the Seine River at Paris was 325 m
3 s
À1 (321 m
3 s
À1 for the 2006–2018 period).
A high-flow period was observed from December to late March, and the rest of the
year was characterised by a low flow rate. The annual water and suspended sediment
discharges at the outlet of the investigated area were estimated at 1.4 Â 10
10 m
3 year
À1
and 3.1 Â 10
5 tons year
À1 , respectively, based on measurements on both the
Seine River at Paris and the Oise River. Previous studies on the sediment yield
in the Seine River basin [17, 18] showed that the average erosion rates over
agricultural lands, forests and urban areas were assumed equal to 18.4, 2.0 and
0.9 tons km
À2 year
À1 , respectively. Thus, the estimated sediment yield to the rivers
at the investigated area scale was 7.6 Â 10
5 tons year
À1 , in good agreement with
the sediment flux estimated at the outlet considering that a fraction of eroded
sediment was deposited on the river bed [18]. Approximately 1.0 Â 10
5 tons year
À1
of sediment are trapped in the reservoirs or on the floodplains upstream of Paris
[2]. In addition, 1.2 Â 10
5 tons year
À1 of river bed sediment were removed during
dredging operations. Either the collected sediment was used for agriculture or bank
reinforcement or it was sent to landfill when the contaminant concentrations exceed
the legal standards. A mass balance analysis of the sediment flux considering the
erosion rate, the deposition rate on the floodplain and in the reservoirs and
the sediment flux at the outlet of the basin provided an estimation of the amount
of sediment stored within the river bed: 2.3 Â 10
5 tons year
À1 .
2.2 Dual-Scale Mass Balance Approach
To quantify the fluxes at the investigated area scale, a two-step method was applied.
First, all urban fluxes were estimated for the Paris conurbation that constitutes
a well-defined and densely urbanised area located in the downstream sector of
the investigated catchment. Thus, the urban fluxes at the basin scale were assessed
either (1) using the same calculation method as for the Paris conurbation but with
an adapted database including all the data available for the investigated area or
(2) multiplying the flux estimated for the Paris conurbation by 1.4 considering the
change in the population from 10 (Paris conurbation) to 14 million inhabitants (the
entire investigated area). This dual approach was chosen as it reduced the number of
complex retroactions, thereby facilitating the consideration of a high level of detail in
the flux charts. In the following, the fluxes are named according to their estimation
method, namely, from direct measurement (F), economic data (E) or a combination
of other fluxes (D).
Urban fluxes included the emissions to the atmosphere (E5a, E5b, E6), the
atmospheric deposition (F12) and the runoff fluxes (F12e, F12f). The domestic
and industrial releases to the sewer system (F22a, E22h) or to the Seine River
(E22g) were also considered. The discharges of the sewer system to the river system
during dry weather (F22d) or wet weather (F22c) and removal during sewer deposit
cleaning processes (F22i) were taken into account. Special attention was paid to
the WWTP-related fluxes including the inflow from the sewer system (F22e), the
outflow to the Seine River (F22f) and urban sludge (F13a, F13b, F13c, E13d).
Mass Balance of PAHs at the Scale of the Seine River Basin
167
3 s
À1 (321 m
3 s
À1 for the 2006–2018 period).
A high-flow period was observed from December to late March, and the rest of the
year was characterised by a low flow rate. The annual water and suspended sediment
discharges at the outlet of the investigated area were estimated at 1.4 Â 10
10 m
3 year
À1
and 3.1 Â 10
5 tons year
À1 , respectively, based on measurements on both the
Seine River at Paris and the Oise River. Previous studies on the sediment yield
in the Seine River basin [17, 18] showed that the average erosion rates over
agricultural lands, forests and urban areas were assumed equal to 18.4, 2.0 and
0.9 tons km
À2 year
À1 , respectively. Thus, the estimated sediment yield to the rivers
at the investigated area scale was 7.6 Â 10
5 tons year
À1 , in good agreement with
the sediment flux estimated at the outlet considering that a fraction of eroded
sediment was deposited on the river bed [18]. Approximately 1.0 Â 10
5 tons year
À1
of sediment are trapped in the reservoirs or on the floodplains upstream of Paris
[2]. In addition, 1.2 Â 10
5 tons year
À1 of river bed sediment were removed during
dredging operations. Either the collected sediment was used for agriculture or bank
reinforcement or it was sent to landfill when the contaminant concentrations exceed
the legal standards. A mass balance analysis of the sediment flux considering the
erosion rate, the deposition rate on the floodplain and in the reservoirs and
the sediment flux at the outlet of the basin provided an estimation of the amount
of sediment stored within the river bed: 2.3 Â 10
5 tons year
À1 .
2.2 Dual-Scale Mass Balance Approach
To quantify the fluxes at the investigated area scale, a two-step method was applied.
First, all urban fluxes were estimated for the Paris conurbation that constitutes
a well-defined and densely urbanised area located in the downstream sector of
the investigated catchment. Thus, the urban fluxes at the basin scale were assessed
either (1) using the same calculation method as for the Paris conurbation but with
an adapted database including all the data available for the investigated area or
(2) multiplying the flux estimated for the Paris conurbation by 1.4 considering the
change in the population from 10 (Paris conurbation) to 14 million inhabitants (the
entire investigated area). This dual approach was chosen as it reduced the number of
complex retroactions, thereby facilitating the consideration of a high level of detail in
the flux charts. In the following, the fluxes are named according to their estimation
method, namely, from direct measurement (F), economic data (E) or a combination
of other fluxes (D).
Urban fluxes included the emissions to the atmosphere (E5a, E5b, E6), the
atmospheric deposition (F12) and the runoff fluxes (F12e, F12f). The domestic
and industrial releases to the sewer system (F22a, E22h) or to the Seine River
(E22g) were also considered. The discharges of the sewer system to the river system
during dry weather (F22d) or wet weather (F22c) and removal during sewer deposit
cleaning processes (F22i) were taken into account. Special attention was paid to
the WWTP-related fluxes including the inflow from the sewer system (F22e), the
outflow to the Seine River (F22f) and urban sludge (F13a, F13b, F13c, E13d).
Mass Balance of PAHs at the Scale of the Seine River Basin
167