BOARD01965

• Board Meeting Date: 3/22/2005
• Description: Flood Section - Presentation of the CWCB's Draft Rules and Regulations for Regulatory Floodplains in Colorado
• Board Meetings - Doc Type: Memo

Guidelines and Specifications for Flood Hazard Mapping Partners [April 2003)

Table A-2. Comparison of Vertical Accuracy Standards

NMAS NMAS NSSDA NSSDA ASPRS 1990
Contuur VMAS Accurac}. RMSE. Class 1/2/3
Interval 90% ~'Onfldenct' level 95% confldenee level Limiting RMSE,
2 feet I foot 1.2 feet 0.6 foot O. Hoot (Class I)
18.5 1.3 feet (Class 2)
centimeters 2.0 feet (Class 3)
4 feet 2 feet 2.4 feet 1.2 feet 1.3 feet (Class I)
37.0 2.7 feet (Class 2)
centimeters 4.0 feet (Class 3)

A.3.3

Accuracy Labeling

[February 2002]

Because contours or DEMs are not printed on DFlRMs, their vertical accuracy does not need to be
labeled on DFIRMs, but the vertical accuracy is still recorded in the metadata of elevation datasets
used for hydrologic and hydraulic modeling. If tested to a vertical RMSE of 0.6 foot
(18.5 centimeters), for example, and recognizing that Accuracyz = 1.9600 x RMSEz when errors
have a normal distribution, the metadata would read as follows:

Tested 1.2-foot vertical accuracy at 95-percent confidence level

DFlRMs published at I "=500' scale with community-provided base maps or digital orthophotos
compiled at 1"=500' or smaller scales (e.g., 1"=400', 1"=200', and I "=100') would be labeled as
follows:

Compiled to meet 19-foot horizontal accuracy at 95-percent confidence level

DFIRMs published at either 1"=500' or 1"=1,000' with default USGS DOQs, compiled at
1"=1000', would be labeled as follows:

Compiled to meet 38-foot horizontal accuracy at 95-percent confidence level

Similarly, DFIRMs published at I "=2,000' would be labeled as follows:

Compiled to meet 45.6-feet horizontal accuracy at 95-percent confidence level

A-9

Section A.3