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<DIV STYLE="text-align:Left;"><DIV><P><SPAN>Last Rev. 01/24/08 - E.Foster, P.E. - FSU/BSRC</SPAN></P><P><SPAN>The Historic Shoreline Database on the Web contains many directories of related types of </SPAN></P><P><SPAN>information about beach changes in Florida over the past 150 or so years. The historic </SPAN></P><P><SPAN>shoreline map images (see the Drawings directory) show precision-digitized approximate mean </SPAN></P><P><SPAN>high water (mhw) shorelines, from the US government coastal topographic maps listed in the </SPAN></P><P><SPAN>associated map bibliography files (see the Sourcebibs directory). These generally show data </SPAN></P><P><SPAN>extending from the mid to late 1800’s to the mid to late 1970’s. The mhw positions have been </SPAN></P><P><SPAN>extracted and tabulated (see the MWHfiles directory) relative to fixed reference “R” points along </SPAN></P><P><SPAN>the beach, spaced approximately 1000 feet (300 meters) apart. Reference points not actually </SPAN></P><P><SPAN>corresponding to actual “in the ground” survey markers are virtual “V” points. Mean high water </SPAN></P><P><SPAN>positions have been and continue to be extracted from FDEP beach profile surveys from the </SPAN></P><P><SPAN>1970’s through the present and added to the tables. The beach profile data files from which mhw </SPAN></P><P><SPAN>data have been extracted and added into the mhw tables can be found in the ProfileData </SPAN></P><P><SPAN>directory and visually (for many areas) in the ClickOnProfiles directory. The beach profile files </SPAN></P><P><SPAN>include elevation information along the entire length of the profiles. This profile data set has </SPAN></P><P><SPAN>undergone up to fifteen additional quality control checks to ensure accuracy, reliability, and </SPAN></P><P><SPAN>consistency with the historic database coordinate and bearing set. Note that any data deeper than </SPAN></P><P><SPAN>wading depth have not yet undergone any extra quality control checks. Note also that there are </SPAN></P><P><SPAN>*.cod text files of notes associated with the review of the profile data files.</SPAN></P><P><SPAN>The digital historic shoreline map image files are given in a DWG autocad-based format, which </SPAN></P><P><SPAN>should be usable on most versions, as well as many GIS systems. The Florida State Plane 1927/79-</SPAN></P><P><SPAN>adjusted and 1983/90 horizontal coordinate systems are used. These are not metric systems, but </SPAN></P><P><SPAN>with the proper software can be converted to whatever systems you may need. Each map image </SPAN></P><P><SPAN>DWG file contains many layers, documented in an ASCII layer list archived with the DWG file.</SPAN></P><P><SPAN>The database has been maintained and greatly expanded by E. Foster since approximately 1987 </SPAN></P><P><SPAN>and by N. Nguyen since 1995. The initial map digitizing effort was done for FDEP at Florida State </SPAN></P><P><SPAN>University, primarily by S. Demirpolat. Final processing and editing of the original map files to </SPAN></P><P><SPAN>make them user-friendly was performed by N. Nguyen and E. Foster in 1995-7. Extensive quality </SPAN></P><P><SPAN>control and update work has been performed by E. Foster since 1987, and by N. Nguyen since </SPAN></P><P><SPAN>1995. Field profile surveys have been performed by the FDEP Coastal Data Acquisition section </SPAN></P><P><SPAN>since the early 1970’s, and by a number of commercial surveyors in recent years.</SPAN></P><P><SPAN>The formats of the mhw tables and profile files are explained in text files included in the respective </SPAN></P><P><SPAN>directories.</SPAN></P><P><SPAN>Note that the digitized map image files were originally created in the UTM coordinate system on </SPAN></P><P><SPAN>Intergraph equipment. The translation from UTM to the State Plane coordinate systems has </SPAN></P><P><SPAN>resulted in some minor textual and other visual shifts in the northwest Florida area map image files.</SPAN></P><P><SPAN>The dates in the map legends in the map images are generally composite dates. It is necessary to </SPAN></P><P><SPAN>use the mhw data tables and map bibliographies for accurate dates for any specific location. The </SPAN></P><P><SPAN>date ranges in the data tables relate to specific information given in the map bibliography files.</SPAN></P><P><SPAN>2</SPAN></P><P><SPAN>Generally it may be assumed that the historic shorelines have been digitized as carefully as possible </SPAN></P><P><SPAN>from the source maps. If a historic shoreline does not contain a systematic position error and </SPAN></P><P><SPAN>is feasible in a physical sense, the accuracy of the mhw position is estimated at plus or minus 15 </SPAN></P><P><SPAN>to 50 feet (5 to 15 m), depending on the source and scale. This is as a position in time, NOT </SPAN></P><P><SPAN>as an average mhw position. Data added from field surveys are estimated at plus or minus 10 feet </SPAN></P><P><SPAN>(3 m) or better.</SPAN></P><P><SPAN>It is to be noted that from the 1920’s onward, aerial photographs have usually been the </SPAN></P><P><SPAN>basis of the US government’s coastal topographic maps. Prior to that, the method was plane </SPAN></P><P><SPAN>table surveying. Along higher wave energy coasts, especially the Florida east coast, if there </SPAN></P><P><SPAN>was significant wave activity in the source photography, it is very possible that the mhw was </SPAN></P><P><SPAN>mapped in a more landward location than was probably correct. Alternatively, the use of </SPAN></P><P><SPAN>photography sets with excessive sun glare may have caused the mhw to be mapped in a more </SPAN></P><P><SPAN>seaward location than was probably correct. These effects have been frequently observed in </SPAN></P><P><SPAN>comparisons of close-in-time FDEP controlled aerial photography with FDEP profile surveys. The </SPAN></P><P><SPAN>use of some photography sets containing high wave uprush or sun glare is probable within the </SPAN></P><P><SPAN>historic data. For example, on the east coast the 1940’s series maps tend to show the mhw </SPAN></P><P><SPAN>more seaward than expected, possibly due to sun glare, and the 1960’s series tend to show the </SPAN></P><P><SPAN>mhw more landward than expected. In the latter case, the effect may be due to the 1960’s being a </SPAN></P><P><SPAN>decade of frequent storms. It is recommended that the analyst be aware that some of these effects </SPAN></P><P><SPAN>may exist in the historic data. A questionable historic shoreline is NOT necessarily one to be </SPAN></P><P><SPAN>discarded, just considered with allowance for its’ potential limitations.</SPAN></P><P><SPAN>Using this database, it can readily be observed that the historic trends in shoreline evolution are </SPAN></P><P><SPAN>very consistent with behavior expected from the longshore transport equation, well known to </SPAN></P><P><SPAN>coastal engineers. This is a non-linear equation. Shoreline change can be expected to be linear or </SPAN></P><P><SPAN>constant only in certain situations. It is NOT recommended that any analyst arbitrarily assume </SPAN></P><P><SPAN>constant or linear shoreline change rates over long periods of time, which is often done but not </SPAN></P><P><SPAN>supported by the evidence. The three primary factors controlling shoreline change are sand supply, </SPAN></P><P><SPAN>wave climate, and local geographic features. In some parts of Florida, major storms since 1995 </SPAN></P><P><SPAN>have also become important factors.</SPAN></P></DIV></DIV> |