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Defining Inlet Hazard Areas (IHA) Using a 30-Year Risk Line Ken - - PowerPoint PPT Presentation
Defining Inlet Hazard Areas (IHA) Using a 30-Year Risk Line Ken - - PowerPoint PPT Presentation
Defining Inlet Hazard Areas (IHA) Using a 30-Year Risk Line Ken Richardson North Carolina Division of Coastal Management 2017 Coastal GeoTools February 9, 2017 What is an Inlet Hazard Area (IHA)? Areas vulnerable to rapid change due to inlet
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North Carolina has 19 active inlets:
- 12 with adjacent development
- 7 no adjacent development
- 2 Deep-draft inlets
- 17 Shallow-draft inlets
- 4 Migrating inlets
- 15 “oscillating” inlets
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IHA Boundary Update Needed:
- IHAs established in 1979
- No longer reflect the “hazard”
Inlet Hazard Area
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Common Inlet Problems:
- Loss of property and infrastructure
- Sandbag structures installed
- Alternative structures used (terminal
groins)
- Continual beach re-nourishment needs
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Inlets Areas Subject to Rapid Change
House (1993)
Constructed on Lea- Hutaff Island in 1990, this private home sat 500 feet from the ocean The same house sat at the ocean’s edge at low tide until finally being destroyed by a storm in 2015
House (2014)
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48% Oceanfront 52% Inlets
Sandbag Use: Inlets vs. Oceanfront
Oceanfront Inlet Areas
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Defining Inlet Hazard Areas Using a 30- Year Risk Line:
- Step 1: Map shorelines & vegetation lines
- Step 2: Map “Hybrid-Vegetation Line”
- Step 3: Analyze shoreline change over time using
Linear Regression (1970-2016)
- Step 4: Define where inlet processes no longer
dominate shoreline location (oceanfront-inlet transition)
- Step 5: Calculate & map projected hazard risk (“30 &
90-Year Risk Line”)
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Step 1: Map shorelines
Hybrid-Vegetation Line
Steps 1 & 2: Map vegetation lines & “Hybrid-Vegetation”
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Step 3: Analyze Shoreline Change
- Transect spacing (50 feet)
- Linear Regression Rate (LRR) (ESRI’s ArcMap & Analyzing
Moving Boundaries using R – AMBUR)
- Smooth Raw Data using 5-Point Running Average (each
transect rate is the average of the transect and the two transects on either side).
Distance (feet) Time (years)
Linear Regression End Point
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Steps 3: Analyze Shoreline Change
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Hybrid-Vegetation Line
Steps 4: Analyze Oceanfront-Inlet Transition Point
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- 6
- 4
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2 4 6 8 50 100 150 200 250 300 1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 67 70 73 76 79 82 85 88 91 94 97 100 103 106 109 112 115 118 121 124 127 130 133 136 139 142 145 148 151 154 157 slope (feet/year) standard deviation (feet) Transects
Lockwood Folly - Holden Beach (1970-2016)
stdev slope
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Measured from “Hybrid-Vegetation” 30-Year Risk Line = 30 x LRR x Multiplier 90-Year Risk Line = 90 x LRR X Multiplier If accreting: Risk Line = 30 x 2 or 90 x 2
If eroding: If SEIHA/SEA ≤ 1, Multiplier = 1 If SEIHA/SEA > 1, Multiplier = SEIHA/SEA
Step 5: Calculate & map projected hazard risk (“30 & 90- Year Risk Line”)
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Step 5: Defining “Hazard” – 30 & 90 Year Risk Lines
90-Year Risk Line 30-Year Risk Line Hybrid-Vegetation
Transect #54
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2010 Proposed IHA Current IHA 2017 Proposed IHA
Transect #54
Inlet Studies: What Next?
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