SLAMM Elevation Defaults and Notes
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SLAMM #CategoryDefault Lower-Bound Elevation Notes
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1&2Upland (dry land)Greater than Salt Elevation1 in 30 day inundation, consider modifying "salt elevation" rather than this range. Shouldn't differ between developed and undeveloped.
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3SwampGreater than Salt ElevationSometimes modified, but not usually, site specific data may suggest tidal swamp conversion is appropriate.
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4Cypress SwampGreater than Salt ElevationDefault is probably misleading. This category can handle being semi-permanently flooded. Set to MLLW for Louisiana based on site specific data. However, once permanently flooded, cannot regenerate.
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5Inland Fresh MarshGreater than Salt ElevationGenerally set to salt elevation. Check for dike issues or tidal influence before modifying this.
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6Tidal Fresh MarshNone Exists, Site SpecificThese categories move as a function of salinity, which is a function of both elevation and local fresh water flow and tide range
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7Transitional Salt Marsh1 HTU (=MHHW)This could be adjusted slightly. Scrub shrub/transitional salt marsh tends to be irregularly flooded so shouldn't go below 1/2 HTU I wouldn't think.
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8Reg Flood Marsh0 HTU (=MTL)Especially in macrotidal may extend below MTL by a few cm. See McKee and Patrick, 1988
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9Mangrove0 HTU (=MTL)Keep near MTL.
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10Estuarine Beach-1 HTU (=MLLW)NWI does not control for tide level when imagery is taken so sometimes the beach to open water interface is closer to MTL. Shouldn't extend much below -1 HTU, however.
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11Tidal Flat-1 HTU (=MLLW)See Estuarine Beach Notes.
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12Ocean Beach-1 HTU (=MLLW)See Estuarine Beach Notes.
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13Ocean Flat-1 HTU (=MLLW)Category rarely utilized by NWI.
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14Rocky Intertidal-1 HTU (=MLLW)Probably the notes from Estuarine beach also apply here.
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15Inland Open WaterGreater than Salt ElevationOpen water, we generally do not worry about
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16Riverine TidalGreater than Salt ElevationOpen water, we generally do not worry about
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17Estuarine WaterN / AN / A
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18Tidal CreekGreater than Salt ElevationOpen water, we generally do not worry about
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19Open OceanN / AN / A
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20Irreg. Flood Marsh0.5 HTULiDAR data suggest that these high marshes tend to extend down to the midpoint between MTL and MHHW but some flexibility on this boundary is certainly appropriate. Shouldn't be all the way to MTL, though nor above MHHW.
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21Not UsedN / AN / A (was "tall spartina")
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22Inland ShoreGreater than Salt ElevationNot often used by NWI. Some flexibility OK.
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23Tidal SwampNone Exists, Site SpecificThese categories move as a function of salinity, which is a function of both elevation and local fresh water flow and tide range
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24BlankN / AN / A
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25Veg. Tidal FlatSite specific. Category not derived from NWI data.
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26BackshoreSite specific. Category not derived from NWI data.
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