Dam Safety

Dam Safety

 

Construct or Modify

This page contains guidance documents and technical notes for dam ownership, new dam construction, and for the modification of existing dams.


Project Planning and Approval

Dam Safety Guidelines

  • Part I - General Information and Ownership Responsibilities - This document contains general information about statutory authority, dam safety activities,and dam owner responsibilities for completed projects.
  • Part II - Project Planning and Approval - This document provides information on the specific activities and actions that are involved in project planning and in the plan review and construction permit process.  An overview of the planning process is provided along with a list of permits and approvals that are normally involved. Submittal requirements and obligations of dam owners during project construction, operation, maintenance and inspection are identified.
  • Suggested Table of Contents for dam safety engineering reports - For engineers with limited experience submitting engineering reports to the Dam Safety Office, a suggested table of contents is offered to provide a framework for compiling the information requested in Guidelines Part II.  A condensed table of contents is provided, along with an annotated version to provide more details about each section of the report.
  • Supplemental guidance for Construction Inspection Plans - The Construction Inspection Plan is a required submittal for the Dam Construction Permit and approval of the plans and specifications for construction or modification of a dam.  Guidance is offered for major sections of the inspection plan and target lengths for the various sections, a matrix of construction activities and inspections and quality assurance testing, and critical stages of construction that Dam Safety is particularly interested in observing.  An example Construction Inspection Plan is included.

Dam Safety Technical Notes

  • Technical Note 1: Dam Break Inundation Analysis and Downstream Hazard Classification  Provides assistance in conducting a Dam Break Inundation Analysis and in assessing the downstream hazard posed by a dam failure.

    Additions to Technical Note 1 - Download the dam breach calculation spreadsheets using the equations from Technical Note 1:

    • Self-extracting file that contains Technical Note 1 Spreadsheets and Documents - Microsoft Excel spreadsheets include calculations for both the dam breach hydrograph and downstream routing of the dam breach flood. Template spreadsheets and worked examples are provided, in both metric and U.S. customary units, along with a separate set of instructions and tips (Instruct.doc) for using the spreadsheets.
  • Technical Note 2: Selection of Design Performance Goals for Critical Project Elements  Critical Project Elements of a project are those elements of a project whose failure could result in dam failure and an uncontrolled release of the reservoir. This technical note provides guidance in selecting design/performance goals for critical project elements. It has application in design of proposed dams and in evaluating the adequacy of existing dams.
  • Technical Note 3: Design Storm Construction: Revised October 2009.  Provides engineering guidance for development of design storms for use in computing Inflow Design Floods using rainfall-runoff computer models for spillway design.

    Required supplement to Technical Note 3: October 2009.  Download the gridded data sets, rainfall calculator spreadsheets and design storm hyetographs to perform the revised design storm calculations:

    • Self-extracting file that contains Technical Note 3 Gridded Data, Spreadsheets and Documents - Microsoft Excel spreadsheets include lookup calculators for precipitation depths plus the new storm hyetographs. Gridded data sets used by the lookup calculators are also included. Template spreadsheets and worked examples are provided, along with a separate set of instructions and tips (Instruct.pdf) for using the spreadsheets. This is a large file, 25 MB, may take a long time to download depending on the speed of your internet connection.
    • The Zip file will extract the necessary files to a folder that will be created on your computer in C:\Temp\install.  From there, you will need to run setup.exe to start the installation wizard to install the necessary files on your computer, then follow the prompts.  The files will be installed in a folder that the installation wizard will create on your computer in C:\Program Files\TechNote3.
  • The following maps are excerpted and adapted from HMR-57 (NWS, 1994) for 1-hour and 24-hour PMP:
    • PMP 1-hr - 1 Hour Local Storm PMP, inches
    • PMP 24-hr - 24 Hour General Storm PMP, inches
  • Recommended protocols for using NRCS Curve Numbers (CN’s) with the Dam Safety short design storm

Downloadable Form


Engineering Design for Dams and Spillways

Dam Safety Guidelines

  • Part IV - Dam Design and Construction - July 1993 92-55D - This document outlines a rational engineering approach to address the majority of cases.  Individual projects may pose unique problems that require specialized measures. Where engineers face such cases, it will be their responsibility to demonstrate that their approach satisfactorily addresses the pertinent engineering issues.

Technical Tools and Materials

  • Hydraulic computations for open spillways and riprap-lined channels
    • Self-extracting file that contains these spreadsheets and document - these Microsoft Excel spreadsheets include stage-discharge curve for the spillway, drawdown from critical flow to supercritical uniform flow in steep channels, and stability calculations for loose riprap.  Template spreadsheets and worked examples are provided, along with a separate set of instructions and tips (Instruct.doc) for using the spreadsheets.  We recommend reading Instruct.doc before getting into the spreadsheets.
  • Hydraulic computations for Drop Inlet Spillways
    • Self-extracting file that contains these spreadsheets and documents - these Microsoft Excel spreadsheets include; stage-discharge curve for the spillway, flow surges and pressure fluctuations in the outlet pipe, and downstream tailwater conditions.  Template spreadsheets and worked examples are provided, along with a separate set of instructions and tips (Instruct.doc) for using the spreadsheets. We recommend reading Instruct.doc before getting into the spreadsheets.  
  • Design details for conduits through earth embankments
  • Design details for air vents for drop inlet spillways

Embankment Dam  

Yakima County. Photo taken January 9, 2007

Low Level Outlet  

Yakima County. Photo taken August 2, 2007

Dam Construction  

Yakima County. Photo taken February 1, 2002

Fish Ladder  

Yakima County. Photo taken August 12, 2003