Idaho Admin. Code r. 37.03.06.060

Current through September 2, 2024

Section 37.03.06.060 - EXISTING DAMS AND RESERVOIRS

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.

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.

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.

b. The Director may lessen or waive the spillway requirement for dams that demonstrate out-of-stream (off-channel) storage.

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:

i. Reconstruction, enlargement or addition of spillways, outlets, diversion facilities, or other constructed conveyance features.

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.

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.

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.

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.

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.

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.

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.

02.Other Requirements.

a. Routine maintenance items include the following:

i. Eradication of rodents and filling animal burrows;

ii. Removal of vegetation and debris from the dam;

iii. Restoring original dimensions of the dam by the addition of fill material;

iv. Addition of bedding or riprap material which will not increase the height or storage capacity;

v. Repair or replacement of gates, gate stems, seals, valves, lift mechanisms or vent pipes with similar equipment; or

vi. Repair or replacement of wingwalls, headwalls or aprons including spalling concrete.

b. The following are not routine maintenance items and are subject to design review and approval prior to commencing construction:

i. Alteration or modification of embankment slopes;

ii. Replacement, reconstruction, or extension of outlets;

iii. Foundation stabilization;

iv. Filter or drain construction or replacement;

v. Spillway size alteration or modification;

vi. Installation of instrumentation or piezometers; or

vii. Release capability or reservoir storage modification.

c. Items not specifically described in Rules 060.02.a. and 060.02.b. will be determined by the Director as either routine or non-routine upon receipt of a written request from the owner or their representative seeking such a determination.

d. Where riprap is required to prevent erosion and to maintain a stable embankment, pipes, cables, brush, tree growth, logs, or floating debris are not acceptable substitutes for rock riprap and granular bedding material. Dams or portions thereof which are stable without riprap, are not required to have riprap.

e. Upon completion of reconstruction of a dam or feature of a dam included in Rule 060.02.b., the owner or their engineer shall provide the Director a written narrative account of all items of work. Record drawings and revised specifications shall be submitted to the Director if the completed project has been substantially changed from the plans and construction specifications originally approved.

f. Upon request, the owner of every dam shall provide their name and address to the Director and shall advise the Director of future changes in ownership. If the owner does not reside in Idaho, the owner shall provide the name and address of the person residing in Idaho who is responsible for the operation, maintenance, and repair of the dam.

Idaho Admin. Code r. 37.03.06.060

Effective March 30, 2023