Mangroves protect against flooding
Flooding in Miranda during the January 5 storm would have been much worse without mangroves, an expert says.
Professor of environmental studies Gordon Maxwell has studied mangroves for 50 years. He has been supporting Miranda farmers whose pasture was destroyed after being inundated by seawater during the storm, which also flooded homes in Kaiaua and the Thames Coast.
The damage would have been much worse without mangroves, which provided a sustainable buffer that anchored the mud and were a natural protector of stopbanks, he said. ‘‘The mangroves defuse some of the force, the velocity of the tides and they do it beautifully,’’ he said.
‘‘Our mangrove is actually very good because a lot of the root system is not seen and it holds the sediment. It’s doing it here in the stopbanks.’’
Maxwell lives in Hikutaia, near Paeroa, and travels to Hong Kong and Thailand for several months of the year to help with the Thailand mangrove restoration project. Mangroves were being replanted to protect against typhoons, he said.
Maxwell has concerns about the Thames-Coromandel District Council and Hauraki District Council Mangrove Management Bill, which aims to allow the councils to maintain acceptable levels of mangrove vegetation in order to restore, protect or enhance the amenity values and/ or ecosystems of the coastal area. Public submissions on the bill close on February 23.
‘‘I’m appalled at this idea of a private members bill to authorise, as I understand it, every community that’s got an interest in mangroves could decide the fate of the mangroves and what to do with them in their own way,’’ he said. ‘‘It sounds very democratic but it’s not that simple.’’
The mangroves created a natural eco-system, he said. ‘‘If you remove all the mangroves, the food chain breaks down. If we destroy them, we cut the above ground stuff and we leave the root systems in, they will die and it will change the mud chemistry, mostly the oxygen level,’’ he said.
High sediment levels washed down from freshly-cut pine forests encouraged mangroves to grow, he said.
The answer to the problem of mangrove overgrowth was to regulate the forestry industry, planting a buffer zone of vegetation near rivers and streams to reduce the amount of soil and sediment washed into them from harvested forestry after rain.