The European pilot on fresh water in DROP will focus on decreasing water quality in water reservoirs in NWE as a result of drought. Institution d Aménagement de la Vilaine and Wasserverband Eifel-Rur will join forces and combine their knowledge to develop and test new measures on drought adaptation for NWE regions dealing with threatened water quality issues of drinking water reservoirs. Focus is on NWE coastal regions and large inland-damcontrolled reservoirs. Low flow conditions and high temperatures in combination with the existing too high nutrient concentrations will lead to more algae bloom (cyanobacteria). More insight is needed on the effect of climate change (CC) on large water reservoirs. Also, different ideas (physical barriers or inland adaptations in the water system) to combat salt intrusion in water reservoirs in coastal areas are not sufficiently tested in practice.

European regions depend on different water sources for the production of drinking water. Climate change and changing weather conditions affect both sources of drinking water. In general in NWE regions there is a conflict of water allocation for agricultural, nature, industry or drinking water purposes (multi-user). This decision conflict is worsened by climate change and lower availability of water in a region. Following these problems, Wasserverband Eifel-Rur will design and evaluate a study on CC effects for large reservoir system and draft a management plan for multi-user water reservoirs; partner Institution d Aménagement de la Vilaine will make a feasibility study regarding changes to larger NWE sea-river locks with the aim to diminish salt-water intrusion into drinking water reservoirs. The aim is to jointly test, evaluate and develop measures applicable to other NWE areas. This EU pilot is therefore a combined effort of the NWE practice regional partners of DROP in FR and DE for the common benefit of NWE.

Results so far

Eifel-Rur [freshwater]

The planning processes for nature and water in the Eifel-Rur region (as for the rest of North-Rhine Westphalia) have a long tradition of collaborative approaches leading to voluntary implementation of actions. Since at least the early 1990s this has been a widespread approach to implementing initiatives in different realms, such as nature conservation, biodiversity protection, and water management. DROP research shows clearly both the benefits of this approach in the region, as well as bottlenecks currently being encountered in the use of this approach.

Interviewees report very constructive discussion processes, which allow actors to understand the requirements of other groups and to identify acceptable solutions, as well as being the basis for collaborative relationships. However, it would seem that the lack of significant political drive behind some of the processes (e.g. the WFD requirements being seen as only due in 2027) have meant that discussions on certain points have become entrenched. What is at stake in some of these discussions would be less the way to implement measures addressing a certain requirement, but rather the requirement itself – i.e. the discussions centre on where (or what!) the goalposts are. Thus the collaborative, somewhat hands-off approach used by authorities could be seen as reaching its limits in this case study, when the questions being negotiated address key interests of stakeholders: security of water supply (and thus of economic production) and economic costs of measures, to name two examples. Whereas actors agree that the approach used delivers results, it is a widespread opinion that the processes are too slow. This could be due to the lack of clear process milestones given by long-term implementation processes.


Brittany [freshwater]

On the downstream part of the Vilaine river, except maybe the well-known drought in 1976, no water stress period seems to have already affected significantly local economic activities. Furthermore, Arzal-Camoël dam represents a huge freshwater reserve to answer to possible drought events. Moreover, in the territory of this lower part of the river drought is not considered as an issue at short or medium time scales for dam managers. Thus drought local governance does not really differ from the national drought plans.

Then, local governance of the downstream of the Vilaine is dedicated to the management of the dam. The major result of this governance is the priority given by all stakeholders to the production of domestic water. Compromises are found for water level in the dam and associated territories as with the wetlands above the dam. Water users agree even if no water use is optimized. The capacity to base decision on a consensus reveals the efficiency of the local water governance.

However, the current multi-functionality of the management of the water of the dam (drinking water production, yachting, tourism, fishing, hunting, biodiversity protection) hides the difference of vulnerability of uses to drought event. While drinking water is the priority, other uses have no management plan in case of drought due to climate change impacts while adaptation measures at the entire catchment scale are described for low flows. Also, inside the Vilaine catchment, the upper part is farmed with irrigated crops, and are areas designated as potentially vulnerable to water scarcity.

In this context and following the required integrated water management at the entire catchment scale, it remains unclear from the DROP governance team analysis, why climate change and its related drought issues are not considered by local water managers, as confirmed by the fact that climate change impacts in the region has never been treated during the catchment water authority commissions.

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


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


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)


Institution d’Aménagement de la Vilaine, Aldo Penasso:
Irstea, Maria-Helena Ramos & Louise Crochemore:  &