Recent (1988-1995) Maryland Shorelines with Erosion Rate AttributesEntry ID: md_SLM
Abstract: In 2000, the Maryland Geological Survey (MGS) was awarded a Coastal Zone Management grant to complete the acquisition of a recent (ca. 1990) digital shoreline for the coastal regions of Maryland -- the Chesapeake Bay, its tributaries, the coastal bays, and the Atlantic coast. MGS contracted the services of EarthData International, Inc. (EDI), currently of Frederick, Md., to extract shorelines ... from an existing wetlands delineation, which was based on photo interpretation of 3.75-minute digital orthophoto quarter quads (DOQQs). In areas where a wetlands coverage was not yet available, EDI interpreted shorelines directly from the orthophotography. DOQQ registration (Maryland State Plane Coordinate System, NAD 83, meters) was transferred automatically to the shoreline vectors. Following shoreline extraction or interpretation, EDI assigned attributes to the vectors based on shoreline type: beach, vegetated, structure, or water’s edge. All four categories are linear features, except “beach,” which, if sufficiently wide, can be both linear and polygonal. Shorelines were merged into 7.5-minute quadrangles, provided that the aerial photography on which the DOQQs were based was flown in the same year.
MGS used the shorelines to create a series of Shoreline Changes maps. In doing so, MGS erased the landward edge of beach polygons, leaving the seaward edge intact as a linear feature.
The Geographic Information Services Division of the Maryland Department of Natural Resources (DNR) merged the shorelines for all of the 7.5-minute quadrangles into a single, statewide coverage.
MGS, working collaboratively with Towson University’s Center for Geographic Sciences (CGIS), subsequently used the recent shorelines, along with historical ones, as input into a U.S. Geological Survey (USGS) program, the Digital Shoreline Analysis System (DSAS) (Danforth and Thieler, 1992; Thieler and others, 2001). DSAS determines linear rates of shoreline change (erosion or accretion) along closely spaced, shore-normal transects. Based on DSAS output, the collaborators assigned the following erosion rate categories as attributes to the recent shoreline, clipped by county from the statewide coverage:
- High erosion rate (more than 8 ft/yr)
- Moderate erosion rate (4-8 ft/yr)
- Low erosion rate (2-4 ft/yr)
- Slight erosion rate (0-2 ft/yr)
- No change
- No Data
The data set contains recent shoreline vectors for sixteen coastal counties and Baltimore City (see Appendix 1), assigned both shoreline type and erosion rate attributes. The vectors represent shoreline positions between the years 1988 and 1995.
The metadata was originally written to document the recent shoreline vectors, interpreted, directly or indirectly, from DOQQs and merged by 7.5-minute quadrangle (see Appendix 2). It was amended to include information about the erosion rate attributes later assigned to the county shorelines.
[Summary provided by the Maryland Geology Survey.]
Purpose: This data set complements a set of historical digital shorelines for the Maryland reaches of the Chesapeake Bay, the coastal bays, and the Atlantic coast (See Section 1.14). That data set spans the period 1841-1977. The two data sets are being used to update a series of Shoreline Changes maps and to determine coastal land loss during the last half of the 20th century. Other State agencies will be able to use this data to analyze and update land loss information, analyze historical erosion trends, and assess the extent and magnitude of shore erosion on a regional geographic basis. In particular, the availability of up-to-date shoreline change data will support the design and implementation of shore protection projects and the development of a comprehensive shore erosion control plan.
Data Set Citation
Dataset Originator/Creator: Maryland Department of Natural Resources, Chesapeake Bay & Watershed Programs, Resource Assessment Service, Maryland Geological Survey (MGS)
Dataset Title: Recent (1988-1995) Maryland Shorelines with Erosion Rate Attributes
Dataset Release Date: 2003
Dataset Release Place: Baltimore, Maryland, USA
Dataset Publisher: Maryland Department of Natural Resources, Chesapeake Bay & Watershed Programs, Resource Assessment Service, Maryland Geological Survey (MGS)
Data Presentation Form: vector digital data
Other Citation Details: CD-ROM CoErosionRatesOnline Resource: http://www.mgs.md.gov
Start Date: 1988-04-17Stop Date: 1995-03-25
Quality Attribute Accuracy: Accuracy of the shoreline type attributes was not assessed.
CGIS checked the accuracy of the erosion rate classification by displaying both the shore-normal transects and the shoreline, color-coded, respectively, by erosion rate (ft/yr) and erosion rate category (high, moderate, low, etc.). If the color of the transects matched the color of the ... associated shoreline segment, CGIS accepted the erosion rate classification. Otherwise, CGIS changed the classification.
Logical Consistency Report: EDI checked logical consistency through a series of quality assurance/quality control (QA/QC) procedures, reported in Section 2.5.2 Process Step (interpretation/extraction of shorelines).
Completeness Report: The area covered includes 125 7.5-minute quadrangles lying at least partially within Baltimore City or one of the 16 coastal counties of Maryland. (Appendix 2 lists the quadrangles for which shoreline rates-of-change were calculated. Appendix 3 lists the constituent quadrangles of each county.) Shorelines located in out-of-state areas, such as the Virginia side of the Potomac River, were excluded.
In digitizing historical shorelines from hard copy maps, MGS had adopted an operational definition of the headward extent of a stream - the point at which the stream was represented on the map by a single line rather than a double line delineating opposite stream banks. That point, dependent as it is on the scale of the map, does not necessarily represent the head of tide. A similar criterion was used in extracting the 1990 shoreline. To the extent that the contractor could fit a double line on photography displayed at a scale of 1:24,000, the shoreline was extracted. Reaches upstream of that point were excluded. Again, the headward extent of a digitized stream does not necessarily correspond with head of tide.
Shorelines in the 1990 data set bounded several different wetlands classifications (Cowardin et al., 1979):
E 1 UB L (Estuarine -- Subtidal -- Unconsolidated bottom -- Subtidal)
E 2 US M (Estuarine – Intertidal – Unconsolidated shore – Irregularly exposed)
E 2 US N (Estuarine – Intertidal – Unconsolidated shore – Regularly flooded)
E 2 US P (Estuarine – Intertidal – Unconsolidated shore – Irregularly flooded)
M 2 US M (Marine – Intertidal – Unconsolidated shore – Irregularly exposed)
M 2 US N (Marine – Intertidal – Unconsolidated shore – Regularly flooded)
R 1 UB V (Riverine -- Tidal -- Unconsolidated bottom -- Permanent tidal (tidally influenced, freshwater system)
R 2 UB 8 – (Riverine -- Lower perennial -- Unconsolidated bottom -- Eusaline)
In addition to designating UB L and UB V as water, M 2 or E 2 US (Unconsolidated shore) M (Irregularly flooded) or N (Regularly flooded) classifications were considered water, given that those areas were more likely to be under water than above. E 2 US P (Irregularly flooded) was considered upland, given that those areas were more likely to be above water than under. In assigning rate-of-change attributes, MGS and CGIS devised and applied a number of rules, which are summarized below:
Classify shoreline segments of the shoreline type “structure” as “protected.”
When adding nodes to distinguish between shoreline reaches with different rates of change, insert nodes only after the occurrence of a series of four or more similarly colored transects. For example, along an extensive reach that has experienced moderate rates of erosion, interrupted by two adjacent transects characterized by high erosion rates, classify the entire stretch of shoreline as “moderate.” If, instead of two high-rate transects, six high-rate transects occur in a row, insert nodes on either side of the six transects, and classify that shoreline reach as “high.”
If shorelines are so complex that it is difficult to distinguish between the two shoreline years or to see that they are properly positioned, assign the erosion rate category “Unknown.” This problem is particularly common in marshy areas and/or along minor tributaries of dubious positional accuracy. A common manifestation of the latter is that one bank of the tributary is erosional along its entire length, while the opposite bank is accretional.
For reaches lacking transects, estimate rates based on the relative positions of the two shorelines. This situation is common along points of land projecting into the water.
Classify stretches represented by a single shoreline as “No Data.”
If the two shorelines interweave over an extended reach, with little lateral displacement, classify the stretch as “No Change.”
Horizontal Positional Accuracy Report: The DOQQs meet National Map Accuracy Standards at the production scale of 1:12,000, using the American Society for Photogrammetry and Remote Sensing (ASPRS) method. The contractor who produced the DOQQs provided a detailed aerotriangulation report for each production area (See DOQQ metadata at the web site listed in Section 2.5 Lineage).
The production of accurately georeferenced DOQQs depends on sufficient ground control. In open water, ground control is necessarily lacking, because land areas, if they exist at all, are small and/or inaccessible. Two quarter quads in the data set, Deal Island NW and Barren Island NE, contain so much open water that they are not properly tied to the adjoining tiles, Nanticoke SW and Honga NW, respectively. Consequently, the corresponding linework (shoreline) is not properly georeferenced. The shorelines derived from those two DOQQs are included in the data set solely for the associated attribute (shoreline type) information. Their positions are inaccurate.
Access Constraints None
Use Constraints The DOQQs from which the shorelines were interpreted meet National Map Accuracy Standards at the production scale of 1:12,000 using the American Society for Photogrammetry and Remote Sensing (ASPRS) method. Consider the scale in displaying and using the vectors. Displaying the vectors at scales larger than those of the source documents is considered bad practice.The aerial photography from which the DOQQs were developed was not tide-coordinated. Therefore, shorelines in this data set do not represent a consistent vertical datum.
Data Set Progress
Distribution Media: Online
Fees: No fees
Role: TECHNICAL CONTACT
Email: lhennessee at mgs.dnr.md.gov
2300 St. Paul Street
Province or State: MD
Postal Code: 21218
Conkwright, R.D. (compiler), 1975, Historical Shorelines Atlas: Maryland Geological Survey, Baltimore, Md., 4 volumes.
Cowardin, L.M., Carter V., Golet, F., and LaRoe, E., 1979, Classification of wetlands and deep water habitats of the United States: U.S. Fish and Wildlife Service, 103 pp.
Danforth, W.W., and Thieler, E.R., 1992, Digital Shoreline Analysis System (DSAS) User’s Guide, Version ... 1.0: U.S. Geological Survey Open-File Report 92-355, 18 p.
Hennessee, L., 2000a, Metadata: Historical shorelines, 1841-1976, Chesapeake Bay region of Maryland (CD-ROM SCSL_RVC): Maryland Geological Survey, Baltimore, Md.
Hennessee, L., 2000b, Metadata: Maryland digital shoreline acquisition from recent orthophotography: Recent (ca. 1990) shorelines, coastal regions of Maryland (CD-ROM RecentSL): Maryland Geological Survey, Baltimore, Md.
Thieler, E.R., O’Connell, J.F., and Schupp, C.A., 2001, The Massachusetts Shoreline Change Project: Technical Report 1800s to 1996, U.S. Geological Survey Administrative Report, Woods Hole, MA.
Extended Metadata Properties
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Creation and Review Dates
DIF Creation Date: 2011-12-27
Last DIF Revision Date: 2017-08-24