JICA field training

JICA (Japan International Cooperation Agency) participants on the course "Irrigation and Drainage Technology Based on Integrated Water Management" joined me at Takiya River for basic hydrological field survey. We measured discharge in three teams using different equipment and compared the results. Sampling of the channel bed materials using the Wolman Pebble Count was also undertaken. Participants came from various countries in Africa and Asia (Cambodia, Malawi, Mozambique, Myanmar, Philippines, Rwanda, South Sudan, Tanzania and Uganda) to study for six months in Japan.

Arakawa from Maruyama Bridge (Sekikawa Village)

Snowmelt season

Today I was joined by participants from my graduate class in Snow Hydrology. We observed the snowmelt runoff condition, and measured the discharge, confirming no changes have occurred in the stage-rating curve.

Above you can see the typical snowmelt runoff pattern in the stage hydrograph. The larger peaks above 0.8m are all connected to rainfall events, while the regular sine-wave fluctuations are due to fine weather snowmelt (e.g. early May). These fluctuations are closely related to the energy balance of the snowpack and the diurnal change in air temperature.

High winter runoff

Takiya River stage during winter 2016-2017 (good agreement between the two logger-sensor systems)

The hydrograph above shows the period from late November to early April, and from this we can see that winter runoff was relatively high due to mild temperatures and a greater proportion of precipitation falling as rain as opposed to snow. This is what we expect in a warmer climate.

There is only a relatively short cold snowy period with decreasing stage from 10-29 January. There are multiple peaks from late November to early January as precipitation was mainly rain, and the period late January to February shows five peaks which are all connected to rainfall events. Snow survey shown in the figure below shows that seasonal snowpack did not accumulate at the basin mouth until 10 January, about 2-3 weeks later than average. Peak accumulations measured on 20 February were also well below average.

Today in very cold but dry conditions we measured the river discharge to check the stage-rating curve. For a stage of 49cm the discharge was 1.66m3/s, or about 6% above the stage-rating curve estimate. The depth and cross-section data showed that the greater than average winter flows may have caused some scour (deepening) of the streambed.

Photos: T. Kobayashi

Young hydrologists

Now into the melt season, today I introduced a young hydrologist to the joys of snow survey. You need to have strong arms to hold up and weigh the snow sample, and stamina to deal with the cold conditions, but today we could enjoy fairly mild spring temperatures. Nearly 50cm snow depth (19cm SWE) remained at the larch site.

Snow survey result
Depth:    larch 48cm / cedar 33cm
Density: larch 0.39 / cedar 0.33
SWE:     larch 18.5 / cedar 10.5
(SWE = snow water equivalent)

Rainy snow survey

Snow survey in the cold rain is one of the hardest conditions in which to do fieldwork. Today Mr. Kobayashi and I sampled two locations close to the river at elevations of about 50m above sea-level. As expected and as always, the larch site had a significantly greater snowpack than the cedar site due to much less snow interception in the canopy.

Snow survey result
Depth:    larch 70cm / cedar 50cm
Density: larch 0.37 / cedar 0.31
SWE:     larch 25.9cm / cedar 15.7cm

Depth and density were higher at the larch site, giving a snow water equivalent (SWE) of about 26cm compared to only 16cm at the cedar site. These values are well below average for late February, reflecting the late start to the snowpack accumulation, which began around 11 January.

Photos: T. Kobayashi

No snowpack yet

About one month earlier Mr. Kobayashi and I had set up and cleaned the snow lysimeters. However, even by mid-January only trace snowpack had accumulated at the lower elevations of the Takiya River basin. In close to 20 years of field work at this site, this is the least snowpack ever recorded for mid-January. Precipitation levels have been normal to high, but it has fallen almost entirely as rainfall rather than snowfall due to warmer than average temperatures. We had to repeat our work of cleaning the lysimeter drains as snowfall just began to accumulate on the ground that morning. Photos by Mr. Kobayashi.

Winter preparation

Today I was fortunate to be joined by Mr. Kobayashi, a prospective graduate student, and we worked in the rain to collect an invaluable discharge measurement. Cold December rain makes some of the hardest working conditions for fieldwork, so thank you very much for your help! Photos by Mr. Kobayashi.

We also worked to clean and set up the snow lysimeter experiment. This experiment has been running since 2002, so 15 years now! The most important device is the tipping bucket which measures the runoff, and this is still functioning well. Key to obtaining good data for lysimeter runoff is the cleaning and maintenance of the collection trays and drainage system. Fallen leaves or needles easily block the drainage holes, until a good cover of snow is achieved. The snow cover, once established, acts as a good filter to keep dirt away from the drains and allow accurate measurement of runoff.