The area, which is enclosed by the Vosges and the Black Forest, was created when the Rhine stopped flowing into the Rhône and on into the Mediterranean, but instead forged its way north at Basel. Because the Taunus to the north posed an insurmountable obstacle, a giant lake formed in what is now the Upper Rhine lowlands, which then drained when the Rhine had levelled the route through the Taunus. The Rhine continued to use the resulting plain as a river bed, thus creating a kilometre-wide tidal floodplain.
However, when the Rhine was subsequently straightened and divided, the floodplains came under threat, and it was only so-called 'loop' solutions that saved areas such as the Taubergiessen.
You can find further information at: