A Geospatial Framework for the Coastal Zone National Needs for Coastal Mapping and Charting (2004) / Chapter Skim
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3 A Common Coastal Zone Reference Frame: The Seamless Coastal Map and Consistent Shoreline
3 A Common Coastal Zone Reference Frame: The Seamless Coastal Map and Consistent Shoreline
Pages 62-73
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From page 62... ...
Yet as seen in the preceding chapter, seamless geospatial datasets across the land-water interface are needed by almost all users wrestling with issues of navigation, resource management, planning, hazard delineation and mitigation, environmental studies, and regulation issues. Often under contractual pressure, the problem of creating a seamless product is frequently solved by ignoring -- through data blending and large-scale spatial averaging -- datum transformation issues and the unmapped intertidal region.
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From page 63... ...
In a funding environment where coastal zone management funds are allocated on the basis of shoreline length, equity among the states requires that a consistent set of definitions and procedures be applied. The lack of accurate maps and charts that seamlessly cross the landsea interface creates a serious obstacle for the coastal zone managers of our nation.
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From page 64... ...
In the following sections the impediments to fulfilling this vision of a seamless coastal geospatial product and possible strategies to overcome these impediments are described in more detail. THE NEED FOR A COMMON FRAMEWORK The most critical technical barrier to completing the vision of a seamless coastal map is the lack of a common reference framework that would allow cartographers and coastal zone data managers to weave together topographic datasets (e.g., USGS Digital Elevation Models [DEMs]
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From page 65... ...
Thus, along with the difficulties in producing mapping products that are continuous across the shoreline, there are also inconsistencies in producing mapping products that are continuous along the shoreline, particularly where such products cross jurisdictional boundaries. With these unresolved differences or discrepancies in vertical datums associated with onshore versus offshore data, it is not possible to generate
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From page 66... ...
data provide elevations compatible with the orthometric heights (approximating MSL) used on USGS topographic maps.
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From page 67... ...
the vertical reference frame established at the discrete points where MLLW has been accurately measured by tide gauges, sophisticated hydrodynamic models are needed. Development of the CTM thus requires vertical datum integration, supported by appropriate tide gauge stations and meteorological observations, together with tools for hydrodynamic modeling.
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From page 68... ...
NOAA, USGS, and other partners have undertaken a pilot project in Tampa Bay, Florida, that has demonstrated both the complexity and the feasibility of generating a seamless bathymetric/topographic dataset (see
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From page 69... ...
Although horizontal datum issues can be readily resolved with existing transformation tools, vertical datum issues present the most serious challenge to this effort. To resolve the vertical datum issues, a project to apply Vdatum tools on a national scale is needed, involving the collection of real-time tide data and the development of more sophisticated hydrodynamic models for the entire U.S.
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From page 70... ...
blended their bathymetric and topo graphic datasets into a DEM with all data initially referenced to the ellip soid. A fully calibrated hydrodynamic model of Tampa Bay was used to determine the geographic distribution of tidal datums, and the Vdatum tool was used to transform all bathymetric data from the MLLW datum to the ellipsoid (Parker et al., 2001)
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From page 71... ...
As the fundamental boundary for so many applications and studies, the lack of a consistently defined shoreline has frustrated coastal zone managers, planners, and scientists for many years. Since shoreline definitions typically relate to a water level, the shoreline is dynamic, changing over
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From page 72... ...
shoreline does not exist, and the use of inconsistent shoreline definitions between maps, charts, GIS outputs, and other products leads to user confusion and ill-informed decision making. Another reason for this lack of consistency appears to be the significant overlap in federal efforts to acquire coastal shoreline data and in the subsequent generation of derived products, such as shoreline erosion and accretion maps.
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From page 73... ...
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.
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