Conditions for establishment and conservation of coastal prehistoric sites along the southern banks of Lake Neuchatel and Lake Morat: Systematic prospection and reconstruction of old banks

The artificial lowering (about 3 meters) of the water level in the three lakes (Neuchatel. Morat and Bienne) at the end of the 19(th) century induced a modification of the equilibrium profile of the lake basins and caused considerable coastal erosion. After these major works, numerous prehistoric coastal sites were discovered up to the beginning of the 20(th) century. In 1994, an extensive program of archeological investigation by non-destructive core-sample drilling was started on the south coast of lake Neuchatel and right around the lake Morat coastline. The objective was to study the conservation of prehistoric vestiges and the effects of erosion in coastal sites. The state of conservation of coastal villages undeniably depends on their position with respect to the present coastline. Already eroded and, therefore in a mediocre conservational state before the lake levels dropped, some Neolithic sites farther from the coast line are not affected by recent erosion. On the contrary. other sites, those protected until 19(th) century, were destroyed at the level of the present coastline. so that almost all architectural vestiges and all archeological strata have disappeared in the lake. Because of the lower lake levels, many sites of the late Bronze age, have been in shallow water for a little more than a century, now are being largely eroded. Stratigraphical analysis shows that the topography of the coast has totally changed since prehistoric times. Villages now situated on a rectilinear coastline were, in prehistoric times. frequently built inside bays and sheltered from the prevailing winds. Moreover. the slope of the ancient coast and the depth to susubstratum are important criterions for the foundation of villages and/or for their conservation; a shallow slope favours vestige conservation. From investigations on the location of certain sites, we propose hypotheses for the reconstitution of the habitats and for the erosive phenomena that affected them. Knowing the position of some of the conserved findings, allows the reconstitution of missing parts of villages. Further, average level of the lakes as they were abandoned can be estimate. It becomes apparent that the artificial lowering of the water level in the region of the three lakes had a disastrous effect, especially on the southern part of Lake Neuchatel and on Lake Morat. In order to recuperate their equilibrium profile, these two lakes progressively did away with the bankings of the early 20(th) century as well as with the prehistoric coastal sites that sheltered them..