Impermeable surfaces adding to residential flooding woes

With soggy basements and swamp-like back yards on the minds of many Aucklanders at the moment, it may be a good time to consider that the recent weather conditions may not be the only culprit for the hundreds of houses that have experienced flooding over the past month.

An increase in the number of properties with a high percentage of impermeable surface can shoulder some of the blame.

Residential houses must have a certain percentage of permeable ground surface (surface that will allow water penetration) to comply with council policy. If these restrictions are not adhered to, especially in higher-density areas, surface run-off is increased and so is the chance of flooding and stormwater pollution.

The percentages vary between zones and depend on the objectives for the zone in question. For example, in the higher-density zones, a greater percentage of paved impermeable surface is permitted. In lower-density zones, where open space, landscaping and large trees are encouraged, the percentage is reduced. Aside from unusually wet weather of recent times, complaints about stormwater to Auckland City have steadily increased over the past year – from 251 in 2002 to 357 in 2003, an increase of 26.3 per cent. The number of permeability policy breaches has mirrored the increase and can be partly attributed to a trend towards higher-density housing and the desire for low-maintenance properties.

With winter coming, property owners need to be aware of the restrictions for their zone and ensure that their properties comply. Auckland City has introduced a new residential 8 zone to accommodate the city’s growth. According to the new policy, if a development is in the residential 8 zone, and exceeds the permeable land coverage limits in the District Plan, the developers must include an on-site stormwater management device. These can take the form of: detention systems, which detain stormwater and release it slowly to prevent pipe overflows retention systems, which detain stormwater, release it slowly, and redirect some of it for use on the property.

For those undertaking new developments, whether in residential 8 zones or not, solutions like this may be of great value when considering the consequences of flooding or breaching council policy.

If a permeability breach is confirmed, the property owner will be given the following options: Amend the development to comply with the District Plan. Apply for and obtain a resource consent within approximately 20 days of notification.

Before applying for a resource consent, property owners should contact the council to discuss details such as whether the property is in a higher-risk area, whether resource consent is likely to be granted and what information will be required for the application.

For more information on this or any other stormwater or flooding issue, please call (09) 379 2020 or visit www.aucklandcity.govt.nz.

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