First Takiya River fieldwork in a long while

Stage = 0.719m, discharge = 0.685 m3/s

 Today three of us made the trip to Murakami to check on the Takiya River monitoring site after a long break of about 18 months. Since the maximum flood on record of August 2022, the channel had been filled with huge volumes of sediment making the channel cross-section very unstable, and making it difficult to establish a meaningful stage-rating curve. So since the flood of August 2022 we have not been able to estimate the discharge hydrograph.

Seeing the condition of the channel today, it appears that the channel still shows high levels of aggradation due to sediment loading. It may still be challenging to establish a stage-rating curve but we will give it a go this year. New logger sensors were installed to monitor the water level and the atmospheric pressure.

Velocity, depth and discharge across the section (upstream view)

 

The stage data below was salvaged from the loggers recovered at the site. Significant flooding occurred on 15 September 2024 (flash-flood) and during 20-22 September 2024 when >330 mm of precipitation occurred at the Miomote Amedas gauge and hourly precipitation reached >70 mm/h. During this flood event it is evident that the channel degraded somewhat towards the pre-2022-flood level.

 Hope to give you another update on the monitoring soon!

New paper published on flow duration curves

Analysis of flow duration curves to evaluate the influence of climate change on the flow regime in the Japan Sea region

Kaba Diallo, Andrew Charles Whitaker, Al- Shakil, Aaron Conte, Antonio Machava Junior

Hydrological Research Letters 20(2), pp 135-142

DOI: 10.3178/hrl.25-00054

Abstract

There is a need to evaluate and understand how ongoing climate change is impacting hydrological regimes and seasonal flows in Japan’s heavy snowfall region along the Sea of Japan. This study analyzed various flow duration curves from the Takiya River (19.45 km2), Ara River (240 km2), and Uono River (1,408 km2) to evaluate the distinct influence of basin characteristics, climate change, and dam regulation on flow regimes. Seasonal flow duration curves showed consistent dominance of spring flows associated with snowmelt, most pronounced in basins with higher elevations and greater snow accumulation. The moderately regulated Uono River exhibits reduced flood peaks, flattened median flows, and more persistent summer–autumn low flows, reflecting dam operations. A comparison of the periods 1961–1990 and 1991–2023 for the Uono River shows significant increases in winter runoff (Q50 +15%) and a significant shift in the spring flow regime (Q10 –16%, Q90 +23%), consistent with warming trends. In addition, the development of stochastic flow duration curves made it possible to assess the impact of climate change on flow regimes in a probabilistic manner. These findings underline the dual impacts of climate change and flow regulation, with implications for flood control and water supply.

Figure 2. Seasonal flow duration curves for the recent period 2000-2022 comparing the dam-regulated Uono River (1,408 km2), with the unregulated Ara River (240 km2), and the unregulated Takiya River (19.45 km2) for each season; (a) winter DJF, (b) spring MAM, (c) summer JJA, and (d) autumn SON

Figure 3. Seasonal flow duration curves for the Uono River showing changes between Period 1 (1961-1990) and Period 2 (1991-2023) for (a) winter (DJF) and spring (MAM), and (b) summer (JJA) and autumn (SON). The change in mean seasonal runoff is notable for DJF (12% increase) and MAM (7.5% decrease), but not notable for JJA or SON. Using a sample of water years (2003-2009), we also show seasonal flow duration curves for measured and reconstructed runoff for (c) winter (DJF) and spring (MAM), and (d) summer (JJA) and autumn (SON). Natural runoff was reconstructed by computing inflow minus outflow for each of the four dams which were operational, and adding the result to the measured runoff