Big Bay Lake Dam Failure

Big Bay Lake Dam Failure

Materials Provided by Robert J. Millette, P.E.Mississippi Department of Environmental Quality

April 19, 2004

Presented By Tom Roberts, DCR Dam Safety & Floodplain Management

Background Information

• Dam was built in 1990• Length of dam 2,000’• Dam height at breach 57’• Water Depth at breach 42’• Normal pool area approximately 900 ac.• Normal pool volume approx. 11,250 ac-ft.• History of seepage through dam and in

conduit joints

A “well maintained” dam

• Grass cover established and mowed

• No trees growing on dam

• Wave action protection in place

• Gate motor checked periodically

• Private engineer called for owner inspections

We have an EAP, now what?

• EAP for this dam was developed mid 2003

– Dam “inspected” every day by maintenance personnel

– Instructions to contact engineer if certain events are noticed

– Prioritized evacuation list with phone numbers developed

Events leading to failure

• Afternoon of March 11, maintenance detected a new seep near the left wing-wall of conduit outlet of dam and notified owner’s engineer.

• Owner’s engineer inspected the boil and advised owner it should be watched overnight and he would look at it again Friday morning.

Events leading to failure

• Owner’s engineer returned Friday morning to inspect the boil and the conduit, which was noted as flowing clear water.

• Due to poor cell phone coverage, engineer left the site to call a contractor to start to work on the problem.

• Engineer summoned back to site when conditions began to rapidly deteriorate.

We’ve got a problem

• Around noon, a pencil sized stream had developed in the boil.

• By 1230, the stream had grown to approx. four feet in diameter. At this point the EAP was activated by calling Lamar Co. EMA

• By 1235, EMA was directing a door to door evacuation and reverse call back to residents to warn them of the breach

We’ve got a problem

• Around 1240, NWS was issuing a flash flood warning for Lamar and Marion Counties.

• Dam Safety was notified about the breach at 1240.

We were very lucky!

• The breach occurred near noon on a weekday. Twelve hours either way or on a weekend or holiday and the EAP would have done us little or no good.

Breach numbers

• Impoundment drained in approximately 90 minutes.

• Breach width was 385’ wide and embankment lost nearly 230,000 cubic yards of material.

• Flowpath was 19.5 miles long and stopped at the Pearl River. The USGS gage at Bogalusa showed a 0.5’ rise on 3/14/04.

Postscript by Thomas I. Roberts, P.E. – Virginia Region IV Dam Safety Engineer

Emergency Action Plan - Was apparently in compliance with minimum regulatory requirements and common practice. EAP list of owners to notify and EAP inundation mapping ended 3 miles downstream of dam where breach flood was calculated to be at or less than 1 foot above the FIRM Floodway Map 100 year flood elevation. Many structures, including a church, were damaged beyond repair between 3 and 9 miles downstream, several including the church had been occupied just prior to inundation water arriving.

Question: Was the EAP to 3 miles downstream enough? What should a qualified professional engineer provide the dam owner in similar situations?



Inspections: Dam was inspected every day! Dam had a history of minor seepage (percolation) and minor leaks at joints of conduit pipe.

New seepage when discovered the day before the breach was less than what is found on the average earth dam in Virginia.

To what degree should a qualified professional engineer inspecting dams measure and record seeps?

What courses of action should a qualified professional Engineer take when changes to a dam are found such as new seeps or previously unrecorded seeps?

Should a graded drain with the ability to monitor flow always be installed?



Big Bay Lake Dam was reported to have been constructed with a Bentonitic Clay core or Bentonitic Soil Treatment.


For High and Medium Hazard Dams where there is a probable or possible loss of life or major economic damage, to what extent should a responsible qualified professional engineer go to confirm what is already believed to be known about a dam?

Should Engineering of all types on dams be to a higher standard-of-care than other less life threatening civil engineering such as water, sewer, stormwater, site grading etc?



A professional engineer claiming to be qualified in any aspect of the field of dams should ask themselves the following questions with each dam and each situation they encounter:

1. “Do I know what I am doing, am I indeed qualified in this field?”

2. “Did I comply with all minimum regulatory standards?”

3. “Did I comply with all minimum common standards of care for all failure modes possible for this dam?”

4. “Will I be able to justify all my actions and inactions and that I gave the adequate amount of care that another reasonable and qualified engineer would give in a similar situation?”

The Taum Sauk Pumped Storage Hydroelectric Plant’s Upper Reservoir stored 1.5 billion gallons (~4600 acReservoir ac--ft) of water.

Approximately $1,000,000,000 to restore the dam to service

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2,000 Homes Destroyed

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St. Francis Dam – Los Angeles Aqueduct in San Fracisquito Canyon, CaliforniaMarch 12, 1928 the concrete gravity dam failed in sunny day conditions, only one day after leakage was observed.

Buffalo Creek Dam Failure – February 26, 1972, Logan County West Virginia, 125 people killed, 1,121 people injured, 4,000 became homeless.

South Fork Dam Failure, Penn. - Johnstown Flood of 1889

2,209 Dead

Documents

Big Bay Lake Dam Failure