25289-001-Rev0 - The Esplanade (1)-compressed

6.4         Drainage
Adequate site drainage must be installed to ensure that stormwater runoff is directed away from building
walls, footings, batters and retaining walls. Although unlikely, if groundwater seepage is encountered
during excavations, Tectonic must be notified to assess the impact on stability.
Subsurface drainage must be installed behind any retaining walls (e.g. slotted ‘aggi’ pipe wrapped in
filter ‘sock’ placed in gravel backfill). Depending on matters such as the extent of drainage installed and
site-specific groundwater conditions, the designer must make an assessment of hydrostatic pressure to
be accounted for in the design of the retaining structure.
Collected roof water should be directed by pipes to the council stormwater system along The Esplanade.
Hydraulic design should be such that under no circumstances are uncontrolled stormwater flows
permitted over the dune face; where channelised erosion and scour features could be allowed to
develop.
Design of the stormwater system should be undertaken by a suitably qualified and experienced RPEQ.



7.          Conclusion
Based on the findings of our assessment it is concluded that a Low Risk of slope instability could be
achieved for the proposed development, subject to the following:
    Implementation of the recommendations given in this report in formulating the feasibility of the
     development, and preparing the final design; and
    Review of the detailed design by Tectonic to confirm compliance with the recommendations herein.

Confirmation of the deeper subsurface profile present along the eastern boundary would be required to
enable detailed design of the shear pile wall system, if required, via further ground investigation
following access being facilitated by the demolition of the existing residence. This should comprise a
borehole taken to a depth in the order of 20 m BGL, using a rotary drill rig capable of solid flight
augering and deep cased wash boring, with standard penetration tests (SPTs).



8.          Limitations
Your attention is drawn to the document Limitations, which is included in Appendix D of this report. The
statements presented in this document are intended to advise you of what your realistic expectations of
this report should be, and to present you with recommendations on how to minimise the risks associated
with the services provided by Tectonic for this project.




Geotechnical investigation
19 November 2025 | 25289-001-Rev0                                                                        22