National Inventory of Dams
Data Dictionary

Dam Name
Official name of the dam. No abbreviations used unless a part of the official name. For dams that do not have an official name, the popular name is used.

Other Dam Names
Reservoir name or names in common use other than the official name of the dam. Names are separated with semi-colons. Leave blank if not applicable.

State or Federal Agency ID
Official State or Agency identification number for the dam.

NID ID
The official NID identification number for the dam, known formerly as the National ID. This is a required field, and must have an entry for each dam included in the NID. This field is used as the unique identifier for each dam record. The first two characters of the identity are the state two-letter abbreviation, based on the location of the dam. The last five characters of the identity are a unique number (AB#####).

Longitude
Longitude at dam centerline as a single value in decimal degrees.

Latitude
Latitude at dam centerline as a single value in decimal degrees.

Section, Township, Range Location
Dam location in terms of Section, Township, and Range. Meridian location is included if it is needed to locate the dam. (Optional field)

County
Name of the county in which the dam is located.

River or Stream
Official name of the river or stream on which the dam is built. If the stream is unnamed, it is identified as a tributary ("TR") to the named river. If the dam is located offstream, the name of the river or stream is entered plus "-OS" or "OFFSTREAM".

Nearest City/Town
Name of the nearest city, town, or village that is most likely to be affected by floods resulting from the failure of the dam.

Distance to Nearest City/Town
Distance from the dam to the nearest affected City/Town/Village, to the nearest mile (and tenth if appropriate).

Owner Name
Name of the owner of the dam.

Owner Type
Code indicating owner type:
F for Federal;
S for State;
L for Local Government;
U for Public Utility;
P for Private.

Dam Designer-----New field
Name of the principal firm(s) or agency accomplishing design of dam and major appurtenant operating features, and major modifications. The original designer is listed first then modification designers (if applicable). The names are separated with semi-colons.

Private Dam On Federal Property
Code indicating whether the dam is a private dam located on federal property:
Y for Yes;
N for No.

Dam Type
Code indicating the type of dam (in order of importance): RE for Earth;
ER for Rockfill;
PG for Gravity;
CB for Buttress;
VA for Arch;
MV for Multi-Arch;
CN for Concrete;
MS for Masonry;
ST for Stone;
TC for Timber Crib;
OT for Other.

Core-----New field
Code indicating the position, type of watertight member and certainty.
Position:
F for upstream facing;
H for homogeneous dam;
I for core;
X for unlisted/unknown;

Type: A for bituminous concrete;
C for concrete;
E for earth;
M for metal;
P for plastic;
X for unlisted/unknown;

Certainty:
K for known;
Z for estimated;

Purposes
Codes indicating the purposes for which the reservoir is used:
I for Irrigation;
H for Hydroelectric;
C for Flood Control and Storm Water Management;
N for Navigation;
S for Water Supply;
R for Recreation;
P for Fire Protection, Stock, Or Small Farm Pond;
F for Fish and Wildlife Pond;
D for Debris Control;
T for Tailings;
O for Other.

Year Completed
Year when the original main dam structure was completed, optionally followed by code ("E") to indicate an estimated date. If unknown, and reasonable estimate is unavailable, "0000" will be used.

Dam Length
Length of the dam, in feet, which is defined as the length along the top of the dam. This length also includes the spillway, powerplant, navigation lock, fish pass, etc., where these form part of the length of the dam. If detached from the dam, these structures should not be included.

Dam Height
Height of the dam, in feet to the nearest foot, which is defined as the vertical distance between the lowest point on the crest of the dam and the lowest point in the original streambed.

Structural Height
Structural height of the dam, in feet to the nearest foot, which is defined as the vertical distance from the lowest point of the excavated foundation to the top of the dam.

Hydraulic Height
Hydraulic height of the dam, in feet to the nearest foot, which is defined as the vertical difference between the maximum design water level and the lowest point in the original streambed.

NID Height
A calculated field based on the maximum value of field items #25 Dam Height, #26 Structural Height, and #27 Hydraulic Height, providing a single height value to facilitate database queries.

Maximum Discharge
Number of cubic feet per second (cu ft/sec) which the spillway is capable of discharging when the reservoir is at its maximum designed water surface elevation.

Maximum Storage
Maximum storage, in acre-feet, which is defined as the total storage space in a reservoir below the maximum attainable water surface elevation, including any surcharge storage.

Normal Storage
Normal storage, in acre-feet, which is defined as the total storage space in a reservoir below the normal retention level, including dead and inactive storage and excluding any flood control or surcharge storage.

NID Storage
A calculated field based on the maximum value of field items #30 Maximum Storage and #31 Normal storage, providing a single storage value to facilitate database queries.

Surface Area
Surface area, in acres, of the impoundment at its normal retention level.

Drainage Area
Drainage area of the dam, in square miles, which is defined as the area that drains to a particular point (in this case, the dam) on a river or stream.

Downstream Hazard Potential
Code indicating the potential hazard to the downstream area resulting from failure or misoperation of the dam or facilities:
L for Low;
S for Significant;
H for High.