under the Submerged Lands Act. The federal government claimed that the sand body was not an island and that consequently the area was under federal jurisdiction. After 17 years of litigation the U.S. Supreme Court ruled in favor of the federal government, denying Alaska the rights to approximately $1.6 billion in oil and gas revenues.

Differences in shoreline definition can also lead to unnecessary duplication of data acquisition efforts (typically the most expensive aspect of coastal mapping), with individual agencies collecting independent datasets in accordance with their own definitions of the shoreline. In the course of presentations to the committee, it became apparent that some agencies maintain their own crews and collect their own shoreline data (e.g., BLM collects its own data to define the vegetation line as the basis for its shoreline). In contrast, other agencies accept shoreline definitions provided by NOAA (e.g., the Minerals Management Service [MMS] uses NOAA’s MLLW shoreline definition). A consistent definition of the shoreline would thus not only reduce legal and jurisdictional confusion but also would undoubtedly lead to increased data acquisition efficiency (see Chapter 6).

While a call for a nationally consistent shoreline is laudable (and practical for some applications), we cannot escape the fact that embedded in local, state, and federal laws are an array of legislative definitions of the shoreline that will not be easily changed. With this in mind, it seems impractical to recommend adoption of a single national shoreline. However, an alternative is the consistent geodetic framework—the CTM—described above. With the CTM and appropriate difference or tidal models, different agencies can adopt common and consistent horizontal and vertical reference frames and have the ability to transform and integrate shoreline definitions within this common framework. National consistency can be achieved when all parties define their shorelines in terms of a tidal datum, so that vertical shifts can be easily calculated between and among the various datum-based shoreline definitions. This approach has the advantage of allowing agencies and users to maintain their existing legal shoreline definitions if required. Accordingly, the Vdatum tool kit and associated Web sites are critical for establishing internally consistent shorelines between and among disparate surveys and studies. In those situations where legislation or application does not preclude adoption of a national shoreline, the internationally recognized shoreline as defined by NOAA-NGS should be adopted.

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