IntroductoryTAG's Flood Management Submission to Panel Hearing—August 2006
Boroondara Planning Scheme Amendment C70, Tooronga Village
Presented by David Williams
Aim
The purpose of this submission is to alert the Panel to the background and possible effects of flooding at the proposed Stockland development at the site known as Tooronga Village and the subject of the Tooronga Planning Scheme Amendment C 70.
References
- Water Technology—Flood Investigations
Tooronga Village Development May 2006—Stephen Clark for Stockland - G.H.D.—Expert Witness Statement on Floodplain at Tooronga Village—George Mallory June 2006 for City of Boroondara
- David Fairbairn—Report on Flood Management Issues—for Snipe Investments July 2006.
Background
Subject to Inundation or Flood Prone
This is a brief history of the flood prone areas of Gardiners Creek in the stretch of creek between Burke
Rd downstream to Tooronga Rd. The notes provide a possible story of flooding on the proposed Stockland
development at Tooronga and on the surrounding residential area.
- Gardiners Creek flows westerly from Burke Rd and eventually falls into the Yarra River below Glenferrie Rd. The catchment for Gardiners Creek is large and drains water from as far east as Blackburn Rd in the east and between Princes Highway in the south to Canterbury in the north.
- In the area between Burke Rd and Tooronga Rd the creek has a wide flood plain, about 300-400 m wide. There was formerly a constriction to flood flows provided by a former ridge running south to the creek from the high land on which the Coles Myer building is located. A large part of that ridge was removed by former quarrying and brick works.
- In the 1920-1930 era the then MMBW straightened part of the creek between Burke and Tooronga Rds, thereby increasing its carrying capacity. Since then all of the catchment has been developed and now probably provides a 90-95% run off factor, combined with a much shorter time of concentration—probably about 1 hour.
Flooding
- In the early 1990s the Monash Freeway was built. This had the effect of cutting off at least half of the off stream flood storage between Burke and Tooronga Rds. In addition, the approach ramps at Burke and Tooronga Rds prevents any high flows from spilling on to the flood plain until the water has passed through the large domed culvert from upstream of Burke Rd to the west side of the former Hawthorn Bowling Club.
- It is presumed that the domed culvert (above) has been designed to carry at least a 100 year run off or flood. Since being completed the culvert has been perilously close to capacity on at least three occasions (field observation).
- Further obstructions in the flood plain on the north side of the creek are caused by the dumping of huge amounts of excavated material from the Monash Freeway. This material was not removed by VicRoads or Melbourne Water following completion of the freeway.
- All these works have caused a loss of about 80 megalitres of off stream storage. The effect of this loss of storage is reflected in local flooding in the southern end of Parkin St in particular.
- In the Planning Scheme Amendment C70 there is limited investigation into the consequences of the above conditions.
Calculation of loss of off-stream storage at approx. 80 megalitres
- Coles Myer land (brickworks site)—Approx. 100m X 100m X 2m of dumped material from building of freeway = 20,000m3 = 20 megalitres
- Council owned land (between Coles Myer land and former Tooronga Bowling Club)—Approx. 40m X 80m X 0.5m of dumped material from building freeway =1600m3 = 1.6 megalitres
- Building of Monash Freeway/overpass—Approx.150m X 400m X 1m =60,000m3 =60 megalitres
Water Technology Report
Note that this report was commissioned by Stockland and contains two options:
- Rix Street—Drain to a possible wetland on council land to the east of the development
- Realignment and improvement to the existing drain within the development site.
Both these options cause no significant change to the present flood prone land. The draw back to option (1) is that the Council and the community have to partially surrender the use of public open space to accommodate off stream storage to benefit the developer. TAG, therefore, does not support option (1).
G.H.D. Report
The G.H.D. report largely agrees with the broad conclusions of the Water Technology Report. It does, however, state that without the wetland area included a rise in flood levels for the 100 year flood may occur (option (1). Both reports refer to possible widening of Gardiners Creek by Melbourne Water.
David Fairbairn Report
This report to Snipe Investments basically refers to flooding problems on the south side of the freeway in the City of Stonnington. However, it does conclude that entry conditions of water south of the creek to Gardiners Creek will rely on at least the capacity of existing sub-freeway culverts being maintained or enlarged.
The report further concludes that there is not sufficient information available to adequately assess flood management issues, particularly south of the freeway. As the whole flood plain and flooding must be considered as a single problem, further information will be required to give a considered and effective definition of flood prone areas of the Coles Myer development site.
Recommendations
- That a thorough and detailed flood prone study be undertaken by a Hydro-Engineering firm in conjunction with Melbourne Water.
- The study should consider flooding on both sides of Gardiners Creek in relation to flood levels on the Stockland/Coles Myer site.
- The fill of excavated material from the Monash Freeway should be removed.
- The proposed wetlands area must remain as a flood storage option to reduce overall flooding in the area. It should not be a flood storage option in relation to the Stockland development.
- A Development Plan is a mandatory requirement within the Planning Scheme. The necessity for the developer of the brickworks site to provide for on-site flood water storage will render the Indicative Concept Plan of little probative value.