{ "culture": "en-US", "name": "", "guid": "", "catalogPath": "", "snippet": "Historical Mean High Water Lines from the State of Florida DEP\nhttps://publicfiles.dep.state.fl.us/DWRM/Beaches/HSSD/readme/readmeb.pdf", "description": "

Last Rev. 01/24/08 - E.Foster, P.E. - FSU/BSRC<\/SPAN><\/P>

The Historic Shoreline Database on the Web contains many directories of related types of <\/SPAN><\/P>

information about beach changes in Florida over the past 150 or so years. The historic <\/SPAN><\/P>

shoreline map images (see the Drawings directory) show precision-digitized approximate mean <\/SPAN><\/P>

high water (mhw) shorelines, from the US government coastal topographic maps listed in the <\/SPAN><\/P>

associated map bibliography files (see the Sourcebibs directory). These generally show data <\/SPAN><\/P>

extending from the mid to late 1800\u2019s to the mid to late 1970\u2019s. The mhw positions have been <\/SPAN><\/P>

extracted and tabulated (see the MWHfiles directory) relative to fixed reference \u201cR\u201d points along <\/SPAN><\/P>

the beach, spaced approximately 1000 feet (300 meters) apart. Reference points not actually <\/SPAN><\/P>

corresponding to actual \u201cin the ground\u201d survey markers are virtual \u201cV\u201d points. Mean high water <\/SPAN><\/P>

positions have been and continue to be extracted from FDEP beach profile surveys from the <\/SPAN><\/P>

1970\u2019s through the present and added to the tables. The beach profile data files from which mhw <\/SPAN><\/P>

data have been extracted and added into the mhw tables can be found in the ProfileData <\/SPAN><\/P>

directory and visually (for many areas) in the ClickOnProfiles directory. The beach profile files <\/SPAN><\/P>

include elevation information along the entire length of the profiles. This profile data set has <\/SPAN><\/P>

undergone up to fifteen additional quality control checks to ensure accuracy, reliability, and <\/SPAN><\/P>

consistency with the historic database coordinate and bearing set. Note that any data deeper than <\/SPAN><\/P>

wading depth have not yet undergone any extra quality control checks. Note also that there are <\/SPAN><\/P>

*.cod text files of notes associated with the review of the profile data files.<\/SPAN><\/P>

The digital historic shoreline map image files are given in a DWG autocad-based format, which <\/SPAN><\/P>

should be usable on most versions, as well as many GIS systems. The Florida State Plane 1927/79-<\/SPAN><\/P>

adjusted and 1983/90 horizontal coordinate systems are used. These are not metric systems, but <\/SPAN><\/P>

with the proper software can be converted to whatever systems you may need. Each map image <\/SPAN><\/P>

DWG file contains many layers, documented in an ASCII layer list archived with the DWG file.<\/SPAN><\/P>

The database has been maintained and greatly expanded by E. Foster since approximately 1987 <\/SPAN><\/P>

and by N. Nguyen since 1995. The initial map digitizing effort was done for FDEP at Florida State <\/SPAN><\/P>

University, primarily by S. Demirpolat. Final processing and editing of the original map files to <\/SPAN><\/P>

make them user-friendly was performed by N. Nguyen and E. Foster in 1995-7. Extensive quality <\/SPAN><\/P>

control and update work has been performed by E. Foster since 1987, and by N. Nguyen since <\/SPAN><\/P>

1995. Field profile surveys have been performed by the FDEP Coastal Data Acquisition section <\/SPAN><\/P>

since the early 1970\u2019s, and by a number of commercial surveyors in recent years.<\/SPAN><\/P>

The formats of the mhw tables and profile files are explained in text files included in the respective <\/SPAN><\/P>

directories.<\/SPAN><\/P>

Note that the digitized map image files were originally created in the UTM coordinate system on <\/SPAN><\/P>

Intergraph equipment. The translation from UTM to the State Plane coordinate systems has <\/SPAN><\/P>

resulted in some minor textual and other visual shifts in the northwest Florida area map image files.<\/SPAN><\/P>

The dates in the map legends in the map images are generally composite dates. It is necessary to <\/SPAN><\/P>

use the mhw data tables and map bibliographies for accurate dates for any specific location. The <\/SPAN><\/P>

date ranges in the data tables relate to specific information given in the map bibliography files.<\/SPAN><\/P>

2<\/SPAN><\/P>

Generally it may be assumed that the historic shorelines have been digitized as carefully as possible <\/SPAN><\/P>

from the source maps. If a historic shoreline does not contain a systematic position error and <\/SPAN><\/P>

is feasible in a physical sense, the accuracy of the mhw position is estimated at plus or minus 15 <\/SPAN><\/P>

to 50 feet (5 to 15 m), depending on the source and scale. This is as a position in time, NOT <\/SPAN><\/P>

as an average mhw position. Data added from field surveys are estimated at plus or minus 10 feet <\/SPAN><\/P>

(3 m) or better.<\/SPAN><\/P>

It is to be noted that from the 1920\u2019s onward, aerial photographs have usually been the <\/SPAN><\/P>

basis of the US government\u2019s coastal topographic maps. Prior to that, the method was plane <\/SPAN><\/P>

table surveying. Along higher wave energy coasts, especially the Florida east coast, if there <\/SPAN><\/P>

was significant wave activity in the source photography, it is very possible that the mhw was <\/SPAN><\/P>

mapped in a more landward location than was probably correct. Alternatively, the use of <\/SPAN><\/P>

photography sets with excessive sun glare may have caused the mhw to be mapped in a more <\/SPAN><\/P>

seaward location than was probably correct. These effects have been frequently observed in <\/SPAN><\/P>

comparisons of close-in-time FDEP controlled aerial photography with FDEP profile surveys. The <\/SPAN><\/P>

use of some photography sets containing high wave uprush or sun glare is probable within the <\/SPAN><\/P>

historic data. For example, on the east coast the 1940\u2019s series maps tend to show the mhw <\/SPAN><\/P>

more seaward than expected, possibly due to sun glare, and the 1960\u2019s series tend to show the <\/SPAN><\/P>

mhw more landward than expected. In the latter case, the effect may be due to the 1960\u2019s being a <\/SPAN><\/P>

decade of frequent storms. It is recommended that the analyst be aware that some of these effects <\/SPAN><\/P>

may exist in the historic data. A questionable historic shoreline is NOT necessarily one to be <\/SPAN><\/P>

discarded, just considered with allowance for its\u2019 potential limitations.<\/SPAN><\/P>

Using this database, it can readily be observed that the historic trends in shoreline evolution are <\/SPAN><\/P>

very consistent with behavior expected from the longshore transport equation, well known to <\/SPAN><\/P>

coastal engineers. This is a non-linear equation. Shoreline change can be expected to be linear or <\/SPAN><\/P>

constant only in certain situations. It is NOT recommended that any analyst arbitrarily assume <\/SPAN><\/P>

constant or linear shoreline change rates over long periods of time, which is often done but not <\/SPAN><\/P>

supported by the evidence. The three primary factors controlling shoreline change are sand supply, <\/SPAN><\/P>

wave climate, and local geographic features. In some parts of Florida, major storms since 1995 <\/SPAN><\/P>

have also become important factors.<\/SPAN><\/P><\/DIV><\/DIV>", "summary": "Historical Mean High Water Lines from the State of Florida DEP\nhttps://publicfiles.dep.state.fl.us/DWRM/Beaches/HSSD/readme/readmeb.pdf", "title": "Historical Mean High Water Lines", "tags": [ "Water" ], "type": "", "typeKeywords": [], "thumbnail": "", "url": "", "minScale": 150000000, "maxScale": 5000, "spatialReference": "", "accessInformation": "Florida Department of Environmental Protection", "licenseInfo": "" }