B08_Attach_7_PMIS_236143_Final_Specifications_-_Appendix_F.pdf

National Park Service U.S. Department of the Interior

Pacific West Regional Office Seattle

909 First Avenue Suite 500 Seattle, WA 98104 206-220-4258 phone

PACIFIC WEST REGIONAL OFFICE Memorandum DATE: September 6, 2016

FROM: Regional Civil Engineer, Pacific West Region (PWR)

TO: Jim Richardson, Superintendent, American Memorial Park, Saipan

SUBJECT: Damaged Seawall, American Memorial Park, Saipan

On March 16-18, 2016, I traveled to American Memorial Park in Saipan to evaluate damage from Typhoon Soudelor (which struck the island on August 3, 2015) and to assist in developing long- and short-term projects. Refer to trip report dated March 28, 2016 (Appendix A).

During the trip, the Superintendent requested that I evaluate damage to the seawall along the west causeway at the entrance channel to Smiling Cove Marina as well as damage at the eastern end of the causeway, and present technical solutions for its repair and/or replacement with budgetary estimates for design and construction. Refer to the aerial map in Figure 1 below.

Figure 1: Aerial Map of American Memorial Park

BACKGROUND:

It is believed that the original seawall along the west face of the west causeway was constructed 40-50 years ago, and possibly as early as the end of WWII. The original seawall was constructed of approximately 800 feet of steel sheet pile wall at the northern-most section and approximately 1,200 feet of a (woven mattress) fabric formed concrete from the end of the sheet pile wall to the boat ramp. Note that the same fabric formed concrete is also used sporadically along the south embankment at Smiling Cove Marina and as formwork to build a man-made island that serves as a breakwater for Smiling Cove Marina.

In 2006, there were several tropical storms on Saipan that caused serious erosion issues throughout the park. The steel sheet pile wall had been corroding and failing for some time, with indications that sections had been repaired with rock backfill and gabions, but the tropical storms accelerated damage to the seawall and erosion of the causeway, resulting in the park submitting PMIS Project #130448 – Storm Damage Repairs Following Tropical Cyclones (Appendix B).

The NPS hired Winzler & Kelly Consulting Engineers (now GHD) to complete the initial seawall inspection and scoping of alternatives. Winzler & Kelly’s findings and recommendation are outlined in a report entitled: American Memorial Park, Damage to Outer Channel of Marina Repair Assessment dated January 22, 2007 (Appendix C).

In this report, Winzler & Kelly evaluated five alternatives including:

1. Backfill and Grade (Short-term 1-5 years, or until the next large typhoon).

2. Gabions and Backfill (Mid-term 1-10 years *).

3. Backfill, Grade, and Rock Armor (Mid-term 1-10 years *).

4. Concrete Retaining Wall and Backfill (Mid-term 5-10 years *).

5. Steel Sheet Pile Wall and Backfill (Long-term > 20 years).

(* Dependent upon the continued viability of the existing sheet pile wall)

The NPS concurred with the findings / recommendation from the Winzler & Kelly report by selecting Alternative 5 for further development. Geotechnical work was completed by Geotesting, Inc. with the results documented in a report entitled: Geotechnical Investigation, Seawall Replacement, Smiling Cove Marina dated February 20, 2008 (Appendix D).

Based on the Winzler & Kelly assessment report, the NPS completed an Environmental Assessment entitled Replace Seawall at Smiling Cove Marina dated May 2008 (Appendix E) and the subsequent Finding of No Significant Impact (Appendix F). The preferred alternative included: Replacement of the 800 feet sheet pile wall with a wall of interlocking steel sheet piles; replacement of 70 feet of the fabric formed concrete with an armored slope of large rip rap rock just south of the new wall; and reconstruction of the west causeway land area. The rock-armored face at the northern tip of the causeway was in good condition and did not require repair.

The NPS hired Winzler & Kelly Consulting Engineers to complete all design and permitting for the preferred alternative. Drawing No. 483 / 41,009 entitled Sea Wall Replacement dated June 2008 (Appendix G) and the project specifications outline the requirements for construction.

The NPS contracted with GPPC, Inc. in 2009 to complete the construction phase of the project.

Construction costs ~ $4,911,195. Onsite work began in May 2009 and was completed in February 2010.

The photos below show the completed sheet pile wall, the armored slope of large rip rap rock, and the reconstructed causeway with added parking and access road.

Photo 1: New Sheet Pile Seawall & Causeway (800 ft) Photo 2: New Armored Slope of Rip Rap Rock (70 ft)

STORM DAMAGE ASSESSMENT:

In recent years, tropical storms have accelerated damage to the (woven mattress) fabric formed concrete seawall and erosion of the west causeway in the area just south of the new armored slope of rip rap rock.

In addition, the east facing shoreline of the east causeway is slowly eroding. Refer to the aerial map in Figure 2 below as well as the associated Photos 3, 4, & 5.

Figure 2: Aerial Map of Seawall / Shoreline Damage

Photo 3: Damaged Seawall (8/12/2016)

Photos 4 /5: Erosion of East Facing Shoreline at Paved Cul-de-Sac / Bus Turnaround on East Causeway (3/17/2016)

The damage to the seawall along the west causeway is spread out over an estimated 250 linear feet, marked by two large and multiple small collapse areas of the fabric formed concrete that makes up the outer face of the seawall. As the concrete collapses, the gravel / earthen subbase behind the seawall is washed out to sea with regular tidal wave action and tropical storm surge, thus, further weakening the seawall, eroding the man-made causeway, and damaging the road that accesses the east causeway boat slips. As of August 2016, the voids within the large collapse areas are estimated to extend very close to, if not directly beneath, the edge of the access road on the causeway. Additional photos of the damage from February 2013 until June 2016, and field notes from June 2016, are attached (Appendix H).

The damage to the east facing shoreline of the east causeway is spread out over an estimated 300 linear feet, marked by erosion of the gravel / earthen base that supports the causeway. This erosion is most notable along a 50-foot stretch at the end of the road, threatening to undermine the paved cul-de-sac where buses turn around, and cutoff access to boat slips on the east side of the outer cove marina.

ALTERNATIVES FOR CONSIDERATION – LONG-TERM REPAIR:

The alternatives to repair the existing seawall damage and shoreline erosion are similar to the alternatives considered under PMIS Project #130448 – Storm Damage Repairs Following Tropical Cyclones. Below is a brief description of the alternatives along with a table showing their estimated longevity and ballpark unit cost estimates (for construction only).

Alternative 1 – Backfill and Grade – EAST CAUSEWAY ONLY Alternative 2 – Rock-Filled Gabions, Backfill, and Grade Alternative 3 – Rock Armor, Backfill, and Grade Alternative 4 – Vertical Concrete Retaining Wall, Backfill, and Grade Alternative 5 – Steel Sheet Pile Wall, Backfill, and Grade – WEST CAUSEWAY ONLY Alternative 6 – (Woven Mattress) Fabric Formed Concrete Wall

Alt # Description Estimated Longevity (Yrs) Unit Costs $/LF 1 Backfill and Grade Short-term 1-2 years or next typhoon $546 2 Gabions, Backfill, Grade Short-term 5-10 years $1,855 3 Rock Armor, Backfill, Grade Mid-term 10-15 years (or more) $1,680 4 Concrete Retaining Wall Mid-term 10-15 years (or more) $2,231 5 Steel Sheet Pile Wall Long-term > 20 years $8,249 6 Fabric Formed Concrete Wall Mid-term 10-15 years (or more) $1,639

Note 1: Unit Costs for Alternatives #1-4 were based upon figures from Table 2 of the Winzler & Kelly report: American Memorial Park, Damage to Outer Channel of Marina Repair Assessment dated January 22, 2007. As outlined in the report: “The repair concepts and related cost estimates developed in Table 2 can be directly applied to spot repair areas by doubling the unit cost and multiplying it times the desired length. This is a simplified approach to account for higher unit costs when constructing smaller quantities. It is important to note, this is not a precise method to estimate the actual cost of constructing smaller quantities and the doubling factor would get closer to 1.0 as the quantity is increased closer to the full length quantity. However, it should suffice for budgetary purposes.” The unit costs for Alt#1-4 include typical NPS markups plus 3% inflation from 2009 (date of estimate) to 2019 (estimated construction).

Note 2: Unit Cost for Alternative #5 was derived from the actual construction cost of $4,911,195 (in 2009) ÷ 800 LF = $6,139 + 3% inflation over 10 years = $8,249. As a cost comparative, doubling the unit costs from Table 2 and adding 3% inflation over 10 years yields a unit cost estimate of $10,665. $8,249 was used as a more likely unit cost estimate.

Note 3: Unit Cost for Alternative #6 was derived from an internet search of similar installations plus the typical NPS markups plus 3% inflation over 3 years = $1,639.

COST ESTIMATE:

Damaged Seawall (West Causeway) – Long-Term Repair

Alt # Description Unit Costs Qty (LF) Total Construction Cost 1 Backfill and Grade $546 250 Not considered 2 Gabions, Backfill, Grade $1,855 250 $463,750 3 Rock Armor, Backfill, Grade $1,680 250 $420,000 4 Concrete Retaining Wall $2,231 250 $557,750 5 Steel Sheet Pile Wall $8,249 250 $2,062250 6 Fabric Formed Concrete Wall $1,639 250 $409,750

Eroded Shoreline (East Causeway) – Long-Term Repair

Alt # Description Unit Costs Qty (LF) Total Construction Cost 1 Backfill and Grade $546 50 $27,300 2 Gabions, Backfill, Grade $1,855 50 $92,750 3 Rock Armor, Backfill, Grade $1,680 50 $84,000 4 Concrete Retaining Wall $2,231 50 $111,550 5 Steel Sheet Pile Wall $8,249 50 Not considered 6 Fabric Formed Concrete Wall $1,639 50 $81,950

ALTERNATIVES FOR CONSIDERATION – EMERGENCY SHORT-TERM REPAIR:

The alternatives to complete an emergency short-term repair of the existing seawall (pictured in Photo #3) are similar to the long-term repairs, with similar unit costs and a smaller quantity (40 linear feet, estimated from photographs). Not all the alternatives considered under long-term repairs are valid or feasible for short-term repairs. And no short-term repair options have been provided for the eroded shoreline at the east causeway, as this is not considered an emergency. Below is a brief description of the alternatives along with a table showing their ballpark unit cost estimates (for construction only).

Alternative 1 – Backfill and Grade – NOT VALID Alternative 2 – Rock-Filled Gabions, Backfill, and Grade Alternative 3 – Rock Armor, Backfill, and Grade Alternative 4 – Vertical Concrete Retaining Wall, Backfill, and Grade – NOT VALID / FEASIBLE Alternative 5 – Steel Sheet Pile Wall, Backfill, and Grade – NOT VALID / FEASIBLE Alternative 6 – (Woven Mattress) Fabric Formed Concrete Wall

COST ESTIMATE:

Damaged Seawall (West Causeway) – Emergency Short-Term Repair

Alt # Description Unit Costs Qty (LF) Total Construction Cost 1 Backfill and Grade $546 40 Not considered 2 Gabions, Backfill, Grade $1,855 40 $74,200 3 Rock Armor, Backfill, Grade $1,680 40 $67,200 4 Concrete Retaining Wall $2,231 40 Not considered 5 Steel Sheet Pile Wall $8,249 40 Not considered 6 Fabric Formed Concrete Wall $1,639 40 $65,560

RECOMMENDATIONS:

LONG-TERM REPAIR:

Based on existing conditions, existing terrain, existing use of the causeway, durability, longevity, material availability on island, and costs, I would recommend Alternative #3 (Rock Armor, Backfill, and Grade) for both the damaged seawall @ $420,000 + eroded shoreline @ $84,000 for a total estimated construction cost = $504,000.

Note that this recommendation should also be evaluated against the other alternatives in a value based decision–making process and an environmental assessment.

SHORT-TERM EMERGENCY REPAIR:

Based on existing conditions, existing terrain, existing use of the causeway, material availability on island, and costs, I would recommend Alternative #3 (Rock Armor, Backfill, and Grade) for the failed section of seawall for a total estimated construction cost = $67,200.

The fabric formed concrete wall alternative should also be considered if obtaining large rock armor or heavy equipment to move large rock on island is problematic or infeasible.

CLIMATE CHANGE CONSIDERATIONS (primarily for long-term repair work):

According to the Climate Change Vulnerability Assessment for the Island of Saipan, CNMI dated January 2014, which was completed by various agencies that were part of a Climate Change Working Group (Appendix I), the park can expect sea level rise and continued coastal erosion as a result of climate change. The level of rise is unclear and based on many factors. Local variability of El Nino and La Nina episodes will also affect sea levels. The effects from climate change should be a consideration when considering the alternatives.

REQUIRED PERMITS (for all long-term and short-term repair work):

1. Army Corps of Engineers (ACOE) Nationwide Permit 3 (Section 10 of the rivers and Harbors Act and Section 404 of the Clean Water Act).

2. Commonwealth of Northern Marianas Islands (CNMI), Department of Environmental Quality (DEQ), Earthmoving & Erosion Control Permit with review by CNMI, Historic Preservation Office and Division of Fish & Wildlife.

3. Commonwealth of Northern Marianas Islands (CNMI), Department of Environmental Quality (DEQ), Section 401 Water Quality Certification.

4. Commonwealth of Northern Marianas Islands (CNMI), Division of Coastal Resources Management (DCRM), Shoreline APC Permit (Coastal Zone Management Act).

Scott Henrickson, P.E., PMP /s/ Scott Henrickson Regional Civil Engineer

Cc: Theo Chargualaf, Facility Manager, WAPA-AMME Dave Kruse, Facility Manager, PWR Lucy Gonyea, Repair-Rehabilitation Funding Program Manager, PWR Debbie Campbell, Line Item Program Manager, PWR Melia Lane-Kamahele, Office Manager, PWRH

Enclosures:

Appendix A – PWR Engineer Trip Report 3-17-16 Appendix B – PMIS #130448 Appendix C – Scoping Report (2007) Appendix D – Geotech Report (2008) Appendix E – EA Seawall (2008) Appendix F – FONSI Seawall (2008) Appendix G - Construction Drawings (2009) Appendix H – Photos-Field Notes (2016) Appendix I – Climate Change Assessment (2014)