2.2 Current State of the Seine River Water Bodies
From 1830 to the present day, most of the water bodies of the Seine River have been
physically modified, from the headwaters to the estuary. These changes have been
gradual and planned for water resources management, navigation development,
agricultural drainage, etc. (Fig. 1, lower part).
In the marl and limestone agricultural parts of the Seine basin (e.g. Beauce and
Brie), the tile drainage of cropland reaches its maximum proportion (20–40%)
[23]. It has been developed since the nineteenth century by specific engineers and
peaked between the 1960s and 1990s (Fig. 1f). Intensification of agriculture has
also led to the transformation of some first-order streams into ditches. Meanwhile
summer sprinkler irrigation was developed. As a result, the wetland area was
reduced, and many order 1 streams are no longer in natural conditions, except in
the forested parts of the basin. Most ponds along stream orders 1–3 have now been
converted into cropland. The Morvan forest ponds linked to rafting have not been
maintained.
Water mills are no longer in operation, but orders 2–4 often keep their heritage of
side channels and weirs. Historical maps allow to connect these past river works to
the river’s cultural history, which gives them a patrimonial value, although they are
now considered by the Water Framework Directive as fish obstacles and devices
blocking the sediment transit of the river, which should be removed.
Small rivers around Paris (orders 2 and 3) have greatly suffered from urban
sprawl: their lower parts have been covered and transformed into sewers and then
into storm runoff sewers (e.g. Bièvre, southwest of Paris, and Croult, north of Paris)
(Fig. 1g). Urbanisation also results in the water sealing of some parts of catchment
surfaces and therefore to riverbed erosion related to peak discharges during heavy
rains [32].
In the floodplain of the Middle and Lower Seine, as far as 150 km from Paris,
demands for sand and ballast for construction of the expansion of Paris, new
railways and a nuclear power plant in the Bassée resulted in the excavation, from
1950 to 2000, of dozens of sandpits, 10–100 ha wide, filled with alluvial groundwaters, 2–5 m deep, some connected with the main channel (Fig. 1h; see also Fig. 6).
Given that the sandpit sedimentation rate is low to medium (less than 1 cm year
À1 ),
the filling of these water bodies will take centuries.
In 1830–1840, the French state initiated a major effort to develop river transport
management for the needs of Paris. The navigated reaches of the Seine, Marne and
Oise rivers are those in which the river course has been completely modified in its
three dimensions. The trajectory of the river works has been uniform for nearly
200 years: the navigation channel is now narrower; the course is straightened,
particularly in floodplains, and equipped with dikes or levees (Fig. 1i); the channel
is deeper and regularly dredged; the connection with floodplain water bodies is
decreased; and the river banks are steep. This has resulted in a major change on these
river reaches, with new types of river works, docks and weirs (Fig. 1j) termed
recalibration by river engineers, a positive expression during this period of river
34
L. Lestel et al.
From 1830 to the present day, most of the water bodies of the Seine River have been
physically modified, from the headwaters to the estuary. These changes have been
gradual and planned for water resources management, navigation development,
agricultural drainage, etc. (Fig. 1, lower part).
In the marl and limestone agricultural parts of the Seine basin (e.g. Beauce and
Brie), the tile drainage of cropland reaches its maximum proportion (20–40%)
[23]. It has been developed since the nineteenth century by specific engineers and
peaked between the 1960s and 1990s (Fig. 1f). Intensification of agriculture has
also led to the transformation of some first-order streams into ditches. Meanwhile
summer sprinkler irrigation was developed. As a result, the wetland area was
reduced, and many order 1 streams are no longer in natural conditions, except in
the forested parts of the basin. Most ponds along stream orders 1–3 have now been
converted into cropland. The Morvan forest ponds linked to rafting have not been
maintained.
Water mills are no longer in operation, but orders 2–4 often keep their heritage of
side channels and weirs. Historical maps allow to connect these past river works to
the river’s cultural history, which gives them a patrimonial value, although they are
now considered by the Water Framework Directive as fish obstacles and devices
blocking the sediment transit of the river, which should be removed.
Small rivers around Paris (orders 2 and 3) have greatly suffered from urban
sprawl: their lower parts have been covered and transformed into sewers and then
into storm runoff sewers (e.g. Bièvre, southwest of Paris, and Croult, north of Paris)
(Fig. 1g). Urbanisation also results in the water sealing of some parts of catchment
surfaces and therefore to riverbed erosion related to peak discharges during heavy
rains [32].
In the floodplain of the Middle and Lower Seine, as far as 150 km from Paris,
demands for sand and ballast for construction of the expansion of Paris, new
railways and a nuclear power plant in the Bassée resulted in the excavation, from
1950 to 2000, of dozens of sandpits, 10–100 ha wide, filled with alluvial groundwaters, 2–5 m deep, some connected with the main channel (Fig. 1h; see also Fig. 6).
Given that the sandpit sedimentation rate is low to medium (less than 1 cm year
À1 ),
the filling of these water bodies will take centuries.
In 1830–1840, the French state initiated a major effort to develop river transport
management for the needs of Paris. The navigated reaches of the Seine, Marne and
Oise rivers are those in which the river course has been completely modified in its
three dimensions. The trajectory of the river works has been uniform for nearly
200 years: the navigation channel is now narrower; the course is straightened,
particularly in floodplains, and equipped with dikes or levees (Fig. 1i); the channel
is deeper and regularly dredged; the connection with floodplain water bodies is
decreased; and the river banks are steep. This has resulted in a major change on these
river reaches, with new types of river works, docks and weirs (Fig. 1j) termed
recalibration by river engineers, a positive expression during this period of river
34
L. Lestel et al.