Idaho Administrative Code › Title IDAPA 37 - Water Resources, Department of › Rule 37.03.06 - SAFETY OF DAMS RULES › Section 37.03.06.050 - NEW DAMS AND RESERVOIRS

Current through August 31, 2023
The following criteria shall be used by the Director as a basis
				to evaluate the design of new embankment dams and reservoirs. These guidelines
				are intended for a broad range of circumstances, and engineers should not
				consider them as a restriction to the use of other sound engineering design
				principles. Exclusion from these established criteria will be considered by the
				Director on a case-by-case basis during design review of plans, drawings,
				reports, and specifications submitted for approval prior to commencing
				construction. Structures which are or will be constructed of other materials,
				for example concrete, timber, steel, or combinations thereof shall comply with
				these criteria as found appropriate by the Director, and with other engineering
				design methods and construction standards of care approved by the Director.
				(3-30-23)
01.
Embankment
			 Stability
. Slope stability analyses shall determine the appropriate
			 upstream and downstream slopes. Unless a discrete slope stability analysis
			 determines otherwise, the embankment slopes of earthen dams shall comply with
			 the following:
Upstream slope
3:1 or flatter
Downstream slope
2.5:1 or flatter
(3-30-23)
a.
			 Embankments shall be designed, constructed, and maintained to assure stability
			 under static loads and prevent instability due to seepage or uplift forces,
			 rapid drawdown conditions, and applied seismic loads. (3-30-23)
b. The design analysis shall consider the
			 need for installing filters, including but not limited to chimney drains,
			 blanket drains, or toe drains, to avoid developing saturated conditions and to
			 protect against piping of the embankment fill material. Transmission of seepage
			 through the embankment, abutments, and foundation shall be controlled to
			 prevent internal erosion, the removal of material, or the creation of
			 instability. (3-30-23)
c. The
			 minimum factor of safety for a steady state loading condition shall be one
			 point five (1.5.) The minimum factor of safety for rapid drawdown loading shall
			 be one point two (1.2.) The minimum factor of safety for seismic loading shall
			 be one point zero (1.0.) (3-30-23)
d. Seismic Stability. (3-30-23)
i. The stability of an embankment subjected
			 to earthquake ground motions may be analyzed by the engineer using either a
			 dynamic response or pseudo-static analyses. Pseudo-static analyses are
			 acceptable for embankment dams and foundations composed of non-liquifiable
			 soils that preclude the generation of excess pore water pressures due to
			 shaking. Otherwise, the stability analysis shall employ a dynamic response
			 method. (3-30-23)
ii. Slope
			 deformation analyses are required for structures that are constructed of
			 cohesionless soils exhibiting fine grain-size gradation and/or on foundations
			 that may be subject to liquefaction. (3-30-23)
iii. The design analysis for regulated dams
			 shall include in the seismic stability analysis peak ground accelerations
			 obtained from Seismic Hazard Maps published by the United States Geological
			 Survey (USGS) 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)
iv. The design
			 analyses for large and high hazard dams shall include a report or report(s)
			 covering geology, geologic hazard, and seismicity. The report(s) shall identify
			 the location of faults, evaluate landslide potential, and include a history of
			 seismicity. A comparison using deterministic and probabilistic analyses to
			 calculate peak ground acceleration at the dam site may be required for
			 geographic areas of the state showing evidence of seismic faults or faulting,
			 as determined by the Director. (3-30-23)
e. Where in the opinion of the Director,
			 embankment design or conditions warrant, the owner may be required to
			 instrument their embankment or foundation. (3-30-23)