Reference Document - OPW25 0085 (AS Published)

4.2          Topography
During the site walk-over, topographic features were noted, and ground slopes were recorded using a
hand-held clinometer. As illustrated in the contour plan in Text Figure 8 below, topography comprises a
meandering central ridgeline which runs over a gentle saddle generally in a north-south direction . A
drainage line was present on the eastern side of the ridge flank, that was dammed at two locations within
the property. Two smaller drainage lines ran off the ridge to the east and west in the southern part. To
the east of the main drainage line (Proposed Lot 9) ground slopes fell westward towards the main
drainage line.
Gradients atop the crest of the ridgelines were gently sloping at about 6° to 10°, steepening to between
about 10° and 17° down the flanks across the anticipated building areas. Steeper gradients up to about
20° were recorded in some areas of the site, generally on the immediate flanks of the drainage lines
where future residential development is not anticipated.
Concave shaped ground was observed near the heads of minor drainage lines on either flank of the
central ridgeline. The natural slopes across the anticipated development areas were relatively linear or
convex shaped, with no obvious signs of previous global instability.

                                                           Existing dams
                                                                                 Subject Site




                                                                      Prevailing natural drainage line




             Minor drainage lines




                Text Figure 8: Image showing ground surface contours (courtesy of QGlobe)


4.3          Surface Drainage
Surface water flows would follow ground surface topography sheeting away from the ridgeline and
flanks and accumulating in the natural drainage lines. Natural surface drainage across the majority of the
elevated areas and minor drainage lines was generally considered to be good, owing to the moderate
natural gradients and clayey residual soils which promote runoff. Some boggy conditions were noted
around the main drainage line and on the flatter crest near the existing agricultural sheds were drainage


Geo-Environmental Investigation for Proposed Subdivision
7 February 2025 | 24386-001-Rev0                                                                           7