Slope Stability Assessment Existing Earthworks - OPW21-0279

Anthony Kelly                                                                                  21354-001-Rev0
                                                                                            17 September 2021

2.3    Groundwater
No seepage or ‘springs’ were observed in the vicinity of the vicinity of the earthworks. Groundwater would
also be expected to be an unlikely occurrence, given the topographical position of the site at the crest of a
prominent ridgeline. Groundwater conditions may vary seasonally, and groundwater seepage could
develop, particularly following periods of prolonged or heavy rainfall.

2.4    Surface Drainage
The natural topography at the site of the earthworks means that there would be a very small catchment for
surface water affecting the earthworks undertaken. Rainfall to surface is therefore expected to be the main
source of waters flowing to the areas identified above in Section 1.1.

Naturally the waters would tend to be spread, and be distributed as sheet flow towards the snout of the spur
to the north, and over the flanks to the east and west.
Well defined drainage channels had been formed to either side of the driveway extension to the south-west
and the cleared southern area. These fed to a culvert at the transition from the pre-existing asphalt surfaced
driveway and the driveway extension, which had been rock lined around the culvert wing-walls, and
discharged to lower ground in the direction of Six Mile Creek. This is shown below in Text Figure 9.


                                                             Pre-existing driveway




                                            Driveway extension




Text Figure 9: Culvert at transition to pre-existing driveway from the driveway extension

A drainage ditch had also been formed on the upslope side of the formalised trackway, which also took
waters from the southern side of the northern cleared area. Drainage was fed to a culvert crossing which
discharged to the natural gully which had formed in the eastern flank of the ridgeline spur running through
the site. Rock lining (including wrapping in geofabric) had been utilised upslope of the crossing point to the
north and south; and had been used at least 10 m downslope of the discharge point.




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