Planting and Restoration
Why do we need to restore streams?
Waterways are vital for the health of the environment. If we clog our streams with sediment, the harbour gets clogged too. This destroys the fish and bird life. When we pollute our streams we kill off the microorganisms that plant and fish life need to live.
Although our streams have changed irrevocably since the time of European settlement, we can restore the condition of them by mitigating some of the changes we know have had a negative impact.
- Agriculture – the sediment washed down the hills created fertile plains for farmers and orchardists. They in turn burnt off the remaining native vegetation. This created more erosion and streams became tipping areas. Cows and sheep roaming through the streams added to the pollution. Settlers also planted exotic species that were part of the natural European landscape but grew out of control in the New Zealand climate, competing with our native plants.
- Urbanisation – increased residential density led to more roads and impervious surfaces that water cannot drain through. The stormwater was drained by underground pipes before entering our waterways and harbours. Without the natural systems to filter the water, heavy metals and other chemical contaminants are polluting our water.
- Deforestation – once the canopy species of the forest was cleared, the undergrowth also died off. Without these plants to stabilize the streambanks, rain has washed escalating amounts of sediment into our streams and beaches. This created mud flats which killed off shellfish and fish life.
What is Project Twin Streams doing to restore streams?
Project Twin Streams is working to restore 56kms of streambanks in Waitakere City through successive planting strategies and waste removal. First, the area is cleared of rubbish and noxious weeds such as bamboo, willow and tradescantia. Then ferns, grasses and other small canopy plants are planted on the streambank, contributing to the food chain. Next fast growing colonizing plants including coprosmas, mahoe, cabbage trees and carex grasses that produce seeds and berries for insects and birds. As these first plants grow, larger, slow-growing species such as kauri, totara and puriri are added.
What effect will this work have?
These plants stabilise the banks, reducing erosion and sediment migration. They also filter heavy metals and other contaminants before they enter our streams. These benefits, as well as providing habitats for insects, birds and animals and creating an attractive recreational environment, start from now. It is projected that gradually the mud and sediment deposited over the past 200 years will wash away and we will be left with clear, clean streams.