From fluvio- +‎ graph.

fluviograph (plural fluviographs)

1. (dated) An instrument for measuring and automatically recording the rise and fall of a river.
   • 1875 October 9, Scientific American‎^[1], page 227:

     We represent in the annexed engravings, for which we are indebted to La Nature, two new registering devices, one termed the marograph, designed for tide measurements, the other the fluviograph, intended for similar examination of river and canal levels.

   • 1903, Factory and Industrial Management‎^[2], volume 24, page 345:

     By fluviograph and rating table the volume was 19,636 cubic feet, the difference .being explained by the fact that the river was falling rapidly.

   • 1904, John Grimes Walker, Report of the Isthmian Canal Commission, 1899-1901‎^[3]:

     More records, however, are at hand for Gamboa than for Bohio, and the lowest reading at the Gamboa fluviograph occurred in the spring of 1901, when for a period of about two and one-half months the fluviograph at Gamboa indicated a stage of less than 14 meters almost continuously.