1. The Var River Project

The Var River, a 114km long watercourse in the southeast of France (Alpes-de-Haute-Provence & Alpes-Maritimes), flows into the Mediterranean Sea between Nice and Saint-Laurent-du-Var in the Provence-Alpes-Côte d'Azur region.

The main characteristics of this basin are :

- A surface of about 2,800km²

- A mean discharge is 49.4 m3/s

 An elevation from 3000 m in the mountains to 0 m at the sea level

Due to its geological features, the case study belongs to the steep-gradient streams, which means important sediment transfer from inland slopes to the sea.

Location

Location of the catchment

Precipitations and discharges

The climate is Mediterranean, temperate with hot and dry summers and wet and soft winters. The mild climate is a result of Mediterranean conditions, being a closed sea it experiences smoothed climatic and atmospheric effects.
The annual precipitation on the Var basin is around 815 mm and is concentrated in a period that varies from 65 to 80 days.
The major floods are usually occurring during the first months of fall, while in summer, the discharges can be very low. This is due to the fact that Var River has a rainfall-fed flow, meaning that no significant ice sheet or reservoirs upstream provides the baseflow, but during summer the groundwater and during winter the precipitation.

Facilities

There are seven weirs on the Var from kilometer 7 to 15.5km upstream the mouth of the river. Their goal is to remediate to the decrease of the river bed. The weirs #2 to #10 were initially constructed with a 5 meters drop, while the weir #1 was built with a 1.5 meters drop at the Napoleon III bridge to protect the bridge but also to keep the salty water to enter the groundwater.

Those thresholds have significantly changed the river, and have lead to a strong sedimentation resulting in floods risks.

 (valleeduvar.fr, 2016)

What happened in 1994?

On November 5th 1994, an important rainfall episode occurred on 2/3 of the Var basin. It rained from November 2nd to November 5th, inducing a total volume of more than 350 mm in less than 72 hours. In some stations, a volume higher than 700 mm was gauged. 
Such runoff values were due to the fact that the groundwater, which had risen in the previous wet days, was unable to adapt to infiltration, being almost saturated already at the beginning of the rainfall event on November 2nd, yielding to a high runoff, peaking almost at the same time as the rainfall. The flood wave practically propagates downstream, without significant reduction, causing a lot of damages on the infrastructures present along the river and on the floodplain.

This event lead to the destruction of some weirs, which led to the release of an even bigger volume of water.

Road RN 202 and highway A in 1994 (source: Nice Matin)

 
Subpages (2): Program Task schedule
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