Report onReport onHerbert Hoover Dike Herbert Hoover Dike

Independent Technical Independent Technical Review Review

Dr. Les Bromwell, P.E.Dr. Les Bromwell, P.E.Dr. Bob Dean, P.E.Dr. Bob Dean, P.E.

Steve Vick, P.E.Steve Vick, P.E.

Expert Review Panel Scope of WorkExpert Review Panel Scope of Work

Review & Analysis of Documents and DataReview & Analysis of Documents and DataMeetings and Site Visit with SFWMD/Corps staff Meetings and Site Visit with SFWMD/Corps staff Meeting with USACE JacksonvilleMeeting with USACE JacksonvilleDike Stability Evaluation (Geotechnical)Dike Stability Evaluation (Geotechnical)Wind & Rainfall Analyses (Hydrology & Wind & Rainfall Analyses (Hydrology & Hydraulics)Hydraulics)Preparation of Evaluation ReportPreparation of Evaluation Report

Herbert Hoover Dike Basic InformationHerbert Hoover Dike Basic Information

Constructed using hydraulic dredges and draglinesConstructed using hydraulic dredges and draglinesFill includes silts, clays, peat, sand, shell, gravel, Fill includes silts, clays, peat, sand, shell, gravel, bouldersbouldersCrest ranges in elevation from 33 to 45 feet.Crest ranges in elevation from 33 to 45 feet.Side slopes range from 2 Horizontal : 1 Vertical to 10:1.Side slopes range from 2 Horizontal : 1 Vertical to 10:1.Recent Lake levels from 9.0 to 18.5 feet NGVDRecent Lake levels from 9.0 to 18.5 feet NGVDFoundation has pervious layers (limestone, shell, clean Foundation has pervious layers (limestone, shell, clean sands), and cohesive layers (hardpan, sandstone, sands), and cohesive layers (hardpan, sandstone, limestone).limestone).Interior borrow channels and exterior rim ditches Interior borrow channels and exterior rim ditches expose uninterrupted flow paths.expose uninterrupted flow paths.

Completed DamCompleted Dam

Construction FlawsConstruction Flaws(Based on Dam Safety Standards)(Based on Dam Safety Standards)

No selection of fill materialsNo selection of fill materials

No compaction to achieve suitable No compaction to achieve suitable engineering propertiesengineering properties

No seepage control through fill or No seepage control through fill or foundationfoundation

Ditches on both sides of dike exposed Ditches on both sides of dike exposed high porosity foundation materialshigh porosity foundation materials

Early Seepage ProblemsEarly Seepage Problems

In 1979, the regulation schedule was changed to In 1979, the regulation schedule was changed to raise the peak managed stage from 15.5 to 17.5. raise the peak managed stage from 15.5 to 17.5.

In early 1980In early 1980’’s, Corps engineers noted evidence s, Corps engineers noted evidence of seepage problems. of seepage problems.

Although Dike was now serving as dam Although Dike was now serving as dam impounding a permanent pool, rather than a impounding a permanent pool, rather than a levee, it continued to be designated as a levee, levee, it continued to be designated as a levee, with no increase in the authorized level of with no increase in the authorized level of protection.protection.

Seepage and Dike StabilitySeepage and Dike Stability

Beginning in 1986, the Corps published first of numerous studiesBeginning in 1986, the Corps published first of numerous studiesdetailing the structural deficiencies.detailing the structural deficiencies.

Internal erosionInternal erosion or or piping piping occurs when water seeping through the occurs when water seeping through the dike transports and removes soil particles.dike transports and removes soil particles.

Continued removal of soil leads to subterranean tunnels or Continued removal of soil leads to subterranean tunnels or ““pipespipes”” that undermine the dike. Their collapse can cause that undermine the dike. Their collapse can cause sinkholes to form on the surface.sinkholes to form on the surface.

As pipes work backwards through the dam, erosive forces As pipes work backwards through the dam, erosive forces increase, eventually causing the embankment to collapse or increase, eventually causing the embankment to collapse or breachbreach, , releasing the impounded water.releasing the impounded water.

Internal erosionInternal erosion is the most common structural is the most common structural cause of earth dam failures.cause of earth dam failures.

Porous Limestone Porous Limestone

Sandbags Around Soil Pipes Sandbags Around Soil Pipes

Sinkhole on Crest 1995Sinkhole on Crest 1995

Repair History

Hydrology & Hydraulics IssuesHydrology & Hydraulics Issues

Because of its previous designation as a levee, Because of its previous designation as a levee, HHD has had a limited level of protection HHD has had a limited level of protection authorized by Congressauthorized by Congress

The current level of protection was determined The current level of protection was determined during the 1950during the 1950’’s implementation of the C&SF s implementation of the C&SF ProjectProject

Level of protection defined by Standard Project Level of protection defined by Standard Project Flood (El. 26 ft) and Project Hurricane (storm Flood (El. 26 ft) and Project Hurricane (storm surge from approx. 100 mph wind)surge from approx. 100 mph wind)

Hurricane EffectsHurricane Effects

Winds Waves & SurgeOver Lake

At Dike:Wave Runup,

Overtopping andDike Erosion

Sketch Illustrating Lake Side Sketch Illustrating Lake Side Erosion by Wave ActionErosion by Wave Action

Hurricane Erosion During Hurricane Erosion During HurricanesHurricanes

April 2005 Designation as a DamApril 2005 Designation as a Dam

When authorized by Congress, will require reWhen authorized by Congress, will require re--evaluation evaluation of safety of safety

Evaluation Criteria will be based on classification as a High Evaluation Criteria will be based on classification as a High Hazard DamHazard Dam

Extreme meteorological conditions must be consideredExtreme meteorological conditions must be considered——combinations of high rainfall and hurricane windscombinations of high rainfall and hurricane windsProbable Maximum Precipitation must be used as inflow design floProbable Maximum Precipitation must be used as inflow design floododAdequate Factor of Safety against structural failureAdequate Factor of Safety against structural failure

Will require significantly more rehabilitation than currently Will require significantly more rehabilitation than currently authorized authorized

Current Status of ImprovementsCurrent Status of Improvements

Only applies to Reach 1 Only applies to Reach 1 (Port Mayaca to Belle Glade)(Port Mayaca to Belle Glade)

Does not increase the authorized level of Does not increase the authorized level of protection (SPF = 26 ft + 5protection (SPF = 26 ft + 5’’ Storm Surge)Storm Surge)

Hydrology and Hydraulics failure modes not Hydrology and Hydraulics failure modes not consideredconsidered

RecommendationsRecommendations

Implement initiatives that will reduce the time required to makeImplement initiatives that will reduce the time required to make adequate repairs to the adequate repairs to the Herbert Hoover Dike.Herbert Hoover Dike.

Modifications to Lake Okeechobee regulation schedule should be cModifications to Lake Okeechobee regulation schedule should be considered to reduce onsidered to reduce the probability of high lakethe probability of high lake--levels until repairs are completed. Reduce operational lake levels until repairs are completed. Reduce operational lake levels by 2 feet while more detailed assessments are underway. levels by 2 feet while more detailed assessments are underway.

Initiate hydrologic simulation modeling.Initiate hydrologic simulation modeling.Initiate postInitiate post--disaster recovery planning.disaster recovery planning.

ReRe--evaluate current rehabilitation design to ensure protection agaievaluate current rehabilitation design to ensure protection against internal erosion and nst internal erosion and slope instability: slope instability:

Extend cutoff depth to fully intercept existing all potential inExtend cutoff depth to fully intercept existing all potential internal erosion pathways.ternal erosion pathways.

ReRe--evaluation of flood and hurricane effects on the dike should be evaluation of flood and hurricane effects on the dike should be initiated promptly in initiated promptly in order to provide assurance that dike repairs will be adequate toorder to provide assurance that dike repairs will be adequate to prevent overtopping in prevent overtopping in extreme events.extreme events.

Recommendations (cont.)Recommendations (cont.)

The likelihood that the dike may fail before effective repairs The likelihood that the dike may fail before effective repairs are completed is sufficiently high to warrant preparing for are completed is sufficiently high to warrant preparing for failure in tandem with attempting to prevent it. failure in tandem with attempting to prevent it.

The Emergency Action Plan should be comprehensively The Emergency Action Plan should be comprehensively reviewed and updated.reviewed and updated.

Increase funding to achieve these objectives.Increase funding to achieve these objectives.