Team 2

Team 3

On Saturday we made an excursion to the Var river valley by bus. It was pretty tough (if to take into account that the most collaborative students had only 4-hour sleep). We started at the airport where the river runs into the sea. From there on, we travelled upstream stopping every 15 minutes to listen to the professional explanation of Prof. JJ Peters, who is a river specialist and has made a series of studies of the Var river. We saw the sills that were destroyed during the 1994 flood as well. Prof. Peters told us about sedimentation which is the main problem of the Var river Because of the fact that the mountains are very close to the sea, the river has a lot of energy to transport coarse sediment. In the past, the local people used that sediment for construction, and as the reason of this the river bed was lowered on some places by more than 4 meters. In this situation, there was no regular small flooding like there used to be before, and the agricultural land became less fertile. That is why in the seventies, the authorities started to build sills to refill the river bed to the original level. Behind each sill however, the water eroded the bed and the waterfall after the sill became bigger than the original design height of the latest. During the 1994 flood the sills 2 and 3 did not resist and were destroyed which resulted in a big movement of the sediment downstream to sill 1. When there is no rainfall, the river uses only 30 meters of the 300- meter- wide riverbed and finds it way between the sediment. On some places, it suddenly crosses the bed which results in a severe erosion of the river banks. The solution that was found to protect the banks was the installation of concrete blocks that slowly slide down on a steep concrete slope and are therefore regularly added to ensure permanent protection. Later that day we visited the higher valley of the river and were able to admire the beautiful view around us. The place where we stopped for lunch was an old village on the mountain side where we had an adorable overview of the lower valley. We returned home tired but very happy.

Team 4

On Saturday, we had the field trip to the Var valley guided by Jean-Jaques Peeters who showed us some weirs that had been destroyed and some that resisted the flood in November 1994.

He explained the working mechanism of the sills, the fish ladders, the so called "sugars" invented by the local people used to support the river banks and problems arising from bad practice in maintenance.

He emphasized the necessity of including the knowledge of the locals in decision making processes instead of only relying on literature. For example, since the rivers we saw are not flowing longitudinal, but, due to their meandering movements caused by grind banks, sometimes hit the river bank in an almost right angle so that the bank is eroded very fast. To prevent this, the locals invented a system of "sugar cubes" which subside due to sediment removal by the river flow and can be recharged from above. To keep this system working, the successive vegetation has to be removed - a fact that was not considered by the engineers since they failed to consult the locals. Then we went to the village of Carros to have a panorama view of the river valley in order to check for trapezoidal respectively v-shaped cross-sections. In our opinion, it would have been much more effective to have a field trip before starting the modelling to avoid spending lots of time working based on false assumptions.