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

classification. Ifthe classification has changed, then the provisions of these Rules and
specifically Rule 5 apply.

6.1.4. I Whenever the methods of Rule 5 apply, the minimum requirements for
determining the spillway capacity are summarized in the following table, but may be
reduced for good cause shown. Spillways designed in accordance with these Rules
will not be required to be enlarged due to subsequent revisions in PMP estimates,
unless, in the opinion of the State Engineer, a substantial increased threat to public
safety exists.

INFLOW DESIGN FLOOD REQUIREMENTS
Hazard Class Hil!h Sil!nificant Low NPH
Dam Size
Large .75 (.9PMP) .50 (.9PMP) 100 YR 50YR
Small .75 (.9PMP) .50 (.9PMP) 100 YR 25YR
Minor .50 (.9PMP) 100 YR 50YR 25YR

INFLOW DESIGN FLOOD REQUIREMENTS FOR EXISTING DAMS
REDUCED FOR ELEVATION

Hazard Classification Hil!b Sil!nificant
Dam Size
Large - General Storm East
6,000 - 12,000 ft MSL .75 (.8 PMP) .50 (.8 PMP)
Above 12,000 ft MSL .75 (.7 PMP) .50 (.7 PMP)
General Storm West
5,000 - 8,000 ft MSL .75 (.8 PMP) .50 (.8 PMP)
Above 8,000 ft MSL .75 (.7 PMP) .50 (.7 PMP)
Local Storm
10,000 - 11,500 ft MSL .75 (.8 PMP) .50 (.8 PMP)
11,501 - 13,000 ft MSL .75 (.7 PMP) .50 (.7 PMP)
Above 13,000 ft MSL .75 (.6 PMP) .50 (.6 PMP)
Small- General Storm East
6,000 - 12,000 ft MSL .75 (.8 PMP) .50 (.8 PMP)
Above 12,000 ft MSL .75 (.7 PMP) .50 (.7 PMP)
General Storm West
5,000 - 8,000 ft MSL .75 (.8 PMP) .50 (.8 PMP)
Above 8,000 ft MSL .75 (.7 PMP) .50 (.7 PMP)

26