1.4. Field Trip

    Field trip on Saturday, 19th February 2017 covers the lower Var catchment.

    A close look at the river bed, sediment transport, weirs, the junction of Estéron river, the river bank and the lake.
We settled down at Carros village, which is located in the mountain along the Var river, where we can see the river view and the surroundings.
Overview of lower Var Catchment from Cliff of Saint-Jeannet

The broadcast FRANCE 3 also came with us to the lower Var river, the following is the news:

    According to Prof. Philippe GOURBESVILLE's speech on Friday, 17th Feb, the answers from the following questions should be considered during the field trip:

During the stop at the airport, look at the bridge:
1. Which effect had the narrowing of the riverbed (from 300m down to 200m) on the flood risk ?
-- It increased the flood risk because the volume of the water that the river can contain decreased. When the width of the river decreased, the discharge could be higher, so the water is more possible to flood.

2. Why is the effect of this narrowing worse here than more upstream ?
--Because there are more urban zone downstream, which means the vulnerability is higher downstream, so the risk is higher. Other reasons could be that upstream water go downstream with higher velocity, which distributes the discharge, so the risk is higher.

Compare elevation of the riverbed and level of the road (build on the dike):
3. Why is this different in the various pars of the Lower Var ?
--Actually, near the river mouth, the elevation of the river is higher than the level of the road.

Look at the sediments in the riverbed:
4. Do the sediment sizes change and where ?
-- Yes, the sediment sizes changed from the edge big to the middle of river bed small, which means at the river bank, the sediments are larger, such as rocks and stones, but at the river bed, the sediments are smaller, such as the sands and small stones. Also, the sediments upstream is bigger than that downstream.

5. Can you find an explanation why ?
-- The reason could be that the velocity is higher at the bank than that in the middle of the river. Also, the bigger sediments need higher velocity and discharge to be transported.

Some pictures from field trip:       

Lower Var exit near the airport

 Sediment transport  
 Weir downstream
Weir upstream
 Overview of Var river from Carros village
La Manda bridge