Coastal Classification Atlas

Mapping Methods

A coastal storm hazard assessment involves two different activities. The first is classification of ground conditions and the second is translation of that information into a storm hazard vulnerability index. Present ground morphology and any man-made alterations of the land were first interpreted in the laboratory using three independent visual sources:

1. airborne color video surveys,
2. 35 mm aerial color slides, and
3. Digital Orthophoto Quarter Quadrangles (DOQQs) obtained from the U.S. Geological Survey EROS Data Center in Sioux Falls, South Dakota (http://edc.usgs.gov/index.html).

Table 1. Type of Imagery Date Aerial Oblique Video Survey September, 1999 Digital Orthophoto Quarter Quadrangle Spring, 1994 Lidar Survey October, 1998 Ground Observation and Map Verification May/June 2001

The video surveys, slides, and DOQQs were used to prepare the coastal classification units (Fig. 2) and to interpret the geomorphological and cultural attributes of each coastal segment. Elevations of the land surface adjacent to the barren backbeach were obtained by processing lidar data. The highest elevations of the foredunes or beach crest (where dunes are absent) are shown as a series of dots. Each dot is color coded to represent a narrow range of elevations. The units of elevation are decimeters, or tenths of meters.

In some local areas there are substantial differences between the backbeach position observed on the DOQQs and those observed on the lidar surveys. These differences are attributed generally to coastal dynamics and specifically to beach erosion, spit accretion, or inlet migration. Examples of discrepancies between the DOQQs and lidar surveys are shown on maps for Dunedin NW and Pass-a-Grille Beach SW. The dates of the surveys (Table 1) will indicate which beach position is most recent. In all areas, the lidar survey will be more recent than the DOQQ survey.