DATABASE
Data Dictionary and Descriptions
NLD Data Specifications
The NLD is a digital dataset that includes geospatial, database tables and document information. Information in the database must conform to a standardized structure, contain standardized data values, hold valid relationships and represent approved content. The NLD Data Management Business Process document provides a breakdown of the data specifications and processes to compile key data to submit and update the database.
NLD Data Dictionary and Data Descriptions
Geospatial Features
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Horizontal Coordinate Reference System: North American Datum of 1983 (NAD 83)
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Vertical Datum: North American Vertical Datum of 1988 (NAVD 88).
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Units of reference: International feet (recent move from US Survey feet)
Baseline Geospatial Features
Typically required for all systems to create a viable levee system record in the NLD.
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The feature may have elevation storage capability, but elevations may not be populated if the data was not provided at the time of loading.
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In the case of point feature the capability to store the elevation value is present in the data model.
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In the case of lines where it is noted of "M" or measure capability then linear referencing measures in feet is supported. Typically, only the System Route lines includes measure to support the levee profile displays.
| Feature Name | Geometry Type | Has Vertical (Z) and Measures (M) | Definition |
|---|---|---|---|
| Embankment | line | Z | Embankment to restrict the intrusion of floodwaters into the leveed area. |
| Floodwall | line | Z | A structure erected to restrict the intrusion of floodwaters into the leveed area. |
| Closure Structure | line | Z | The means to close a vehicular, railroad, pedestrian or other opening in the flood control system. |
| Alignment Line | line | Z | The features that make up the levee system alignment including high natural ground, highway embankments, floodwalls, railroads embankments. |
| System Route | line | Z & M | The all-encompassing levee system alignment/profile line and includes vertical elevation and measures. |
| Leveed Area | polygon | NA | The area of a floodplain from which flood water is excluded by the levee system. |
| Stationing | point | NA | A location of a specific levee distance mark along the length of the flood control system from a designated beginning point. |
| Crossings | point | Z opt | A location on a levee or floodwall where crossings occur (utilities or other features). |
| Cross Section | line | Z | A geometric line perpendicular to the flood control segment detailing the elevations along that line. |
| Channel (Associated with levee system and not standalone project) | line | NA | Natural, concrete lined, or armored diversion feature for floodwater flows to be released into less critical areas. |
System Infrastructure Geospatial Features
Additional infrastructure features to add important supporting feature to performance of a levee system. These features, if present on the levee system, are highly recommended to be captured and input into the NLD.
| Feature Name | Geometry Type | Has Vertical (Z) and Measures (M) | Definition |
|---|---|---|---|
| Piezometer | point | Z | The location of an open tube placed in the ground or a structure which is used to measure subsurface water elevation. |
| Pipe | point | Z | A structure designed to allow flow of water from the interior of a levee unit to the waterside. |
| Gate | point | Z | Gate associated and attached to a Pipe |
| Pump Station | point | Z | An area or location where a pump is located to pump water from the interior of a levee. |
| Relief Well | point | Z | Well location installed to reduce interior pore pressures. |
| Toe Drain | line | Z | Trench that runs parallel to the levee or floodwall at the landside edge, that provides a positive outlet for local under seepage and a check for controlling piping and/or excessive uplift pressure. |
NLD Data Fields
A detailed NLD Data Dictionary can be downloaded here. Detailed data fields can be accessed through the various data web services listed at the beginning of the page or through a login account to the website. For more information contact the helpdesk.
Calculated fields in the NLD
Several fields in the NLD are not editable by data managers and are calculated automatically by the system as geometries are created or change. For example, a new levee is input into the NLD, the length is automatically calculated and displayed. The use of spatial intersections with other national datasets and spatial calculations like length and area routinely occur in the NLD and are tagged as such with hover text or other metadata references.
Acronyms
| API | Application Programming Interface |
| FEMA | Federal Emergency Management Agency, Department of Homeland Security |
| GCS | Geographic Coordinate System |
| GIS | Geospatial Information Systems |
| JSON | JavaScript Object Notation |
| NLD | National Levee Database |
| LIDAR | Light Detection and Ranging |
| NFIP | National Flood Insurance Program |
| NSI | National Structure Inventory |
| USACE | U. S. Army Corps of Engineers, Department of Defense |
| USGS | U. S. Geological Survey, Department of the Interior |
