BOARD01548

• Board Meeting Date: 1/25/2005
• Description: Proposed Revisions to the Rules and Regulations for Dam Safety and Dam Construction
• Board Meetings - Doc Type: Memo

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5.5.6.8 The minimum size spillway for all High Hazard, Significant Hazard, and
Large and SmaIl Low Hazard jurisdictional size dams shaIl be capable of passing the
inflow design flood generated by a 24-hour, I OO-year rainstorm event.

5.5.7 The HMR PMP used to determine the IDF may be reduced based on the average
elevation of the drainage basin. The HMR PMP value may be adjusted for the determination
of the IDF for drainage basins above 5,000 (ft) MSL in accordance with the foIlowing:

General Storm
East of the Continental Divide
Elevation (ft)
6,000 to 12,000
Above 12,000

%Reduction
20
30

West of the Continental Divide
Elevation (ft)
5,000 to 8,000
Above 8,000

% Reduction
20
30

Local Storm
Statewide
Elevation (ft)
10,000 to 11,500
11,501 to 13,000
Above 13,000

%Reduction
20
30
40

INFLOW DESIGN FLOOD REQUIREMENTS
REDUCED FOR ELEVATION

Hazard Classification Hieh Sienificant
Dam Size
Large - General Storm East
6,000 - 12,000 ft MSL .8PMP .75 (.8 PMP)
Above 12,000 ft MSL .7PMP .75 (.7 PMP)
General Storm West
5,000 - 8,000 ft MSL .8PMP .75 (.8 PMP)
Above 8,000 ft MSL .7PMP .75 (.7 PMP)
Local Storm
10,000 - 11,500 ft MSL .8PMP .75 (.8 PMP)
11,501 - 13,000 ft MSL .7PMP .75 (.7 PMP)
Above 13,000 ft MSL .6PMP .75 (.6 PMP)

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