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On my neighbour's property is the exit point of an underground stormwater concrete pipe culvert. Below the exit is a pool of water, which then narrows into a stream/open watercourse and runs alongside his house. The stream continues on alongside my house then past a vacant lot, then enters another underground concrete pipe culvert, allowing the stormwater to continue downstream underground.
Recently we have been concerned about the stream bursting its banks during heavy rain events. We have spoken with the Auckland Council about this and their answer was that the watercourse has not been vested in Council (it is showing in their records as a 'Private Unlined Channel') and therefore we, as the property owners, are responsible for the watercourse. This is the case even though run-off from the nearby roads is conveyed through the watercourse.
So we engaged an engineering company to do a hydrological modelling and catchment assessment report. This came back recommending that the watercourse be widened (though there's not much space for that on our property). One important point in the report was that the level that water would be expected to rise to during a 1% AEP flood event was the same level as the FFL (finished floor level) of our house. This means that there is no freeboard.
Auckland Council's 'Code of Practice for Land Development and Subdivision', 1 November 2015, which refers to Section 4.3.1 of E1/VM1 (Compliance Document for New Zealand Building Code: Clause E1 Surface Water (Department of Building and Housing, 2011), states that the freeboard requirement for 1% AEP events for overland flow paths, where flow is equal to or in excess of 2m3/s, is 500mm for vulnerable activities (permanently occupying a residential property is considered a vulnerable activity).
Our house was built in 1996. The LIM report shows that a Code Compliance Certificate was issued for the new dwelling at that time.
In order to mitigate the flood risk, we are going to need to get a detailed design created for the channel upgrade, which will then need to go to Council for building consent. This will be further expense on our part, after having already forked out for the hydrological modelling report. So if anyone has answers to the following two questions, that would be very helpful:
1) Auckland Council (at the time was Waitakere City Council) issued a Code Compliance Certificate for this house to be built which had less than 500mm freeboard (i.e. the finished floor level was less than 500mm above the water level in a 1% AEP event). Does this place liability on the Council to assist us with the costs of the detailed design for the channel upgrade?
2) Because underground pipes can only cope with relatively small rain events, overland areas such as the watercourse on our property, where overflow from these pipes can run, are important. Overland flowpaths are designed to convey the rainwater generated in an extreme storm event and stop it from flooding houses. So upgrading this watercourse is in Council's best interests because as well as stopping our house from flooding it would reduce risks upstream and downstream.
Is it likely that Council would assist us with the costs of the detailed design for the channel upgrade due to this second reason, or is the first reason a better bet?
Recently we have been concerned about the stream bursting its banks during heavy rain events. We have spoken with the Auckland Council about this and their answer was that the watercourse has not been vested in Council (it is showing in their records as a 'Private Unlined Channel') and therefore we, as the property owners, are responsible for the watercourse. This is the case even though run-off from the nearby roads is conveyed through the watercourse.
So we engaged an engineering company to do a hydrological modelling and catchment assessment report. This came back recommending that the watercourse be widened (though there's not much space for that on our property). One important point in the report was that the level that water would be expected to rise to during a 1% AEP flood event was the same level as the FFL (finished floor level) of our house. This means that there is no freeboard.
Auckland Council's 'Code of Practice for Land Development and Subdivision', 1 November 2015, which refers to Section 4.3.1 of E1/VM1 (Compliance Document for New Zealand Building Code: Clause E1 Surface Water (Department of Building and Housing, 2011), states that the freeboard requirement for 1% AEP events for overland flow paths, where flow is equal to or in excess of 2m3/s, is 500mm for vulnerable activities (permanently occupying a residential property is considered a vulnerable activity).
Our house was built in 1996. The LIM report shows that a Code Compliance Certificate was issued for the new dwelling at that time.
In order to mitigate the flood risk, we are going to need to get a detailed design created for the channel upgrade, which will then need to go to Council for building consent. This will be further expense on our part, after having already forked out for the hydrological modelling report. So if anyone has answers to the following two questions, that would be very helpful:
1) Auckland Council (at the time was Waitakere City Council) issued a Code Compliance Certificate for this house to be built which had less than 500mm freeboard (i.e. the finished floor level was less than 500mm above the water level in a 1% AEP event). Does this place liability on the Council to assist us with the costs of the detailed design for the channel upgrade?
2) Because underground pipes can only cope with relatively small rain events, overland areas such as the watercourse on our property, where overflow from these pipes can run, are important. Overland flowpaths are designed to convey the rainwater generated in an extreme storm event and stop it from flooding houses. So upgrading this watercourse is in Council's best interests because as well as stopping our house from flooding it would reduce risks upstream and downstream.
Is it likely that Council would assist us with the costs of the detailed design for the channel upgrade due to this second reason, or is the first reason a better bet?
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