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City of Canning modified the existing single carriage Sevenoaks Street in Cannington into double carriage road. The new road was designed to comprise landscaped verges and 6m wide landscaped median.  The northern verge of Sevenoaks Street is adjacent to Public Transport Authority land and their railway tracks.

As a consequence of the road being widened the existing Mills Street Main Drain was required to be modified to allow for accommodation of an additional two traffic lanes. 

David Wills and Associates have been employed to prepare civil and structural design of the existing Mills Street Main Drain modification.

The design covered removal of existing open drain and installation of 1500x1200 box culvert extension, two large diameter 1050mm concrete pipes extension, design of new drainage chamber between two extended pipes and culvert and modification of existing chambers in the vicinity of upgraded Sevenoaks Street area.

Prior to construction the existing Water Corporation structure no. A020 has been located in the verge. The structure was affected by the proposed road widening works as after completion of works it will be located under the trafficable section of the road and therefore it had to be structurally checked. Moreover, the existing large water distribution main crosses the Mills Street Main Drain at the A020 structure. Due to the change of A020 access chambers environment the water pipe had to be protected during construction and taken into consideration for the design. The modified chamber allows for further maintenance of both water and drainage services. The design has been prepared taking into consideration extensive loads from upgraded Sevenoaks Street and was accepted by Water Corporation.


Additionally, due to the street upgrade the City of Canning planned for improvement of the existing landscaping areas on both sides of Sevenoaks Street and the future median between intersections with Hamilton Street and Wharf Street. Due to these plans, an irrigation system was installed in the road.


Modification of the existing Mills Street Main Drain structures allowed for water extraction directly from the main drain and storage of this extracted water in a new storage tank which were designed to be constructed during the road modification and installed underground in the road reserve. 


David Wills and Associates have been engaged by City of Canning to determine the maximum possible summer yield of water in the Mills Street Main Drain for reuse in the proposed irrigation system.


David Wills and Associates have liaised with Department of Water and Water Corporation to obtain historical Mills Street Main Drain flow records and water levels at Anvil Way Compensating Basin (an artificially created, permanently inundated basin within Mills Street Main Drain, upstream of the crossing with Sevenoaks Street).

Overall Outcomes:

  • Mills Street Main Drain flow control due to removal of open drain from closed Public Transport Authority area;

  • Upgrade of existing single carriage road into double carriage road; and

  • Negotiation between City of Canning, Water Corporation and Public Transport Authority

Project Summary


April 2015


Sept 2018


Services Provided:

Civil and structural design of Mills Street Main Drain modification, analysis of flow and rainfall data, modelling of the irrigation system and irrigation design.

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