The breach of the dam and critical appurtenant structures and the subsequent downstream routing of the resulting breach hydrograph shall be modeled in accordance with the requirements of this section. Failure scenarios shall be applied separately to the dam and each critical appurtenant structure. The results of the inundation model shall be used to prepare an inundation map.
(a) Modeling Assumptions for each Failure Scenario. A sunny-day loading condition is required for the modeled breach of each dam and critical appurtenant structure. A storm-induced loading condition is not required, but may be submitted in lieu of a sunny-day loading condition.
(1) Each failure scenario shall assume the following:
(A) The reservoir is at the maximum possible storage elevation.
(B) The breach height of the dam or critical appurtenant structure as defined in section 335.2(a)(2).
(C) Any impounded sediment shall be modeled as water. In addition, a dam owner may also request to model impounded sediment as provided in section 335.6(a)(2).
(2) If a dam owner contends that impounded sediment should not be modeled as water, the dam owner may request department acceptance of a sediment release modeling approach.
(A) A request for acceptance of a sediment release modeling approach includes the following:
1. A letter requesting department acceptance of a sediment release modeling approach, and
2. Data and analyses that support the requested modeling approach. This includes, but is not limited to, volume of impounded sediment, bathymetry data, geotechnical data from sediment samples, and proposed inundation sensitivity analyses of the sediment characteristics such as volume released and flowability.
3. An inundation map with any impounded sediment modeled as water.
(B) After receiving a complete request, the department may require additional information that is necessary to evaluate the request before making a determination about whether to accept a sediment release modeling approach.
(C) After reviewing the complete request and other required information, the department shall notify the dam owner of its decision to accept or not accept the sediment release modeling approach. The acceptance of a sediment release modeling approach does not constitute approval of the resulting inundation map. All inundation maps are subject to department approval based on all applicable requirements of this article. If the department approves an inundation map based on the accepted sediment modeling approach, the approved map will supersede any previously approved maps for that dam or critical appurtenant structure.
(3) Failure scenarios for dams shall comply with the following:
(A) The dam owner shall select one of the following methods that are applicable to the dam for estimating breach parameters, except breach height, prescribed in section 335.6(a)(1)(B):
1. Table 9-3 of FEMA P-946, incorporated here by reference.
2. Chapter 2, Appendix II-A, Table 1 of Federal Energy Regulatory Commission's Engineering Guidelines for the Evaluation of Hydropower Projects (August 2015), incorporated here by reference.
3. A sensitivity analysis using equations appropriate for the dam in Table 2 of U.S. Department of the Interior's DSO-98-004 Prediction of Embankment Dam Breach Parameters (July 1998), incorporated here by reference, that produces the largest peak outflow.
4. Upon pre-approval by the department, alternative breach parameters that fulfill the purpose of section 335.6(a)(3)(A).
(B) If the release from a failure scenario could impact separate watercourses based on the assumed failure locations, the dam sections located upstream of each respective watercourse shall be failed independently as separate failure scenarios.
(4) Failure scenarios for critical appurtenant structures shall comply with the following, as applicable:
(A) For saddle dams, failure scenarios shall be modeled as described in section 335.6(a)(3).
(B) For gated critical appurtenant structures, all gates shall be breached simultaneously together with the control structure.
(C) Multiple gates affixed to concrete dams shall be failed collectively but separately from the dam.
(D) All critical appurtenant structures, except for saddle dams, shall assume a nearly instantaneous and complete failure.
(E) For any type of critical appurtenant structure and upon pre-approval by the department, the dam owner may assume an alternative failure mode that produces the largest peak outflow, as substantiated by a sensitivity analysis.
(5) If a failure scenario is expected to cause the failure of any downstream dams or critical appurtenant structures, the failure of those downstream dams and critical appurtenant structures shall be included in the model and map.
(b) Inundation Modeling Assumptions. The inundation model shall satisfy the following requirements:
(1) The elevation data shall be appropriate for the downstream development and terrain that would potentially be impacted by the failure scenario. The horizontal resolution of the data shall be ten meters or finer.
(2) The following describes the modeling software requirements used to simulate the inundation.
(A) An unsteady hydraulic model appropriate for the downstream development and terrain shall be used. The model must be capable of performing dynamic routing to approximate the temporal and spatial changes in inundation magnitude and extent. In areas of lateral spreading, a two-dimensional hydraulic model is generally appropriate.
(B) Upon pre-approval by the department, the dam owner may submit an alternative model for review that produces the inundation extent and timing described in section 335.6(b)(2)(A).
Credits
Note: Authority cited: Sections 6078 and 6162, Water Code. Reference: Sections 6160 and 6161, Water Code.
History
1. New section filed 10-19-2017 as a deemed emergency pursuant to Water Code section 6162; operative 10-19-2017 (Register 2017, No. 42). A Certificate of Compliance must be transmitted to OAL by 4-17-2018 or emergency language will be repealed by operation of law on the following day.
2. New section refiled 4-16-2018 as a deemed emergency pursuant to Water Code section 6162; operative 4-18-2018 (Register 2018, No. 16). A Certificate of Compliance must be transmitted to OAL by 7-17-2018 or emergency language will be repealed by operation of law on the following day.
3. New section, including amendments, refiled 7-12-2018 as an emergency pursuant to Water Code section 6162; operative 7-18-2018 (Register 2018, No. 28). A Certificate of Compliance must be transmitted to OAL by 10-16-2018 or emergency language will be repealed by operation of law on the following day.
4. Certificate of Compliance as to 7-12-2018 order, including renumbering of former section 335.6 to section 335.16 and new section 335.6, filed 11-29-2018; operative 11-29-2018 pursuant to Government Code section 11343.4(b)(3) (Register 2018, No. 48).
This database is current through 6/21/24 Register 2024, No. 25.
