The hydrograph above shows two small floods which were caused by rainfall, just as the snowmelt season is drawing to a close in the Takiya River basin. The diurnal snowmelt pattern is almost completely lost now, and the water levels and discharge are decreasing steeply. Temperatures have been fluctuating widely during the second half of May, from highs of around 12 degrees C to highs of over 30 degrees C. With mid-summer temperatures, the rates of ET rise sharply and speed the decline in river discharge.
Today I was joined in fieldwork by participants and staff from JICA, as part of a training course in irrigation and water management. We measured the discharge of Takiya River using three different current meters - the usual electromagnetic meter, a hand-held propellor meter, and a large propellor meter for use from the bridge. We also enjoyed surveying the channel bed materials using Wolman Pebble Counts, and walked the river channel about a kilometer downstream to the small irrigation diversion point.
To complete our 2-day field trip we visited the lower Arakawa and Tainai Basins, including the irrigation diversion headworks on the Arakawa River as shown in the photos below. This is an excellent example of water management, where the irrigation water for both the left and right banks of the river is taken at the same point, just as the river exits from the mountains and flows onto the coastal plain.
