Seine river basin hub – STARS4Water

Seine river basin hub

At a glance

76,238 km³

drainage area
18%

of the French territory
> 25% of the French

industrial sector
15,000,000

inhabitants
4 upstream

dam reservoirs
1,600 Mm³/year

surface water withdrawals

Water users:

High interannual variability of surface water, with important amplitude between high flows in winter (February) and low flows in summer (August).
Groundwater has an important role in the basin: on average, 50% of the streamflow in the estuary, throughout the year, comes from groundwater, 60% of drinking water supply comes from groundwater abstraction. Groundwater abstraction can reduce streamflow by 10 m³/s,
which is a significant impact during low flow.
Water demand is highly heterogeneous due to the high concentration of population and economic activities in Paris and its surrounding urban areas.
The water quality status of ground and surface waters is expected to decrease by 2027 (twice more rivers are expected to be polluted by nitrate in comparison to 2013). First concerns are on pesticides (41% of watercourses), nitrate , phosphorous and organic matter (27%) from water treatment plant, leading to the development of toxic algae in the Seine estuary, also impacting fishing and shellfish farming activities.
The upstream dams also have a role on flood protection, which is challenged by the more frequent and intense floods.

Main challenges exacerbated by climate change: