2003 Seattle Annual Meeting (November 2–5, 2003)

Paper No. 4
Presentation Time: 2:30 PM

MAPPING SHORELINE CHANGE USING DIGITAL ORTHOPHOTOGRAMMETRY ON MAUI, HAWAII


FLETCHER, C.H.1, BARBEE, M.1, ROONEY, J.1, GENZ, A.1, LIM, S.-C.1 and RICHMOND, B.2, (1)Geology and Geophysics, Univ of Hawaii, 1680 East-West Rd, Honolulu, HI 96822, (2)Pacific Science Center, U.S.G.S, Santa Cruz, CA, fletcher@soest.hawaii.edu

Digital, aerial orthophotomosaics with 0.5 – 3.0 m horizontal accuracy, used with NOAA topographic maps (T-sheets), document past shoreline positions on Maui Island, Hawaii. Outliers in the shoreline position database are determined using a least median of squares regression. Least squares linear regression of the reweighted data is then used to determine a shoreline trend (AEHR – average annual erosion hazard rate or accretion). The resulting database consists of approximately 3350 separate erosion rates spaced every 20 m along 70 km of sandy shoreline. Three regions are analyzed: Kihei, West Maui, and North Shore coasts. The Kihei Coast has an average annual erosion hazard rate (AEHR) of about 0.3 m/yr, over 2 km of beach loss and 26 percent beach narrowing in the period 1949 - 1997. Over the same period the West Maui coast has an average AEHR of about 0.2 m/yr, about 3 km of beach loss and 37 percent beach narrowing. The North Shore has an average AEHR of about 0.4 m/yr, 0.8 km of beach loss and 12 percent beach narrowing. The mean, island-wide AEHR is about 0.3 m/yr. Island wide changes in beach width show a 25 percent decrease over the period 1949/1950 to 1997/2002. Island-wide, about 6 km of dry beach has been lost since 1949 (i.e., high water against hard engineering structures and natural rock substrate). Over the next 30 years over 4 km of coastal roadway is threatened by erosion.