ABOUT REINVENTING INNOVATIVE TECHNOLOGIES FOR LEVEE
MONITORING
Patrik Peeters1
Koen Haelterman2
Klaas Pieter Visser3
ABSTRACT
In order to prioritize (visual) inspection as well as maintenance and strengthening of
levees, numerous non-destructive techniques are listed. The use of geophysical, remote
sensing and more recent mobile mapping techniques can result in an improved imaging of
the geometry, layer structure, heterogeneity. Consecutive measures can yield information
on the behavior and possible deterioration of the embankment.
However, today’s levee management is only just starting to deploy these technologies in
everyday practices on a (very) slow pace. In addition, techniques are called innovative
and often labeled as on-going research, which keeps them from being applied on large
and structural scale. Moreover, measured parameters have no direct geotechnical
meaning, inverse modeling is applied to interpret the measurements and therefore highly
qualified and trustworthy personnel are needed. Finally, due to charlatans, these
technologies do not receive the credits they possibly deserve.
Therefore, aiming for a large scale robust application of promising non-destructive
techniques such as electromagnetic methods, spontaneous potential log, sonar imaging,
thermography ..., different private companies were asked to solve several imaging or
monitoring issues ranging from indicating the presence of anomalies and the detection of
the phreatic line to indicating leakage. This paper wants to contribute to a solid
knowledge transfer regarding the application of these (so-called) innovative technologies
and in doing so, prevent levee managers from reinventing hot water again and again and
again.
INTRODUCTION
In the late eighties, a report entitled “Supervision and control of long lateral
embankments” was prepared within the Permanent International Association of
Navigation Congresses (PIANC). The increase of river development schemes for
navigation, energy, irrigation, flood control, led to embankments which, although often
with modest heights, following their substantial length, must be monitored throughout
their life time (PIANC, 1990). Accounting for various geological environments, avoiding
possible damage for a simple check, indicating weak links, helping to understand the
behavior of the embankment, detect any anomaly, rapidly identifying any abnormal event
and/or zones with problems, alerting within the shortest possible delay were all on the
1
Flanders Hydraulics Research, Antwerpen, Belgium, email: [email protected]
Geotechnical Division, Flemish Authorities, Gent, Belgium, email: [email protected]
3
Flanders Hydraulics Research, Antwerpen, Belgium
2
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wish list of the low-cost monitoring system to deploy. PIANC (1990) commences with
comprehensive description of different types and elements of embankments, followed by
an overview of failure mechanisms and a failure tree. Definitions of terms, a subdivision
of measurements according to their purpose as well as explanatory notes on each method
(e.g. multispectral scanning, electromagnetic, geo-electric, acoustic techniques,
radioactivity measurements,…) are provided. Finally, in evaluating the usage of various
surveying techniques, PIANC (1990) takes different parameters into account, such as
speed of intervention, delay of interpretation, cost, results, … yielding a table intended to
facilitate the choice of methods for a diagnosis. Moreover, thermography, self-potential,
electromagnetic and electric resistivity are highlighted as most complementary to visual
inspections. Two additional remarks are worthwhile mentioning.
First, the collation of information and experience from organizations responsible for long
embankments who have used these methods (opposed to universities, societies or
research centers developing these techniques), is recommended. Secondly, the junction
zones between embankments and structures assimilated to an embankment deserve
special attention.
(GREAT) ADVANCES IN RECENT YEARS
According to Niederleithinger et al. (2008), geophysical methods, conducted in a nondestructive manner from the surface, have been used on embankments for decades now.
In many cases these methods were successful in detecting material changes, man-made
objects or other relevant features, but there were also a noteworthy number of
misinterpretations. Since 2005, the most relevant and standard geophysical techniques,
i.e. electromagnetics (EM), electrical resistivity tomography (ERT), capacitively-coupled
resistivity meter (CCR), seismic, ground penetrating radar (GPR) and self-potential (SP,
sometimes referred to as ‘induced potential’ or IP), were evaluated in a.o. Czech
Republic (Boukalová & Beneš, 2005), France (Fauchard & Mériaux, 2007), Germany
(Niederleithinger et al., 2008), Belgium (Depreiter et al., 2010; Wildemeersch et al.,
2013a), … These studies provide guidelines to allow for method selection when
diagnosing levees, all similar to the table provided by PIANC (1990). So besides data
processing technology and capacity, what great advances in recent years can be
mentioned?
Fauchard & Mériaux (2007) and Van Alboom et al. (2009) stress the complementary
usage of geophysical and geotechnical techniques following preliminary studies, such as
historical research, topographical survey, … in order to identify all the points of
weakness and anomalies. The list of surveying techniques is extended with underwater
acoustic measurements, e.g. multibeam, sector scanning, side scan sonar and 3D sonar,
by a.o. Depreiter et al. (2010) and Deleu & Moerkerke (2013). More recent, airborne and
satellite imaging as well as mobile mapping technics, e.g. infrared measurements, passive
microwave radiometry and satellite radar interferometry, were deployed to levees
(STOWA, 2010; de Jeu et al., 2011; Wildemeersch et al., 2013b; Schouten, M., 2013).
Figure 1 shows a wide range of non-destructive methods recently applied on levees in
Flanders (Belgium).
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Figure 1. Illustration of non-destructive methods recently applied on dikes in Flanders
(Belgium).
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In all cases, research institutes and private companies jointly executed the work as socalled pilot or feasibility studies. Experiences on a large scale within organizations
responsible for long embankments are still lacking. One reason for this can be the high
degree of specialization needed to analyses and interpret outcomes. The application of
indirect measuring techniques and the use of not straightforward post-processing
protocols, e.g. inverse modeling, hampers the general acceptance of these (maybe
doomed to be called forever) innovative methods. In brief, more transparency is
welcome! Only illusionists are allowed to not reveal theirs secrets.
Table 1 presents a wide range of promising (however not all equally transparent)
geophysical methods together with some pending issues. It is strongly suggested to start
deploying these non-destructive technics on a large scale to levees or dikes
(complementary to classical geotechnical research). Gaining (more) insight in the
embankment is the main goal. However, getting dike managers acquainted to and
experienced with these kind of data sources is as much as important to bring these
technologies to a higher level.
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Table 1. Geophysical methods promising enough for deployment on a large scale on
levees or dikes: setup, application and some pending issues.
Method
Setup
Application
Issues
RTK GPS
Handheld,
Crest height
Satellite communication
Mobile
mapping
LIDAR
Airborne
Geometry
Proven technology
3D Laser
Mobile
Deformation,
Proven technology
Scanning
mapping
revetment state
Multispectral Airborne
Grass cover state
Wave length of a ‘good’
imaging
grass cover?
Passive
Mobile
Potential seepage
Accessibility
microwave
mapping
radiometry
IR
Mobile
Potential seepage
Accessibility
measurement mapping
Airborne
Potential seepage
Compromising camera
quality
Falling
Mobile
Asphalt revetment
Significance of measured
Weight
mapping
strain?
Deflectometer
3D GPR
Handheld,
Revetment, top layer
Limited penetration depth
(high
Mobile
frequency)
mapping
EM
Handheld,
Top layer (EM38),
Proven technology
Mobile
presence of (ferrous
mapping
and non-ferrous)
anomalies (EM31)
ERT
Stationary
Continuous layer
Presence of revetment:
structure
transversal profiles not
evident
SP (river
Mobile
Potential seepage
Cable between measuring
side)
mapping
and reference electrode
Multibeam
Mobile
Geometry
Proven technology
(river side)
mapping
Side scan
Mobile
Deformation,
Proven technology
sonar (river
mapping
revetment state
side)
3D Sonar
Mobile
Deformation,
Proven technology
(river side)
mapping
revetment state
NEED FOR EXTRA EYES
Fortunately, levee managers and owners are becoming more and more aware of their duty
of care. Not only following governing standards and responding adequately in case, being
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continuously in control will be the target or even the absolute minimum given risen
public awareness, increased economic values together with acting climate change.
Figure 2 shows the PDCA-cycle (Plan-Do-Check-Act) applied to levee management on
the left. Somewhere in between maintenance and assessment, levee inspection will have
its place. The inspection process itself can also be seen as a PDCA-cycle (Figure 1, right).
Figure 2. Levee management (left) and Inspection cycle (right) (Source: STOWA).
In order to fulfill the inspection cycle, dike managers are looking for extra eyes in which
extra means additional as well as special(ist). Although visual inspection is without doubt
the most important tool towards a sustainable management, staff limitations, in number
and in terms of experience, accessibility issues, lacking any reference framework, make
the deployment of additional and special(ist) monitoring techniques a necessary next step.
By applying these techniques, not only your view on the dike will be extended (e.g.
monitoring outside the visible domain), also (gradually occurring) processes or trends
could be identified earlier and moreover, can be described in a more quantitively way,
assisting any forecasting and hence prioritizing maintenance and/or further (visual)
inspection.
MONITORING PLAN FOR LEVEES AND DIKES
Based on the (limited) experiences in Flanders with non-destructive dike monitoring
techniques, it is strongly believed that transparent sens(or)ing can assist with
•
•
•
•
•
•
•
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Bridging between proven and calculated strength;
Steering frequency of (visual) inspection;
Prioritizing damage types;
Assessing severity and hence need for (preventive) maintenance;
Reporting status;
Surveillance;
Being ‘in control’.
Changing Times: Infrastructure Development to Infrastructure Management
Inspired by the monitoring systems explained in PIANC (1990), a monitoring plan was
elaborated for (Flemish) dikes combining non-destructive geophysical and classical
geotechnical techniques at three levels, i.e. large scale imaging, large scale surveying and
detailed monitoring.
Large scale imaging (step 1) – one time measurement campaign
In order to have an inside view on what the embankment is composed of, a stepwise
procedure is proposed: 1th electromagnetic, 2nd geo-electric and 3rd (classical)
geotechnical measurements (Figure 3). Beside the layer structure, a quantification of the
strength characteristics of the dike is aimed at. An additional outcome is the identification
of anomalies (possible indication of weak links).
1.
2.
3.
Figure 3. Standard strategy for dike imaging in Flanders (Belgium): 1. EM31, 2. ERT, 3.
CPT.
Large scale surveying (step 2) – periodic measurement campaigns
In order to have a better understanding of the behavior of the levee, a periodic survey of
different characteristics is scheduled. The main advantage of these consecutive
measurements is a quantification of occurring (possible deteriorating) processes and
mechanisms. Table 2 presents an overview of large scale survey techniques (in addition
to visual inspection) to be applied in Flanders in the near future.
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•
•
•
Table 2. Large scale (periodic) surveying techniques.
Remote sensing
• Geometry (LIDAR)
• Multispectral survey
Mobile mapping
• Crest level (RTK GPS)
• Moisture measurements (IR, passive microwave radiometry)
Survey from the water side
• Seepage (SP)
• revetment (Side scan sonar, 3D SONAR)
• Bathymetry (multibeam)
Detailed monitoring (step 3, if necessary)
Following dike failure, in order to avoid excessive dike strengthening works, … detailed
field monitoring can be the solution. Table 3 contains a (non-exhaustive) list of detailed
monitoring techniques with which the step towards smart (as in clever) dikes becomes
small.
•
•
•
•
•
•
•
Table 3. Detailed monitoring techniques.
Moisture sensor: water level logging, moisture probe, piezometer, TDR,
…
Inclinometer
In situ gamma-based density measurement
Satellite radar interferometry
3D GPR
3D Laser Scanning
Falling Weight Deflectometer
CONCLUSION
In order to be continuously ‘in control’, todays levee management has multiple (nondestructive) measurement techniques available which allow for an inside view on what
the embankment is composed of. These techniques can also provide a better
understanding of the behavior of the levee and, if needed, allow for detailed monitoring
of a (possible) critical situation. However, although methods have been widely tested for
the last decades, general acceptance is lacking due to unclear explanations, erroneous
applications, no straightforward outcomes. In addition, the experiences gained were
mostly research driven instead of being based on the needs of the levee manager.
Therefore, to become more acquainted with these (unfortunately still) innovating
techniques, levee managers in Flanders (and elsewhere) are advised to first set-up large
scale imaging campaigns and start with some (transparent) levee surveying consisting of
different proven and promising technologies. Besides collation of information and
information on a large scale, a (levee) data management tool is needed which can act as a
bridge between levee managers and researchers. Data processing and jumping into a
(unfortunately still) mystic sens(or)ing adventure can then be a next step for the near
future.
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