Ask Phoebe: Rain entering city's wastewater system skews operator's figures

There is more water leaving the water treatment plants than there is entering the wastewater treatment plants at the moment. Pictured is the Mangere waste water treatment plant.

I recently received the monthly bill from Watercare, and included was a leaflet which proudly proclaimed that, daily, it delivered about 326 million litres of drinking water to 1.4 million Aucklanders, and it treated and disposed of 378 million litres of wastewater. What I would like to know, if you can find out, is where does the extra 52 million litres of wastewater a day come from, if it doesn't originally deliver it, and who pays for its treatment and disposal. Alan McKibbin, Panmure

Watercare spokesman John Redwood says the difference is rain (more formally known as stormwater), which enters the wastewater system both officially, in the areas serviced by a combined network (central city and inner west around to Mt Eden), and unofficially, via infiltration and cross-connections.

At the moment, there is more water leaving the water treatment plants than there is entering the wastewater treatment plants, because of the dry spell.

I walk my dog daily in the tree-lined streets of Epsom. I note the once beautifully pruned and shaped trees on the roadsides have not been pruned. They urgently need it. They look terrible, sprouting branches everywhere. I am now also having to duck beneath low-hanging branches covering the footpaths. Is the council shirking another of its responsibilities by not pruning its trees?
Tony Bouchier, Epsom

David Stejskal, arborist for Auckland Council's local and sports parks, offers the following explanation: In the mid-90s, Auckland's pollarded London plane tree stock was assessed to check the condition of trees that had suffered from the many years of pollarding (which is where the upper branches of the trees are removed, promoting a dense head of foliage and branches). The aim was towards the discontinuation of pollarding. Trees that were in good condition were able to be managed to restore their crown into a more natural shape and form, for example in Franklin Rd.

Where trees were in poor condition containing significant decay, council's preference was to remove them and replace with other, more desirable species. This was supported and successfully carried out in many locations. In certain locations and particularly the Epsom area, there was some community objection to the pollarded plane tree removal proposal. It was these locations where trees were left and pollarding continues today.

The pollarded plane trees are pruned twice yearly. In summer (December/January), sprouts from the base and lower crown are removed to improve appearance and take away growth that might interfere with pedestrians or parked vehicles. This pruning regime is nearing completion and should address the reader's concerns.

The second prune occurs in autumn.

And a bit of information about pollarding: In urban areas it is practised primarily to maintain trees at a predetermined height. One consequence of pollarding is that pollarded trees tend to live longer than unpollarded specimens because they are maintained in a partially juvenile state, and they do not have the weight and windage of the top part of the tree.