Field Trip to Ara river

Today was our first field trip. We went to the Ara river, Super Levee Shinden, the Arakawa Museum Of Aqua, and the Disaster Prevention Station in the Ukima area. Oversea conference visitors might recognize the Ara river Lock Gate as most field trips go to this river. Without a doubt, this is a highly informative location to see river management put into practice.

The Ara river is a man made channel. After a major flood in 1910 the original course of the Ara river was renamed to Sumida river. The new course of flow was mainly constructed by manual and horse labor, and in the last 100 years many people have moved to the new floodplains. At the time, these were safe lands that could not flood, as the river was created to be lower than the surrounding land. However, due to the high population increase, large amounts of groundwater have been pumped up, causing land subsidence. Today, the floodplains house over 10,000 inhabitants per square kilometer and the ground has subsided considerably, making many people vulnerable to floods. Hence the need for super levees.

 Visiting the Super Levee Shinden was amazing, as I had gotten the Japanese information about these areas some years ago and I was eager to finally see it. The new government has authorized only a minor part of the initial plan of > 400 km of super levees to be constructed. As a consequence there are now parts of the river with super levees and parts without super levees. The whole idea is that the super levee has a less chance of breaking during floods, so I wondered how the interaction of these different areas was imagined. What if a normal levee breaches and the water pours in at the backside of the super levee? Our guide reassured us that this could not happen, as the non-super levee parts were reinforced against water seepage underneath. However, he added, if the water came to high, there was no additional protection against over-topping at the moment.

In the Arakawa Museum Of Aqua (AMOA) you can see the history of the Ara river yourself, along with an impressive movie about the triple disaster of March 11, mainly focusing on the tsunami. The Disaster Prevention Station has storage material in case of floods, mainly for river engineering itself. There is rubble and foot protection blocks in case of an imminent river breach. Luckily the material at the station has not had to be used as of yet. Today was very informative, and it was nice to see the various activities that could be performed in the floodplains next to the river on this sunny day.