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Mike 11

Modelisation of Var as a channel of 24 km in length, with boundary conditions, cross section, HD parameters flow and time series of inflow.

In this Exercise, we use MIKE 11 the analyze the response of the Var river to different boundary conditions (upstream in this case), and to study to which extend does the bed resistance of the river and adding new structures (e.g. weir) affect the flow along the Var river.

1)      We observe water variation with 3 differents chainages during 5 days, there is no difference between water level height neither between 3 chainages nor between the 5 days of simulation.

2)      We change the flow at he upsteam of the model to fit with 1994 flood event. We notice the increase of water height in the channel, we focuse our attention on a section of the river (chainage 7500)  where maximum water level is quite close of the right river bank height (difference of 51.3 centimeters only) We consider this portion as a location of a flood risk.

3)      We change the Strickler coefficient of the bed river (bed resistance) from 15 to 80 and observe the water level on two chainages (Upstream and middle of the channel).

 

15

80

Upstream (VAR 0.00)

129.5 m

128 m

Middle (VAR 10.00)

60 m

58.5 m

 

Decrease of the water level height with an increase of velocity (« Manning coefficient is reversibly proportional to the velocity and thus to the discharge and water level »)

4)      We implement a Broad Crested Weir at the chainage 15200 with different geometry (10x50m and 10x100m). We notice an increase of the water table at the level that can be explained by the change in the actual cross section from the river to the relatively small weir, and thus blocking a full capacity flow of the river. In the same way when we decrease the width of the river bed we decrease the cross section giving bigger wet area for the water to cross.


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