Assessing the Structural Integrity of Stopbanks

Aim

This project set out to evaluate the integrity and performance of stopbanks. By combining several geophysical techniques, the investigation sought to:

• Detect stratigraphic changes along the embankments

  
  

• Locate culverts and other buried utilities

  
  

• Identify potential seepage pathways or weak zones

This non-invasive approach provided insights into how the stopbanks were originally constructed and how well they may perform under flood conditions.

Approach

A 10 km section of stopbanks was investigated using complementary geophysical methods to build a detailed picture of subsurface conditions:

• 2D MASW (Multi-Channel Analysis of Surface Waves): measured shear wave velocities to identify softer, less competent zones.

  
  

• 250 MHz GPR (Ground Penetrating Radar): mapped shallow stratigraphy and detected buried culverts.

  
  

• Vs30 profiling: extended MASW results to 30 m depth, allowing a broad geotechnical characterisation.

  
  

• ERT (Electrical Resistivity Tomography): highlighted variations in soil moisture, potential seepage zones, and lateral heterogeneity.

Data from all techniques were integrated to generate 2D cross-sections of the stopbanks, enabling engineers to pinpoint areas requiring closer attention.

Results

Across the sites, the following data were collected:

• 33 MASW lines

  
  

• 96 Vs30 profiles

  
  

• 106 GPR lines

  
  

• 19 ERT profiles

Key findings included:

• Significant lateral and vertical variability, with shear wave velocities ranging between 100–250 m/s.

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• Water table depths interpretable in several locations.

  
  

• Buried culverts and man-made features clearly resolved, providing confidence in the geophysical interpretations even without invasive testing.

Outputs & Value

The combined geophysical dataset delivered:

• Clear visualisations of stopbank construction and internal variability

  
  

• Early identification of soft spots, utilities, and seepage-prone areas

  
  

• Actionable insights for councils and engineers, supporting proactive maintenance and flood protection planning

By covering the entire length of the stopbanks, the approach proved to be a cost-effective alternative to intrusive testing, reducing project time and cost while still highlighting zones requiring further detailed investigation.