Inspection of
Spillways

Gated
and
Uncontrolled

FEMA Workshop - Issues, Remedies and Research Needs Relating 
to Service and/or Emergency Spillways

FEMA Workshop - Issues, Remedies and Research Needs Relating 
to Service and/or Emergency Spillways

FEMA Workshop - Issues, Remedies and Research Needs Relating 
to Service and/or Emergency Spillways

FEMA Workshop - Issues, Remedies and Research Needs Relating 
to Service and/or Emergency Spillways

Chutes, Tunnels, & Stilling Basins

FEMA Workshop - Issues, Remedies and Research Needs Relating 
to Service and/or Emergency Spillways

FEMA Workshop - Issues, Remedies and Research Needs Relating 
to Service and/or Emergency Spillways

FEMA Workshop - Issues, Remedies and Research Needs Relating 
to Service and/or Emergency Spillways

FEMA Workshop - Issues, Remedies and Research Needs Relating 
to Service and/or Emergency Spillways

FEMA Workshop - Issues, Remedies and Research Needs Relating 
to Service and/or Emergency Spillways

FEMA Workshop - Issues, Remedies and Research Needs Relating 
to Service and/or Emergency Spillways

Inspection
Techniques

FEMA Workshop - Issues, Remedies and Research Needs Relating 
to Service and/or Emergency Spillways

Presentation 17:
Geophysics for Spillway and Seepage
Evaluation

FEMA Workshop - Issues, Remedies and Research Needs Relating 
to Service and/or Emergency Spillways

Geophysics for Spillway & 
Seepage Evaluation 

So what is Geophysics

The study of the earth (and other materials)
using non-intrusive measurements of
physical properties.

Some typical examples of parameters we measure are:

* Resistivity
* Seismic velocity
* Localized magnetic field!
* Gravity field
* Radar wave velocity & reflectance

FEMA Workshop - Issues, Remedies and Research Needs Relating 
to Service and/or Emergency Spillways

How is Geophysics Helpful?

* Non-lnvasive "Screening " Tool
* Does not Generate Waste (Environmental)
* Supplements Subsurface Data Between Borings.
* Help Subsurface Characterization by “Seeing the Big Picture”
* Quickly Search for Specific Targets
* Trace What is Not Easily Seen (Water Seepage)
* In-Situ Estimation of Engineering Properties of Subsurface Earth Materials

Some of Our Common Tools

* Resistivity Sounding and Imaging (2-D & 3-D)
* Electromagnetics (EM)
* Ground Penetrating Radar (G P R)
* Magnetics
* Induced Potential (IP)
* Spontaneous Potential (SP)
* Seismic Techniques
* Microgravity

FEMA Workshop - Issues, Remedies and Research Needs Relating 
to Service and/or Emergency Spillways

What Can you Do with Geophysics?

* Trace Seepage through 
Embankment Dams/Ponds
* Define Limits of Voids underneath Spillway Slabs
* Determine Shear Wave Velocities for Seismic Design
* Karst Investigations 
* Detect Abandoned Mines
* Map Voids and Sinkhole Potential
* Subsurface Stratigraphy
* Characterize Geologic Structure
* Determine Depth to Bedrock
* Determine Depth to Non-rippable Bedrock
* Map Contaminant Plumes
* Locate steel Reinforcing in Concrete Slabs
* Locate Underground Storage tanks (USTs)
* Define Limits of Abandoned Landfills
* Confirm Fractures in Bedrock for Groundwater Well Siting
* Assess Concrete Quality
* Monitor Vibrations from Blasting/Construction/Demolition
* Define GW Well Capture Zones in Fractured Bedrock
* Locate Buried Metallic Debris

Performing Geophysical Investigations

Investigation Design > Data Collection > Data Reduction > Analysis > Interpretation

FEMA Workshop - Issues, Remedies and Research Needs Relating 
to Service and/or Emergency Spillways

Object of This Presentation

NOT to teach the theory of geophysics;

RATHER, to provide examples where geophysics is used to provide valuable information

Example 1, Moore’s Creek Dam, Lexington, VA

Outlet Structure

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Sinkhole in downstream face above spillway conduit

Boil at Toe of Dam

Geophysical Investigation to Define Seepage Pathways

Complimentary
Geophysical
Techniques

* Self Potential (SP)
(measures voltages from water
moving through porous
medium)

* Two-Dimensional
Resistivity
(measures low resistivity
zones caused by increased
water saturation)

FEMA Workshop - Issues, Remedies and Research Needs Relating 
to Service and/or Emergency Spillways

Spontaneous Potential

Causes of SP Anomaly

Ground Surface
Fixed Electrode
Roaming Electrode
Electrical Potentials
Non-Polarizable Electrode

* Mineralization
* Geothermal gradients
* Bioelectric activity
* Varying electrolytic concentrations in ground water
* Geochemical variations
* Corrosion
* Changes in topography
* Telluric currents
* Streaming

Plan View of the Dam

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to Service and/or Emergency Spillways

Plan View of SP Results

Self Potential (milli-volts)

Resistivity Data Layout

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to Service and/or Emergency Spillways

Electrical Flow Through Earth Materials

Resistivity Results

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Example 2: SP on Water, Chagrin Falls, OH

Seepage Through or Around Spillway?

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Through Embankment Adjacent to Intake

Example 3, Lake Logan, NC 
Sonic Analysis of a
Concrete Arch Spillway 

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Tomographic Analysis of the Sonic Data to Locate Poor Concrete Sections

Example 4, Concrete Spillway Slab

Finding Voids Under Spillways

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to Service and/or Emergency Spillways

Ground Penetrating Radar (GPR)

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to Service and/or Emergency Spillways

GPR Results – “Typical” Voids

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to Service and/or Emergency Spillways