Region: Bretagne | Partner: Institution d Aménagement de la Vilaine and IRSTEA

At the Vilaine basin partner Institution d’Aménagement de la Vilaine designs a new anti-salt intrusion lock at the Arzal dam. Partner IRSTEA develops and tests a drought forecasting system at the basin.

Project – Development of an integrated tool to support drought adaptation and decision making in the Arzal water reservoir

Location

Arzal, Morbihan, France

Project scale

Vilaine basin scale : 10 000 km2
The water plant that collects in the freshwater reservoir supplies nearly 1 000 000 inhabitants in summer

Project owner

Institution d’Aménagement de la Vilaine

In collaboration with

Irstea

Short description

The Arzal dam, located at the outlet of the Vilaine basin (10,000 km²) in Brittany (western France), controls a large water reservoir (50 hm3). The water from this reservoir is used for many purposes: drinking water supply, sailing, agriculture and fish by-passing.

In the summer period, during the low-flow season, inflows to the reservoir may not be sufficient to satisfactorily ensure all water uses. This project proposes to develop a tool to help in forecasting low flows and anticipating critical drought situations for a better management of the reservoir. In addition to providing hydrological forecasts upstream the dam (inflow forecast model), the tool will investigate different management strategies to minimize the impact of future low flow conditions. Last, management rules will be tested in a changing context of climate change.

Project actions

The following actions are included in DROP:
•Development of a drought forecasting system upstream the dam (inflow forecasting model), with a visual tool for drought risk assessment and decision-making;
•Development of a reservoir water management model;
•Testing of the resilience of the forecasting-management system in conditions of climate change.

Status of the actions

Drought forecasting system and visual tool for drought risk assessment and decision-making (2013/2014):
•Hydrometeorological data from the three gauging stations upstream the dam were collected and data controlled;
•A hydrological model was calibrated and tested for low-flow forecasting under different scenarios,
•Several visual tools have been developed and tested and one operational tool has been evaluated,

Development of a reservoir water management model: still to come (2014)
Resilience of the system in a climate changing context: still to come (2015)

Contacts

Institution d’Aménagement de la Vilaine, Aldo Penasso: aldo.penasso@eptb-vilaine.fr
Irstea, Maria-Helena Ramos & Louise Crochemore: maria-helena.ramos@irstea.fr  & louise.crochemore@irstea.fr

Project – design of a new lock at the Arzal dam

Location

Arzal, Morbihan, France

Project scale

Vilaine basin scale : 10 000 km2

The water plant that collects in the freshwater reservoir supplies nearly 1 000 000 inhabitants in summer

Project owner

Institution d’Aménagement de la Vilaine

In collaboration with

Irstea

Short description

The Arzal dam, located at the outlet of the Vilaine basin (10,000 km²) in Brittany (western France), is controlling a large water reservoir (50 hm3) which plays a central role in water supply, sailing, agriculture and fish by-passing.

This project focuses on salt intrusions issues, which are at the origin of many conflicts between stakeholders and users of the water reservoir. Indeed, the water resource is mainly used for water supply and salt intrusions may cause a contamination of fresh water which can lead to problems in terms of public health.

IAV is working on a project of new anti salt intrusions lock in the Arzal dam, which main objectives are:
•Avoid the risks of contamination of fresh water used for water supply;
•Prevent losses of fresh water during periods of water scarcity;
•Avoid requiring restrictions in the use of lock during the sailing peak season;
•Avoid preventive flooding of agricultural land during haymaking season.

Project actions

•The global cost of the project is estimated 20 million euros (based on preliminary studies). The following actions are included in Drop:
•Physical model of the lock to optimize the anti salt intrusions system;
•Pilot study of the lock: design plans and detailed cost estimation
•3D modeling of the freshwater reservoir to asses the efficiency of anti salt intrusions system for water supply

Status of the actions

3D modeling of the reservoir: nearly finished
•Model is calibrated
•Nearly all the simulations have been achieved
•1st version of the final report is available

Design plans : on progress

Physical model :

•Construction of the model is finished
•Model have been calibrated
•All the simulations have been achieved
•The final report is being drafted – should be finished by the end of march
•A film will be realised

Contacts

Institution d’Aménagement de la Vilaine, Aldo Penasso: aldo.penasso@eptb-vilaine.fr
Irstea, Maria-Helena Ramos & Louise Crochemore: maria-helena.ramos@irstea.fr  & louise.crochemore@irstea.fr