Phase 5 $8000000 - Town of North Topsail Beach

Town of North Topsail Beach
Shoreline Protection Presentation
Future Planning
November 1, 2012
Disposal Area 143
ƒ
ƒ
ƒ
ƒ
ƒ
ƒ
Cores collected from island in December 2011
Geotechnical analysis completed on 13 separate cores
Only beach quality sand was considered
ƒ Small lenses of silty material existed within prime sand
Grain size analysis for each layer
ƒ 52 separate samples taken and analyzed
Volumes for each core layer were calculated
Weighted Average calculated based on grain size statistics and represent separate stratigraphic layers within island
Comparison to Native Sand
Source
% Fines
% Carbonate
% Granular
% Gravel
Mean (mm)
Volume (cy)
Acreage
Native Beach
1.5
25.8
1.1
.4
0.23
N/A
N/A
State Cutoff
6.5
40.8
6.1
5.4
N/A
N/A
N/A
DA‐143
3.7
7.0
.9
1.4
0.22
1,940,000
48
ƒ
ƒ
ƒ
Native sand numbers from December 2009 EIS
State Standard Allowance used as threshold for grain size parameters and characteristics
ƒ Gravel is greater than or equal to 4.76 mm
ƒ Granular is between 2 mm and 4.76 mm
ƒ Fines are smaller than .0625 mm
Calcium Carbonate testing done by USACE approved lab
ƒ Completed for each sample collected
ƒ Weighted averages for each core and entire island
EXISTING PHASED PLAN
Phases 1 & 2
Phases 4 & 3
Phase 5
Costs of Existing Plan
EVENT 1
Construct Phase 1 $5,614,000
597,000 cy
EVENT 2
Construct Phases 2 & 4
Nourish Phase 1
$18,916,000
1,493,300 cy
200,000 cy
EVENT 3
Construct Phases 3 & 5
Nourish Phase 1,2, & 4
$17,265,000
806,200 cy
530,000 cy
TOTAL CONSTRUCTION COST
Through 2025
$41,795,000
DA 143 Material Can feasibly be used in Phases 1‐4
USACE & CAMA Permitting
Modifying the EIS will require a supplemental document
Main Hurdle is the Grain Size Restriction “Point of Intercept Design”
Section 6.1 of EIS and associated permit conditions.
Hard Bottom Profiles
New Dune and Berm Construction
300’
ƒ
ƒ
ƒ
October 2011 beach cross section from North Topsail Beach ƒ Monitoring Station 106+00, near N. Topsail Beach Fire Department
8 years of Historic Data from Figure 8 Island
ƒ Direct or indirect impact from 6 separate tropical systems
ƒ Ophelia, Ernesto, Andrea, Hanna, Earl, Irene
ƒ 3 separate beachfill events (~900,000 CY total)
All profiles tie in before impacts to hard bottom would occur
ƒ 300’ buffer with new primary dune and berm construction
Hard Bottom Profiles
New Berm Construction
400’
ƒ
ƒ
ƒ
October 2011 beach cross section from North Topsail Beach ƒ Monitoring Station 106+00, near N. Topsail Beach Fire Department
8 years of Historic Data from Figure 8 Island
ƒ Direct or indirect impact from 6 separate tropical systems
ƒ Ophelia, Ernesto, Andrea, Hanna, Earl, Irene
ƒ 3 separate beachfill events (~900,000 CY total)
All profiles tie in before impacts to hard bottom would occur
ƒ 400’ Buffer with new berm construction only
Hard Bottom Profiles
New Berm Construction
450’
ƒ
ƒ
ƒ
October 2011 beach cross section from North Topsail Beach ƒ Monitoring Station 106+00, near N. Topsail Beach Fire Department
2 years of Historic Data from Figure 8 Island
ƒ 980,000 CY and 147,500 CY beachfill projects
ƒ Hurricane Irene in August 2011
All profiles tie in before impacts to hard bottom would occur
ƒ 450’ Buffer with new berm construction only
Inlet Maintenance
Crossroads Dredging
ƒ
ƒ
ƒ
ƒ
USACE maintains inlet crossroads yearly
While dredge is on site, address other areas of shoaling
ƒ Improves overall navigation
ƒ MOB cost is spread out over multiple projects
Material is placed on North End of Topsail Island
ƒ Specs do not dictate placement of material
Control where material is disposed of on beach front
ƒ Sand must remain in system between events
ƒ Reduce amount of material lost back into inlet
Cu
rre
nt
P
Ar lac
ea em
en
t
Additional Navigation
Maintenance
Working with the USACE
ƒ
ƒ
ƒ
ƒ
Dredge Murden just added to USACE hopper fleet in late 2011
Shallow draft dredging capabilities of less than 10’ MLW
ƒ Need to allow these dredges to access shoaling within New River Inlet
ƒ Current authorized depths of ‐6+2’ MLW within Inlet
Material is moved from shoal to nearshore surf zone
ƒ Naturally distributed on beachface by wave activity
ƒ Adds sand to beach’s sediment budget
Great solution for moving inside shoaling from New River to Phase 5 nourishment area
Costs of a Revised Plan
Use of Disposal Area 143
$275,000
Permitting
Engineering & Design
$200,000 $ 75,000
Estimated Cost of Construction
$15,900,000
Place 1,900,000 cy in Phase 2,3, & 4 Areas
($7.25/cy and $1,500,000 Mobilization)
Construction Management & Surveys
$15,300,000
$600,000
Phase 5 $8,000,000
700,000 cy through MOA USACE Hopper Fleet
500,000 cy utilizing Inlet Material and Pump Out
Construction Management & Surveys
$300,000**
Revised Long Term Plan FEMA Compliance
$40,000
Summary
• Initial Construction Phases 2‐4
$16,175,000
Material to come from DA143 (2015)
• Phase 1 Maintenance
$150,000/yr
AIWW & Cedar Bush Cut (cost differential)
• Phase 5 $8,000,000
Maintenance Material from Inlet Cut
Potentially over 4‐5 years 2014‐2018
• Long Term Maintenance from Inlet & Cross Roads
• Offshore Borrow Areas Held in Reserve for
Coastal Storm Events
Partnering