An open letter to Melbourne Water and Kingston Councillors
Mr. Laurence Newcome
Urban Growth Engineer
- cc Minister for Planning
- cc Kingston Council Officers
- cc Kingston Councillors
- cc Dingley Village residents
Floods in and around Kingswood Golf Course, also in much of the south of Dingley Village will exceed currently unacceptable levels if development proceeds
Dear Mr. Newcome,
Flood volume estimates for the proposed overfill of dwellings on Kingswood Golf Course, no matter how well calculated, are deeply inaccurate due to grossly underestimated input criteria.
Melbourne Water's plans show the Golf Course park is a natural flood plain and during floods innundates housing beyond its perimeter. So much so, there are building overlays.
The hugely lacking input statistics include no reference to floods in Golfwood close on the flood map, yet in recent years the floods were above knee deep at that location. It was at the height of water restrictions, so some residents washed their cars with the floodwaters.
Further, floods in Centre Dandenong road reach levels where they cannot possibly be allowed to reach higher levels (see photographs).
Most of all, at present the Golf Course park has 54ha of sandy loam soak, known for its ravenous water absorption properties. This soak acreage is greatly assisted by one of Victoria's largest aquifers below. Further - pumps run constantly in flood events, drawing water from the retarding basin onto the Golf Course holding dam.
The Aquifer was equipped and enhanced with State Government financial assistance not so long ago - over $100,000 "down the drain", should the overfill proceed.
The interim building plans submitted to date will reduce this magnificient soak of nearly 54ha to an estimated 5ha, after blocks of units and blocks of buildings, plus roads and paths are in place.
Any household water collection will be overwhelmed by a sustained downpour.
Already the storm drains cannot cope with present rainfall downpours thus any further increase will causing further flooding on the roads. The base infrastructure cannot take away rains so what hope is there to take any extra?
Given all the above, the input criteria for Kingswood drainage calculations are hopelessly incorrect.
As we now make this flood information public, who can residents sue when we are proven correct?
At a meeting I attended with Melbourne Water, your organisation's staff stated that they were no longer permitting building where a development will export floods downstream, creating massive problems in other areas under Melbourne Water's responsibility, ultimately leading to increased bayside flooding.
Save Kingswood Group incorporated.
The addition of streets, driveways, buildings, patios, swimming pools, paths etc., creates impervious areas where surface water can no longer infiltrate. The greater the impervious area, the greater the runoff.
Drainage does not stop inundation if inadequate
Drainage in many developments receives less attention, and the result is greater than normal runoff occurring in the higher parts of the development, and the excess water flowing to the lower elevations in the development. The problems are almost always transferred downstream to significant areas in Dingley Village.
The proponent's (developers) contractors have done modelling to avoid floods, but modelling and calculations only work if the input includes the information presented here by the Save Kingswood Group incorporated.
To date, the majority of proposed mitigation strategies and management plans have been heavily focused on controlling surface water sources; however they have missed flood events and mitigation strategies plus management solutions which only take into account overland flow may solve only part of the flooding issues.
The greatest risk of not understanding the groundwater dynamic during flooding events is the possibility of triggering unintended consequences of mitigation and management strategies.
Groundwater flood mapping is not a new concept. Flooding legislation recently introduced in Europe and transposed into law in the United Kingdom has recognised the importance of groundwater flooding by incorporating a requirement to assess the risk and undertake measures to reduce this risk where groundwater flooding is significant.
Melbourne Water no longer accepts excessive run-off from estates
From Save Kingswood: At a recent meeting with Melbourne Water we were advised that new estates can be well-drained, however when excessive inundation occurs, they then export their flood problems downstream. In this instance, apartments may have tanks to contain some water and the area can include a larger retarding basin, however in regular downpours they overflow. (See photographs) This run-off plus the water from streets, will block innundation from existing residences in Dingley Village, increasing floods where there were less problems before.
The proponent intends to leave almost no sandy loam soak uncovered, so the retarding basin capacity needs to be immense, or better still, halted as an impossible project.
The photograph in section 1 shows the retarding-basin lake, which overflows. To reduce the flood impact, water is pumped into storage dams, but that buffer will reduce or cease to exist. So there’s the combined threat of hugely increased run-off, with massively reduced “soak” area.
There is also the immense Aquifer or underground water storage, which the Government reportedly contributed $100,000 to develop not so long ago. This is one of the best Aquifers in the country and should not be built on, due to loss of flood control and shifting soil foundation quality as it dries out. Construction within metres and lack of attention will also threaten the survival of native trees identified for retention.
“Land subsidence occurs where large amounts of ground water have been withdrawn from a thick layer of saturated fine-grained sediment that is susceptible to compaction. ... in some areas concentric cracks develop over smaller areas where compaction is occurring.”
Ref: Ground Water and the Rural Homeowner, by Roger M .Waller.
Below: Melbourne Water
At a meeting with Melbourne water attended by Save Kingswood, their staff explained they will no longer allow flood water from estates to cause huge problems downstream, even as far as Kananook Creek and further south.
Melbourne Water has demanded that any water excess to the norm resulting from floods in Kingswood must be contained within the development and only released at a rate that will not cause flooding in the rest of Dingley Village.
Therefore the proponent's contractors made calculations and plans for retarding dams, then announced that their overfill of houses will benefit Dingley Village, by stopping flooding elsewhere!
They also changed their statement that all utilities were agreeable, to "we have allocated $15 million to works to avoid flooding in Dingley Village".
That shows how little they know or care about the area, with Melbourne Water data inadequate as well.
The floods modelling is based on inadequate data and ignores known flood events.
So no matter how many complex calculations are made, if the input data is wrong, so are the resultant findings.
As the developers build and bolt, yet this Save Kingswood Group Inc. document questions the hydrology data, who can residents sue when they are flooded?
From the proponent (developer)