We have been working since 1975 on phreatic stations providing two old meanders of the French river Rhone with interstitial water. The hydrological characteristics are quite different (see diagrams in the text):

  • The one (station 2) is a particular under-flow circulating laterally to the river (“paraécoulement”), which is closely subordinate with the varying level of the Rhone.
  • The other (station 8) is the confluence of continental phreatic water proceeding from a Northeastern plateau (the “Dombes”) with the hyporheic of the river Ain (eastern tributary of the Rhone). The Rhone has no influence on the characteristics of this second interstitial flow.

The physico-chemical disparity of these stations clearly appeared during two extremely opposite climatic periods; the inferences on resident populations are considered.