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Technical Note in response to action notice
Ref No 20648-R1 – Rev 2 TECHNICAL NOTE IN RESPONSE TO COUNCIL DEVELOPMENT COMPLIANCE NOTICE FOR NEW DWELLING AT 22 TURPENTINE ROAD RINGTAIL CREEK I refer to Council’s letter dated 9th November 2020, reference COM20/0693 regarding outstanding development conditions for the second dwelling at the above address. The two issues raised in this letter relate to stormwater/flooding conditions and the construction of a second driveway. The purpose of this technical note is to address these matters to the satisfaction of Council. BACKGROUND DOCUMENTS On 2 February 2018 Council issued a Referral Agency Response ref RAL17/0523 approving a Development Application for Building Works – Detached House (secondary dwelling) at 22 Turpentine Road, Ringtail Creek (lot 2 RP846208). Condition 8 & 9 of RAL17/0523 read as follows: 8. The minimum floor levels of all habitable rooms must be the greater of the following: a. The minimum specified floor level if in an area where minimum floor levels are available b. 300mm above the modelled flood level if in an area where flood modelling is available c. 300mm above the highest known flood level if in an area where flood modelling is not available 9. The development of the site (buildings, driveways, paths and landscaping) must not impede the existing overland flow of stormwater from the adjoining property or cause additional ponding on stormwater on any adjoining properties or the road reserve. There is no mention in the conditions about the driveway requirements however the approved plans show the secondary dwelling being accessed via an extension to the driveway from the existing/main dwelling. OVERLAND FLOW PATHS/STORMWATER MANAGEMENT The subject lot is not located within a flood hazard zone and as such there is no minimum specified floor level. Refer screen shot from Council flood hazard mapping below. We are unaware as to whether there has been any flood modelling in this specific location but suspect none exists. There is also no historical flood level to determine the highest known flood. Notwithstanding the image below shows that the flood hazard area extends to areas below RL 3.5-3.8 AHD (approx.) Page 1 of 8
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Page 2
Ref No 20648-R1 – Rev 2
The subject dwelling is located on land with a surface level of approx. RL 10.5
according to the aerial contours – refer to the image below. This is well above any
known flood level in the area. It should also be noted that existing dwellings to the
east of the subject dwelling are sited on ground much lower than this.
In addition, the new dwelling has been constructed approximately 500mm above
existing ground levels – refer photos on the following pages.
In regard to the overland flow paths. The general lay of the land falls from the south
west to the north east. As part of the construction for the secondary dwelling the
owners have constructed an open drain within their property to collect the overland
flows and direct these to Turpentine Road to the east. Refer marked up image below
and site photos. As such the new dwelling does not cause additional ponding of
stormwater on any adjacent property.
Page 2 of 8
Page 3
Ref No 20648-R1 – Rev 2 Page 3 of 8 [OCR of page images] TODE engineers & project managers Ref No 20648-R1 — Rev 2 eye M Eee -1n) Ree ie tedhe, 4 flows to'road Genetal direction.of oY a Evite ile ln Noosa: 07 5449 9600 i i Noosa: 075449 9600 outstanding results personal service Mackay; 07 4840 2337 infrastructure buildings subdivisions placemaking PO Box 61, Noosaville, QLD 4566, Australia www.todconsulting.com TOD CONSULTING PTY LTD ABN: 39128805336 Page 3 of 8
Page 4
Ref No 20648-R1 – Rev 2
DRIVEWAY
A second access to the lot was constructed to facilitate the installation of the new
prefabricated dwelling. We have undertaken an inspection of this access and it
generally complies with Council standard drawing RS-056 for rural access
crossovers with a few minor exceptions -copy of the standard drawing is attached to
the back of this report. We have been informed that the access was constructed
approximately 2 years ago.
The access is approx. 5.3m wide at the narrowest point and is constructed over a
375mm diameter PVC Stormpro pipe – set back approx. 3m back from the road
edge. There is 500mm of cover over the pipe. The headwalls are constructed from
grouted rock. The access pavement is unsealed gravel more than 125mm thick. The
inlet and outlet to the culvert contains some un-grouted rock but there is no evidence
of scouring, indicating the scour protection unnecessary in this case which is
understandable as the road drain is on a very flat grade. Refer photos below:
Page 4 of 8
Page 5
Ref No 20648-R1 – Rev 2 Page 5 of 8 [OCR of page images] TODE engineers & project managers Ref No 20648-R1 — Rev 2 Noosa: 07 5449 9600 outstanding results personal service Sunshine Coast: 07 5329 3190 Mackay; 07 4840 2337 infrastructure buildings subdivisions placemaking PO Box 61, Noosaville, QLD 4566, Australia www.todconsulting.com TOD CONSULTING PTY LTD ABN: 39128805336 Page 5 of 8
Page 6
Ref No 20648-R1 – Rev 2
We initially assessed the catchment for the access culvert as 1.27 Ha as per the
marked-up aerial below, however on closer inspection of the site we discovered that
the property two doors to the south contained a landscaped mound that diverted
overland flows from this property to the south instead of towards the subject property,
substantially reducing the catchment directed to the new access.
Following completion of the house construction the owners also installed a
landscaped berm along their boundary to the west of the house site to help divert
overland flows away from the house and into the open drain. The revised catchment
area for the access culvert is shown below.
Page 6 of 8
Page 7
Ref No 20648-R1 – Rev 2
In accordance with the standard drawing the culvert size should be 450mm diameter
however it was observed that the neighbouring driveway to the south (upstream of
the subject driveway) also contained a 375mm pipe. It was observed that there is
approximately 50mm of fall between the two driveway culverts. As such it is not
deemed necessary to upgrade the pipe on the subject driveway.
The longitudinal grade of the access does not comply with the standard drawing in
that there is no low point in the pavement above the pipe culvert. This is not
considered critical in this location due to the low grade of the road and open drain.
Again, it was observed that the neighbouring (upstream) property did not contain a
low point either.
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Page 8
Ref No 20648-R1 – Rev 2
The access was assessed for sight distance requirements. Turpentine Road does
not have a posted speed limit but other streets in this area such as Illoura Place have
a 60kph speed limit. Based on the road geometry (road width and horizontal
alignment) and observations of actual traffic using the road, it is our opinion that
60kph is a reasonable estimation of the speed environment. The visibility to the south
was measured as being over 200m to the south which exceeds the minimum
requirement for 60kph speed limit of 123m (and would exceed the requirements for
80 kph). The visibility to the north was restricted by the horizontal bend in the road
to only 60m, however given that Turpentine Road is a dead-end street, vehicles
exiting the property will virtually never turn to the right meaning sight distance to the
left is not critical for the safe operation of the driveway. It is noted that a similar sight
distance would apply for the existing access on the neighbouring property to the
south.
CONCLUSION & CERTIFICATION
In conclusion I certify that the secondary dwelling constructed at 22 Turpentine Road
is constructed well above local flood levels and does not cause additional ponding
of stormwater on any adjoining properties.
In addition, although the access to the property that services the second dwelling
does not fully comply with Council standard drawing RS-065 it is deemed to be a
suitable and safe access, constructed to a standard that is suitable for ongoing use
and is consistent with or exceeds the standard of other accesses on this road. As
such we request Council consider this report to be an Operational Works Application
to allow the driveway to be retained and continue to be used by the owners to access
their dwelling at 22 Turpentine Road, Ringtail Creek.
Doug Reynolds, Director (RPEQ 9072)
07 5449 9600 | [email protected]
TOD consulting engineers
11 June 2021
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