Akiyamago Province is located in the Nakatsu River valley and has been formed over a long period through the geological processes of erosion, transportation, and sedimentation. However, reliable hydro-engineering records prior to 1950 concerning the river’s transitions do not exist. Consequently, attempts to reconstruct the historical flow conditions of the Nakatsu River from Shimizu Gawahara to Sarutobi Bridge downstream, using aerial photographs taken in the 1960s, have confirmed the existence of three ancient river channels.
Bokushi Suzuki’s writings from the 1820s describe the conditions of the Nakatsu River, including impressions of river flow, seasonal water level changes, and impacts on bridges, but they lack direct descriptions of changes in the river’s course. He seemed to have a keen interest in meteorological phenomena, observing sleet, hail, graupel, and snow. Notably, in “Hokuetsu Seppu,” the micrographic images of snow crystals illustrate Bokushi Suzuki’s profound interest in nature.