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Flat Bush area safer from flood
24 January 2006
By MICHAEL OTTO
Homes in the planned new town of Flat Bush should suffer little flooding damage in a one-in-100-year flood but other parts of Manukau city are more vulnerable.
Manukau City Council clean environment manager Mohammed Hassan says the catchment design for Flat Bush means flooding after a big storm should be minimised.
Design features include dozens of storage ponds in the catchment, using streams to carry stormwater instead of pipes in some places and not allowing building in an identified 100-year floodplain in the area.
But other areas of Manukau city are likely to be more affected by a one-in-a-100 year event, Mr Hassan says.
"The most vulnerable areas would be some of the older catchments such as Papatoetoe, some parts of Manurewa and the lower-lying areas of the Puhinui catchment – or downstream of the city centre.
"Those are the low-lying areas where, if you get a 100-year flood event, then potentially some properties could be affected.
"The main reason for that is that the areas are extremely flat and the water cannot get away fast enough through streams and channels."
The design of the Flat Bush catchment uses modern stormwater engineering thinking, Mr Hassan says.
Natural, planted areas will be used to manage stormwater, rather than underground pipes, the Flat Bush Community Plan says.
Up to 40,000 people are expected to be living in the new town by 2018.
"The traditional way of managing stormwater has been to pipe it - even the major streams have been piped in many locations. It's only until it goes to a large receiving environment, then the pipe terminates," Mr Hassan says.
"But the whole Flat Bush system is designed to preserve the 100-year floodplain."
The Manukau City Council has been buying land around stream arms coming up from Otara for the catchment plan and public open space, Mr Hassan says.
A paper given to the 2005 Ingenium Conference in Nelson says the Flat Bush development area is about 1800 hectares and is contained within a single catchment.
The paper's authors, Y Krpo of Tse Group and J Sheppard of Brookfields Lawyers, say 48 stormwater ponds will buffer the waterways from the urbanised sub-catchment.
The paper says the estimated cost for implementing the catchment management scheme is about $100 million, which will be funded by developers through a council contribution scheme.
The paper says a key feature of the planning process for Flat Bush is the protection and enhancement of about 45km of natural streams and gullies, of which 20km will be owned and managed by the council.
"Hence 90 percent of natural waterways are to be protected, of which 40 percent will be integrated into the urban fabric and provided with one-sided roads, which open and define those `green corridors'," the paper says.
"Every house will be located within a five-minute walk to its nearest green corridor."
24 January 2006
By MICHAEL OTTO
Homes in the planned new town of Flat Bush should suffer little flooding damage in a one-in-100-year flood but other parts of Manukau city are more vulnerable.
Manukau City Council clean environment manager Mohammed Hassan says the catchment design for Flat Bush means flooding after a big storm should be minimised.
Design features include dozens of storage ponds in the catchment, using streams to carry stormwater instead of pipes in some places and not allowing building in an identified 100-year floodplain in the area.
But other areas of Manukau city are likely to be more affected by a one-in-a-100 year event, Mr Hassan says.
"The most vulnerable areas would be some of the older catchments such as Papatoetoe, some parts of Manurewa and the lower-lying areas of the Puhinui catchment – or downstream of the city centre.
"Those are the low-lying areas where, if you get a 100-year flood event, then potentially some properties could be affected.
"The main reason for that is that the areas are extremely flat and the water cannot get away fast enough through streams and channels."
The design of the Flat Bush catchment uses modern stormwater engineering thinking, Mr Hassan says.
Natural, planted areas will be used to manage stormwater, rather than underground pipes, the Flat Bush Community Plan says.
Up to 40,000 people are expected to be living in the new town by 2018.
"The traditional way of managing stormwater has been to pipe it - even the major streams have been piped in many locations. It's only until it goes to a large receiving environment, then the pipe terminates," Mr Hassan says.
"But the whole Flat Bush system is designed to preserve the 100-year floodplain."
The Manukau City Council has been buying land around stream arms coming up from Otara for the catchment plan and public open space, Mr Hassan says.
A paper given to the 2005 Ingenium Conference in Nelson says the Flat Bush development area is about 1800 hectares and is contained within a single catchment.
The paper's authors, Y Krpo of Tse Group and J Sheppard of Brookfields Lawyers, say 48 stormwater ponds will buffer the waterways from the urbanised sub-catchment.
The paper says the estimated cost for implementing the catchment management scheme is about $100 million, which will be funded by developers through a council contribution scheme.
The paper says a key feature of the planning process for Flat Bush is the protection and enhancement of about 45km of natural streams and gullies, of which 20km will be owned and managed by the council.
"Hence 90 percent of natural waterways are to be protected, of which 40 percent will be integrated into the urban fabric and provided with one-sided roads, which open and define those `green corridors'," the paper says.
"Every house will be located within a five-minute walk to its nearest green corridor."
