Project I M P A C T WP6: Geophysical Monitoring Vojtech Benes, Zuzana Boukalova, Michal Tesar, Vojtech Zikmund GEO Group a.s.

Objectives of WP6 Geophysical monitoring testing the capabilities of geophysical methods for the description of the condition of the dikes and detection of the dike defects incorporation of geophysical measurements into the process of dike inspection and maintenance planned application of geophysical methods in the monitoring of large scale field tests of breach formation (unfortunately, this planned task due to late inclusion of WP6 activities into IMPACT project has not been executed)

Steps taken in meeting the objectives during IMPACT project retrieval of information testing measurement optimizing of methodology of measurement and processing of data consultation with end user Deliverables D6.1  D6.2  D6.3 

The scope of testing geophysical measurements performed within IMPACT project 3 stages of repeated measurements : Jilešovice location Špluchov location Velký Bělčický pond location 3 test sites: April 2003 September 2003 March 2004 Milestones  M6.2.1  M6.2.2  M6.2.3

Overview of applied geophysical methods: Geoelectric methods resistivity profiling (RP) self potential method (SP) multielectrode method (MEM) electromagnetic frequency method (EFM) Seismic methods shallow seismic method (SSM) seismic tomography (ST) multi-channel analysis of seismic waves (MASW) Microgravimetric method GPR method Geomagnetic survey, Gamma-ray spectrometric survey

During the testing measurement, we focused on the following: methodology of measurement (measurement spacing, orientation of profiles, etc.) methodology of processing (database of the measured data, statistical evaluation) weather effects on repeatability and errors of measurement effects of water level fluctuation in a dike and underlying beds

Example of weather effect

During the execution of IMPACT project there arose 3 basic questions : What tasks and problems can be dealt with by geophysical methods in the process of maintenance and keeping dike safety? In this respect, what requirements are most often laid by dike owners/managers? What is the optimal methodology of geophysical measurement which would be able to tackle these typical tasks?

What tasks and problems can be dealt with by geophysical methods in the process of maintenance and keeping dike safety? Geophysical Monitoring Large-scale, laboratory and mathematical simulation

In this respect, what requirements are most often laid by dike owners/managers? …… we have approx. 10 – 100 km of old dikes with no information available. We need to roughly know what materials were used during construction, whether some parts were subjected to repairs, and whether there occur major construction defects or hidden defects in the dikes …… pace, simplicity and productivity of measurement, acceptable costs …… we have approx. a 200 m long questionable part of a dike where there occur leakages, slope deformations, etc. We need to know dike defect extent and location …… resolution of measurement, accuracy …… in some parts of a dike we need to approximately know geomechanical properties of dike material, and whether there occur changes in such properties in time (for example, in the cases of new repairs where we check the work quality and gradual consolidation of the used material) …… geotechnical intepretation of measured data

What is the optimal methodology of geophysical measurement which would be able to tackle these typical tasks? Geophysical Monitoring System = GMS What do we mean by the term monitoring – a long-term observation of the condition of the dikes by means of repeated measurements What is the advantage – we acquire a new type of information, we are able to differentiate in time the stable and unstable anomalies What has to be eliminated in the interpretation – weather effects, instrumentation, etc.

Geophysical Monitoring System newly included in inspection and maintenance of the dikes (together with airborne photographs analyses, visual inspection, etc.)

Quick testing measurement Plan of repairs Diagnostic measurements Measurement of geotechnical condition

Quick testing measurement: Basic methods: electromagnetic frequency method (with multi-frequency and GPS navigation system) GPR method Output: basic description of the dike structure and material, delimitation of quasihomogeneous blocks

Diagnostics measurents of problematic segments Basic methods: - multielectrode resistivity method - self potential method - thermovision, thermometry - microgravimetry - seismic method Outputs: - detailed identification of problematic segments (seepages, slope deformations, etc.) - analysis of reasons for a defect occurrence - grounds for the repair project

An overview of common dike defects and geophysical methods appropriate for the detection of such defects

METHOD PARAMETERS/ DEFECTS Geoelectric method GPR Seismic method Gravity measure ment Thermo metry Magneto metry X-ray measur ement In frame IMPACT Geomechanical Parameters OO++ -OOYes Dike Structure and Homogeneity OOYes Contact Dike vs. Subsoil +++ +OO-Yes Seepage +++OO+--Yes Piping ++O++--No Fissuring +++O---Yes Slope Deformation ++++O--No Overtopping (*) No Legend: ++ Most suitable method + Appropriate method O Conditionally appropriate method - Mostly inappropriate method (*) Remark: In some cases, geophysical methods allow us to detect reasons for dike surface subsidence at the point of overtopping.

Contact Dike vs. Subsoil

METHOD PARAMETERS/ DEFECTS Geoelectric method GPR Seismic method Gravity measure ment Thermo metry Magneto metry X-ray measur ement In frame IMPACT Geomechanical Parameters OO++ -OOYes Dike Structure and Homogeneity OOYes Contact Dike vs. Subsoil +++ +OO-Yes Seepage +++OO+--Yes Piping ++O++--No Fissuring +++O---Yes Slope Deformation ++++O--No Overtopping (*) No Legend: ++ Most suitable method + Appropriate method O Conditionally appropriate method - Mostly inappropriate method (*) Remark: In some cases, geophysical methods allow us to detect reasons for dike surface subsidence at the point of overtopping.

Seepage detection

METHOD PARAMETERS/ DEFECTS Geoelectric method GPR Seismic method Gravity measure ment Thermo metry Magneto metry X-ray measur ement In frame IMPACT Geomechanical Parameters OO++ -OOYes Dike Structure and Homogeneity OOYes Contact Dike vs. Subsoil +++ +OO-Yes Seepage +++OO+--Yes Piping ++O++--No Fissuring +++O---Yes Slope Deformation ++++O--No Overtopping (*) No Legend: ++ Most suitable method + Appropriate method O Conditionally appropriate method - Mostly inappropriate method (*) Remark: In some cases, geophysical methods allow us to detect reasons for dike surface subsidence at the point of overtopping.

Fissuring

METHOD PARAMETERS/ DEFECTS Geoelectric method GPR Seismic method Gravity measure ment Thermo metry Magneto metry X-ray measur ement In frame IMPACT Geomechanical Parameters OO++ -OOYes Dike Structure and Homogeneity OOYes Contact Dike vs. Subsoil +++ +OO-Yes Seepage +++OO+--Yes Piping ++O++--No Fissuring +++O---Yes Slope Deformation ++++O--No Overtopping (*) No Legend: ++ Most suitable method + Appropriate method O Conditionally appropriate method - Mostly inappropriate method (*) Remark: In some cases, geophysical methods allow us to detect reasons for dike surface subsidence at the point of overtopping.

Slope Deformation

Measurement of geotechnical condition Basic methods: detailed seismic measurement (MASW) microgravimetry Outputs: description of geomechanical properties: bulk density, modulus of elasticity, porosity, long-term changes of properties after the floods (ageing of earth structures)

Organization of geophysical measurements within the framework of GMS A) Initial stage 1) fast starting measurement in a selected part of a catchment area 2) analysis of starting measurements and grounds received from dike owners/managers (results of visual inspection, airborne photographs) 3) selection of questionable dike parts for detailed diagnostic measurement 4) interpretation of diagnostic measurements – proposal of repairs and potential fixed monitoring points for observation of geomechanical properties 5) preparation of monitoring points in the field 6) establishment of GMS database for the purpose of keeping files of all types of measurements performed within GMS

B) Check stages 1) after approx. 3 years or in the case of a flood, repeated fast testing and monitoring measurement will be performed 2) the results will be compared on the basis of relative changes of the measured parameters (elimination of weather effects) 3) in the case of detection of new anomalies or impaired dike condition, diagnostic measurement for selected dike parts will be recommended 4) ditto A4 5) inclusion of newly acquired data into GMS database Organization of geophysical measurements within the framework of GMS Possibility of implication GMS information to the dike breach modelling in the catchment

Summary  Definition of the objectives of measurement in communication with end user. Example: diagnostic measurement cannot be mistaken for quick testing measurement – both types of measurement provide us with different levels and quality of information.  Monitoring (repeated measurement) brings a new type of information. Example: detection of seepages at a dike base at high water level  Geophysical Monitoring System (GMS) newly incorporated in dike inspection and maintenance system

Summary  Geophysical Monitoring System (GMS) newly incorporated in dike inspection and maintenance system  Qick testing measurement of long dike segments sufficient capacity of measurement is required the basic method is EFM, GPR  Diagnostic measurement sufficiently detailed grid of measurement and penetration depth is required the basic methods here are geoelectric methods  Measurement of geotechnical condition correlation between geotechnical parameters determined by geophysical methods and in laboratory the basic methods here are seismic methods and microgravimetry

Next planned activities to prepare for a new grant covering establishment of GMS demonstration database for a selected catchment area

Thanks for your attention!