3.1 Numerical Models Simulate Hydrosystem
Biogeochemical Functioning Across the Land–Ocean
Continuum
The models developed within the PIREN-Seine are descriptions of the components
of the hydro-socio-system of the Seine basin and their relationships, through the
biogeochemical processes of the hydrosystem. For example, nitric contamination is
presented as resulting from the opening of the terrestrial cycle of nitrogen linked to
the development of agriculture and the modern agri-food chain. The fluxes of heavy
metals transferred by the river network are seen as a consequence of the flows related
to the production and consumption of these metals by industrial and domestic
activity, as well as of regulations. Alongside the ecology of the aquatic environment,
the industrial ecology of the Seine basin system has been also considered.
One of the main outputs of the PIREN-Seine models has been to provide a general
model of the contribution of groundwater to the flow of the Seine. The CaWaQS/
MODCOU model performs the hydrological and hydrogeological coupling between
seven aquifer units from the recent alluvial deposits to the lower cretaceous formations, with water residence times ranging from a few months to decades. The model
has recently been focused on alluvial aquifer exchanges, and operates at the daily
scale with a kilometric resolution over the whole river basin, which is well suited to
certain needs of the basin authorities, and is completed by the modelling of nitrate
reactivity and transfer from the unsaturated zone to the aquifer. This set of models,
from the soil surface and unsaturated zone to aquifers, is well suited to addressing the
evolution of water resources with climate change and the scenarios of variable water
demand, particularly in the agricultural sector, as well for the study of diffuse
pollutants (nitrates, pesticides, atmospheric pollutants) and their evolution with
possible agro-economic measures.
Several families of numerical models have been generated. Their common
characteristic is their continuous evolution: More processes are taken into account,
their resolution is finer, and they are extended temporally (backcasting, scenarios of
the basin futures), as well as spatially (to the estuary, to other basins). Sub-models
are added and gradually connected to the original ones (as presented in Box 3).
Models work with data sets acquired at different time stages. They also provide an
opportunity to check data consistency with the partners. ‘The models appeared also
very useful for confronting the various databases gathered by Water Authorities on
human pressures and those on water quality. Many incoherent data could be detected
during the process of informing the models, resulting in a significant improvement of
the databases and hypotheses that have been hotly debated. As far as the Water
Authorities were directly concerned with the results, a real dialog was
established’ [17].
River Basin Visions: Tools and Approaches from Yesterday to Tomorrow
391
Biogeochemical Functioning Across the Land–Ocean
Continuum
The models developed within the PIREN-Seine are descriptions of the components
of the hydro-socio-system of the Seine basin and their relationships, through the
biogeochemical processes of the hydrosystem. For example, nitric contamination is
presented as resulting from the opening of the terrestrial cycle of nitrogen linked to
the development of agriculture and the modern agri-food chain. The fluxes of heavy
metals transferred by the river network are seen as a consequence of the flows related
to the production and consumption of these metals by industrial and domestic
activity, as well as of regulations. Alongside the ecology of the aquatic environment,
the industrial ecology of the Seine basin system has been also considered.
One of the main outputs of the PIREN-Seine models has been to provide a general
model of the contribution of groundwater to the flow of the Seine. The CaWaQS/
MODCOU model performs the hydrological and hydrogeological coupling between
seven aquifer units from the recent alluvial deposits to the lower cretaceous formations, with water residence times ranging from a few months to decades. The model
has recently been focused on alluvial aquifer exchanges, and operates at the daily
scale with a kilometric resolution over the whole river basin, which is well suited to
certain needs of the basin authorities, and is completed by the modelling of nitrate
reactivity and transfer from the unsaturated zone to the aquifer. This set of models,
from the soil surface and unsaturated zone to aquifers, is well suited to addressing the
evolution of water resources with climate change and the scenarios of variable water
demand, particularly in the agricultural sector, as well for the study of diffuse
pollutants (nitrates, pesticides, atmospheric pollutants) and their evolution with
possible agro-economic measures.
Several families of numerical models have been generated. Their common
characteristic is their continuous evolution: More processes are taken into account,
their resolution is finer, and they are extended temporally (backcasting, scenarios of
the basin futures), as well as spatially (to the estuary, to other basins). Sub-models
are added and gradually connected to the original ones (as presented in Box 3).
Models work with data sets acquired at different time stages. They also provide an
opportunity to check data consistency with the partners. ‘The models appeared also
very useful for confronting the various databases gathered by Water Authorities on
human pressures and those on water quality. Many incoherent data could be detected
during the process of informing the models, resulting in a significant improvement of
the databases and hypotheses that have been hotly debated. As far as the Water
Authorities were directly concerned with the results, a real dialog was
established’ [17].
River Basin Visions: Tools and Approaches from Yesterday to Tomorrow
391