NAC535.240. Requirements for approval.

     1. Except as otherwise provided in NAC 535.220, to obtain the approval of the State Engineer pursuant to NRS 535.010, the plans and specifications must, in addition to all other applicable requirements, demonstrate to the satisfaction of the State Engineer that:

     (a) The dam and reservoir are able to accommodate the inflow design flood for the tributary watershed without the failure of the dam or any other unintended release of water.

     (b) The inflow design flood selected is appropriate given the intended purpose, hazard classification and size of the dam.

     2. For the purposes of this section, the inflow design flood used for design purposes must not, except as otherwise provided in subsection 3, be less than:

     (a) A probable maximum flood, if the dam:

          (1) Is classified as high hazard or is a large dam and classified as significant hazard; or

          (2) Lacks one or more spillways.

     (b) The greater of one-half of the probable maximum flood or a flood whose annual chance of exceedence is 0.2 percent, if the dam is a small or medium dam and is classified as significant hazard.

     (c) A flood whose annual chance of exceedence is 1 percent, for all other dams.

     3. The State Engineer will approve plans that use an inflow design flood which is less than those set forth in subsection 2 if the applicant provides an incremental damage analysis that demonstrates, to the satisfaction of the State Engineer, that a lesser event is appropriate.

     4. An applicant may use one or more watershed diversion structures in lieu of spillways for the protection of a dam embankment so long as:

     (a) The impoundment created by the embankment so protected is temporary; and

     (b) The diversion structures are designed to accommodate the greater of the inflow design flood or five times the expected life of the impoundment.

     5. A dam must have freeboard adequate to prevent overtopping by wave run-up and reservoir fetch above the storm surcharge elevation. The adequacy of the freeboard must be demonstrated by evidence satisfactory to the State Engineer in the form of:

     (a) A wave run-up and reservoir fetch calculation; or

     (b) Proof that the freeboard is not less than 3 feet above the storm surcharge elevation.

     6. As used in this section, “storm surcharge elevation” means the elevation that the water surface would reach if the inflow design flood of a dam were added to a reservoir that is at its maximum conservation elevation.

     (Added to NAC by St. Engineer by R124-02, eff. 5-30-2003)