CoastGIS'99: geomatics and coastal environment
Introduction
It is well known that inputs of matter to the ocean surface come from
three main sources: atmospheric inputs, continental freshwater inputs
and deep water upwelling. For instance, in the southern part of the Bay
of Biscay, geochemical inputs from the atmosphere are as high as those
from rivers (Maneux et al., 1 999a). However, most studies try to assess
sediment and geochemical fluxes to the coastal zones (CZ) carried by
rivers (Meybeck & Ragu, 1 996). These studies are important in understanding the biogeochemical and sedimentological processes which
occur in lagoons, estuaries and coastal margins. For example, riverine
organic matter entering estuaries is rapidly mineralised, as shown in
the Gironde estuary (Abril et al., 1999). Moreover, a great part of the
human population lives near the coast in close relationship with its
natural resources which can be endangered by anthropogenic pollution and
activities (Pernetta & Milliman, 1995). In the case of the Gironde
estuary, water and sediments are contaminated with cadmium which is
primarily adsorbed on riverine particles (Lapaquellerie et al., 1995).
Thus, the first significant assessment is to determine the total suspended
matter (TSM) flux to the CZ by rivers. Many authors have already estimated the river sediment budget to the ocean on clifferent time and
spatial scales. Firstly, field data were extrapolated or compiled (Milliman
& Meade, 1983). Concurrently, geomorphologists, agronomists and
hydrologists developed empirical or physically-based models of soil
erosion and TSM fluxes from watersheds (Wishmeier et al., 1958; Ahnert,
1970; Pinet & Souriau, 1988; De Roo et al., 1994). More recently, as
a restilt of studies on climate change and biogeochemical cycles, empirical models have been proposed to correlate river sediment fluxes
(Milliman & Syvitski, 1992) with simple environmental watershed
features. The latest improvement is the use of global spatial databases
(Ludwig & Probst, 1996, 1998).
Now, availability of environmental databases and progress in remote
sensing techniques make it possible to assess the soil erosion risk and
river TSM fluxes from watersheds on a regional scale. Thus, for the
southern part of the Bay of Biscay, these risks and fluxes were studiecl
in the Gironde and Adour watersheds on different time and spatial
scales (De Maisonneuve et al., 1997; Maneux, 1998). The aim of this
paper is to describe the different methods applied. The significance of
these empirical models as well as the interest of the available databases
will be discussed.
Sites and methods
A network of 50 schools, the Classes-EcoFleuves was managed for river
monitoring from 1 994 to 1 997.This program was part of the GIS EcoBAG research program supported by the Aquitaine and Midi-Pyrénées
regions, and by the agence de l’Eau Adour-Garonne water board.
246
Introduction
It is well known that inputs of matter to the ocean surface come from
three main sources: atmospheric inputs, continental freshwater inputs
and deep water upwelling. For instance, in the southern part of the Bay
of Biscay, geochemical inputs from the atmosphere are as high as those
from rivers (Maneux et al., 1 999a). However, most studies try to assess
sediment and geochemical fluxes to the coastal zones (CZ) carried by
rivers (Meybeck & Ragu, 1 996). These studies are important in understanding the biogeochemical and sedimentological processes which
occur in lagoons, estuaries and coastal margins. For example, riverine
organic matter entering estuaries is rapidly mineralised, as shown in
the Gironde estuary (Abril et al., 1999). Moreover, a great part of the
human population lives near the coast in close relationship with its
natural resources which can be endangered by anthropogenic pollution and
activities (Pernetta & Milliman, 1995). In the case of the Gironde
estuary, water and sediments are contaminated with cadmium which is
primarily adsorbed on riverine particles (Lapaquellerie et al., 1995).
Thus, the first significant assessment is to determine the total suspended
matter (TSM) flux to the CZ by rivers. Many authors have already estimated the river sediment budget to the ocean on clifferent time and
spatial scales. Firstly, field data were extrapolated or compiled (Milliman
& Meade, 1983). Concurrently, geomorphologists, agronomists and
hydrologists developed empirical or physically-based models of soil
erosion and TSM fluxes from watersheds (Wishmeier et al., 1958; Ahnert,
1970; Pinet & Souriau, 1988; De Roo et al., 1994). More recently, as
a restilt of studies on climate change and biogeochemical cycles, empirical models have been proposed to correlate river sediment fluxes
(Milliman & Syvitski, 1992) with simple environmental watershed
features. The latest improvement is the use of global spatial databases
(Ludwig & Probst, 1996, 1998).
Now, availability of environmental databases and progress in remote
sensing techniques make it possible to assess the soil erosion risk and
river TSM fluxes from watersheds on a regional scale. Thus, for the
southern part of the Bay of Biscay, these risks and fluxes were studiecl
in the Gironde and Adour watersheds on different time and spatial
scales (De Maisonneuve et al., 1997; Maneux, 1998). The aim of this
paper is to describe the different methods applied. The significance of
these empirical models as well as the interest of the available databases
will be discussed.
Sites and methods
A network of 50 schools, the Classes-EcoFleuves was managed for river
monitoring from 1 994 to 1 997.This program was part of the GIS EcoBAG research program supported by the Aquitaine and Midi-Pyrénées
regions, and by the agence de l’Eau Adour-Garonne water board.
246