Tom Jones

The creek system fed from the Adelaide Hills is prone to sporadic flooding. Much has been done and spent since the days of early settlement but an element of danger remains. Five councils, including Unley, are endeavouring to achieve the safest way to alleviate the problem but, as always, balancing cost and local interests against the best engineering solution is problematic! 

Within Goodwood Ward are three of these watercourses: Brown Hill, Keswick and Glen Osmond Creeks. The method of flood mitigation chosen by the councils will affect the property owners on their banks, and also many hundreds of families subject to potential flooding. 

A new report listing eight options has been released. It proposes combinations of an upstream detention dam, clearing and widening of the existing stream beds and under street culverts. The culvert solution has been rejected as too expensive, also disruptive to residents and damaging to street trees. 

The rural upstream dam on Brown Hill Creek or its tributary in Ellisons Gully has been vigorously opposed by some residents but has been advocated by several of the engineering reports commissioned by the councils. It is to be a detention dam – normally dry with a restricted outlet to arrest flash flooding and to drain at a steady rate. 

The creek beds will need work. Portions are degraded with weeds and other vegetation having grown in the watercourses and some of the old concrete works being damaged. But the last of the eight options is to use the creeks alone to carry the full flow of expected floods, so this will require more extensive creek works than other solutions. There is also discussion regarding the councils taking easements over portions of privately owned land. 

Easements – for: Property owners no longer have to exercise responsibility for maintenance of the section concerned.

Easements – against: Property owners lose their rights over the area for ever. Should major works be thought necessary as part of the current project or at any time in the future, these could proceed without further consultation or negotiation.

Ducks in Brownhill Creek

   Part of old Adelaide map, 1849 

Just as those residents of affected streets campaigned against the proposed culverts, a number of residents along the creeks are concerned about degradation of their properties and loss of amenity due to the substantial number of trees to be removed and loss of bird and wildlife corridor. Reinstatement would take years. 

Some simple statistics from the November 2005 flood, where homes were lost and life endangered, serve to show a compelling case for an upstream dam. During that night of 7th – 8th, the flow rate of Brown Hill Creek was measured at Scotch College at 26 cubic metres per minute. At the Anzac Highway bridge, it reached 38 per minute, an increase contributed by the urban catchment, of 12 cubic metres per minute. Hence more than twice the urban volume was flowing down from the hills. Let’s say that a dam might have reduced the upstream flow by half during the critical 3 hours of the worst flooding. This would have resulted in about 13m3/min, plus our urban 12, totalling 25 m3/min, a flow which should have remained within the existing banks.

There is to be a period of public consultation during early 2015 regarding the final decision for the five councils. It will be the biggest council project ever undertaken in Adelaide. It is most important that we find the best, most cost effective and safest solution. I intend to remain closely informed on this issue and to consult widely with Goodwood Ward residents.