Dams and Dam Safety

Dam Guidelines - Design

The design of a dam will differ greatly depending on the type of dam, local geology, type of impoundment, size of structure, seismic zone, downstream hazard, upstream conditions etc. Appendix D is an example of the check sheet that the State Engineer uses to guide a review of a dam design. Not all components are applicable to all dams, but it gives the design engineer an idea of what the Division examines under review. Ultimately the dam designer and owner are responsible for constructing and operating a safe structure and the review process in no way creates a warranty by the State Engineer for the adequacy of the design. Some analyses (although not all inclusive) that could be a part of a dam design is as follows (NAC 535.210(3)):

• Stability Analysis - Many times this is included in the geotechnical report?

• Loading Condition with acceptable factor of safety (FOS):

• End of Construction (static) - not less than 1.3

• Steady State Seepage - not less than 1.4

• Rapid Draw Down - not less than 1.25

• Seismic - not less than 1.1

• Foundation suitability

• Liquefaction potential

• Ability to support the load/settlement

• Fault traces or bedrock fractures

• Horizontally contiguous zones of high permeability, etc.

• Ability to support the load/settlement

• Embankment settlement

• Seep Analysis - flow net, numeric analysis, etc.

• Sediment Transport - as it relates to inflow of sediment into the reservoir or scouring and deposition downstream.

• Material properties

• Susceptibility to alkali-aggregate reaction

• Dispersive soils

• Filter compatibility between zones

• Gabion basket infill material, etc.

• Describe the drainage area

• Extreme events

• Flooding

• Storm choice - e.g. "100 year" 6-hour, PMP, etc.

• Runoff calculation methodology

• Flood routing through the reservoir

• Earthquake

• Stability analysis - especially for liquefaction

• Deformation analysis

• Unnecessary if the embankment meets the requirements set forth in NAC 535.250(3) - embankment slopes specified are 3H:1V (18.43Â°) for earth or 2H:1V (26.56Â°) for rock.

• Elevation/discharge relationships

• Curves showing elevation/discharge relationships for all outlets and spillways

• Dam break/overtopping analysis•Dam break/overtopping analysis.

• Necessary for development of an EAP

• Inundation mapping

• Time to wave front