During 33 years, from January 1986 to December 2018, seawater temperature has then been registered daily at 4pm in the pumping station[1] of the Nuclear Power Station of Flamanville located 25 km south west of Cherbourg. In order to cool their condensers, seawater has been drawn off with a water flows of 45 m3s-1.

The monthly average seawater temperature minimum has been registered in February (8,90°C), with extremes values in 1986 (6,80°C) and 2016 (10,33°C). The maximum of the seawater temperature has been registered in august (17, 81°C), varying from 16,28°C in 1986 to 18,60°C in 2014. The annual average seawater temperature is 13,09°C when using monthly average values and 13,13°C using all 12053 individuals values. Mean annual values differ from 11,37 °C in 1986 to 14,18 °C in 2014.

Before this time-series of 33 years, the only dataset available had been registered between 1904 and 1923 and had been published in 35 by J. R. Lumby[2], from the Ministry of agriculture and fisheries of London (627 values during 20 years at the point R 26[3] , the closest from the head of Flamanville. In order to complete the time-series, EDF, in collaboration with the National Laboratory of Hydraulic (LNH[4]), uses the two sensors Fertex and Aanderaa[5] at 12 meter depth to get an additional time-series of 999 seawater temperatures recorded from September 1976 to May 1980, in a discontinuous way.

An increase of 1,2 °C in the annual mean seawater temperature is observed between the first and the third time-series. A key point when analysing those three time-series is to keep in mind the difference in the location, depth and in the sensor. Conclusions from comparisons of those three time series need to be done carefully.

Those data are now updated each year before being published in an annual report for Ifremer and EDF[6] about the ecological and fishery monitoring of Flamanville Nuclear Power Station location.

[1] Geographical coordinates of the pumping station : 49,53 N – 1,88 W

[2] LUMBY, J.R. 1935.- « Salinity and temperature of the English Channel ». Fishery Investigations, series II, vol. XIV, n°3

[3] Coordonnées géographiques du R 26 : 49° 37’ N – 02° 14’ W

[4] Today Laboratoire National d'Hydraulique et Environnement (LNHE)

[5] Geographical coordinates  of Fertex and Aanderaa : 49° 32’ 29’’N -  001° 53’ 49’’W

[6] ROPERT M., E. ANTAJAN, G. COURTAY, L. DREVES, A. FOVEAU, T. HERNÀNDEZ FARIÑAS, C. LOOTS, I. SCHLAICH , B. SIMON. (2019). Surveillance écologique et halieutique du site électronucléaire de Flamanville : Année 2018. RST/ODE/UL/LERN-19.001. Conv. EDF C4493C0850. 217 p.