National Levee Database

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

Baseline Geospatial Features

Typically required for all systems to create a viable levee system record in the NLD.

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