22244-002-Rev1 Barina Ct

Mark Kussrow                                                                                   22244-002-Rev1
C/- CadCon Surveying & Town Planning                                                          26 February 2024




Text Figure 4: Views of the overflow channel below the dam embankment

Historic aerial photographs from Nearmap and Qimagery were reviewed which suggest that the dam was
constructed sometime between 1986 and 1993. Since then the embankment has remained relatively
unchanged. What appeared to be cattle tracks developed in the south-eastern corner of the main
embankment sometime between 2015 and 2017. These seemed to have been reinstated between 2022 and
2023. No obvious signs of previous global dam wall instability were observed in higher resolution imagery as
part of the historic aerial review, nor were there any surface features identified during the investigation which
would indicate recent instability.

2.0        METHOD OF INVESTIGATION
2.1       Fieldwork
An experienced geotechnical engineer from Tectonic undertook a site walk-over on 22 January 2024 to
visually assess any indicators of past slope instability around the main dam wall. The walk-over included
assessment of soil outcrops, surface drainage conditions, topography, evidence of erosion, and vegetation
coverage/condition. This was complimented by a subsurface investigation comprising:
          One borehole (designated BH1) drilled to a depth of 7.5 m below ground level (BGL), in the eastern
           part of the dam wall crest (highest embankment area).
          One borehole (designated BH2) was drilled to 3.5 m BGL, on the gently sloping ground below the
           toe of the dam wall.
          One standalone dynamic cone penetrometer (DCP) test was conducted within the drainage line
           adjacent to the toe of the dam wall for an assessment of the consistency/density of the materials in
           the bed.

Boreholes were drilled using a 4WD mounted solid flight auger rig in the presence of an experienced
geotechnical professional from Tectonic. In situ strength of soil materials in the boreholes was estimated
from DCP testing adjacent to and within each borehole, along with pocketer penetrometer testing on
relatively undisturbed auger cuttings. Disturbed samples were collected from selected horizons in the
boreholes through the dam embankment, and natural soils at depth below.

Logs of the boreholes are attached, together with explanatory notes. Approximate borehole locations are
shown in Figure 1, attached at the end of the report text.

2.2       Laboratory Testing
Selected soil samples were dispatched to Construction Sciences, a NATA accredited geotechnical laboratory
located in Kunda Park, for testing in accordance with Australian Standard AS1289 Method for Testing Soils
for Engineering Purposes. The laboratory testing scheduled comprised two Atterberg Limits, Particle Size
Distribution and Emerson Class Number (ECN) tests to assist with assessment of material properties and
classification. Laboratory test results are summarised in Section 3.3, and test certificates are attached at the
end of this letter.




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