2011 Nags Head Beach Nourishment Project Update. Tim Kana & Haiqing Kaczkowski

Transcription

1 2011 Nags Head Beach Nourishment Project Update Tim Kana & Haiqing Kaczkowski NCBIWA Conference 3 April 2017

2 Outline of the Presentation 1 Review 2011 Nourishment Project Post-project monitoring efforts 2 Project Performance Condition and 5 Year Summary Volume analysis methodology Monitoring results 3 Post-Hurricane Results 2016 Storm Losses Summary of Storm Processes

3 Part 1 Review of the 2011 Nourishment The largest locally funded beach nourishment accomplished to date in the United States. 4.6 million cubic yards Along 10 miles Over 100 borings to confirm high quality offshore sand source Construction cost of $30.8 million Unit Price $6.70 per cy 5 months for summer construction between 24 May and 27 Oct 2011

4 Part 1 Review of the Post-Project Monitoring Required by state and federal permits Prerequisite for FEMA s post-storm beach restoration funding Scope of Work (2012 thru 2016) Compaction tests for 3 years Semi-annual condition surveys in Year 1 Annual condition surveys in Years 2-5 Sediment sampling in Years 2 & 4 Aerial orthophotos in Year 3 Annual oblique aerial & ground photos Annual monitoring reports Biological studies & reports in Years 1 & 2* (*Conducted by CZR)

5 Part 2 Project Performance Methodology Beach Condition Analysis The Littoral Sand Box Lens 1 Foredune From the ~crest of dune to +6 ft NAVD* Lens 2 Beach Between +6 ft and -6 ft NAVD Lens 3 Underwater Between -6 ft and -19 ft NAVD *NAVD-North American Vertical Datum of 1988 = ~mean sea level

6 Project Reaches and Subreaches Reach 1 MP 11 to to Reach 2 MP 16.8 to 19.2 R to Reach 3 MP 19.2 to to o R3N to R2 R3 Dune o R3S to Reach 4 MP 20.8 to to

7 Reach 3 (Subreach 3S) & 4 (Project Taper) Seagull Dr. South most one mile of Nags Head Erodes ~4 Times Faster Than 90% of Nags Head

8 Part 2 Project Performance Results Results include: Sand volumes along Nags Head Volumes by reach and subreach Dune growth along Nags Head Results compared to: Pre-nourishment condition (2016 vs. 2010) Previous years (eg vs. 2015) Historical analysis

9 Results Sand Volumes by Station along Nags Head

10 Results* Total Volume by Reach and Subreach *Before Hurricane Matthew

11 Results Compared to Historical Analyses First data set in 1994 Lack of historical data Estimated annual erosion rate by the USACE*: 900,000 cy/yr Adopted annual erosion rate by CSE**: 275,000 cy/yr Actual annual erosion rates since project completion have varied Max erosion rate: ~500,000 cy/yr (2012 to 2013) Max accretion rate: ~250,000 cy/yr ( ) Average change erosion at 100,000 cy/yr (before 2016 Storms!) *USACE Final feasibility report and environmental impact statement: Dare County beaches. ** CSE 2005 & Preliminary and Final design reports for beach nourishment at Nags Head.

12 Results Dune Growth along Nags Head

13 Results Dune Behavior Before/After Nourishment Above +6 ft NAVD

14 Review of a Previous Dune Construction Project at Nags Head After Hurricane Isabel (18 September 2003) Dec 2003 April 2004 Post-Isabel Dune Building (FEMA) Nov 2010 May 2004

15 Nags Head Post-Nourishment Dune Growth Jun 2012 Jun 2014 Jun 2016 Jun 2015

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18 Nags Head Average* Profile Evolution Higher & Wider Foredune Greater Underwater Volume Similar Dry Beach Width *n=104

19 Results Beach Width by 1-Mile Average

20 Pre Post Matthew October 2016 Reach 1 Nags Head Pier Post-Storm Images: Courtesy NOAA-USGS

21 Pre Post Matthew October 2016 Reach 4 McCall Court- National Seashore 7 Jun Oct 2016 Post-Storm Images: Courtesy NOAA-USGS

22 Post storm Condition Foredune Net Losses in the Foredune & Visible Beach Were Minor Dune & Visible Beach

23 Dune, Visible Beach & Underwater

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25 Winds, Waves & Tides At Duck USACE FRF Hurricane Matthew Wind Shift East to North Then Prolonged North Winds Data: Courtesy USACE - FRF

26 5 Year Summary 2011 to 2016 Overall lost 10% of nourishment sand Before Hermine & Matthew North ~5.8 miles gained ~300,000 cy Middle to south ~2.4 miles were stable South ~1.8 miles lost~680,000 cy Average Annual Loss ~100,000 cy/yr 2016 Post-storm Condition: Overall lost 30% of nourishment sand R1 R4 lost 22, 29, 37 and 46 cy/ft, respectively Nourishment Volume Remaining = ~61% Average Annual Loss ~360,000* cy/yr (Nov 11-Nov 16) vs Design = ~275,000 cy/yr Conclusion: The nourished beach is performing like a natural beach along Nags Head and average annual losses are expected to be below design after the next monitoring period.