Instrumentation and
Monitoring Processes
in Dams
Hersília de Andrade e Santos
Post-Graduation Program of Civil Engineering
Post- Graduation Program of Mining Engineering
Foto: www.entura.com.au
The purpose of instrumentation and
monitoring
The aims
The purpose of instrumentation and monitoring is to maintain and improve dam safety by
providing information to:
1. evaluate whether a dam is performing as expected
2. warn of changes that could endanger the safety of a dam.
Failure hazard
The concrete dam failures and incidents
The common causes of concrete dam failures and incidents are:
• overtopping from inadequate spillway capacity or spillway blockage resulting in
erosion of the foundation at the toe of the dam or washout of an abutment or adjacent
embankment structure;
• foundation leakage and piping in pervious strata, soluble lenses, and rock
discontinuities;
• sliding along weak discontinuities in foundations.
The embankment dam failures and incidents
The principal causes of embankment dam failures and incidents are:
• overtopping from inadequate spillway capacity, spillway blockage, or excessive settlement resulting in
erosion of the embankment;
• erosion of embankments from failure of spillways, failure or deformation of outlet conduits causing
leakage and piping, and failure of riprap;
• embankment leakage and piping along outlet conduits, abutment interfaces, contacts with concrete
structures, or concentrated piping in the embankment itself;
• foundation leakage and piping in pervious strata, soluble lenses, and rock discontinuities;
• sliding of embankment slopes due to overly steep slopes, seepage forces, rapid drawdown, or rainfall;
• sliding along clay seams in foundations;
• cracking due to differential settlements;
• liquefaction.
Visual Observation
• Instrumentation and monitoring, combined with vigilant visual observation, can provide
early warning of many conditions that could contribute to dam failures and incidents.
• Example:
• While water pressure data and deformation data (such as inclinometer data and/or
surveyed monuments) would be important for a potentially unstable slope, visual
inspections for cracking, bulging at the toe area, etc., would also be important.
Importance of Visual Monitoring
Importance of Visual Monitoring
Key monitoring issues associated with internal erosion potential failure modes include:
• Is there evidence of material transport by seepage flow?
• Are seepage flow rates increasing with time?
A number of the
• Are there any new seepage areas or wet areas?
items listed above
• Are there any existing wet areas or downstream ponds that are increasing in size or depth over time? cannot realistically
• Are there any new areas of lush vegetation, or changes in existing vegetation appearance, that could be be effectively
due to new or changing seepage conditions? addressed using
• Is there any woody vegetation on the embankment with roots that could create paths for concentrated instruments.
seepage flow?
• Is there animal burrow activity that could give rise to shortened seepage paths and concentrated
seepage flows?
• Are there any sinkholes or depressions?
• Are there any transverse cracks through the dam embankment?
Importance of Visual Monitoring
• The need for both instrumented and visual monitoring would exist for many other
potential failure modes as well.
• A knowledgeable inspector is able to examine all visible aspects of a dam, its dam site, and
its appurtenant structures, and potentially can find evidence relating to a potential failure
mode that has not been previously identified for the dam.
• However there are two main drawbacks to relying solely on visual inspections for routine
dam safety monitoring:
- Visual examinations may not be able to detect subtle changes at the site.
- Parameters of the performance or functioning of a dam that are within the dam,
foundation, or abutments would not be detected by a visual inspection.
Seepage Monitoring
Seepage Monitoring
• Flow rates should be routinely and accurately determined for all seepage, drain, and
relief well flows at every embankment dam unless safety or access problems cannot be
overcome, in which case visual flow rate estimates (at a minimum) should be regularly made.
• Monitoring of seepage and drain flows also must include awareness concerning possible
transport of materials occurring in conjunction with the flow, with materials potentially
carried in suspension being the primary concern.
Seepage Monitoring
• Bucket and Stopwatch Monitoring;
• Weirs;
• Flumes;
• Velocity Meters;
• Water Quality Analyses;
• Capturing Suspended Solids;
• Turbidity Meters;
• Thermal Monitoring Using Probes
Acoustic doppler current profiler (ADCP)
• The ADCP measures water currents with sound, using a principle of
sound waves called the Doppler effect.
• A sound wave has a higher frequency, or pitch, when it moves to you
than when it moves away.
• The ADCP works by transmitting "pings" of sound at a constant
frequency into the water. (The pings are so highly pitched that humans
and even dolphins can't hear them.)
• Particles moving toward the instrument send back higher frequency
waves. The difference in frequency between the waves the profiler
sends out and the waves it receives is called the Doppler shift. The
instrument uses this shift to calculate how fast the particle and the
water around it are moving.
Water Pressure Monitoring
Water Pressure
• Slotted-Pipe Piezometers;
• Porous-Tube Piezometers;
• Hydraulic Piezometers;
• Pneumatic Piezometers;
• Resistance Strain Gauge Piezometers;
• Vibrating-Wire Piezometers;
• Fiber-Optic Piezometers;
• Bubbler Line;
•
Comparison of Commonly Used Major Piezometer
Types
Comparison of Commonly Used Major Piezometer
Types
Earth Pressure Monitoring
Earth Pressure Monitoring
• Total Pressure Cells or Earth Pressure Cells;
• Load Cells;
Deformation Monitoring
Deformation Monitoring
• Internal Vertical Movement Installations; • Probe-Type Extensometers;
• Baseplates; • Joint Meters or Crack Meters;
• Inclinometers; • Linear Variable Differential Transformer;
• Shear Strips; • Surveys;
• Fiber-Optic Cable Deformation Monitoring; • Real-Time Monument Movement Monitoring;
• Time Domain Reflectometry; • Interferometric Synthetic Aperture Radar.
• Settlement Sensors;
• Overflow Settlement Gauges;
• Simple Distance Measuring Devices;
• Simple Extensometers;
• Multipoint Extensometers;
Deformation Monitoring
Advantages and Disadvantages Associated with
Commonly Used Deformation
Monitoring Instruments
Advantages and Disadvantages Associated with
Commonly Used Deformation
Monitoring Instruments
References
• Bartholomew, Charles L., and Michael L. Haverland. Concrete dam instrumentation manual. US
Department of the Interior, Bureau of Reclamation, 1988.
• FERC Instrumentation Program, CHAPTER IX INSTRUMENTATION AND MONITORING
