Mangrove coasts: a muddy story (Part 1)
By Han Winterwerp -
I am an engineer. I am a civil engineer and I work with “cohesive sediment”, which is a fancy term for mud. Mud is all over the place, in lakes and rivers, in river mouths (estuaries) and inlets, along the coast and in the deep ocean.
Mud is actually very important, as it brings food to the ecosystem, and provides proper habitat for many animals and plants. But mud can become a nuisance as well, for example when it blocks navigation channels.
Living in the Netherlands and working as a professor and researcher on the behaviour and properties of mud, I am very familiar with the Netherlands’ struggle with water. In 2000 I joined a multi-disciplinary study team which was asked to help defend a part of the eroding coast of Thailand. Our study area was a stretch of about 7 km in the Gulf of Bangkok, locally known as Bang Khun Thien. However, in fact almost the entire western and northern coast of the Gulf, at a length of about 200 km, was eroding at a rate of about 30 m per year since the early 1960s.
Aerial photo of Bang Khun Thien mangrove-mud coasts with relics of coast-parallel breakwaters, eroding at 30 m/yr – in the back, large areas of shrimp ponds are visible.
Our idea at that time was to protect the coast from further erosion by constructing a kind of dam parallel to the coast, made of big bags filled with mud. At that time, I also became fascinated with mangroves. Mangrove trees grow on tropical mud coasts and they provide many benefits, including:
- a decent living and income for many people,
- timber and fuel,
- shelter, spawning grounds and nurseries for numerous marine species,
- coastal protection against storms and hurricanes,
- chemical purification of the water (water quality),
- large sequestration of carbon.
At that time, I also learned that these important ecosystems are being destroyed at a very fast rate: more than half of the total area of mangrove in the world has disappeared since the mid-1900s. Moreover, this loss is accompanied by large amounts of coastal erosion, such as in Thailand.
Since my work in Thailand, I have been involved in similar studies in British Guyana and Suriname, and nowadays I am working with Wetlands International in Indonesia. So watch this space in the coming months, because I will be sharing our ideas on the causes of these large coastal erosion rates, and their relation with the over-exploitation of the mangrove coast. I will also discuss how this erosion can be stopped, and possibly be reversed, and I will keep you up to date with our progress with pilot projects in Indonesia.
I hope this blog series will make you more aware of what happens to our beautiful mangrove coasts throughout the world. If you can contribute with identifying other coasts under high stress, or if you are able/willing to help us with pilot projects to save our mangrove heritage, please get in touch!
Han Winterwerp works for the Dutch research institute Deltares and is a professor at the Delft University of Technology, where he teaches and develops instruments to measure and predict the behaviour and properties of mud. He specialises in the behaviour of mud in open waters.