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 Accretion Protected Unknown No DataThe 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. It was amended to include information about the erosion rate attributes later assigned to the county shorelines.
1. E 1 UB L (Estuarine -- Subtidal -- Unconsolidated bottom -- Subtidal) 2. E 2 US M (Estuarine -- Intertidal -- Unconsolidated shore -- Irregularly exposed) 3. E 2 US N (Estuarine -- Intertidal -- Unconsolidated shore -- Regularly flooded) 4. E 2 US P (Estuarine -- Intertidal -- Unconsolidated shore -- Irregularly flooded) 5. M 2 US M (Marine -- Intertidal -- Unconsolidated shore -- Irregularly exposed) 6. M 2 US N (Marine -- Intertidal -- Unconsolidated shore -- Regularly flooded) 7. R 1 UB V (Riverine -- Tidal -- Unconsolidated bottom -- Permanent tidal (tidally influenced, freshwater system) 8. 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."
1. Color-coding transects according to previously established rate-of-change categories: High - High erosion rate (more than 8 ft/yr) Moderate - Moderate erosion rate (4-8 ft/yr) Low - Low erosion rate (2-4 ft/yr) Slight - Slight erosion rate (0-2 ft/yr) Accretion 2. Visually grouping similarly colored transects, 3. Inserting nodes between transects that differed in color, and 4. Assigning the appropriate classification code to the shoreline reach.The rules that CGIS followed in the process are described in Completeness Report.