Okla. Admin. Code § 785:25-3-6

Current through Vol. 42, No. 3, October 15, 2024

Section 785:25-3-6 - Minimum spillways performance standards

(a)General performance standards.

(1) Except as otherwise provided in this Chapter, all dams must meet or exceed the following performance standards as determined by analysis of plans and specifications for the dam and existing site conditions.

(2) Owners of existing dams which do not meet the following performance standards must make necessary changes in the dam to meet the applicable performance standards.

(3) The discharge capacity and/or storage capacity of the project shall be capable of passing the indicated spillway design flood without infringing on the minimum freeboard requirements, provided that a design which includes overtopping of the dam may be authorized if specifically approved by the Board.

(4) The minimum performance standards expressed as magnitude of spillway design flood and minimum freeboard will be assigned to the various size and hazard potential classification determined under 785:25-3-3 as described in Appendix B.

(b)Amending minimum freeboard. The minimum freeboard requirement may be amended by the Board on a case-by-case basis for good cause shown by the owner.

(c)Probable maximum flood.

(1) PMF means and refers to the Probable Maximum Flood and is defined as the flood that may be expected from the most severe combination of critical meteorologic conditions, defined as the Probable Maximum Precipitation (PMP), and critical hydrologic conditions that are reasonably possible in the region.

(2) Since design floods are usually determined by using mathematical computations through computer modeling and since several different acceptable models are available, flood design calculations must fall within plus/minus 5% PMF of the Board's current model results.

(3) The PMF storm should be the most conservative PMP storm type and duration to adequately reflect the size and hydrologic characteristics of the watershed in which the dam is located.

(4)Regional Probable Maximum Precipitation Study for Oklahoma, Arkansas, Louisiana, and Mississippi (Applied Weather Associates, 2019) shall be used in determining precipitation depth, area, and duration relationships for the PMP. The location-specific precipitation depth-area-duration relationship shall be applied to the spatial and temporal distribution methods described in Hydrometeorological Report No. 52 (National Oceanic and Atmospheric Administration, 1982).

(d)PMF on dam designated for regulation. Adam which the Board has determined is subject to regulation because of its high hazard potential, although otherwise considered too small, shall be required to safely pass 25% PMF with no minimum freeboard.

(e)Dams constructed prior to June 13, 1973.

(1) Any dam constructed prior to June 13, 1973, classified as having high hazard-potential as described in 785:25-3-3 shall be required to pass a minimum design flood as follows:

(A) Small size - 25% PMF with one foot of freeboard.

(B) Intermediate size - 50% PMF with no minimum freeboard.

(C) Large size - 75% PMF with no minimum freeboard.

(2) Proposed designs to enlarge, alter, or repair a spillway of any dam constructed prior to June 13, 1973, may be required meet the general performance standards set forth in 785-25-3-6(a) as determined by the Board. Provided that any dam constructed prior to June 13, 1973, that does not meet minimum spillway performance standards in Appendix B, and the spillway/spillways is/are proposed to undergo substantial modification, the minimum spillway performance standards defined in 785-25-3-6(a) shall be met by the proposed design.

(f)Dams constructed after 1973 without Board approval. An owner of a dam constructed after 1973 without prior approval by the Board shall remove the dam or may request a variance or waiver from the requirement for submittal of plans and specifications as provided for in 785:25-5-2 and 785:25-5-3, provided the owner of the dam shall submit an application containing the following:

(1) A topographic map of the dam site showing the location of spillway and outlet works.

(2) Drawings showing the length, width, and height of dam.

(3) Detailed plans of spillway structures, spillway profile, and procedures for operating of the spillway structure.

(4) Hydrologic and hydraulic analysis report as described in Hydrologic and Hydraulic Guidelines for Dams in Oklahoma, Oklahoma Water Resources Board, Dam Safety Program, August 2011.

(5) Complete a dam breach inundation analysis and map if Board staff determines the dam may be a significant or high hazard-potential structure.

(6) Inspection of the dam by a registered Professional Engineer and submit a written inspection report to the Board not later than 30 days after the inspection and shall contain information as set forth in a Board hazard inspection report.

(7) Pay minimum application fee as provided in 785:5-1-9(a) and 785:5-1-9(f).

(8) In addition, the applicant may be required to submit a detailed geotechnical investigation and analysis of the dam and report on such investigation. The geotechnical investigation shall include a minimum boring layout as follows:

(A) One (1) crest boring extending through the embankment and foundation materials to bedrock.

(B) Two (2) crest borings extending through the embankment and foundation materials to bedrock, one near each abutment.

(C) One (1) boring extending through the embankment and foundation materials to bedrock near the mid-height on the downstream slope of the dam.

(D) One (1) boring extending through the embankment and foundation material to bedrock along the toe of the dam.

Okla. Admin. Code § 785:25-3-6

Amended at 9 Ok Reg 1675, eff 5-11-92 ; Amended at 12 Ok Reg 2687, eff 7-1-95 ; Amended at 30 Ok Reg 881, eff 6-13-13

Amended by Oklahoma Register, Volume 37, Issue 24, September 1, 2020, eff. 9/11/2020

Amended by Oklahoma Register, Volume 41, Issue 22, August 1, 2024, eff. 8/11/2024