'Jakarta, Indonesia 20-25 million people'"
"We are heading to the sea. We are going to check and see how Jakarta currently is sinking under sea level. At the moment we started our research, our investigation on these floods. In June 2007, suddenly the north coast of Jakarta got flooded. This area, where we are here, now. At the time everybody thought that this clearly was sea level rise. And that Jakarta was one of the most impacted cities for climate change in the world. But climate change, sea level risk is a slow process.
And we could not understand that these floods were caused by sea level rise. And when we looked better, we discovered that Jakarta was sinking really fast."
Here we come from the lower city and here is the sea. You can see how high it is compared to the city level. Here we have the wall that is currently defending Jakarta. At this moment it is low tide. During high tide and also in November, December, the water will be about 1 meter higher to the top of this dyke. Here it is sinking about 10 to 20 centimetres per year.
If this wall breaks, then the water will enter within 1 or 2 days into Jakarta for about 4 to 5 kilometres. Abot 900,000 people will be under 3 to 4 metres of water.
The reason that the city is sinking is that there are many high rise buildings, there are many shopping malls, there is a lot of industry and they use deep groundwater. The hard rock under Jakarta is about 500 metres away. In this 500 metres there are some sand layers, but also clay layers. And because of this over-abstraction of the groundwater, the clay layers fall dry and start to compact. That causes the sinking of Jakarta. So the whole area is going down.
It can be stopped by stopping the deep groundwater abstraction. That can be done by connecting everybody to the public water supply. At this moment the connection rate in Jakarta is about 30-40% that needs to be increase to a 100%. If Jakarta would not do anything then, until the end of the century, Jakarta will sink at least 5 to 6 metres.
A huge defence is required. It is very difficult to build these dykes because there are many people in the way. That is along the whole coast of Jakarta. Heightening these walls is not the only solution. It's not the only thing you need to do. Because from the mountains, rivers and channels are flowing to the sea.
You can heighten these walls, but you can't close these rivers. And these rievrs are also sinking. That means the sea will come in through these rivers."
These rivers bring so much water from the mountains. The mountains are about 20 to 30 kilometres from here. The average rainfall is about 5 to 6 metres per year."