Submission in relation to the Draft Torrens Road Stormwater Management Plan
Introduction
This submission is in relation to the Draft Torrens Road Stormwater Management Plan as it impacts
upon the suburb of Ottoway.
As has been referred to within the draft plan, a number of residents have expressed concern about
the open section of the Eastern Parade drain that runs through residentially-zoned Ottoway.
While the focus of the Draft Plan is on flood mitigation, this submission also considers the impact of
stormwater management from the perspective of health, safety, nuisance, ecology, aesthetics and
recreational perspective.
In regard to Ottoway, the Draft Plan notes:
Floodplain modelling has predicted significant flooding in the Ottoway area, particularly in
the streets surrounding Eastern Parade south of the railway line. This is partly due to flows in
Eastern Parade exceeding the capacity of the channel and railway culverts, resulting in flows
spilling into the surrounding street network. The more significant cause of flooding in this
area is flows from the local catchment being unable to drain into the Eastern Parade outfall
under high flows, resulting in significant ponding of stormwater in low lying areas south of
the railway.
There is an opportunity to increase the capacity of the Eastern Parade outfall and improve
underground drainage to relieve this flooding.
The Draft Plans presents a number of options and these are discussed further below.
Current configuration
The Eastern Parade drain is at the end of the Torrens Road catchment region.
The drain is covered for its first 200 metres from Grand Junction Road, but is uncovered for the next
600 metres. It is then covered for another 150 metres where the drain changes direction and goes
under the railway line.
Currently, the width and height of the drain are approximately 10.0 metres x 1.75 metres. This
equates to a face area of 17.5m2, as illustrated below. The perimeter of the walls and floor is
therefore approximately 12.5m.
10.0m x 1.75m = 17.5m2
The drain has never over-flowed, however it is claimed that the capacity of the drain will need to
increase to accommodate a one-in-a-hundred-year flood, particularly as the stormwater run-off in
the ‘upstream’ catch region increases due to greater housing density and the coverage of natural
land with roads, paths, buildings and fixtures.
Flood mitigation
The Eastern Parade drain has never over-flowed, however it is acknowledged that the risk will
increase as ‘up-stream’ development continues without sufficient controls.
Five potential flood-mitigation strategies are presented in the draft plan in relation to the drain, viz:
1. Development Controls
2. Outfall Improvements – Ottoway
o Walling Eastern Parade Channel
o Drain Cleveland Terrace and Agnes Street into Eastern Parade Further Downstream
3. Detention Basin in Eastern Parade Reserve
4. Upgrade Railway Culverts
5. Covering the Eastern Parade Drain
Each of these strategies has tended to be presented in isolation from each other, rather than in
combination; eg, the covering of the drain is, among other things, dismissed on the grounds that the
expected increase in future flows will demand greater capacity, without also discussing the potential
relief provided to it by the other options, such as the creation of a basin at the Ottoway Reserve (aka
Eastern Parade Reserve).
Upstream development controls
Upstream development controls are key to limiting the amount of water entering the drain from
upstream, and yet there is almost deference to the need to respond to increased flows over time. As
recognised by the Local Government Association:
… a number of metropolitan councils do not have significant stormwater related problems,
largely as a result of the size and topography of the contributing catchments and the age
and condition of infrastructure. These councils, however, can be contributors to
downstream problems, and therefore should be part of the solution.1
The response of walling of the Eastern Parade channel is a desperate one, which would not be
seriously contemplated in any other residential area. Indeed, such a construction detracts from the
following principle:
Development should include stormwater management systems to mitigate peak flows and
manage the rate and duration of stormwater discharges from the site to ensure the
carrying capacities of downstream systems are not overloaded.2
As recognised in the Draft Plan, upstream rainwater tanks are an important part of the solution:
Provision of on-site measures to limit discharges from new development will protect the
standard of downstream drainage systems, and by managing flow volumes, will also protect
the standard of the downstream ponding basins and wetlands. In order to meet this
1
2
Local Government Association, Metropolitan Adelaide, Stormwater Management: Part A,
http://www.lga.sa.gov.au/webdata/resources/files/Part_A_Report_rev0.pdf
Port Adelaide Enfield Council Development Plan, page 73,
http://www.sa.gov.au/upload/franchise/Housing,%20property%20and%20land/PLG/Online%20DPs/Greate
r%20metropolitan/Port_Adelaide_Enfield_Council_Development_Plan.pdf
requirement, systems such a rainwater tanks plumbed into the house or infiltration devices
will be required.3
Indeed, this is already a requirement of the Port Enfield and Charles Sturt Councils.4,5
From 1 July 2006, additional rainwater tank supplies have had to be plumbed to supplement the
mains water. Development Regulation 78AA(2) provides:
If a relevant authority, on granting a development authorisation in relation to a building to
which this regulation applies, directs that 1 or more on-site stormwater retention devices
be incorporated as part of a stormwater drainage system, then any relevant requirements
of Minister's Specification SA 78AA must be complied with (unless the relevant authority
accepts an alternative solution).
However, it is known that there is a significant rate of non-compliance and therefore greater policing
is required.
Further to the installation of rainwater tanks that are plumbed to mains water, another area for
possible control include the extent to which ground areas can be paved. With the increased subdivision of land, there will be more land covered by buildings, fixtures, pavers and concrete. While
there are restrictions imposed by the Port Enfield Council in relation to the percentage of open land
that a residential land-owner may cover with a verandah, there are no such restrictions on the area
that may be covered by concrete and pavers. Thus, the policy seems inconsistent.
Ultimately, there may need to be restrictions on the number of subdivisions, units and flats that can
be built upstream.
The importance of upstream measures cannot be over-emphasised, which is some ways appears
analogous to South Australia’s recent challenge to upstream states in relation to Murray River flows.
Stormwater flow reduction
Measures to reduce stormwater peak flows, and in some cases volume, can and have been achieved
using a number of methods, including, but not limited to the following:
•
•
•
•
•
3
4
5
6
providing a limit to site coverage;
detention basins;
additional underground pipe and tank detention storage;
detention using rainwater storage tanks;
retention using soakage, infiltration and aquifer disposal methods including the
encouragement of discharging stormwater runoff onto pervious areas including garden beds
in areas of suitably sandy soils.6
At page 39.
Port-Enfield Council, Development Guide No. 19,
<http://www.portenf.sa.gov.au/webdata/resources/files/DG%2019%20Sustainable%20Design%20for%20N
ew%20Houses%20&%20Extensions_May%202013.pdf>
City of Charles Sturt, Stormwater Management Plan,
<http://www.charlessturt.sa.gov.au/webdata/resources/files/Development_Information_Guide_56__Stormwater_Management_Plan.pdf>
KBR, Metropolitan Adelaide Stormwater Management Study, Section 2.9, p.2-25,
http://www.lga.sa.gov.au/webdata/resources/files/Part_A_Report_rev0.pdf
Each of the options that are identified and discussed in relation to Ottoway, other than increasing
the height of the channel walls, are supported.
Channel walling
Increasing the capacity of the channel wall of the open part of the Eastern Parade drain in Ottoway
by heightening the walls by 600mm (to 2.35m) is inappropriate and unnecessary.
This proposal would increase the face area of a wall of water at capacity to 23.5m2 and thereby
notionally increase the capacity of the drain by 34.3%. The perimeter of the walls and floor would
increase to 14.7m.
10.0m x 2.35m = 23.5m2
Increasing the height of the walls is the only option presented in relation to increasing the capacity
of the drain.
The option of widening the drain has not been considered, but if it were, it would seem that a similar
result would be possible.
While the drain is approximately 10m wide, the distance between the roads on either side of it is
approximately 16.0m. Thus, is seems possible to widen the drain to, say, 14.0m.
This would increase the face area of a wall of water at capacity to 24.5m2 and thereby notionally
increase the capacity of the drain by 40.0%. The perimeter of the walls and floor would increase to
16.25m.
14.0m x 1.75m = 24.5m2
It is acknowledged that the marginal increase in capacity from the previous option would be offset
by the increase in friction associated with the increased surface area with which the flowing
stormwater would be in contact with, however, the results would still be comparable.
Note that if the capacity of the drain is to be increased, then the capacity of the railway culverts will
also need to increase. Doing so will be an expensive exercise in itself. Assuming that the capacity of
the culverts will have to be increased, then the additional cost associated with widening and
covering the open part of the drain would be less than if it were done in isolation. Also, assuming
that State and/or Federal funding would need to be obtained to widen the railway culverts, then the
opportunity is created to submit for additional funding to also cover the open part of the drain.
Covering the drain
The option of covering the open part of the Eastern Parade Drain that runs through Ottoway is
discussed in the Draft Plan, but is not supported by its authors, due to (i) increased friction between
the stormwater and the cover during peak flows; and (ii) cost.
An increase in friction between the stormwater and the cover during peak flows will only occur if
other measures are not also undertaken. However, the risk of flooding could be mitigated if some or
all of the other options were also undertaken, such as (i) managing upstream flows; (ii) increasing
the capacity of the drain by widening it; (iii) creating a basin in the Ottoway Reserve and/or
elsewhere in the vicinity; and (iv) upgrading the Agnes Street and/or Cleveland Street drains as
proposed.
In addition to flood-mitigation objectives, covering the drain would also achieve health and safety
objectives.
Development Regulation 55(d) provides:
Any drain which is necessary in accordance with recognised engineering practice for the
safe and efficient drainage of the land and for the safe and efficient disposal of stormwater
and effluent from the land must be provided and constructed. [emphasis added].
Indeed, the Port Adelaide Enfield Council’s Development Plan requires stormwater management
systems should take into account the safety of children and other likely users.
The open part of the drain running through Ottoway is not safe. Children have been seen playing in
the drain and it is a popular canvas for graffiti artists. A number of cars have also driven into it. It is
foreseeable that one of these events could occur at the time of a flash flood and so the relevant
authorities need to act.
Furthermore, the Port Adelaide Development Plan states that:
Stormwater management systems should not create conditions conducive to the breeding
of vectors of disease and nuisance pests. 7
The drain is a breeding ground for mosquitos and is a thoroughfare for rats and foxes. It also smells
and has been used on occasions as a dumping ground.
Creation of a basin
The creation of a basin at Ottoway Reserve to accommodate 1/100 year flood-waters is supported,
however this is not the only piece of nearby land where this could be done.
According to the Local Government Association of South Australia:
Detention basins historically have been successful in flow reduction and should continue, where
possible (i.e. where space is available), to be a desirable form of relief for both the minor and major
drainage system at a catchment or sub-catchment level.8
7
PAE Council Development Plan, page 74,
http://www.sa.gov.au/upload/franchise/Housing,%20property%20and%20land/PLG/Online%20DPs/Greate
r%20metropolitan/Port_Adelaide_Enfield_Council_Development_Plan.pdf
The State Department of Planning and Infrastructure owns a strip of land parallel to Eastern Parade
which could also be used as a basin and a reserve. The land is a disused railway line and connects to
Eastern Parade near the intersection with the existing railway line. NB: that this land is depicted as
residential on the map of the draft plan (Figure 2.1 on page 3). The Minister for Transport has said
that the land is surplus to the Department’s needs, and so there is an opportunity to also use this
land as a basin.
Similarly, there is vacant land on the other side of Eastern Parade which could be used as basins,
including that which has been identified for a basin with the Cleveland Street and Agnes Street drain
outlets. Another parcel of land adjacent to the drain on the Gilman side of the railway is owned by
the Australian Rail Track Corporation (a Commonwealth Government QUANGO); the land is currently
for lease.
Importantly, the use of such land to create stormwater basins would serve both an ecological and
recreational purpose.
In regard to the ecological perspective, the Port Enfield Development Plan states that:
Stormwater management systems should:
(a) maximise the potential for stormwater harvesting and re-use, either on-site or as
close as practicable to the source
(b) utilise, but not be limited to, one or more of the following harvesting methods:
(i) the collection of roof water in tanks designed in accordance with the average
rainfall for the area and roof size
(ii) the discharge to open space, landscaping or garden areas, including strips
adjacent to car parks
(iii) the incorporation of detention and retention facilities
(iv) aquifer recharge
(c) take into account the safety of children and other likely users
(d) minimise impacts on the useability of public open space.9
In regard to the recreational perspective, Port Enfield Development Plan states that:

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
8
9
10
11
Public open space and recreation areas should be of a size, dimension and location that …
enable effective stormwater management.10
Open space should be designed to incorporate … re-use of stormwater for irrigation
purposes
Public open space used for stormwater retention or detention should provide a range of
recreational opportunities that ensure its primary function for recreation is maintained or
enhanced.11
Local Government Association of SA,
http://www.lga.sa.gov.au/webdata/resources/files/Part_A_Report_rev0.pdf
PAE Council Development Plan, page 74,
http://www.sa.gov.au/upload/franchise/Housing,%20property%20and%20land/PLG/Online%20DPs/Greate
r%20metropolitan/Port_Adelaide_Enfield_Council_Development_Plan.pdf
ibid, page 78.
ibid, page 79.
Financing
The estimated costs associated with the presented options are high, but not insurmountable.
Options for improved stormwater management that were identified within the Draft Stormwater
Management Plan include:




Eastern Parade Channel Raising (around $1.3m capital cost);
Eastern Parade Reserve Basin (around $2.0m capital cost);
Cleveland Terrace Drain (around $1.8m capital cost);
Agnes Street Drain (around $1.4m capital cost);
Covering the drain is estimated to cost in the order of $10m.
By comparison, the City of Charles Sturt initially noted that the Port Road project was valued at
approximately $18m. The Federal and State governments are significant contributors to this project
and the same could be expected for this significant project (particularly considering that the Eastern
Parade drain services a high number of upstream users).
Moreover, a contribution from upstream users is supported by the Local Government Association:
… a number of metropolitan councils do not have significant stormwater related problems, largely as
a result of the size and topography of the contributing catchments and the age and condition of
infrastructure. These councils, however, can be contributors to downstream problems, and therefore
should be part of the solution.12
In regard to possible State funding, on 5 June 2013, the Hon Tom Koutsantonis MP, Minister for
Transport and Infrastructure provided a written response regarding a proposal to cover the drain.
While confirming that it is a Council responsibility, he also said that he had invited the Council to
seek State Government support for the development of the drain, through the Minister for Water
and the River Murray, the Hon Ian Hunter MLC. It is not clear as to whether the Port Enfield Council
approached the Hon Ian Hunter MLC yet.
Conclusion
It is unacceptable that the open part of the Eastern Parade drain running through Ottoway be left
uncovered. Ottoway is a residential suburb and leaving the drain uncovered is unsafe. In association
with better upstream development management and the creation of one or more basins (which
could also serve recreational and other purposes) and possible widening of the channel, the drain
can be made safe while at the same time accommodating projected increases in upstream
stormwater flows over time. While the cost of doing this will run into the millions of dollars, it is not
unreasonable to expect the Charles Sturt Council and the State and Federal governments to
contribute. Indeed the State Government has already extended an invitation to the Port Enfield
Council to seek support from it.
12
Local Government Association of SA,
http://www.lga.sa.gov.au/webdata/resources/files/Part_A_Report_rev0.pdf