22244-002-Rev1 Barina Ct

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

        For long term conditions the reservoir water level was plotted at about 1 m below the crest wall, with
         the associated groundwater level reducing through the embankment to ‘daylight’ just below the toe
         level. This was consistent with the measured groundwater inflow level in borehole BH1 drilled
         through the embankment during the investigation.

        For short term more adverse conditions, a ‘rapid drawdown’ scenario was considered, where the
         reservoir level remains high (at 1 m below the crest) and groundwater extends at a similar level
         through the embankment, with the maximum extent of the downstream toe ‘dry’.

        The spillway will need to be upgraded based on design for the anticipated stormwater flows and
         velocities, such that the main dam wall does not overtop during flooding events.

Results of the numerical slope stability analysis are illustrated in Text Figures 6 and 7 below and overleaf.
The key points from our analysis are summarised as follows:

        Unit weight and shear strength parameters adopted for the soil strata were taken from the mid-range
         of values recommended for similar materials in Appendix D of Australian Standard AS4678-2002
         Earth Retaining Structures.

        Analysis was undertaken for specified slip entry and exit zones, generally covering the upstream
         dam face and crest area, together with the downstream face and toe area, respectively.

        Minimum FOS values of 1.3 and 1.5 were calculated for the existing dam for short- and long-term
         conditions, respectively. This assumes that a minimum freeboard of 1 m is maintained below the
         crest of the dam wall.

Our analysis indicates that an acceptable FOS, and subsequent Low Risk, against global slope instability is
achievable for the existing dam, subject to implementation of the recommendations in Section 5.




Text Figure 6: Slope/W output for existing dam wall – long term conditions




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