It’s been a wet winter. Roads have been damaged and closed. Carterton’s wastewater treatment plant was “underwater and overwhelmed”. Farmers are heartily sick of the wet, muddy conditions and everyone is looking forward to seeing the sun again.
The effects of climate change are well known and reported. Flood events and droughts are likely to get worse. Land management choices are already becoming increasingly critical as climate change heats up, bringing with it more frequent extreme weather.
In August 2018 the Ruamāhanga Whaitua Committee produced its final report, the Ruamāhanga Whaitua Implementation Programme (WIP). The report was the result of four years work and consultation with communities, both urban and rural, throughout the Wairarapa. As a member of the committee I learnt that there are nature-based solutions that will reduce flood peaks and also help provide water resilience in times of drought.
Historically, we removed forest cover and drained wetlands to make room for pasture. Unfortunately, one of the effects of doing this has been to make the water move faster through the catchment, resulting in higher flood peaks.
If removing forest cover is one of the main reasons behind our water woes, then planting trees is the most obvious solution. Farmers have been doing this since the devastating winter of 1977 when there was widespread erosion in the hill country. Since 2009, the Wellington Regional Erosion Control Initiative (WRECI) has provided assistance to farmers for planting willows and poplars. More recently, our attention has been drawn to the practice of planting trees in order to capture carbon, but trees can provide many other benefits in terms of ecosystem services (benefits to humans provided by the natural environment and from healthy ecosystems) e.g. improved water quality and oxygenation, lower water temperatures and habitat restoration.
Nature-based solutions are well proven. The town of Pickering, North Yorkshire, England has explored a new approach to flood management called Slowing the flow at Pickering. They reduced the yearly risk of flooding from 25% to 4% through construction of detainment bunds and leaky dams. Farm scale measures also included sediment ponds, swales and check dams, cross drains on tracks and small scale storage. Here in New Zealand, the Phosphorus Mitigation Project has run trials in Rotorua using detainment bunds to remove phosphorus and sediment from runoff on farms. These bunds will also slow water down and moderate peak flows. In urban environments stormwater can be slowed down with permeable pavements, bioswales, rain gardens and constructed wetlands. These can also filter and clean the water so that it can be stored and utilised as a resource. In China, the sponge cities initiative aims to make urban regions better able to absorb rainfall and release it when needed.
The Wairarapa Water Resilience Strategy was published last year and it made a distinction between green and grey projects. The claim was made that grey solutions are faster than green to be effective. However, many solutions are a blend of green and grey — it’s not useful to make a binary distinction. Trees are slow to grow, but swales and leaky dams are much faster to get going. We urgently need to trial and test solutions which work with nature and give us more bang for our buck. We need to be better prepared for the next wet winter.
This story was originally published in the Wairarapa Times Age on 11 August 2022.