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Maui Shoreline Atlas
Overview
Researchers at the University of Hawaii, under contract from Maui County, have developed maps of coastal erosion hazards along Maui's shoreline. The erosion hazard maps depict the average annual erosion rate calculated by linear regression of historical shoreline positions. These maps are available for locations on the Kihei, West Maui, and North Shore coasts.

Past shoreline positions are measured using georectified nautical and topographic sheets from the pre-WWII era, and all available sets of aerial photographs covering long continuous segments of shoreline. These are usually flown in stereo from the post-WWII era. Pre-WWII N- and T-sheets are made available through the Shoreline Data Rescue Program of the National Oceanographic and Atmospheric Administration Coastal Services Center.

Accuracy
In most cases, aerial photographs have a minimum ground resolution of 0.25 meters (the worst case is 0.47 meters). Photographs have been digitally corrected in three-dimensions (orthorectified) to minimize distortion and maximize position accuracy and precision. Approximately 780 individual aerial photographs are used to calculate erosion rates along 75 kilometers of coast at more than 3,700 locations spaced 20 meters apart.

Calculations are based on six to nine separate shoreline positions between 1899 and 2002. Past shoreline positions that significantly diverge from the historical trend are eliminated from the rate calculation using the least median of squares technique. The 80th percentile uncertainty associated with each erosion rate is available from Maui County Planning Department records.

Lost Beaches
In cases where a beach has been lost over time, erosion rates apply only to the period when that beach was extant. Stabilized shorelines do not experience erosion, so erosion rates reflect only the period prior to the complete loss of dry beach seaward of the stabilizing structures. Actual rates of erosion may differ from calculated rates due to methodological uncertainties, human impacts, and natural patterns of shoreline change.

Future Movements
Future shoreline movements may be greater or less than the historical average. Seasonal changes in shoreline position may greatly exceed the historical average. Additional information regarding erosion rate establishment, shoreline setbacks and coastal hazards can be obtained from the Planning Department.

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