In developing various coastal zone databases for the LMPDS, the majority of data (e.g., shoreline classification, recession rates, land use, etc.) have been ascribed to the shoreline using a series of 1 kilometer reach segments that were defined during the IJC Water Level Reference Study in the early 1990s, using what, at that time, were the best available mapping products to "define" the shoreline. With the advance in digital mapping and digital photographic techniques over the past ten years, a new digital shoreline, with a much higher resolution, has been produced by USACE Detroit that is much more accurate than the shoreline used in 1993 and that has corrected a numbers of errors that were present in the 1993 shoreline. As a result of this, the 1 kilometer reach segments that were defined in 1993 were no longer applicable and needed to be revised to reflect this higher resolution mapping.

In addition, data collected for these 1 kilometer reach segments had been summarized (averaged) over this 1 kilometer segment and has been visually represented on various mapping products using a symbol tied to the center point of each 1 kilometer reach segment. While this presented a general characterization of the reach section for the data in question, it did not accurately reflect variations that might occur within this 1 kilometer stretch.

Given that new GIS shoreline data for the LMPDS is being collected in a "continuous" fashion along the shoreline, not on a kilometer-by-kilometer basis, there was a need to reinterpret and reattribute the kilometer-by-kilometer classification data to bring it into consistency with the remainder of the GIS data being developed for the study and provide a more accurate representation of the open coast classification data.

Methodology

Reattribution of data in 2000 was confined to classification data and recession rate data for the five prototype counties that have been the focus of investigation in 1999 and 2000. The data to be re-classified included the three levels of shoreline classification information (shoreline type, shoreline protection and nearshore geology) as well as historic recession rate data that had been developed in 1994 and updated in 1997. In addition, USACE Detroit required a new reach delineation for reference purposes to be developed on a county by county basis. Recall that the original reach delineation started and ended at the south and north ends of the Mackinac Bridge respectfully, a total of 2436 reach segments.

Reach Delineations

To define new reaches for each county, the new digital shoreline was imported into ArcMap and then segmented into 1/10th of kilometer reach segments using the Divide Tool. For Michigan counties (Ottawa and Allegan), reaches began with a zero point at the northern border of the county. For Wisconsin counties (Sheboygan, Manitowoc and Ozaukee), reaches began with a zero point at the southern border of the county. This was in keeping with the original clockwise progression of reach numbering around the lake. This new segmented shoreline shape file was then brought back into ArcView as a separate GIS coverage.

Shoreline Classification Data

For the three levels of shoreline classification data, the start and end points of each shore type, shore protection type, or nearshore geology type, were mapped within ArcView using a combination of recent air photography and videos, along with existing classification data, topographic maps, new digital shoreline position and bluff crest mapping, digital orthophotos and Mr. Sid scanned air photo images. The new digital shoreline was segmented accordingly based on the start and end point of each feature and then color themed accordingly to represent the different classes within each level of the classification tier. Each classification tier was then developed as a separate continuous GIS coverage for each county.

Historic Recession Rate Data

To represent historic recession rate data as a GIS coverage for the five counties, the original source data used to develop the kilometer-by-kilometer recession rate database was re-visited. For Ottawa and Allegan County, this consisted of recession rate data developed by the Michigan Department of Natural Resources (now Department of Environmental Quality) and for Sheboygan, Manitowoc and Ozaukee County, it consisted of data developed by the Southeastern Wisconsin Regional Planning Commission and the Bay-Lake Regional Planning Commission in 1997.

Each recession rate point (profile/transect) contained in the original source data was plotted along the new digital shoreline within ArcView and the associated recession rate data for each point was then tied to this point as attribute data. Data points were plotted as accurately as possible given the limitations of the original source data. Where more than one period of record and related historic recession rate existed for a data point, it was also recorded in the attribute table associated with the data point. These new recession rate data points were then developed as continuous GIS coverages for each county.

An example of the mapping product for this activity is presented below.

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