Inlet Hazard Area (IHA) Boundary Update & Rule Amendments:
Ken Richardson – NC Division of Coastal Management January 9, 2020 Outline:
1. CRC’s Science Panel on Coastal Hazards
2. What is an Inlet Hazard Area (IHA)? • Rule definition: CAMA & 15A NCAC 07H.0304(2) • Geomorphology definition: Ocean vs. Inlet influences
3. The Inlet Hazard Area Method (IHAM)
4. Rule Amendments 1. CRC’s Science Panel on Coastal Hazards:
• Mr. Steve Benton (DCM geologist - retired) • Mr. Bill Birkemeier (USACE Field Research Facility retired Science Panel Co-Chair) • Dr. Bill Cleary (UNC Wilmington emeritus) • Mr. Tom Jarrett, PE (USACE –retired & Coastal Planning and Engineering) • Dr. Margery Overton (Science Panel Co-chair, NC State University) • Dr. Charles “Pete” Peterson (UNC Chapel Hill Institute for Marine Sciences) • Mr. Spencer Rogers (NC Sea Grant) • Mr. Greg “Rudi” Rudolph (Carteret County Shore Protection Office) • Dr. Beth Sciaudone, PE (NC State University)
• & NC DCM Staff
Image source: Town of North Topsail Beach 2. What is an Inlet Hazard Area (IHA)?
1 of 3 Areas of Environmental Concern (AEC) making up the Ocean Hazard Area, and defined in rule as:
“…natural-hazard areas that are especially vulnerable to erosion, flooding, and other adverse affects of sand, wind, and water because of their proximity to dynamic ocean inlets.” (15A NCAC 07H.0304(2))
Image source: Town of North Topsail Beach 2. Ocean Hazard Area: (OEA & IHA)
Ocean Erodible Area (OEA) • Dynamic boundary (not mapped) • Measured from vegetation line • 90 x Setback Factor (min.=180 ft.
Vegetation Line
Ocean Erodible Area Inlet Hazard Area (example) (current)
Note: OEA example measured from 2016 vegetation line using current (2013) erosion rate setback factors. Image source: NC DCM GIS 2. Inlet vs. Ocean: Open Coast Sediment Transport
Waves at an Angle: overwash • longshore & cross-shore cross-shore transport
transport Since 1979, North Carolina has defined the Ocean Storms: Erodible Area (OEA) to longshore transport recognize the greater risk • cross-shore transport & associated with ocean overwash dynamics.
Shoreline Response: • linear & shore parallel wind-blown • adjacent areas move the same (erosion or accretion) • Ocean Erodible Area (OEA)
source: Bill Birkemeier 2. Inlet vs. Ocean: Inlet Sediment Transport New Topsail Inlet • Interrupt longshore transport • downdrift beaches cut off from sediment
• Trap sediments Since 1979, North Carolina • flood shoal on the inside has defined the Inlet Hazard • ebb shoal outside Area (IHA) to recognize the • Have long-term influence greater risk associated with • New Topsail Inlet opened in 1726 tidal inlets dynamics. • still affecting coast ~300 years later • Since 2009, 0.7 mile of erosion at Shackleford Banks (Beaufort Inlet) Rich Inlet • Migrate • in the direction of net longshore current • New Topsail Inlet moved ~6 miles southwest • Oscillate • eroding one side, accreting on the other • then the pattern reverses
source: Bill Birkemeier 2. Why Update Inlet Hazard Area Boundaries?
Current (1978) Current (1978) Inlet Hazard Area Inlet Hazard Area 3. Inlet Hazard Area Method (IHAM): Extent of Inlet Influences
Mapping & Spatial Inlet History Expert Knowledge Analysis Technology • Shorelines • Geology • GIS • Vegetation Lines • Hydrography • USGS’s Digital • Oscillating vs. Migratory • Topology Shoreline Analysis • Erosion Rates • Engineering System (DSAS) • Analyzing Moving Boundaries Using R (AMBUR) 3. IHAM: Defining the Alongshore IHA Boundary
Transect - 291
500 450 Standard Deviation – Ocean Isle 400 350 300 Transect - 291 250 200 Ocean Isle Shallotte 150 Tubbs Inlet STANDARD DEVIATION STANDARD 100 Inlet 50 Atlantic Ocean
0
1
81 11 21 31 41 51 61 71 91
281 101 111 121 131 141 151 161 171 181 191 201 211 221 231 241 251 261 271 291 301 311 321 331 341 351 361 TRANSECTS Standard Deviation (ft) 3. IHAM: Defining the Landward IHA Boundary
Transect - 291
shorelines
Standard Deviation – Ocean Isle Inlet Hazard Area (IHA) • Static boundary (mapped) • Measured from hybrid-vegetation line • 90 x Erosion Rate (min.=180 ft.) Transect - 291 Landward boundary
Transect - 291 Hybrid-Vegetation Line
vegetation lines 3. Tubbs Inlet: 2019 Inlet Hazard Area Boundary Update
Inlet Hazard Area (Current ~ 1979)
Inlet Hazard Area (Update ~ 2019) 3. New River Inlet 3. Shallotte Inlet: 2019 Inlet Hazard Area Boundary Update
Inlet Hazard Area (Current ~ 1979)
Inlet Hazard Area (Update ~ 2019) 3. New River Inlet 4. Inlet Hazard Area Rule Amendments
Current IHAs Updated IHAs
• 1979 Boundaries • 2019 Boundaries • Setbacks - adjacent OEA rates • Setbacks – inlet erosion rates • New Construction • New Construction • Residential 4 units or less • Size: 5,000 sqft. or less • Commercial < 5,000 sqft. • Density: Only 1 unit per • Density: Only 1 commercial or 15,000 sqft. of land area residential unit per 15,000 sqft. • Existing grandfathering applies of land area (15A NCAC 07H.0306(a)(5)(L) • Existing grandfathering applies • IHA boundaries & Setbacks (15A NCAC 07H.0306(a)(5)(L) evaluated every 5 years 4. IHA Rule Amendments: 15A NCAC 07H.0304
Reference 2019 IHA Report 4. IHA Rule Amendments: 15A NCAC 07H.0304
Reference IHA Setback Factors Report - instead of Oceanfront (OEA) 4. IHA Rule Amendments: 15A NCAC 07H.0310
IHA Setback not adjacent OEA
Density
Size Tubbs Inlet Existing IHA (1979) Proposed IHA (2019) 1 Land Area ~ 124 acres ~ 84 acres
2 Structures 56 structures 31 structures SBFs based on inlet erosion rates Construction Applies adjacent OEA (oceanfront) SBF throughout IHA (not oceanfront/adjacent OEA) 3 (2) Setback (2)
Structure Size Residential must be 4 units or less & New structures less than 5,000 sqft. 4 Limit Commercial less than 5,000 sqft.
Development No more than 1 structure per 15,000 sqft (~1/3 acre) of No more than 1 structure per 15,000 sqft (~1/3 5 Density land area acre) of land area
15A NCAC 07H.0306(a)(5)(L) 15A NCAC 07H.0306(a)(5)(L) 6 Single-family or duplex > 5,000 sqft., or Single-family or duplex > 5,000 sqft., or commercial/multi-family < 10,000 sqft. commercial/multi-family < 10,000 sqft. Constructed prior to 08/11/2009 Constructed prior to 08/11/2009 Grandfathering Does not exceed original footprint Does not exceed original footprint (existing rules) Not possible to meet graduated setback Not possible to meet graduated setback requirements requirements Meets the minimum setback (30 x SBF) Meets the minimum setback Rebuilt as far landward as feasible Rebuilt as far landward as feasible 07H.0301 (lots platted after 06/01/1979) 07H.0301 (lots platted after 06/01/1979) Shallotte Inlet Existing IHA (1979) Proposed IHA (2019) 1 Land Area ~ 65 acres ~ 217 acres
2 Structures 0 structures 110 structures
Construction Applies adjacent OEA (oceanfront) SBF throughout IHA SBFs based on inlet erosion rates 3 Setback (Ranges from 2 to 6.5) (Ranges from 2 to 14)
Structure Size Residential must be 4 units or less & New structures less than 5,000 sqft. 4 Limit Commercial less than 5,000 sqft.
Development No more than 1 structure per 15,000 sqft (~1/3 acre) of No more than 1 structure per 15,000 sqft (~1/3 5 Density land area acre) of land area
15A NCAC 07H.0306(a)(5)(L) 15A NCAC 07H.0306(a)(5)(L) 6 Single-family or duplex > 5,000 sqft., or Single-family or duplex > 5,000 sqft., or commercial/multi-family < 10,000 sqft. commercial/multi-family < 10,000 sqft. Constructed prior to 08/11/2009 Constructed prior to 08/11/2009 Grandfathering Does not exceed original footprint Does not exceed original footprint (existing rules) Not possible to meet graduated setback Not possible to meet graduated setback requirements requirements Meets the minimum setback (30 x SBF) Meets the minimum setback Rebuilt as far landward as feasible Rebuilt as far landward as feasible 07H.0301 (lots platted after 06/01/1979) 07H.0301 (lots platted after 06/01/1979) Inlet Hazard Area Boundary Update & Rule Amendments
Frequently Asked Questions:
1. Is development prohibited? 2. Is my house now non-conforming? 3. Can I rebuild? 4. Will my flood insurance rates increase? 5. Will this effect my property value? 6. When will updates go into effect?