B Y : J EFF C OFFIN, P.E. S R. C IVIL E NGINEER /H YDROLOGIST K LEINSCHMIDT A SSOCIATES

M IDLIFE C RISIS What causes a midlife crisis for a dam......and what can happen as a result?

M IDLIFE C RISIS ! Symptoms: old, tired feeling in a rut may seek new partner

T OOLS... Can’t monitor dam’s mental/emotional health, so need to focus on physical health.

C ONGESTIVE D AM F AILURE Want to avoid this type of midlife (or young-age) crisis.

W HY BE C ONCERNED ? C ONSEQUENCE : Owner: Lose ability to generate power Others: Lose water supply, navigation, recreation benefits

C ONSEQUENCE ( CONT.): Downstream: Can be heavily impacted

D AM -S AFETY C HECKUP – B ASIC A PPROACH 1. Hazard Potential 2. Regular Inspections/Evaluations 3. PFMA / DSSMP

1. H AZARD P OTENTIAL D ETERMINATION Based on Consequence of Failure: High: Loss of life possible due to breach Significant: No loss of life, but major property damage Low: No significant impacts

2. R EGULAR I NSPECTION /E NGINEERING E VALUATION Yearly by FERC engr. Every 5 years by IC Protocol: Visual inspection to assess condition Analysis (or review) of: Spillway adequacy Structural stability Review of S&M data Single most important inspection tool?

T HE M OST I MPORTANT D AM I NSPECTION T OOL : The Eyes! (thanks to Kim de Rubertis)

3. P OTENTIAL F AILURE M ODE A NALYSIS Multi-disciplinary team Review background info. Identify PFMs Classify PFMs (priority) Focus DSSMP on PFMs

T WO R ECENT D AM M IDLIFE “I NCIDENTS ” 1.Embankment Dam with boils at toe after 9+ year drought 2.Gravity Dam hit by piece of rock from abutment

1.E MBANKMENT D AM – N EBRASKA Constructed (age 70) / 163 ft high, 3.1 mi long Earth foundation, sheetpile cutoff wall Drought in CO-WY-NE: reservoir failed to fill High 2010 precip., raised res. 25 ft higher than prior 7 years Boils at toe – raised concern, prompted investigation

1.E MBANKMENT D AM ( CONT.) Boils noted in toe drains – lateral and longitudinal drainage ditches at toe of dam Investigation: Review of current and historical data (seepage flows, piezometer levels) Site visit Preliminary seepage analysis

1.E MBANKMENT D AM ( CONT.) Findings: Boils present historically (e.g. 1987) 2010 boils similar to 1987 but smaller No evidence of transport of soil Current seepage flows and piezometer levels were within historical ranges (data since 1953) Vert. hydraulic gradient estimated to be approximately ft/ft (boils gen. result from )

1.E MBANKMENT D AM ( CONT.) Recommendations: Continue monitoring: Visual monitoring of boils Toe drain flows Piezometer levels Install 2 nested piezometers to verify vert. gradients Evaluate in detail during next Part 12D inspection ( )

2.G RAVITY D AM – M ONTANA Rock-filled timber crib construction Constructed (age 104) 38.5 ft high, 257 ft long 3-ft thick reinforced concrete overlay with post-tensioned anchors added in

2.G RAVITY D AM ( CONT.) Rock bolts added in 1974 to stabilize left abutment cliff

2.G RAVITY D AM ( CONT.) POOP HAPPENS: August 2010 – piece of rock cliff fell from left abutment onto dam Piece estimated at 205 tons: 32’ L x 11’ H x 2- 17’ W Damage to steel superstructure and gates, relatively minor apparent damage to dam crest

2.G RAVITY D AM ( CONT.) Findings and follow-up: PFM ID’d in 2005 PFMA (PFM No. 1, Cat. II) – est. up to 285-ton rock could fall Rock fall came from formation to left of that stabilized in 1974 Reservoir lowered to aid damage inspection/repair Detailed inspection of rock face and rock bolts by geotech. engr. Repairs to gates and superstructure planned Further stabilization of rock cliff planned

R E -C AP : T O A VOID D AM M IDLIFE C RISIS 1. Know Dam’s Hazard Potential 2. Regular Inspections/Evaluations (Eyes!) 3. PFMA – to ID & Prioritize PFMs 4. DSSMP – focused on PFMs

L ET ’ S K EEP O UR D AMS H EALTHY & H APPY, W ITH L ONG L IVES