compensation to farmers; moreover, restrictions in the use of the lock at the dam
during summer periods are seen by boat owners as an infringement of their freedom
of navigation, a practice especially resented by boaters, as they invest money to
maintain this activity.
This context has prompted IAV, over a long period of time, to consider the
implementation of new solutions. The DROP project, comprising interactions with
other practice partners managing freshwater reservoirs and with experts in governance analysis, was an opportunity to improve the reflections that were initiated in
the course of optimizing the management of the reservoir during drought periods.
Concretely, two main pilot measures were taken during the DROP project, a new
lock and drought forecasting:
(a) The implementation of a new lock at the dam
IAV has worked on developing a new and innovative lock at the dam to prevent
salt water intrusion when boats cross the dam. Significant efforts have been put into
designing this new lock: preliminary and feasibility studies, 3D hydraulic modelling, and even a physical model at the 1/12 scale. Currently, all preliminary
studies are finished, hydraulic and physical models have been calibrated, all simulations have been completed, design plans have been achieved, and a consolidated
estimate of the cost of the project has been conducted.
(b) The development of drought forecasting and risk management tools
In parallel, IAV has been working with the IRSTEA research centre, which is
also a partner of the DROP project, to develop a modelling system to forecast
inflows to the reservoir during the low-flow season and help anticipate critical
situations to ensure better drought risk management. The system incorporates
weather information into a hydrological forecasting model and translates the results
into a graphical representation of the drought risk. Future possible weather scenarios over the Vilaine catchment can thus be considered and transformed into river
inflows all the way upstream to the dam. The graphical representation of the
drought risk provides a visual assessment of the risk of being below given critical
low-flow thresholds in the next weeks or months, both in terms of flow intensity and
duration (i.e. mean flow and number of days below each critical threshold,
respectively). This risk assessment visualization tool aims to help the managers of
the dam in deciding whether to release water from the reservoir and on how to
operate the corresponding dam components. It can be integrated into the various
reservoir operations and management rules necessary to fulfil its multiple operational uses, connecting the utilities in a pre-operational framework. The tool is
based on the development of a global forecasting chain, including the development
of weather scenarios combining a short-term meteorological forecast (9 days), a
long-term meteorological forecast (3 months) and an analysis of past events over
the last 50 years. This pilot answers to the needs of drought alert tools, as also
promoted by the national methodological guidelines presented earlier (Sect. 6.2.3).
122
I. La Jeunesse et al.
during summer periods are seen by boat owners as an infringement of their freedom
of navigation, a practice especially resented by boaters, as they invest money to
maintain this activity.
This context has prompted IAV, over a long period of time, to consider the
implementation of new solutions. The DROP project, comprising interactions with
other practice partners managing freshwater reservoirs and with experts in governance analysis, was an opportunity to improve the reflections that were initiated in
the course of optimizing the management of the reservoir during drought periods.
Concretely, two main pilot measures were taken during the DROP project, a new
lock and drought forecasting:
(a) The implementation of a new lock at the dam
IAV has worked on developing a new and innovative lock at the dam to prevent
salt water intrusion when boats cross the dam. Significant efforts have been put into
designing this new lock: preliminary and feasibility studies, 3D hydraulic modelling, and even a physical model at the 1/12 scale. Currently, all preliminary
studies are finished, hydraulic and physical models have been calibrated, all simulations have been completed, design plans have been achieved, and a consolidated
estimate of the cost of the project has been conducted.
(b) The development of drought forecasting and risk management tools
In parallel, IAV has been working with the IRSTEA research centre, which is
also a partner of the DROP project, to develop a modelling system to forecast
inflows to the reservoir during the low-flow season and help anticipate critical
situations to ensure better drought risk management. The system incorporates
weather information into a hydrological forecasting model and translates the results
into a graphical representation of the drought risk. Future possible weather scenarios over the Vilaine catchment can thus be considered and transformed into river
inflows all the way upstream to the dam. The graphical representation of the
drought risk provides a visual assessment of the risk of being below given critical
low-flow thresholds in the next weeks or months, both in terms of flow intensity and
duration (i.e. mean flow and number of days below each critical threshold,
respectively). This risk assessment visualization tool aims to help the managers of
the dam in deciding whether to release water from the reservoir and on how to
operate the corresponding dam components. It can be integrated into the various
reservoir operations and management rules necessary to fulfil its multiple operational uses, connecting the utilities in a pre-operational framework. The tool is
based on the development of a global forecasting chain, including the development
of weather scenarios combining a short-term meteorological forecast (9 days), a
long-term meteorological forecast (3 months) and an analysis of past events over
the last 50 years. This pilot answers to the needs of drought alert tools, as also
promoted by the national methodological guidelines presented earlier (Sect. 6.2.3).
122
I. La Jeunesse et al.