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AVOIDING A DAM MIDLIFE CRISIS

BY: JEFF COFFIN, P.E.SR. CIVIL ENGINEER/HYDROLOGISTKLEINSCHMIDT ASSOCIATES

MIDLIFE CRISIS

What causes a midlife crisis for a dam...

...and what can happen as a result?


MIDLIFE CRISIS!

Symptoms:

• old, tired feeling• in a rut• may seek new partner


TOOLS...

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


CONGESTIVE DAM FAILURE

Want to avoid this type of midlife (or young-age) crisis.


WHY BE CONCERNED? CONSEQUENCE:

Owner: Lose ability to generate power

Others: Lose water supply, navigation, recreation benefits


CONSEQUENCE (CONT.):

Downstream: Can be heavily impacted


DAM-SAFETY CHECKUP – BASIC APPROACH

1. Hazard Potential

2. Regular Inspections/Evaluations

3. PFMA / DSSMPwww.KleinschmidtUSA.com

1. HAZARD POTENTIAL DETERMINATION

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. REGULAR INSPECTION/ENGINEERING EVALUATIONYearly 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?


THE MOST IMPORTANT DAM INSPECTION TOOL:

The Eyes!

www.KleinschmidtUSA.com(thanks to Kim de Rubertis)

3. POTENTIAL FAILURE MODE ANALYSIS

Multi-disciplinary team

Review background info.

Identify PFMs

Classify PFMs (priority)

Focus DSSMP on PFMs


TWO RECENT DAM MIDLIFE “INCIDENTS”

1. Embankment Dam with boils at toe after 9+ year drought

2. Gravity Dam hit by piece of rock from abutment


1. EMBANKMENT DAM – NEBRASKA

Constructed 1937-41 (age 70) / 163 ft high, 3.1 mi longEarth foundation, sheetpile cutoff wallDrought in CO-WY-NE: reservoir failed to fill 2002-2009High 2010 precip., raised res. 25 ft higher than prior 7 yearsBoils at toe – raised concern, prompted investigation


1. EMBANKMENT DAM (CONT.)Boils noted in toe drains – lateral and longitudinal drainage ditches at toe of damInvestigation:

Review of current and historical data (seepage flows, piezometer levels)

Site visit Preliminary seepage analysis


1. EMBANKMENT DAM (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 0.5-1.0 ft/ft (boils gen. result from 0.5-0.8)


1. EMBANKMENT DAM (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 (2011-12)


2. GRAVITY DAM – MONTANA

Rock-filled timber crib constructionConstructed 1905-07 (age 104)38.5 ft high, 257 ft long3-ft thick reinforced concrete overlay with post-tensioned anchors added in 1989


2. GRAVITY DAM (CONT.)

Rock bolts added in 1974 to stabilize left abutment cliff


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


2. GRAVITY DAM (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


RE-CAP: TO AVOID DAM MIDLIFE CRISIS

1. Know Dam’s Hazard Potential

2. Regular Inspections/Evaluations (Eyes!)

3. PFMA – to ID & Prioritize PFMs

4. DSSMP – focused on PFMs


LET’S KEEP OUR DAMS HEALTHY & HAPPY, WITH

LONG LIVES


www.kleinschmidtusa.com b y : j eff c offin, p.e. s r. c ivil e ngineer /h ydrologist k leinschmidt...

Documents

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