Conservation Comment: Where will the water go?

Can we restore our much needed wetlands? Photo / 123rf

While watching and listening to the horrendous flooding events in coastal Auckland, Coromandel, Tai Rāwhiti and especially poor sodden Hawke’s Bay, we have become more concerned about things we see happening around our neck of the woods.

We are aware that Whanganui sits at the mouth of an important New Zealand river. Not only the outlet for this great awa but also for numerous smaller waterways and wetlands lying in its flood plain, for river mouths are usually areas of wetlands, and ours was no exemption.

Unfortunately, since the arrival of European settlement, these important features have rarely been respected or nurtured. Wetlands are still seen as places to drain to make more land to farm, build houses, factories, or warehouses on.

Drainage and infilling with little thought given to where water at flood time is to flow to or how. Besides causing issues for neighbours and those downstream the changes to landform and use also change biological communities that inhabit wetland areas.

Recently we have become aware that wetlands are also carbon sinks. New Zealand’s largest peat bog, Kopuatai in the Waikato, for example, holds 2400 tonnes of carbon per hectare. This compares very favourably with mature pine forests which only store 300 tonnes of carbon per hectare!

Pine forests also reach an old-growth stage when carbon absorption plateaus. Whereas peatland continues accumulating more carbon for as long as the wetland remains wet!

Driving around Whanganui you realise few original wetlands remain. Some were converted into parks, school grounds, housing, commercial property sites, even a racecourse and of course a previous rubbish dump.

We have watched over the last few years ponds around the Fitzherbert, Mosston, Mills Rd area being destroyed and filled in. Often being replaced by hard, impenetrable surfaces and rarely by plants other than grass. We are now seeing every time we get a downpour, areas of ponding alongside Manuka St, but are yet to see the outcome of a seriously heavy downpour.

Being aware of what happened in Whanganui East, Putiki and along the awa in Whanganui’s last major flood, how this recovery was managed and now knowing that such events are becoming more common is not reassuring.

Looking to the future, planning of new housing and industrial developments increasingly needs to allow for water storage on site, permeable surfaces and areas for water to temporarily pond, thus reducing a storm surge. Pipes and culverts need to be of sufficient size to prevent flooding. We need to remember that the increasing ice melts in the colder parts of our world means that there is more water being circulated in the world’s weather systems. It is vital we make allowances for this as storm strength and frequency increase.

We understand that the WDC has purchased an area at the junction of Mosston and Mill roads to form a wetland and ponding area but are yet to hear or see this project begin.

A Tupoho initiative, for the future of the Kokohuia area, supported by the neighbouring kura, WDC and Horizons proposes the reinstatement and development of part of the Kokohuia Wetland. An initiative already working on increasing our storm resistance.

Extensive plantings are required in these areas, and all rainwater ponding areas around our city.

Future planning needs to incorporate these considerations to reduce the possibility of flooding in Whanganui as we adapt to a warming and wetter future.

Congratulations to WDC, and especially councillor Alan Taylor, for finally accepting the concerns of many citizens, and declaring a climate emergency, then following this by appointment of a climate officer.

We look forward to seeing in WDC’s next Long Term Plan a strong focus on Climate Change Actions which includes a strong focus on mitigating flooding events.

Lyn and Graham Pearson are members of NZ Forest & Bird Soc, Progress Castlecliff Coast Care & supporters of Sustainable Whanganui