o W 50 40'' 30'' 20 10 159 Lumahai, Kauai, · PDF file The preparation of this poster was...

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Transcript of o W 50 40'' 30'' 20 10 159 Lumahai, Kauai, · PDF file The preparation of this poster was...

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    30'' 20" 159o31'00'' W10"40''159o32'00'' W 50"

    30'' 20" 159o31'00'' W10"40''159o32'00'' W 50"

    50" 40"

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    22 o12' 30" N

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    HISTORICAL SHORELINES

    Erosion rate measurement locations (shore-normal transects)

    Historical beach positions, color coded by year, are determined using orthorectified and georefer- enced aerial photographs and National Ocean Survey (NOS) topographic survey charts. The low water mark is used as the historical shore- line, or shoreline change reference feature (SCRF).

    Movement of the SCRF along shore-normal transects (spaced every 66 ft) is used to calcu- late erosion rates.

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    1987

    1950 1963

    May 1975

    1930 T-sheet

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    1988 1999 2002 2006Sept

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    Kauai

    LumahaiavaLumahai, Kauai, Hawaii

    Contract C25514 Contract 7249

    Charles Fletcher, Matthew Barbee, Siang-Chyn Lim, Matt Dyer and Ayesha Genz University of Hawaii Coastal Geology Group School of Ocean and Earth Sciences and Technology 1680 East West Road, Honolulu, HI 96822, U.S.A.

    The preparation of this poster was financed in part by the Coastal Zone Management Act of 1972, as amended, administered by the Office of Ocean and Coastal Resource Man- agement, National Ocean Service, National Oceanic and Atmospheric Administration, United States Department of Commerce, through the Office of Planning, State of Hawaii.

    Latitude/Longitude coordinates UTM coordinates

    159o32'00" W 2455900mN

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    1200 900600

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    Scale 1:3000 Meters

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    5052

    55 5658

    Kuhio Highway Makahoa Point

    Kolokolo Point

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    ah ai

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    er

    Erosion Rate Accretion Rate

    SHORELINE CHANGE RATES

    Historical shoreline positions are measured every 66 ft along the shoreline. These sites are denoted by yellow shore-perpendicular transects. Changes in the position of the shorelines through time are used to calculate shoreline change rates (ft/yr) at each transect location.

    Annual shoreline change rates are shown on the shore-parallel graph. Red bars on the graph indicate a trend of beach erosion, while blue bars indicate a trend of accretion. Approximately every fifth transect and bar of the graph is numbered. Where necessary, transects have been purposely deleted to maintain consistent alongshore spacing. As a result transect numbering is not consecutive everywhere. The rates are smoothed alongshore using a 1-3-5-3-1 technique to normalize rate differences on adjacent transects.

    AREA DESCRIPTION The Lumahai study area (transects 0 – 58) is located on the north shore of Kauai. The area is bounded by Kolokolo Point to the west and Makahoa Point to the east. Lumahai River flows through the westernmost portion of the area. The area is exposed to large seasonal swell during the winter months while strong tradewinds drive alongshore currents that transport sediment during the summer months. The sandy shoreline is composed of carbonate sand and fine grained terrigenous sediment.

    Lumahai Beach is highly variable. Changes in the shoreline positions indicate an average summer-winter difference of 176 ft with a maximum of 300 ft (transect 47). Overall, Lumahai Beach is experiencing erosion at an average rate -0.4 ft/yr. The eastern portion of the area (transects 29 – 58) is eroding at an average rate of -0.6 ft/yr while the western portion (transects 0 – 28) is experiencing mild erosion at an average rate of -0.1 ft/yr. Previous studies1 did not analyze the Lumahai Beach study area shoreline.

    1 Makai Ocean Engineering and Sea Engineering, 1991 Aerial Photograph Analysis of Coastal Erosion on the Islands of Kauai, Molokai, Lanai, Maui, and Hawaii. State of Hawaii Office of Coastal Zone Management Program.

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    Shoreline Change Rate (ft/yr)