Idaho Administrative Code › Title IDAPA 37 - Water Resources, Department of › Rule 37.03.06 - SAFETY OF DAMS RULES › Section 37.03.06.060 - EXISTING DAMS AND RESERVOIRS

Current through August 31, 2023
All dams and reservoirs regulated by the Department shall be
				operated and maintained to retain the existing structural dimensions, to resist
				deformations or movement, and to maintain the hydraulic capacity of the outlet
				works, spillway, and other discharge features as designed and constructed, or
				as otherwise required by these rules. (3-30-23)
01.
Analyses Required
. The
			 analyses required by Rule
			 035 shall apply to all existing
			 dams when the Director specifically requires the analyses. Where applicable,
			 non-embankment dams shall comply with the following criteria. (3-30-23)
a. Every dam shall have an overflow spillway
			 with a capacity that will pass an inflow design flood of one percent (1%)
			 probability of occurrence (i.e., Q100) or more, with the reservoir or the
			 impoundment full to the spillway crest while maintaining the freeboard required
			 by Rule 050.06.
			 (3-30-23)
b. The Director may
			 lessen or waive the spillway requirement for dams that demonstrate out-ofstream
			 (off-channel) storage. (3-30-23)
c.
			 The release capability or discharge capacity can include the combined rates of
			 flow for multiple appurtenances; for example, spillways, outlets, diversion
			 facilities, or other constructed conveyance features. Approved operating
			 procedures which can be shown to utilize upstream storage, diversion, and
			 reservoir flood routing to reduce flood runoff events may also be considered.
			 The remainder of the required release capacity, if any, may be met by the
			 following: (3-30-23)
i. Reconstruction,
			 enlargement or addition of spillways, outlets, diversion facilities, or other
			 constructed conveyance features. (3-30-23)
ii. A showing acceptable to the Director that
			 potential failure of the dam during a flood of the specified magnitude
			 described in Rule 050.11
			 would be incrementally small in comparison to the flood being considered, and
			 that the release of reservoir would not substantially increase downstream
			 damages to life and property which are anticipated to result from any natural
			 flood equal to or exceeding that magnitude. (3-30-23)
iii. A showing acceptable to the Director
			 that limiting physical factors unique to the project site exist that prevent
			 construction of a spillway or other release capability mechanisms during a
			 flood of the specified magnitude described in Rule O5O.11, and provided the
			 owner implements storage operational procedures, or restrictions, or provides
			 for emergency warning to protect life and property.
			 (3-30-23)
d. Seismic
			 loads shall be evaluated and applied to dam stability. The Director may require
			 that evaluation of seismic loads for large and high hazard structures shall use
			 the maximum ground motion/acceleration generated by the maximum credible
			 earthquake. For any existing dam, the Director may accept maximum ground
			 motion/acceleration corresponding to specified return intervals using a
			 probabilistic evaluation of earthquake history in accordance with USGS hazard
			 maps using a minimum return interval of 2 percent (2%) probability of
			 exceedance in fifty (50) years, or greater interval, as determined by the
			 Director. (3-30-23)
e. The Director
			 may accept existing studies relative to requirements of Rule
			 060.01.
a. and Rule
			 060.01.d., if the Director
			 determines the information provided fulfills the requirements of the rules.
			 (3-30-23)
f. The Director may allow
			 the owner of an existing dam a compliance period to complete structural
			 modifications or implement other improvements deemed necessary to provide the
			 necessary hydraulic capability. (3-30-23)
g. The Director may allow the owner of an
			 existing dam a compliance period to complete structural modifications or
			 implement other improvements deemed necessary to resolve seismic stability or
			 safety concerns. (3-30-23)
h.
			 Within thirty (30) days after completing the analyses required in Rules
			 060.01.a. or 060.01.d., the
			 owner of an existing dam found deficient by either analyses shall file with the
			 Director a plan and schedule for mitigating the deficiency.
			 (3-30-23)