COLORADO DAM SAFETY BRANCH

Comprehensive Dam Safety Evaluation Report

XXXXXX DAM, DAMID XXXXXX

XXXX Hazard

XXXXXX County, CO

Water Division XX

2/16/2021

Table of Contents

1.        Executive Summary And Safe Storage Level Determination:        - 3 -

2.        BACKGROUND DOCUMENTATION        - 6 -

2.1.        Summary of Facility – Current Configuration – General Summary Only        - 6 -

2.2.        Summary of Construction History        - 7 -

2.3.        Summary of Investigations, Analyses, & Design History        - 8 -

2.4.        Summary of Performance History, Incidents & Significant Noted Deficiencies        - 8 -

2.5.        Summary of Operations        - 9 -

2.6.        Summary of Monitoring & Instrumentation        - 9 -

3.        POTENTIAL FAILURE MODES ANALYSIS        - 10 -

3.1.        PFM Brainstorm/Screening List        - 10 -

3.2.        Potential Failure Mode (PFM) Summary Sheets For Yellow and Red Category PFMs        - 10 -

4.        Dam Failure Consequences & Preparedness        - 11 -

4.1.        Summary of Consequences Estimation        - 11 -

4.2.        Summary of Emergency Preparedness        - 12 -

5.        Key Conclusions & Risk Reduction        - 13 -

5.1.        Potential Failure Modes Judged Yellow or Red Dam Safety Risk Categories        - 13 -

5.2.        Inspection & Monitoring Checklist        - 13 -

5.3.        Consequence Reduction Actions5        - 13 -

5.4.        Summary of Operations & Maintenance Recommendations        - 14 -

APPENDICES

Appendix A        PFM Summary Sheets for Developed PFMs        - 16 -

Appendix B        Site Orientation Photographs        - 17 -

Appendix C        Pertinent Drawings        - 18 -

Appendix D        Geologic Cross Sections/Boring Logs        - 19 -

Appendix E        Pertinent Instrumentation Locations & Readings        - 20 -

Appendix F        PFM Likelihood Summary Table, Possible Risk Reduction Actions, Confidence, and Consequence Definitions        - 21 -

  1. Executive Summary And Safe Storage Level Determination:

What is a CDSE?

The Comprehensive Dam Safety Evaluation (CDSE) Risk Assessment report is a Colorado Dam Safety tool to consider all available information about a particular dam within a Potential Failure Modes Analysis (PFMA) and risk framework to determine the Safe Storage Level in accordance with Colorado Revised Statute 37-87-107, which assigns the State Engineer the responsibility to determine the safe storage level for all reservoirs in the State. Further information for the CDSE can be found in the following Guidelines for Comprehensive Dam Safety Evaluation (CDSE) Risk Assessments & Risk Informed Decision Making.

This CDSE report summarizes our detailed review of State Engineer’s Office (SEO) Dam Safety files including: construction history, past investigations and analyses, performance history (past inspections & incidents), and monitoring results (seepage, piezometers, etc.). The report creates a single summary document for this information as well as key properties of the dam, a summary of emergency preparedness and expected consequences of dam failure.  All of the researched and documented information is then used to evaluate industry-standard Potential Failure Modes (PFMs) for dams. PFMs are detailed descriptions of mechanisms by which dams can and do fail, showing detailed steps that must occur from initiation to dam failure.

SPECIFIC DAM RISK CONCLUSION STATEMENT

This should be an Executive Summary of any PFMs that are judged to be in the Yellow or Red Dam Safety Risk categories that require action reduce risk. Any significant regulatory actions such as a storage restriction should be summarized in this section with a short synopsis of who, what, when, where, and why. Any more specific actions required to reduce PFM likelihood, refine confidence, reduce consequences, and focus future monitoring and inspections should be summarized in Tables 5.1 to 5.4 in this document.

The PFMs and associated confidence portrayal should be plotted on the Risk Matrix and presented in this section for overall summary.

  1. BACKGROUND DOCUMENTATION

  1. Summary of Facility – Current Configuration – General Summary Only

Feature

Description

Dam Name

State of Colorado DAMID

Dam Owner

Dam Purpose

Type of Dam

Hazard Classification

County

Nearest Town

Latitude/Longitude

River or Stream

Dam Geometry

Dam Structural Height

Dam Hydraulic Height

Crest Length

Crest Width

Dam Crest Elevation

Reservoir

Surface Area

Normal Capacity

Maximum Capacity

Pool of Record

Outlet Works

Outlet Description

Outlet Capacity

Drawdown time

Spillway

Drainage Basin Area

Total Spillway Capacity

Capacity / Sq mi

Principal Spillway

Emergency Spillway

Type

Width

Freeboard

Discharge Capacity

  1. Summary of Construction History

Date

C #

Brief Description

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  1. Summary of Investigations, Analyses, & Design History

Report Type

In File?

(Y/N)

Author, Date

Brief Summary

Hazard Classification

Spillway

Geotechnical

Geology

Subsurface

Seismicity

Stability

Seepage

Filter design

Outlet Works

Instrumentation

  1. Summary of Performance History, Incidents & Significant Noted Deficiencies

Date

Description of Deficiency

Action Taken

Resolved?

Reference

  1. Summary of Operations

Type

Description

Owner Participation?

Owner Dam Safety Program

Dam Caretakers

Owner Inspections

Owner Monitoring of Instruments

Outlet Operations?

Upstream Control

Routine Exercising

Routine Internal Inspections

Reservoir & Spillway Operations?

Normal Operating Procedures

Pool of Record

Spillway Activated Normally

  1. Summary of Monitoring & Instrumentation

Instrumentation Type

Monitoring Frequency

Reporting to SEO?

Analysis of Data?

Discussion of Trends

PFM Pathway or Mechanism

Threshold or Alert Level

Staff gage

Survey Monuments

Piezometers

Seepage

Other

  1. POTENTIAL FAILURE MODES ANALYSIS

  1. PFM Brainstorm/Screening List

<Copy & paste from screening list worksheet> or Insert into Appendix A

  1. Potential Failure Mode (PFM) Summary Sheets For Yellow and Red Category PFMs

<Copy & paste PFM worksheets> or Insert into Appendix A

  1. Dam Failure Consequences & Preparedness

  1. Summary of Consequences Estimation[1]

  1. Sunny-Day Dam Breach Analysis

Item

Description

Dam & Reservoir Parameters

Breach Estimation Methodology

Breach Parameters

Qp

Anticipated Infrastructure Impacts

Infrastructure Description

Distance from Dam

Routed Peak Flow

Arrival Time

  1. Precipitation-Induced Dam Breach Analysis

Item

Description

Dam & Reservoir Parameters

Breach Estimation Methodology

Breach Parameters

Qp

Anticipated Infrastructure Impacts

Infrastructure Description

Distance from Dam

Routed Peak Flow

Arrival Time

  1. Life loss & Infrastructure Impacts Estimation by PFM

PFM #

Life Loss Potential

(PAR)

Estimated Infrastructure Impacts

Discussion of Warning Time

Level

  1. Summary of Emergency Preparedness

Item

Description

Comments

Document Date & Description

Format

Inundation Mapping

Contact information

Exercise Frequency

Site access during emergency

Roads

Equipment access

Accessible during spillway/outlet operation

Security

General site security

Outlet operators

Emergency Supplies

Materials Availability

Equipment Availability

  1. Key Conclusions & Risk Reduction

  1. Potential Failure Modes Judged Yellow or Red Dam Safety Risk Categories[2]

PFM #

PFM Name

Likelihood

Confidence

Actions

Initial Date

Due Date

  1. Inspection & Monitoring Checklist[3]

Required Inspection or Monitoring Action

Action Level/Threshold

PFM #

  1. Consequence Reduction Actions5

Required Actions[4]

Action Level/Threshold

PFM #

  1. Summary of Operations & Maintenance Recommendations[5]

Type

Concerns

Actions

Initial Date

Due Date


  1. SLRA PFM Summary Sheets for Developed PFMs

  1. Site Orientation Photographs

  1. Pertinent Drawings

  1. Geologic Cross Sections/Boring Logs

  1. Pertinent Instrumentation Locations & Readings

  1. PFM Likelihood Summary Table, Possible Risk Reduction Actions, Confidence, and Consequence Definitions

PFM Failure Likelihood Rating

Failure Likelihood Description[6]

Possible Actions to Reduce Probability of Failure

Possible Actions to Reduce Consequences

VERY HIGH

An active failure mode is in process or likelihood of a failure is judged to be extremely high, such that immediate actions are necessary to reduce risk.

*Should be accompanied by a Strong Confidence.

There is direct evidence or substantial indirect evidence to suggest it is occurring and/or is likely to occur (or a flood or an earthquake with an annual exceedance probability more frequent (greater) than 10E-2 would likely cause failure.

Strong Confidence

  • Immediate draining of reservoir under SEO Authority
  • Emergency actions to avoid failure
  • Expedite investigations and designs
  • Zero Storage with Expedited Compliance Plan to Complete Investigations, Designs, and Construct Repairs,
  • OR issue Breach Order
  • Ensure that emergency action plan is current and functionally tested for initiating event.
  • Initiate intensive emergency management and situation reports based on continuous monitoring.
  • Develop early warning system specific to PFM.

HIGH

Potential failure mode is judged to present very serious risks, due to high probability of failure, which justifies an urgency in actions to reduce risk.

The fundamental condition of defect is known to exist; indirect evidence suggests it is plausible; and key evidence is weighted more heavily toward likely than unlikely (or a flood or an earthquake with an AEP between 10E-4 and 10E-2) would likely cause failure.

Medium to Strong Confidence

  • SEO Storage Restriction to mitigate PFM.
  • Strict Deadlines for Compliance Plan to Complete Investigations, Designs, and Construct Repairs.
  • Conduct Heightened Monitoring specific to PFM.

Poor Confidence

  • Strict Deadline Expedited, high priority Compliance Plan to complete investigations & Studies to increase Confidence in PFM and justify further actions.
  • Conduct Heightened Monitoring specific to PFM.
  • Ensure that emergency action plan is current.
  • Complete EAP functional exercise for initiating event.

MODERATE

Potential failure mode appears to be dam safety deficiency that poses a significant risk of failure, and actions are needed to better define risks or to reduce risks.

The fundamental condition of defect is known to exist; indirect evidence suggests it is plausible; and key evidence is weighted more heavily towards unlikely than likely (or a flood or an earthquake with an AEP between 10E-5 and 10E-4 would likely cause failure.

Strong Confidence

  • Engineering judgment to consider possible storage restriction OR conditional full storage.
  • Conduct Heightened Monitoring specific to PFM.

Poor to Medium Confidence

  • Strict Dates for Compliance Plan to complete investigations and analyses to increase confidence in PFM and support justification for remediation and remediation design, as appropriate.
  • Conduct Heightened Monitoring specific to PFM.
  • Ensure that emergency action plan is current and functionally tested for initiating event.

LOW

Potential failure mode(s) appear to indicate a potential concern, but do not indicate a pressing need for action.

The possibility cannot be ruled out, but there is no compelling evidence to suggest it has occurred or that a condition or flaw exists that could lead to its development (or a flood or an earthquake with an AEP more remote than 10E-5 would likely cause failure).

Medium to Strong Confidence

  • Use Engineering Judgment to consider Conditional Full Storage OR Full Storage
  • Long term monitoring & instrumentation towards PFM to assess for worsening conditions.

Poor Confidence

  • Plan to complete investigations to increase confidence in PFMs.
  • Determine whether action can wait until after the next comprehensive review of the dam and appurtenant structures.

REMOTE

Potential Failure mode(s) at the facility do not appear to present significant risks, and there are no apparent dam safety deficiencies.

Several events must occur concurrently or in series to create failure.  Most, if not all, events are unlikely to very unlikely, and failure potential is negligible or non-credible.  The failure probability is unlikely to change with additional investigations or study.

Medium to Strong Confidence

  • Full Storage
  • Continue routine dam safety risk management activities, normal operation, and maintenance.
  • Keep PFMs on list to indicate have been evaluated.

Confidence Level Definitions

Confidence Level

Description

STRONG

The team is confident in the order of magnitude for the assigned category and, it is unlikely that additional information would change the estimate.

MEDIUM

The team is relatively confident in the order of magnitude of the assigned category, but key additional information might possibly change the estimate

POOR

The team is not confident in the order of magnitude for the assigned category, and it is entirely possible that additional information would change the estimate.

Consequences

Consequence Categories

LEVEL 1

Downstream discharge results in limited property and/or environmental damage. No life loss expected. Although life-threatening releases occur, direct loss of life is unlikely due to severity of location of the flooding, effective detection and evacuation.

LEVEL 2

Downstream discharge results in moderate property and/or environmental damage. Average life loss is in the range of 1 to 10. Some direct loss of life is likely, related primarily to difficulties in warning and evacuating recreationists/travelers and small population centers.

LEVEL 3

Downstream discharge results in significant property and/or environmental damage. Average life loss is in the range of 10 to 100. Large direct loss of life is likely, related primarily to difficulties in warning and evacuating recreationists/travelers and small population centers, or difficulties evacuating large population centers with significant warning time.

LEVEL 4

Downstream discharge results in extensive property and/or environmental damage. Average life loss is in the range of 100 to 1,000. Extensive direct loss of life can be expected due to limited warning for large population centers and/or limited evacuation routes.

LEVEL 5

Downstream discharge results in extremely high property and/or environmental damage. Average life loss is greater than 1,000. Extremely high direct loss of life can be expected due to limited warning for very large population centers and/or limited evacuation routes.

XXXXXX DAM (XXXXXX)Page  of

[1] Section intended to succinctly summarize parameters developed and utilized for Life Loss estimation.  Can be supported through RCEM analysis, DSS-Wise, etc.  These references and supporting documents can become an Appendix of the report, as necessary.

[2] Potential Failure Modes judged in the Yellow Or Red Dam Safety Risk Categories require actionable items to reduce probability of failure and reduce consequences associated with that Potential Failure Mode. Actions for these PFM’s will be tracked until the PFM’s meet ALARP principles.

[3] Based on Risk Assessment Workshop.  Actions and thresholds should be developed and assigned to focus effort in future inspections.

[4] Examples of “Consequence Reduction Actions” include EAP updates, identification of high flow condition warnings & thresholds, acquisition of construction materials or equipment for emergency responses, improvements to site access.

[5] Conditions observed that do NOT currently relate to a PFM, but could lead to dam safety concerns or expensive repairs if left unattended

[6] Use this column to differentiate AEP’s between High, Significant, and Low Hazard Dams in the future.