inspection Photos: Rock Sizing 29

Inspection Photos: Geotextile Filter Fabric 33

Inspection Photos: Posted Signage 34

Shoreline Erosion Over Time 36 Appendix 37

Introduction Moffat and Nichol (M&N) performed a field investigation at MZB VOR Mission Bay Ion April 14, 2022. The investigation included a shoreline and seafloor assessment as presented in the M&N Proposal for Mission Bay VOR Island Seawall Investigation.

The inspection was used to investigate the failing shoreline protection occurring on the northern and southern extremity of MZB VOR Mission Bay Island. The proposed scope of work included three task elements:

Task 1 – Site Observation

• Measure elevations and slope of existing revetment rocks with rock depth and elevation measurement at change of grades

• Measure revetment slope – horizontal and vertical measurements will quantify the extents of the failure(s)

• Collect size and quality of the existing stone to quantify the level of protection

• Collect the condition of backing stone and/or geotextile filter fabric serving as a foundations

• Photograph site thoroughly for the review and study

Task 2 – Document Review

• Collect, review and record drawings of the existing revetment and relevant in-house information related to tides, currents, wave data, wave runup, wind data, etc.

• Review historical aerial images to compare the conditions prior to shoreline failure

• Collect and review relevant performance issues and/or maintenance activity

Task 3 – Condition Assessment

• Analyze collected data and determined leading cause of failure

• Compile finding from the investigation into a summery letter report

• Provide engineering and maintenance recommendations

• Compile cost estimate for each engineering and maintenance recommendation

Elevation data in this report is relative to the Mean Lower Low Water datum (MLLW). The construction drawings provided (1961) reference a “Mean Low Tide” datum. This is synonymous with Mean Low Water (MLW), as described by the National Oceanic and Atmospheric Administration. The correlation is depicted in Figure 1 below. In summary, the correction factor of +0.9 feet is applied to MLW to arrive at MLLW elevations.

Figure 1: San Diego Tidal Datum Correlation (NOAA)

Description of Shoreline MZB VOR Mission Bay Island’s land surface is approximately 90,000 ft2 and located at (latitude/longitude) 32°46’57”N by 177°13’29”W. The MZB VOR Mission Bay Island has four main shoreline failures. Shoreline Failures 1 thru 3 are present at the northern extremity of the island. Each of these shoreline failures has created a concave void with an arc length of approximately 50 ft. The Shoreline Failure 4 was identified at the southern extremity of the island. The location for the shoreline failures are shown in Figure 2. The labeling system and sounding depths based on MLLW for Shoreline Failure 1 thru 3 are shown in Figure 3, and Shoreline Failure 4 is shown in Figure 4.

Figure 2: MZB VOR Mission Bay Island Shoreline Failure locations and labeling

Figure 3: Labeling System for northern extremity Shoreline Failures 1 thru 3 and sounding depths

Figure 4: Labeling System for southern extremity Shoreline Failure 4 and sounding depths

Inspection Procedure The shoreline and seafloor assessment were performed on April 14, 2022. Environmental conditions were satisfactory. Daytime air temperature was typically between 58-65 degrees (Fahrenheit). The wind speed was mild and tides ranged between +5.4 feet to +0.14 feet

(MLLW).

Original Shoreline Construction

Based on record documents, MZB VOR Mission Bay was originally built in 1961 by the FAA using fill, geotextile filter fabric, and revetment stones, as shown in Figure 5. Through field investigation, it was observed that the fill was likely hydraulically place from dredge operations in the Bay. A geotextile filter fabric was visible at discreet points along the shoreline but not prevalent. Small geotextile filter fabric stones, typically two to four inches in diameter, exist beneath the geotextile filter fabric and the armor stones. Armor stones between eight and ten inches in diameter (typically) were placed on top. The field inspection showed that the revetment stones migrated away from the shoreline. In localized locations, the original fill material washed out and exposed the formational material.

Figure 5: Typical Section from 1961 Construction Drawings

Site Observation

The shoreline inspection involved collecting horizontal and vertical revetment measurement for each shoreline failure. The shoreline slope values are documented in Table 5 located in Report Data. A sonar was used for seafloor mapping to collect sounding data at distances of 15 feet, 20 feet, 25 feet, and 30 feet from the shoreline. This information was collected to determine the mudline elevations. The sonar data is presented in Report Data as Table 6.

Compiled Data M&N used the collected data from the inspection to determine the current shoreline sections from the shoreline failure scarps to 30 feet off the shoreline. Wind and wave data was collected from the M&N personal library.

Shoreline Sections

The shoreline cross sections are shown in Graph 1 for Shoreline Failures 1 thru 4. Shoreline Section 3.1 is used as a section of nonfailure for comparison.

Graph 1: Shoreline cross sections

-4

-2

0 10 20 30 40 50 60 70

M u d lin e El

. b as ed o n M

LL

W ft

Length (ft)

Shoreline Cross Sections

Shoreline Failure 1

Shoreline Failure 2

Shoreline Failure 3

Shoreline Failure 4

Shoreline 3.1 w/o failure

Wind and Wave Data

M&N possesses a large library of information and data for Mission Bay. This includes directional wind speeds and directional wave heights and periods. This data was collected by an array of scientific instruments (anemometer and pressure gauges) sampling at ten-minute intervals.

Data was collected from instruments located to the northeast of MZB VOR Mission Bay Island along the western perimeter of the De Anza “boot” between De Anza Cove and the Rose Creek Inlet. The measurement record associated with each of the instruments extended from May 26, 2021, to November 17, 2021.

Data shows that wind speeds typically range between 0-10 knots, with the median speed of ≥ 6 kts. Winds were generally directed from the west (W) and west southwest (WSW), though winds were periodically noted from the northwest (NW) and occasionally from the north (N) during the fall season.

Waves are typically less than 4 inches in height and are associated with periods of three seconds or less. Maximum wave height observed is 5.4 inches. Peak wave events occur more frequently during summer (May through early September). Highest weekly wave events typically occur on weekends and highest daily events usually occur around midday. Peak wind speeds were similar in magnitude throughout the record with no observed correlation to peak wave height. This indicates that the measured waves were more likely generated by boat wake as opposed to wind.

The majority of shoreline failures occur at the northern end of the island, further suggesting that wind waves were not a major factor in shoreline erosion. The fetch of the bay, north of the island, is severely limited, meaning water has limited space to travel and accumulate energy.

Typical wind direction originates from the southwest, meaning wind waves usually travel towards the northeast. Therefore, the island serves as a barrier protecting its northern coast from the majority of wind wave action.

It is likely that natural tidal fluctuations, augmented by periodic boat wake, caused scour at the toe of the rock shoreline, which resulted in the shoreline failure. This is evidenced by visual inspection of the shoreline failures relative to the remaining revetment, along with revetment slope measurements. The failure of the shoreline allowed for overtopping to occur, causing erosion.

Alternative 1 Repair Concepts and Recommendations The proposed repair concept incorporates a geotextile filter fabric underlayer on top of which the underlayer and armor rock will be placed. Underlining the proposed RSP with geotextile filter fabric reduces the possibility of seepage-induced erosion and the potential effects of scour and/or winnowing. The geotextile filter fabric also stimulates improved sediment retention and could potentially minimize the washing out of proposed backfill material. Placement methodology plays a crucial role in geotextile filter fabric integrity and longevity. It is recommended that the geotextile filter fabric be secured to the larger toe apron stones.

Due to the limited wave forces at the site (excluding smaller wind / boat wake waves), it is recommended that two layers of armor stone be placed on a 1V:3H slope with a minimum layer thickness of 2 ft. By establishing a more gradual slope than the originally built RSP, the proposed repair concept would enhance structural stability. The increase in armor rock size on a more gradual slope would provide increased wave dissipation impacts via the rough voids between units – though reflection waves and overtopping are not immediate threats. Coastal Engineering Manual (CEM) provides design guidance for rock slope protections to have a minimum crest width of at least 3𝐷𝐵, or a nominal width of 3 armor stones. M&N recommends that a minimum 0.5 ft layer of stone be placed on the geotextile filter fabric following the alignment of the existing topography as a bedding underlayer - though underlayer thickness will vary and increase to obtain the required design crest elevation while staying relatively within the existing footprint. Inspection photos depict an ample amount of 0.5 ft diameter stone at various locations throughout the island that could potentially be used in the underlayer.

M&N recommends that larger stones be placed at the toe and that any existing rock that was displaced since the original construction be left in place. The larger rock at the toe will enhance the structural stability and mitigate potential future toe scouring overtime. Field inspections confirmed numerous displaced armor units at Failure Pockets 1 thru 4, though additional analysis - coupled with frequent monitoring of toe unit positions before, during, and after major storm events in respect to changing sea levels - would have needed to be conducted to accurately comment on a sole cause for displacement. This area was likely subjected to time-induced scour. Therefore, the proposed toe apron rocks could mitigate these impacts by means of supplementary protection, hereby behaving as a sort of “falling apron”. The toe rock would combat toe scour by falling in successive fashion overtime and self-realigning, while offering the adequate thickness of rock as opposed to completely unraveling and failing. Excluding the addition of stabilizing rock in the toe, the repair concept is designed within the original footprint extents to reduce any agency backlash and associated permitting difficulties.

A typical cross-section of the proposed repair concept is shown by Figure 6. It should be noted that the recommendations provided in this report are evaluated at a preliminary and conceptual level and do not represent fully engineered designs. An additional site-specific analysis should be conducted to provide proper design guidance and should be pursued before any construction commences.

Figure 6: Alternative 2 Typical Repair Concept Cross-Section

Construction Considerations / Methodology

Before constructing the proposed repair, the failure pockets should be scrubbed of any debris that would potentially inhibit geotextile filter fabric placement at each site. Prior to placement, there are two options to stimulate successful geotextile filter fabric installment:

A. The site is scrubbed of all larger rocks that could potentially tear the geotextile filter fabric during operations.

B. Bedding material be used as a filler to create a more uniform surface face on which the geotextile filter fabric is placed.

If scrubbing, these rocks can be stockpiled and used in the underlayer where feasible. However, it is recommended that Option B be prioritized. The success of a geotextile filter fabric installment relies heavily on the placement methodology and can rip during initial operations ,if not cautious. Because the proposed footprint extends beyond the water line, divers may be required to place the geotextile filter fabric at wetted locations.

The size of rocks currently existing below the water line at the failure locations range anywhere from approximately 3 to 18 inches in diameter, though the exact quantity is unknown. If enough large rocks exist (preferably >12” inch), it is recommended that the contractor implore options of salvaging and beneficial reuse via clamshells and barge operations. Otherwise, needed underlayer and armor rock stone would be hauled to the site via landside trucking from a local quarry and then loading / offloading onto a smaller barge. Placement operations would most likely integrate the use of hoppers to dump and place the material to the desired slope.

From a constructability standpoint, backfill operations would need to be phased such that the placement of the landward portion of armor rock have some sort of support from built-up fill material to increase overall stability and mitigate any impacts from potential slope failure during initial construction operation. Similarly, this interaction between the rock and backfill material would reduce the potential for the sediment to be lost by acting as a form of retention.

Because the wave climate at the site is driven primarily by boat wakes, it is recommended that any construction work occur on the weekend and outside any days of high public / recreation use. There are numerous launch locations and potential offsite contractor staging areas around Mission Bay. Overall, the proposed construction operations for the RSP repair alternative can be summarized as follows:

1. Scrub failure pockets for any debris & stockpile any rocks that may compromise geotextile filter fabric placement.

2. Conduct rock salvage using small barge and clamshell.

3. Use bedding (underlayer) to flatten the existing rock slope where necessary.

4. Place geotextile filter fabric in proposed footprint using divers and landside crew.

5. Place bedding (underlayer) waterside using barge & hopper.

6. Place bedding (underlayer) landside using hopper.

7. Place armor rock waterside using barge & hopper.

8. Partially backfill material in existing pocket (elevation and phasing TBD).

9. Place armor rock landside using hopper.

10. Complete backfilling of material in existing pocket to final grade.

ROM Cost Estimate

The costs have been developed based on historical and current data using in-house sources, information from previous studies, as well as budget price quotations solicited from local suppliers and contractors. Pricing is provided in US Dollars; 1st Quarter 2022 and escalation is not included. The proposed repair work is anticipated to cost anywhere from approximately $100K to $170K, though these are opinion-based ROM costs made by the consultant. In providing this level of opinion, it is recognized that neither the client nor the consultant has control over the cost of labor, equipment, materials or the contractor's means and methods of determining constructability, pricing or schedule. These costs are based on the consultant's reasonable professional judgement and experience and does not constitute a warranty, expressed or implied, that contractor's bids or negotiated prices for the work will not vary from the clients.

In general, the RSP repair will be significantly influenced by the sourcing of these materials. For example, money could potentially be saved via the beneficial reuse of dredged sand from the Bay as opposed to the hauling of non-native sand from local quarries. Crushing up rock that is currently on-site to use in the underlayer or the salvaging of viable rock could potentially save money in rock sourcing as well. Factors such as these would most likely reduce overall project costs and associate more closely with the lower end of the cost range. It is recommended that further surveys be conducted to better understand the existing materials and bathymetry to pursue potential salvaging efforts. The proposed material quantities and ROM are presented in Table 1 and 2.

Table 1: Proposed Quantities

Material Quantities MATERIAL Pocket 1 Pocket 2 Pocket 3 Pocket 4 Total

Geotextile Filter Fabric 1500 SF 1500 SF 1500 SF 1200 SF 5700 SF

Armor Rock 156 tons 156 tons 156 tons 124 tons 591 tons

Underlayer 65 tons 65 tons 65 tons 52 tons 246 tons

Backfill Material 93 CY 98 CY 65 CY 31 CY 288 CY

Table 2: ROM Costs

ROM Cost

Item Description ROM Cost

F&I Geotextile Filter Fabric (SF) $11,500

F&I Armor Rock (Tons) $47,300

F&I Underlayer (Tons) $4,900

Backfill Material (CY) $4,500

Mobilization / Demobilization $12,500

Excavation $5,000

Temporary Construction Measures

$5,000

Equipment $10,000

Total $90,300

Permitting

A number of decisions, approvals, and permits must be obtained to implement the proposed repair. Key regulatory agencies that could potentially become involved include California Coastal Commission (CCC), California State Lands Commission (CSLC), U.S. Army Corps of Engineers (USACE), Regional Water Quality Control Board (RWQCB), County of San Diego (County), National Oceanographic Administration Association (NOAA), and California Department of Fish & Wildlife (CDFW). According to the California Coastal Commission, a permit is required when there is a replacement of 20 percent or more of the materials of an existing structure with new materials. The Coastal Act requires permits for the repair and maintenance of revetments or other shoreline work to existing structures. Historically, repairing structures within the original footprint extents has been met with reduced agency backlash and permitting difficulties. Larger operations such as rock salvaging will potentially provoke further regulatory actions due to potential concern over existing habitats.

Obtaining necessary approvals from regulatory agencies impacts construction schedules, and in some cases, specific design elements. The following agency approvals would be required for the proposed work:

1. CSLC – Correspondence with CSLC is required for work in the coastal zone. However, the existing settlement and lease may help expedite this process.

2. CCC – Correspondence with CCC is required for work in the coastal zone. Processing time is dependent on which office it is processed through. The Coastal Development Permit may include special conditions.

3. CEQA Compliance – Processing time is dependent upon the determination of required impact analysis level. However, it is anticipated that the proposed work may be exempt under Categorical Exemption 15301 for repair or maintenance to existing facilities.

4. USACE – Correspondence with USACE is required for dredging/filling activities within waters of the U.S. (i.e. ocean) below the high tide line (based on NOAA tidal data).

Acquisition of a Section 10 and 404 Permit would be required, per 33 CFR §328.3(d).

5. RWQCB – A Section 401 Certification is required for work within waters of the U.S.

Additionally, City Outreach Permits may be required.

Alternative 2 Repair Concepts and Recommendations The proposed marine mattress / concrete block revetment applies a prefabricated matrix of interconnected articulated concrete block (ACB) units in a stable revetment-type configuration.

These units are connected via geometric interlocks and/or cables, geotextiles, or geogrid in combination with a geotextile underlayment for erosion mitigation and subsoil retention. The prefabricated mattress is typically engineered in such a way as to form a stable revetment of required thickness, weight, and configuration with the underlying subsurface. The rows of blocks are sufficiently rough enough to prevent sliding of the blocks on the geotextile filter fabric. Advantages of applying an ACB over a standard RSP include:

• reduced variable particle distribution of non-interlocked units,

• premanufactured systems for reduced on-site unpredictability,

• and site-specific design configurations.

M&N has recently experienced success with ACB from local manufacturers such as Contech Engineered Solutions, ECOncrete, and a few others.

Because the site is subject to local wind and (boat) wake waves, it is recommended that a bedding layer be placed under the prefabricated concrete mattresses. This can be trucked in or constructed from on-site material, with the latter being preferred. The underlying existing grade varies and is comprised of a mixture of different rock sizes from the existing shoreline. It is recommended that the bedding (underlayer) be placed on top of the existing grade and within the voids of the existing armor rock, to flatten and raise the subsurface prior to placing any geotextile filter fabric. Once the subsurface is relatively flat, it is recommended a geotextile filter fabric be placed. The thickness of the bedding layer would vary depending on the existing conditions at the time of construction to make the structure robust. Typical concrete block units range anywhere from 6-12 inches. Overall structure width will be highly influenced by the subsurface and thickness of underlayer. Due to current site conditions, it is recommended that the bedding layer be placed such that the ACB lies on a constant 1V:3H slope starting at the existing toe (approximately ~50 ft out from the existing failure step). Due to a combination of the relatively short design life of 20 years, footprint restrictions, and practicality of keeping the underlayer to a reasonable thickness, the top of mattress elevation of ~ +7.0 ft MLLW should be sufficient.

Manufacturers suggest burying the top two rows (minimum) of concrete units and an adequate toe trench two rows deep. This will promote added stability to the structure. It is recommended that the backfill material be placed and graded from the top of the failure step down to meet the top of the ACB. A conceptual cross-section of the proposed ACB alternative is provided in Figure 7.

Figure 7: Alternative 2 Typical Repair Concept Cross-Section

Construction Considerations / Methodology

Overall, the proposed construction operations (per manufacturer details) for the ACB alternative can be summarized as follows Manufacturer details outline the following process for implementing an ACB:

1. Scrub Failure Pockets for Any Debris & Stockpile Any Rocks that may Compromise the Geotextile Filter Fabric Placement.

2. Bedding (Underlayer) stones are either salvaged or trucked in and used to flatten the existing rock slope where necessary.

3. After the subgrade has been prepared, the ACB arrives on-site via flat bed trailers as a system of factory-assembled mattresses along with the required geotextile filter fabric.

The prefabricated mattress and geotextile filter fabric is then loaded onto a small to medium sized barge with appropriate placement equipment (crane and spreader bar).

4. Place Geotextile Filter Fabric in Proposed Footprint using a combination of divers, landside crew, and necessary placement equipment where necessary.

5. A proper toe trench requires a minimum of two rows of block be buried below the predicted soil depth for stability. Similarly, manufacturer details for this application typically indicate burying a minimum of two rows of block at the top of the proposed structure.

6. Mattresses are placed on the geotextile filter fabric and prepared subgrade according to the site plans with the spreader bar to aid in lifting, aligning, and placing the mattress to the desired configuration. Portions above the waterline have the capability to be topsoiled if desired and if the chosen ACB allows for it.

Manufacturer details for this application typically indicate burying the top of the ACB/bags to minimize slippage on the slope. An ACB subject to larger wave attack are recommended to have a bedding underlayer. Once the subgrade is relatively flat, the geotextile shall be laid flat and smooth so that it is in direct contact with the subgrade. The geotextile shall be free of tension, folds, and wrinkles. The number of seams and overlaps shall be minimized by selective orientation of geotextile panels, within the limitations of maintaining a consistent pattern.

Seams shall be overlapped a minimum of 17.5 inches. Geotextile panels shall be secured before block placement by adequate sandbags, spare blocks, or pins/staples.

It is recommended that the mattresses be placed directly into position, with a maximum space or gap between mattresses of 3 inches more than the nominal joint spacing of blocks within the mattress. Mattresses out of alignment shall be lifted and reset. Mattresses shall not be pushed or pulled laterally after they are in contact with the geotextile. It is recommended that overlapping of mattresses is not acceptable and can jeopardize the integrity of mattress. No blocks shall project vertically more than 1 inch beyond the adjacent blocks. As adjacent mattresses are placed, they shall be secured to each other by fastening the protruding horizontal and vertical cable connections and end cable loops together along each side of the mattresses. Displaced or broken blocks shall be removed and replaced to conform to all requirements of this section. An example of placing the ACB is shown in Figure 8.

Figure 8: Example of ACB being Placed

Some major considerations that will impact schedule, cost, and overall constructability would be the amount of in-water work and diver work vs. landside operations. It should be noted that barges will need enough water depth to conduct placement operations close to shore. On the contrary, landside operations will be heavily dictated by the amount of space required for equipment near the failure pockets. Contractor BMPs (such as construction mats) will be needed to ensure constructability is feasible.

ROM Cost Estimate

The costs have been developed based on historical and current data using in-house sources, information from previous studies as well as budget price quotations solicited from local suppliers and contractors. Pricing is provided in US Dollars; 1st Quarter 2022 and escalation is not included. The proposed repair work is anticipated to cost anywhere from approximately $220K to $410K, though these are opinion-based ROM costs made by the consultant. In providing this level of opinion, it is recognized that neither the client nor the consultant has control over the cost of labor, equipment, materials, or the contractor's means and methods of determining constructability, pricing, or schedule. These costs are based on the consultant's reasonable professional judgement and experience and does not constitute a warranty, expressed or implied, that contractor's bids or negotiated prices for the work will not vary from the clients. The proposed material quantities and ROM are presented in Tables 3 and 4.

Table 3: Proposed Quantities

Material Quantities MATERIAL Pocket 1 Pocket 2 Pocket 3 Pocket 4 Total

Geotextile Filter Fabric 2000 SF 2000 SF 2000 SF 1600 SF 7600 SF

ACB 2000 SF 2000 SF 2000 SF 1600 SF 7600 SF

Underlayer 130 tons 130 tons 130 tons 104 tons 4934tons

Backfill Material 93 CY 98 CY 65 CY 31 CY 287 CY

Table 4: ROM Costs

ROM Cost

Item Description ROM Cost

F&I Geotextile Filter Fabric (SF) $15,200

F&I ACB (SF) $159,300

F&I Underlayer (Tons) $9,900

Backfill Material (CY) $4,500

Mobilization / Demobilization $19,900

Excavation $5,000

Temporary Construction Measures

$5,000

Equipment $10,000

Total $228,800

Permitting

Permitting will closely mirror the approvals needed from the aforementioned agencies outlined above. It should be noted that this alternative is considered a “hard” or “grey” solution and can sometimes produce backlash form various agencies.

Data Tables

Table 5: Shoreline Slope Data

Shoreline Slope

Location Scarp Height

1-2 2-3 1-3 Horiz.

Distance Vert.

Distance Horiz.

Distance Vert.

Distance Horiz.

Distance Vert.

Distance ft ft ft ft ft ft ft

1 3'-4" 22'-0" 3'-4" 12'-0" 2'-6" 34'-0" 5'-10"

2 3'-6" 23'-0" 3'-2" 12'-0" 2'-6" 35'-0" 5'-8"

3 2'-0" 21'-0" 2'-0" 13'-0" 3'-4" 34'-0" 5'-4"

3.1 NA 0'-0" 0'-0" 10'-0" 6'-0" --- ---

3.25 NA 0'-0" 0'-0" 10'-0" 6'-6" --- ---

4 1'-0" 11'-0" 3'-6" 10'-0" 3'-0" 21'-0" 6'-6"

Table 6: Sonar Data

Sonar Data

Location Feet offshore Time Sounding Depth

Tide El.

(Based on MLLW)

Mudline El.

(Based on MLLW) ft PTZ ft ft ft 0.5S 0 9:02 0 +5.35 5.35

0.5A 15 9:02 5.40 +5.35 -0.05

0.5B 20 9:10 5.50 +5.30 -0.20

0.5C 25 9:15 6.10 +5.25 -0.85

0.5D 30 9:23 6.50 +5.16 -1.34

1S 0 9:02 0.00 +5.35 5.35

1A 15 9:02 4.80 +5.35 0.55

1B 20 9:10 5.60 +5.30 -0.30

1C 25 9:15 6.50 +5.25 -1.25

1D 30 9:23 6.20 +5.16 -1.04

1.5S 0 9:01 0.00 +5.35 5.35

1.5A 15 9:01 5.30 +5.35 0.05

1.5B 20 9:09 5.80 +5.32 -0.48

1.5C 25 9:14 6.30 +5.26 -1.04

1.5D 30 9:22 6.00 +5.17 -0.83

2S 0 9:01 0.00 +5.35 5.35

2A 15 9:01 5.10 +5.35 0.25

2B 20 9:09 5.30 +5.32 0.02

2C 25 9:14 6.30 +5.26 -1.04

2D 30 9:22 6.90 +5.17 -1.73

2.5S 0 9:00 0.00 +5.35 5.35

2.5A 15 9:00 5.50 +5.35 -0.15

2.5B 20 9:08 5.90 +5.33 -0.57

2.5C 25 9:13 7.00 +5.27 -1.73

2.5D 30 9:21 7.80 +5.18 -2.62

Table 6: Sonar Data Continued

Sonar Data

Location Feet offshore Time Sounding Depth

Tide El.

(Based on MLLW)

Mudline El.

(Based on MLLW) ft PTZ ft ft ft 3S 0 9:00 0.00 +5.35 5.35

3A 15 9:00 4.60 +5.35 0.75

3B 20 9:08 5.20 +5.33 0.13

3C 25 9:13 6.20 +5.27 -0.93

3D 30 9:21 7.80 +5.18 -2.62

3.1S 0 9:00 0.00 +5.35 5.35

3.1A 15 9:00 5.60 +5.35 -0.25

3.1B 20 9:07 6.50 +5.34 -1.16

3.1C 25 9:12 7.00 +5.28 -1.72

3.1D 30 9:20 7.10 +5.19 -1.91

3.5S 0 9:25 0.00 +5.14 5.14

3.5A 15 9:25 5.50 +5.14 -0.36

3.5B 20 9:27 6.40 +5.12 -1.28

3.5C 25 9:30 6.10 +5.09 -1.01

3.5D 30 9:32 8.50 +5.07 -3.43

4S 0 9:25 0.00 +5.14 5.14

4A 15 9:25 5.40 +5.14 -0.26

4B 20 9:27 6.00 +5.12 -0.88

4C 25 9:30 6.60 +5.14 -1.46

4D 30 9:32 7.10 +5.07 -2.03

4.5S 0 9:25 0.00 +5.14 5.14

4.5A 15 9:25 5.70 +5.14 -0.56

4.5B 20 9:27 6.00 +5.12 -0.88

4.5C 25 9:30 7.20 +5.09 -2.11

4.5D 30 9:32 7.00 +5.07 -1.93

Inspection Photos: Shoreline Failure 1

Photo 1: Shoreline Failure 1

Photo 2: Scarp height from Shoreline Failure 1

Inspection Photos: Shoreline Failure 2

Photo 3: Shoreline Failure 2

Photo 4: Scarp height from Shoreline Failure 2

Inspection Photos: Shoreline Failure 3

Photo 5: Shoreline Failure 3

Photo 6: Scarp height from Shoreline Failure 3

Inspection Photos: Shoreline Failure 4

Photo 7: Shoreline Failure 4

Photo 8: Rock toe from Shoreline Failure 4

Inspection Photos: Rock Sizing

Photo 9: Rock sizing from 1-3 inches in diameter

Photo 10: Rock sizing from 4-8 inches in diameter

Photo 11: Rock sizing from 9-14 inches in diameter

Photo 12: Varies rock sizes

Inspection Photos: Geotextile Filter Fabric

Photo 13: Geotextile filter fabric

Inspection Photos: Posted Signage

Photo 14: No Trespassing Signage

Photo 15: Least Tern Natural Preserve Signage

Shoreline Erosion Over Time

Photo 16: Island aerial from 2015 Photo 17: Island aerial from 2017

Photo 18: Island aerial from 2020 Photo 19: Island aerial from 2022 across Draft Print

Appendix