Isere.fr

In the Quarternary era, the Isère glacier had two tongues: one dug what is today the Bièvre Plain, the other the lower Isère Valley. The current plain is broad, flat and uniform and made up of fluvio-glacial and fluviatile alluvial deposits.

The Bièvre Plain, a dry valley, has a minimal drainage system. The plain, once dry and not very fertile, was covered by forests for a long time. Today the water table is tapped to irrigate large-scale crops (cereals, sown pasture land, maize). The Bièvre Plain is vast and perfectly flat, and, though spared urbanisation, is crossed by the network of Lyon-Grenoble roads and railway lines. It was especially well suited for an airport, in an area where there are not many possibilities. Today the large open spaces of the plain are helping to "pull" urbanisation westwards. Unfortunately, this urban development does not always take into account the exceptional landscape features, such as the Cluse de Voreppe , the Cirque de Moirans , and the Seuil de Rives .

The Bièvre Plain and its extension up to Sardieu and Marcilloles is the largest uninterrupted cultivated space in the department. A glance at a map shows the exceptional singularity of this patchwork of cropland that covers some 20,000 hectares/77 square miles in a series of geometrical shapes: an extensive area of forests on the surrounding hillsides and urban build-up along its circumference, like on the edge of an internal sea.

This can be seen by crossing the plain. It is the very archetype of an open space of large-scale cropland. Only a few trees or rows of trees, like the plane trees along the road from Crozes to Côte-Saint-André, stand as reminders of the thousands of trees that once spread over the plain's broad straight lines in woodlands and undergrowth on the relatively unused space. The layout still remains. Part of the network of hedges from the former bocage reflects the grand tradition still symbolised in the Beaucroissant trade show, Europe's leading cattle fair. This network of hedges competes with the large-scale cropland, as well as being exposed to pressure from the transportation infrastructure in the area.

In the eastern part of the plain, the contrast between the motifs of the bocage and of modernity can be seen clearly in the A48 motorway and the build-up trailing in its wake. As for the major Bièvre road, that leads to the Grenoble-Saint-Geoirs airport, its steeply sided setting makes it difficult to see, but once discovered, it is clear that it is a difficult barrier to traverse.

The impact of farming on the plain has thus been intensified by the transportation infrastructure and its related effects. The bocage systemis becoming more fragile. And, having cut the plain into three parts, how accessible is it, and what remains of the country lanes that traversed it? This is a continual problem whenever a bocage model is transformed into a new model whose obvious strength tends to turn the area into a territory impervious to anything other than agricultural activity. This is all the more so as there are virtually no villages, and individual buildings are even much less common than in the Côte Saint-André area in Banchet . Is it inevitable that the transformation of the plain will follow what has happened in the Cluse de Voreppe giving a foretaste of Grenoble over kilometres and kilometres? If this is not to be the case, a plan to redevelop a system of local roads accompanied by the planting of hedges should help re-establish certain ecological and landscape continuities.

The image of the plain is different in the Côte-Saint-André area. The network of roads and lanes is much denser and more regular, serving in particular the communes of Brézins, Sardieu and Marcilloles, as well as the groups of buildings installed on the plain, linking them to others at the foot of the Côte-Saint-André hills to the north and Chambarans to the south.