Town of Duck, North Carolina

Transcription

1 Tracking No Erosion Mitigation And Shoreline Management Feasibility Study Town of Duck, North Carolina Coastal Planning & Engineering of North Carolina August 15, 2012 Tom Jarrett Robert Neal Ken Willson 1

2 Tracking No Outline: Review Goals of Study Phase 1 Coastal Process/Erosion Impacts Phase 2 Concepts/Cost/Timeline Results of Phase 1 Shoreline Change Rates Trends/Reversals Pier Impacts Erosion Economics Phase 2 Concepts 2

3 Tracking No Goals of the Study Evaluate shoreline changes along entire town Investigate the cause, extent, and severity of the chronic erosion area or Hot Spot just north of the Research Pier Develop an erosion mitigation strategy to address this Hot Spot Develop a long term shoreline management strategy for the entire Town

4 Tracking No OUR APPROACH Develop Comprehensive Understanding of Coastal Processes Project Shoreline Change Rates (5, 10, 15, 30, and 50 Years) Develop Short-Term and Long-Term Management Alternatives to Address Erosion Determine Permitting Costs Potential Sand Sources Construction Costs 4

5 Tracking No OUR APPROACH Develop Comprehensive Understanding of Coastal Processes PHASE 1 Project Shoreline Change Rates (5, 10, 15, 30, and 50 Years) Develop Short-Term and Long-Term Management Alternatives to Address Erosion Determine Permitting Costs Potential Sand Sources Construction Costs PHASE 2

6 Tracking No Phase 1: Coastal Process and 1. Shoreline Change Rates Shoreline Impact Analysis What are the Shoreline Change Rates? 2. Trends or Reversals Should we expect past shoreline trends to remain constant or could they reverse? 3. Pier Impacts Is the Pier impacting shoreline change rates? 4. Economic Losses Due to Shoreline Change Rates How much public and private property is threatened (Short-Term and Long-Term)?

7 Tracking No Phase 1: Coastal Process and Shoreline Impact Analysis 1: Shoreline Change Rates 11 LiDAR data sets between 1996 and Analysis extends from 1 mile south of Town through 1 mile north of Town. 543 Transects established (100 ft. Spacing) Transects grouped into 10 segments with similar trends between Analysis extended back to 1940 using USGS data

8 8 Example of Shoreline Transects

9 Cumulative Change (ft) 9 40 Cumulative Shoreline Change since 1996-South of the FRF Pier Jun-96 Jun-98 Jun-00 Jun-02 Jun-04 Jun-06 Jun-08 Jun-10 Date of LiDAR survey Seg 1 ( to ) Seg 2 ( to -8000) Seg 3 (-8000 to -6000) Seg 4 (-6000 to -2000) Seg 5 (-2000 to 0)

10 Cumulative Change (ft) Cumulative Shoreline Change since 1996-North of the FRF Pier Jun-96 Jun-98 Jun-00 Jun-02 Jun-04 Jun-06 Jun-08 Jun-10 Date of LiDAR survey Seg 6 (0 to 1000) Seg 7 (1000 to 6000) Seg 8 (6000 to 14000) Seg 9 (14000 to 16000) Seg 10 (16000 to 30000)

11 Cumulative Change (ft) Cumulative Shoreline Change South of FRF Pier Since Jan-40 Jan-50 Jan-60 Jan-70 Jan-80 Jan-90 Jan-00 Jan-10 Date of survey Seg 1 Seg 2 Seg 3 Seg 4 Seg 5

12 Cumulative Shoreline Change (ft) Cumulative Shoreline Changes North of FRF Pier Since Jan-40 Jan-50 Jan-60 Jan-70 Jan-80 Jan-90 Jan-00 Jan-10 Date Seg 6 Seg 7 Seg 8 Seg 9 Seg 10

13 13 Phase 1: Coastal Process and Shoreline Impact Analysis 1: Shoreline Change Rates Shoreline Segment Average Shoreline Trend by Segment for Transect Grouping Distance From Pier (ft) 1996 to 2011 (ft/yr) Overall Trend Total Movement (ft) 1 9 to 89-22,000 to -14, to ,000 to -8, to 169-8,000 to -6, to 209-6,000 to -2, to 229-2,000 to to to 1, to 289 1,000 to 6, to 369 6,000 to 14, to ,000 to 16, to ,000 to 30,

14 14 Dune Toe

15 15 Comparison MHW Change to Toe of Dune Change

16 Tracking No Phase 1: Coastal Process and Shoreline Impact Analysis 2: Trends and Reversals Reviewed Wave Data from FRF and other gauges. Possibility of Sand Wave Migration. Influence of shore oblique sand bars

17 17

18 Meters / 57 Feet FRF Pier

19 Tracking No Potential Monthly Alongshore Sediment Transport (CY) Potential Monthly Sediment Transport Rates Oct 1996 to Nov 2011 (Based on Gauge 3111) , , ,000 50,000-50, , , ,000 Oct-96 Oct-98 Oct-00 Oct-02 Oct-04 Oct-06 Oct-08 Oct-10 Date Transport to South Transport to North Dominate Littoral Transport to the North

20 Tracking No Phase 1: Coastal Process and Shoreline Impact Analysis 2: Trends and Reversals Net northward sediment transport No clear correlation between wave data and shoreline change based on LiDAR data sets No significant differences in average storm conditions when comparing and No major difference in storm conditions from 1980 to 1996 compared to other time period.

21 Rate (ft/yr) 21 2: Shoreline Trends and Reversals Transect 1940 to to to 2011 Southern Town Limit FRF Pier Northern Town Limit

22 Tracking No Phase 1: Coastal Process and Shoreline Impact Analysis 3: Pier Impacts Analytical method to independently evaluate cross-shore (EVEN) and alongshore (ODD) shoreline changes due to potential obstruction. Cross-shore influences (storms) should impact the shoreline about the same up-coast and down-cost of pier, hence EVEN influence. Pier could potentially influence alongshore sediment transport and cause unequal impacts up-coast and down-coast, hence ODD influence. Cross-shore plus alongshore equals total shoreline response. 22

23 Tracking No Even Odd Analysis Limit of Long- Shore Influence

24 24 Phase 1: Coastal Process and Shoreline Impact Analysis 4: Economic Losses Due To Shoreline Change Rates Mean High Water Mean Sea Level Mean Sea Level

25 25 Phase 1: Coastal Process and Shoreline Impact Analysis 4: Economic Losses Due To Shoreline Change Rates Erosion Rate of 5 ft./ Year 40 ft. Mean High Water Mean Sea Level Mean Sea Level

26 26 Phase 1: Coastal Process and Shoreline Impact Analysis 4: Economic Losses Due To Shoreline Change Rates Apply 10 Years of Erosion Erosion Rate of 5 ft./ Year Mean High Water Mean Sea Level Mean Sea Level

27 27 Phase 1: Coastal Process and Shoreline Impact Analysis 4: Economic Losses Due To Shoreline Change Rates Apply 10 Years of Erosion Erosion Rate of 5 ft./ Year 5 ft./yr. X 10 years = 50 ft. Mean High Water Mean Sea Level Mean Sea Level

28 28 Phase 1: Coastal Process and Shoreline Impact Analysis 4: Economic Losses Due To Shoreline Change Rates Apply 10 Years of Erosion Erosion Rate of 5 ft./ Year 5 ft./yr. X 10 years = 50 ft. Mean High Water Mean Sea Level Mean Sea Level

29 Tracking No Phase 1: Coastal Process and Shoreline Impact Analysis 4: Economic Losses Due To Shoreline Change Rates shoreline change rates were applied to the existing dune toe Developed predicted dune toe position for 5, 10, 15, 30, and 50-year timeframes Parcel value reduced based on percentage lost Structure considered total loss when the predicted dune toe intersected or became landward of the structure. Pools $50K deduction from structural value

30 30 Predicted Dune Toe Positions

31 31 Phase 1: Coastal Process and Shoreline Impact Analysis 4: Economic Losses Due To Shoreline Change Rates Years Cumulative Area Lost (acres) Parcels Lost (US Dollars) $72,617,984 $6,164,873 $6,168,610 $18,526,114 $17,937,543 $121,415,125 Building Affected Pools Affected Lost Infrastructure (USD) $350,000 $3,163,900 $13,168,650 $9,518,950 $1,026,600 $27,228,100 Results from Phase 1

32 Tracking No Phase 2: Alternative Analysis Now That We Have Identified The Problem: What alternatives do we have that will mitigate erosion damage to public and private property? What are the cost of implementing these alternatives? How long will it take to implement these alternatives? Considered economic value, innovative solutions, and Town-wide benefits

33 Tracking No Phase 2: Alternative Analysis Develop a cost estimate for obtaining permits for the project. Develop a schedule to obtain permits for the project Develop a cost and schedule associated with Construction of the Project: (Note: Town may want to consider continuing shoreline monitoring by FRF)

34 Tracking No Phase 2: Alternative Analysis No Action Alternative Erosion Mitigation Beach Fill Project Segmented Truck Haul Beach Fill Economic Impacts of Short Term vs. Long Term Mitigation

35 35 Erosion Mitigation Beach Fill:

36 36 Erosion Mitigation Beach Fill:

37 37 Erosion Mitigation Beach Fill:

38 38 Erosion Mitigation Beach Fill:

39 Existing Geotechnical Information (Potential Borrow Sites) 39

40 40 What About Impacts of Sea Level Rise? = 1.35 ft/100 yrs

41 41 Sea Level Rise = 1.46 ft/100 yrs

42 Cumulative Nourishment Volume - Carolina Beach Cumulative Volume (cubic yards) 18,000,000 16,000,000 14,000,000 12,000,000 10,000,000 8,000,000 6,000,000 4,000, Nourishment Operations Since Initial Construction in Annual Nourishment =~300,000 CY/YR Funding Gap 1971 to ,000,000 0 Dec-64 Dec-69 Dec-74 Dec-79 Dec-84 Dec-89 Dec-94 Dec-99 Dec-04 Dec-09 Nourishment Dates Cumulative Nourishment Volumes Linear (Cumulative Nourishment Volumes)

43 43 Segmented Beach Fill (Truck Haul):

44 44 CONVEYOR SYSTEM: Images Provided By: Eastman Aggregates Inc.

45 Tracking No Comparison Between Long Term Projects Truck Haul vs. Dredging Projects Look at Scale of Cost Look at any permanent infrastructure that could make one of these more cost efficient Sustainability

46 Tracking No Types of Beach Fill Projects: Mitigate Long-Term Erosion Storm Damage Reduction

47 Tracking No Storm Damage Reduction Before Fran (After Bertha) USGS After Fran USGS

48 Tracking No Storm Damage Reduction

49 Tracking No

50 Tracking No ELEVATION PROFILE EVOLUTION OF BEACH NOURISHMENT DISTANCE

51 Tracking No ELEVATION PROFILE EVOLUTION OF BEACH NOURISHMENT 10 Nourishment 0-10 Design Beach DISTANCE

52 Tracking No ELEVATION PROFILE EVOLUTION OF BEACH NOURISHMENT 10 Advance Fill 0-10 Design Beach DISTANCE

53 Tracking No ELEVATION PROFILE EVOLUTION OF BEACH NOURISHMENT Design Beach DISTANCE

54 Tracking No ELEVATION PROFILE EVOLUTION OF BEACH NOURISHMENT Design Beach DISTANCE

55 Tracking No ELEVATION PROFILE EVOLUTION OF BEACH NOURISHMENT 10 Post-Construction Adjustment in 1-3 years 0-10 Design Beach DISTANCE

56 56

57 57 Approx. February 1993 Wet/Dry Line

58 58 Approx. February 1993 Wet/Dry Line

59 59 Approx. February 1993 Wet/Dry Line

60 60

61 61 Storm Vulnerability

62 62

63 63 SBEACH Storm-induced BEAch CHange Model Simulates cross-shore erosion of the dune, berm, and foreshore caused by storm waves and water levels

64 85M102006D Omaha Beach FS18 (Sta ) Thule St 100 Year Return Interval Storm

65 85M102006D Omaha Beach FS18 (Sta ) Thule St 100 Year Return Interval Storm

66 85M102006D Omaha Beach FS18 (Sta ) Thule St 100 Year Return Interval Storm Post-Storm Profile

67 85M102006D Omaha Beach FS18 (Sta ) Thule St 100 Year Return Interval Storm Beach Fill: Alternative 1 & 3

68 85M102006D Omaha Beach FS18 (Sta ) Thule St 100 Year Return Interval Storm Post-Storm Profile: Alternative 1 & 3

69 85M102006D Omaha Beach FS18 (Sta ) Thule St 100 Year Return Interval Storm Post-Storm Profile: Alternative 1 & 3

70 85M102006D Omaha Beach FS18 (Sta ) Thule St 100 Year Return Interval Storm Post-Storm Profile

71 71 Summary Phase 1 analysis is generally complete, report being prepared Concepts to be vetted for Phase 2 have been outlined Over the next 2 months we will finish Phase 2 Recommend considering SBEACH analysis to determine storm vulnerability for entire town

72 72 Thank You For Your Time!! Questions? Tom Jarrett Robert Neal Ken Willson

73 73