North Topsail Beach North End Sand Bag Revetment Maintenance Plan
Presented to:
Town of North Topsail Beach
Prepared by:
Coastal Planning & Engineering of North Carolina, Inc.
May 14, 2015
North Topsail Beach North End Sand Bag Revetment Maintenance Plan
Table of Contents
Introduction ........................................................................................................................................1
Construction .......................................................................................................................................2
Maintenance .......................................................................................................................................8
List of Figures
Figure No.
1
2
3
4
5
6
7
8
9
10
11
12
Cross section of the permitted sand bag revetment at approximately
Station 7+00 ......................................................................................................................2
Northernmost temporary containment tube installed December 13, 2014 .......................3
Southernmost temporary containment tube installed December 22, 2014 .......................3
Installation of base and 2nd layer of bags along the northern 145 ft.
of the revetment between December 29, 2014 and January 1, 2015 ................................4
Installation of base and 2nd layer of bags along the northern 145 ft.
of revetment between December 29, 2014 and January 1, 2015 ......................................4
Representative cross section showing the revised design used to construct
the revetment from stations 3+91 to 15+36 ......................................................................5
Two typical cross sections showing the area between the erosional scarp
(left side) and the tie in point for the proposed backfill. Authorized
additional backfill to raise the elevation of the area seaward of the proposed
backfill to 4.0 ft. NAVD88 is shaded in yellow ...............................................................6
Representative cross section showing design used to construct the
northern extension .............................................................................................................7
Plan view drawing showing design used to construct the northern extension ..................7
Photos showing examples of sewn repairs to sand bags ...................................................9
Photos showing examples of patched repairs to sand bags...............................................10
Photo showing an example of where the filter fabric has fallen down
from the top of the revetment............................................................................................11
i COASTAL PLANNING & ENGINEERING OF NORTH CAROLINA, INC. SandBagMaintenancePlan:
INTRODUCTION
The Town of North Topsail Beach completed Phase 1 of its beach and inlet management plan in February
2013. Phase 1 included relocating the main bar channel of New River Inlet to a preferred position and
alignment with deposition of the dredged material along approximately 7,730 feet of the Town’s shoreline
south of New River Inlet. The intent of the bar channel relocation was to induce a build-up of material on
the south side of New River Inlet which would eventually result in accretion along the northern portion of
the Town’s shoreline. CPE-NC stated in the engineering report associated with the Final Environmental
Impact Statement (EIS) that predictions of the actual time for the shoreline between stations 1140+00
(area from between Buildings #5 and #6 of Topsail Reef) and 1160+00 (south shoulder of New River
Inlet) to respond to the new channel cannot be made with a high degree of certainty; however, significant
accretion should occur within 5 years with full recovery occurring within 15 years following the channel
relocation (CPE-NC, 2009). These projections were based on the implementation of a channel
maintenance program that would maintain the channel in the preferred location.
The northern portion of the project from baseline station 1140+00 north to the inlet has experienced
inordinate erosion with most of the fill material placed in this area being eroded as of September 2014.
The loss of the fill material placed the homes north of Topsail Reef in imminent danger requiring interim
erosion response measures to prevent the loss of homes and roads until such time that long term
protection is established.
The Town began pursuing an emergency permit in August 2014 to install a sand bag revetment along the
portion of the Phase 1 project north of the Topsail Reefs. The state permit was received in late November
and federal authorizations were received in early December. The permitted revetment included a 5-stack
configuration of sand bags, with sand backfilled landward of the structure. Figure 1 shows a cross section
of the permitted revetment. The base width of the revetment was permitted at 30 ft. wide, composed of
two 15-foot long bags laid end to end in a shore-perpendicular fashion. The structure was to be
constructed at grade and was assumed to achieve a height of approximately 7.5 ft. as measured from the
base of the bottom bag to the top of the uppermost bag. The backfill, shown in Figure 1 as the gray
shaded area landward of the structure was designed to extend 5 feet landward of the top of the uppermost
bag and then slope down to grade on a 1V:3H slope.
Also included in the permitted design was a temporary containment tube, which was proposed by the
contractor for the purposes of construction. The temporary containment tube would be installed first to
slow the erosion of sand from the project area and allow for a sheltered work environment landward of
the containment tube in which the revetment could be constructed. The Town and the Topsail Reefs
Home Owner’s Association agreed to the condition that the temporary containment tube would not come
within 50 ft. of the Topsail Reefs sand bag revetment.
1 COASTAL PLANNING & ENGINEERING OF NORTH CAROLINA, INC. Figure 1. Cross section of the permitted sand bag revetment at approximately Station 7+00.
CONSTRUCTION
Mobilization of equipment for the construction of the sand bag revetment project began on December 9,
2014. The first containment tube was placed on December 13, 2014 (Figure 2). The 10th tube was placed
on December 22, 2014 (Figure 3). The original plan was that the tube would extend south along the
shoreline and terminate in a shore parallel orientation 50 ft. away from the Topsail Reefs revetment.
However, during the installation of the tube, the contractors and CPE-NC onsite observers observed high
velocities during ebbing tides that if channeled toward the Topsail Reefs revetment could have caused
scour around the base of the return wall. The contractor and CPE-NC agreed to turn the southern end of
the geotube toward shore and tie into high ground prior to shutting down for the Christmas break. Figure
3 shows the final orientation of the southernmost temporary containment tube.
2 COASTAL PLANNING & ENGINEERING OF NORTH CAROLINA, INC. Figure 2. Northernmost temporary containment tube installed December 13, 2014.
Figure 3. Southernmost temporary containment tube installed December 22, 2014.
The contractor returned to the project site on December 28, 2014 and began laying the base layer of bags
in the vicinity of 2378 New River Inlet Road on the northern end of the project area. During the
installation of the initial bags, the contractor recommended to CPE-NC that the design be reconsidered
with respect to the shore parallel bag proposed to be installed along the landward edge of the 2nd layer.
The concern was that this bag could potentially be scoured our during installation and role landward
damaging structures. CPE-NC approved the change and provided a revised design that shifted the 2nd
layer landward so that the landward edge of the bag aligned with the bags placed above the 2nd layer.
Layer 2 through 5 would be offset 5 feet seaward from the landward edge of the base layer. The base
layer and second layer were installed along the northern 145 feet of the revetment between December 29
and January 1 (Figure 4).
3 COASTAL PLANNING & ENGINEERING OF NORTH CAROLINA, INC. Figure 4. Installation of base and 2nd layer of bags along the northern 145 ft. of the revetment between
December 29, 2014 and January 1, 2015.
The contractor began installing bags along the south end of the project area on January 2, 2015. Between
January 2 and January 7, 2015 the contractor completed the southern 125 ft. of the revetment with 5
stacks of bags (Figure 5). This section of the revetment ran from the Topsail Reefs sand bag revetment up
to the southern edge of the southernmost containment tube.
Figure 5. Installation of base and 2nd layer of bags along the northern 145 ft. of the revetment between
December 29, 2014 and January 1, 2015.
4 COASTAL PLANNING & ENGINEERING OF NORTH CAROLINA, INC. On January 4, 2015, the contractor notified CPE-NC that the bags were filling to a much higher
dimension, which would result in a higher finished elevation; however, in achieving a greater height the
filled bag width was less than anticipated. If the project were to have been constructed as designed, the
finished revetment would have been approximately 2 ft. higher than the design; however, significantly
more bags would be required due to the bag width achieved. Discussions between the contractor and
CPE-NC also included the option of placing additional sand landward of the temporary containment tube
in order to raise the base elevation to achieve a higher finished elevation of the revetment. CPE-NC
requested survey data from the contractor so that modifications of the design could be considered.
On January 8, 2015 the contractor began installing bags from 2304 New River Inlet Road (approximate
station 3+91) south toward the southernmost containment tube. The contractor installed the base 2 layers
of the revetment over the course of several days. On January 9, 2015, CPE-NC provided the contractor
with an updated design for the sand bag revetment. This design change revised the number of stacks in
the revetment from 5 stacks to 4 stacks. The section of the revetment from station 3+91 south to station
1+25 was constructed as follows: Layer 1 – 2 15-foot bags laid end to end, Layer 2 and 3 – 1 15-foot bag
offset 5 ft. seaward of the landward edge of the landwardmost base bag, Layer 4 – 1 12.5-foot bag with
the landward edge aligned with Layer 2 and 3. On January 14, 2015 the contractor cut through the
southernmost containment tube in order to tie into the previously constructed section to the south.
On January 16, 2015 CPE-NC provided the contractor with a revised design for which the remainder of
the revetment should be constructed (Stations 3+91 to 15+36). Figure 6 shows the revised cross section.
The section from Stations 3+91 to 15+36 was constructed as follows: Layer 1 – 2 15-foot bags laid end
to end, Layer 2 – 1 15-foot bag offset 5 ft. seaward of the landward edge of the landward most base bag,
Layer 3 – 1 12.5-foot bag with the landward edge aligned with Layer 2, and Layer 4 – 1 10-foot bag with
the landward edge aligned with Layer 2 and 3. The revised design also included adding fill to any area
necessary in order to establish a base grade elevation of 0.0 ft. NAVD88 on which the sand bag revetment
was constructed (Figure 6).
Figure 6. Representative cross section showing the revised design used to construct the revetment from
stations 3+91 to 15+36.
On January 16, 2015 CPE-NC provided the contractor with a revised design for which the remainder of
the revetment should be constructed (Stations 3+91 to 15+36). Figure 6 shows the revised cross section.
The section from stations 3+91 to 15+36 was constructed as follows: Layer 1 – 2 15-foot bags laid end to
end, Layer 2 – 1 15-foot bag offset 5 ft. seaward of the landward edge of the landwardmost base bag,
5 COASTAL PLANNING & ENGINEERING OF NORTH CAROLINA, INC. Layer 3 – 1 12.5-foot bag with the landward edge aligned with Layer 2, and Layer 4 – 1 10-foot bag with
the landward edge aligned with Layer 2 and 3. The revised design also included adding fill to any area
necessary in order to establish a base grade elevation of 0.0 ft. NAVD88 on which the sand bag revetment
was constructed (Figure 6).
Continued erosion between the time initial designs were developed and the time that installation of the
temporary containment tube was completed, resulted in the lowering of the beach profile along the project
area. Surveys conducted in mid-January indicated elevations at which the base of the backfill will tie into
the existing grade ranges from -0.5 ft. NAVD88 to +2.0 ft. NAVD88 along a significant portion of the
central and northern portion of the revetment. On January 20, 2015 CPE-NC recommended the Town
authorize the contractor to fill the area between the landward toe of the backfill and the erosion scarp to
an elevation of 4.0 ft. NAVD88 as shown in Figure 7. The Town authorized this additional fill to reduce
the risk of the backfill being washed down into lower lying areas landward of the revetment during events
where water overtops the crest height of the sand bags, exposing the landward side of the revetment.
Figure 7. Two typical cross sections showing the area between the erosional scarp (left side) and the tie
in point for the proposed backfill. Authorized additional backfill to raise the elevation of the area seaward
of the proposed backfill to 4.0 ft. NAVD88 is shaded in yellow.
On February 5, 2015 the Town authorized CMS to construct the northern extension of the revetment. The
extension was constructed from the northern return wall of the initial structure located to the northeast of
2378 New River Inlet Road northeast to the north side of the structure located at 2392 New River Inlet
Road. Due to time constraints, the Town applied for and obtained a general permit for the northern
6 COASTAL PLANNING & ENGINEERING OF NORTH CAROLINA, INC. extension, which limited the size of the structure to a 20 ft. width and 6 ft. height. Figure 8 shows the
cross section of the permitted structure and Figure 9 shows the plan view.
Figure 8. Representative cross section showing design used to construct the northern extension.
Figure 9. Plan view drawing showing design used to construct the northern extension.
Construction of both the original sand bag revetment extending approximately 1,536 ft. north from the
Topsail Reefs, and the northern extension were substantially completed on February 25, 2015.
7 COASTAL PLANNING & ENGINEERING OF NORTH CAROLINA, INC. MAINTENANCE
The State of North Carolina allows sand bag revetments to “temporarily protect imminently threatened
oceanfront structures”. The state recognizes that if left in place permanently, sand bag revetments act as
hard structures and can cause damage to the beach. For this reason the state requires a time limit for
which such revetments can stay in place. Likewise, the state limits the design specifications for such
structures to ensure that they will be temporary. In that regard, the nature of sand bag revetments as
permitted by the state, require maintenance.
A description of expected maintenance activities are described below. The maintenance activities have
been divided into those actions the Town of North Topsail Beach may undertake and those actions to be
undertaken by property owners.
Town of North Topsail Beach:
Replacement Bags: As previously mentioned, from time to time it is expected that sand bags may need
to be replaced or additional bags added to maintain the integrity of the revetment until such time that the
shoreline has been stabilized. The Town will develop a Request for Quotes (RFQ) and advertise to
eligible contractors that could install replacement bags on an as needed basis. The intent of the Town is
to execute an agreement with a contractor to retain their services to install additional bags as needed to
maintain the structure as built.
The scope outlined in the RFQ should include at a minimum:
The CONTRACTOR shall provide the labor, equipment, supplies, and materials to repair and replace
damaged sand bags as required to maintain the initial structure constructed between December 13, 2014
and February 25, 2015.
Sand Bags, defined as hydraulic filled geosynthetic containers, shall be filled by using a slurry mixture
that is pumped into each container. The Sand Bag shall be sealed according to the manufacturer's
recommendations which include a self-sealing filling port system. The material needed to fill the sand
tubes and sand bags will be obtained from the nearshore seaward of MLW.
Equipment to be used for excavation of sand shall be described in the submittal. Filling shall occur in
place along the revetment where replacement bags are required. Care shall be taken during filling so as
not to cause tearing of the seams around the fill ports. Before and during filling, the Sand Bags shall be
prevented from shifting from the existing alignment. The Sand Bags shall be filled to the maximum
capacity to achieve a fill volume of 85%. Care shall be taken not to puncture or damage the Sand Bag
during this process, and at no time shall mechanical or hydraulic powered equipment be used to tamp,
compress or attempt to move the filled unit. Failed seams or ruptures in the sand bags shall be repaired or
replaced and filled to the required elevation.
The RFQ should request a per bag installation cost for multiple ranges of bags (i.e. Cost for replacement
of 1 – 10 bags, Cost for replacement of 11 – 20 bags, Cost for replacement of 21 – 50 bags, etc.) and the
cost to install the different size bags listed below. The RFQ should also request a cost for site visit to
repair or patch a damaged bag.
8 COASTAL PLANNING & ENGINEERING OF NORTH CAROLINA, INC. Pre-Purchase of Sand Bags: The sand bags used to construct the Town’s sand bag revetment were
provided by Macaferri, Inc. As a courtesy to the Town, Macaferri provided the following quotes for
MacBag OS150 bags in the event that the Town wanted to pre-purchase bags wholesale to have on site
for the selected contractor to fill the bags as needed.
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MacBag OS150 - 5' x 15'
MacBag OS150 - 5' x 12.5'
MacBag OS150 - 5 'x 10'
$83.75/bag + freight
$74.69/bag + freight
$53.13/bag + freight
($1,675.00/pallet + $145 freight)
($1,493.80/pallet + $145 freight)
($1,062.60/pallet + $145 freight)
The bags quoted herein are the same bags used to construct the project. If the Town wishes to purchase
bags direct from the original supplier, they may do so by contacting Rusty Payne at Telephone Number:
(301) 223-6910 or Cell Number: (240) 520-0092. In the event that the Town does not wish to prepurchase bags, CPE-NC can provide sand bag specifications to include in the RFQ upon request.
Patching Ruptured Bags: From time to time, sand bags and tubes may rip or tear due to pressure on the
bags or impacts from sharp objects. If damage is observed, further inspection should be conducted to
identify whether the damage extends down underneath the bag. In the event that the damage is
underneath, a patch may be tried; however, it is unlikely to be able to contain or repair fabric in that
location and the bag may need to be replaced. For other damage locations, depending on the size and
orientation of the tear, a number of remedies are available. If the fabric is torn in such a way that the
material can be pulled back together, a type of braided line with a wax coating can be used to sew the
edges together. Materials needed are sewing needles, sewing thread, 3M 5200 Marine adhesive, and
sandbag patching fabric. Figure 10 shows examples of a sewn repair to sand bags.
Figure 10. Photos showing examples of sewn repairs to sand bags.
If the edges cannot be sewn together a patch can be used to close the tear. Patches are typically composed
of the same material as the filter fabric. A patch is cut to the appropriate size and 3M 5200 Marine
Adhesive is used to attach the patch to the bag or tube. Figure 11 shows examples of patched repairs to
sand bags. Sand can be piled onto the patch to apply pressure while the adhesive is curing.
9 COASTAL PLANNING & ENGINEERING OF NORTH CAROLINA, INC. Figure 11. Photos showing examples of patched repairs to sand bags.
The recommended patching procedure is as follows:
a) First clean around the damaged area to determine the dimensions of the breach.
b) If the sand has been removed from the bag, place and compact the void to the best result possible,
c) Use the sewing needle and thread to attempt stitching the void closed or to put the fabric into
tension. Try to suture the fabric along the outside of the breach by at least 1 to 2 inches around
the entire tear.
d) Clean sand and dry the area around the repaired segment.
e) Cut the fabric to size in a circular or oval shape to include an additional 3 to 4 inches along the
perimeter of the damaged area so as to allow 3 to 4 inches of overlapping between the patch and
the existing bag material.
f) Apply marine adhesive to the sandbag patch limits along the perimeter of the damaged area.
g) Take a sewing needle and thread to sew the outside edge of the patch (1 inch) to the sandbag.
The Town has been provided with braided line and needles for use if sewing is feasible to repair a
damaged bag or tube. Likewise, filter fabric has been provided to the Town to allow for patches to be cut
to size depending on the size of the damaged area. 3M 5200 Marine Adhesive is available at retail
suppliers as well as online distributors.
For more information on repairing bags, please contact Mr. Rusty Payne with Macaferri, Inc. at
Telephone Number: (301) 223-6910 or Cell Number: (240) 520-0092. Mr. Payne has also offered to
conduct a site visit and train Town staff on repairing sand bags.
Managing Filter Fabric: As previously stated, the amount of erosion that occurred prior to the
installation of the temporary containment tube lowered the elevation of the backfill landward of the
revetment. The Town authorized placement of sand between the revetment and the erosion scarp to
achieve a uniform 4.0 ft. NAVD88 elevation. However, this still leaves a portion of the back of the
revetment exposed. The method used by the contractor to hold the filter fabric in place along the majority
of the main 1,536 ft. section of the revetment north of the Topsail Reefs, was only meant to temporarily
hold the fabric in place until such time as backfill could be placed. All backfill required by the design
10 COASTAL PLANNING & ENGINEERING OF NORTH CAROLINA, INC. was placed; however, due to frequent overtopping, the backfill has since washed back onto the portion of
the backfill raised to elevation 4.0 ft. NAVD88. Because the backfill is not staying in place, the filter
fabric has fallen in some areas.
CPE-NC recommends the Town leave the filter fabric attached, in the event that additional bags or sand
are placed landward of the revetment. At that time, the filter fabric can be uncovered and pulled up so
that the filter fabric barrier is maintained at a higher elevation. Tacking the fabric to the bags is not
recommended.
Figure 12. Photo showing an example of where the filter fabric has fallen down from the top of the
revetment.
Request for Inspection: The Town may request an inspection by a CPE-NC representative at any time.
The request should be submitted to the project manager who will coordinate with Town staff regarding
the time to conduct the inspection. The inspection will include one trip to the site to perform a site visit
and inspection of the revetment. CPE-NC will then prepare an inspection report to include:
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A description of the condition of the revetment;
A description of any recommended maintenance;
Photographs of any areas in need of maintenance; and
A cost estimate for the recommended maintenance.
The standard price for an inspection is $2,953.00.
11 COASTAL PLANNING & ENGINEERING OF NORTH CAROLINA, INC. Property Owners:
Placement of Additional Bags: In order to obtain a permit for the 1,536 ft. section of the revetment
directly north of Topsail Reefs, a variance was requested and approved by the North Carolina Coastal
Resources Commission. The variance was issued on November 19, 2014. The variance allowed for the
construction of a sand bag revetment 45 ft. wide and up to an elevation of 12.0 ft. NAVD88. Upon
receiving bids from contractors for the project and due to continued erosion along the project area, the
Town and its engineers made several design modifications. These design modifications were ultimately
incorporated into the permit issued by the North Carolina Division of Coastal Management on November
26, 2014. As previously discussed, the permit allowed for a total footprint of 45 ft., which included both
the temporary containment tube and the revetment with base width of 30 ft. The permitted elevation of
the revetment was 12.0 ft. NAVD88. The as-built structure ranges in elevation from a minimum of 7.0 ft.
NAVD88 to achieving the design elevation of 12.0 ft. NAVD88 along the southern end where the base
grade elevation was highest.
If individual property owners wish to add bags to the revetment the process would be as follows:
1. Provide the Town of North Topsail Beach a design plan for adding additional bags. The plan,
which must be approved by an engineer, should include plan view and cross section diagrams
showing the configuration of the proposed bags. The proposed action should not exceed the
limits authorized in the variance issued by the CRC to the Town. If the design were to exceed
the limits authorized by the variance, the individual would have to go through a separate variance
process. The Town will review the plan and approve if satisfactory.
2. The existing Major CAMA Permit (92-14) would need to be modified to include the individual
property owner as a designated agent on the permit. This process would require a letter from the
Town requesting the modification and a $100 fee to be paid to the Division of Coastal
Management. Multiple property owners could be added to the permit under the same
modification for the single $100 modification permit fee.
3. The Property owner must apply for a permit to the Town to implement the improvements.
Placement of Additional Sand: As previously mentioned, during construction fill was added to the
area landward of the revetment to achieve an elevation of approximately 4.0 ft. NAVD88. If an
individual property owner desires to add fill to their property landward of the revetment a CAMA Minor
permit is required. Property owners can find the minor permit application on the Division of Coastal
Management’s website at: http://portal.ncdenr.org/c/document_library/get_file?uuid=5775e8eb-a50a44d9-b8c0-ef2f092f107a&groupId=38319. A $100 permit fee is required to process the application.
Applicants will be required to provide a sample of the fill to DCM staff to ensure that the material to be
placed is beach compatible.
12 COASTAL PLANNING & ENGINEERING OF NORTH CAROLINA, INC. LIABILITYSTATEMENT:
CPE-NC is providing this maintenance plan to the Town of North Topsail Beach as a general guide for
maintenance and repair of the sandbag revetment. CPE-NC will perform observations of the sand bag
revetment at the request of the Town of North Topsail Beach. CPE-NC will document the readily
observable portion of the structure during these visits and provide recommendations for repair based on
the conditions of the revetment at that time. Damage to the structure may not be visible during a site visit
or may occur after a site visit. CPE-NC will not perform invasive tests to document the condition of the
revetment. Observation of the sand bag revetment does not imply a guarantee of the future performance
of the sand bag revetment. While CPE-NC can provide guidance that follows the manufacturer’s
recommendation, CPE-NC is not responsible for the quality of any work performed to maintain or repair
the sandbag revetment.
13 COASTAL PLANNING & ENGINEERING OF NORTH CAROLINA, INC.