Winter arrives

Stage = 50.5cm, Q = 0.96m3/s

December 16 brought the sudden arrival of winter. The weather changed from mild sunny days to snow. And once the snow arrives it usually continues right through to early April. I was caught out by not having the snow lysimeters fully primed and ready for the arrival of snow. So I was digging out and cleaning the lysimeters while the students made a discharge measurement in rather frigid conditions.

We also did our first snow survey of the season. About 23cm snow depth and 5cm snow water equivalent (SWE) at the larch site giving a snow density (SWE/depth) of about 0.2. We charged the winter precipitation storage gauge with anti-freeze at the paddy field site, but we ran out of time to climb up to the tributary site. That would be our job next time in early January.

Snow survey (larch site): depth 22.8cm, SWE 4.6cm, density 0.20.

Winter storage gauge at the paddy field site

Rising baseflows

Stage = 57cm, Ta = 7C, Tw = 10C

From the hydrograph below we can see that the stage has been quite high at 60-70cm during late November due to some steady rains. There are no large peaks, however, as rainfall intensities have been moderate. This has raised the baseflow level as we head into December.

Snow lysimeter fixed

Stage = 51.5cm, Ta = 4.6C, Tw = 9.2C

Today's work included measuring discharge for Takiya River and the tributary, then fixing the leak in the drainage pipe at the mature cedar snow lysimeter site. The third lysimeter tray had become disconnected at the elbow, likely when the tray was moved during a flood. We repositioned the tray and reconnected and glued the PVC pipe quite easily.

The first snows of winter have already fallen in Niigata. We could see snow on the mountains down to about 500m elevation. For the high peaks this snow will stay and accumulate right through the winter, but for the lower elevations the snow will come and go through autumn until winter arrives for real.

PVC pipe reconnected and glued at the elbow

Autumn recession flow

Stage = 55.5cm, Ta = 8.7C, Tw = 12.4C

The hydrograph below shows and long period of recession flow (6 days) during which the weather was dry, followed by a medium size peak due to a rainfall event. Notice how the flow recession is steep right after the peak, becoming more gradual as the water level falls.

Dragon-fly season

Stage = 51cm, Ta = 8.8C, Tw = 11.6C

Dragon-fly season in fall brings some perfect weather for fieldwork. The air was dancing with red dragon-flies or "aka tonbo" as they are known in Japanese. I introduced two new students to Takiya River field site, and showed them how to make a discharge measurement. Our work went very smoothly - I think they will make a great team.

You can see in the hydrograph below that September and October has brought some periods of heavy rain, with two flood peaks of around 90cm. See how the summer low-flow season came to an end around 19th September, and how the base flows have increased in recent weeks. This is due to the frequent rain showers, and the much cooler temperatures and reduced evapotranspiration (ET) which comes with the autumn season.

A helping hand

Stage = 46cm, Ta = 16.8C, Tw = 15.5C

Today I received a helping hand from two students who are considering joining my lab for their graduation thesis next year. I introduced them to the Takiya River monitoring site, and the surrounding Miomote and Murakami region.

We took the all-important discharge measurement, and I then gave them a quick tour of the lower part of the basin. It was cool and raining a little, but I hope that my student guests could appreciate the beauty of the river and the importance of the research work being done there. Perhaps it caught their interest?

The light rain had raised the water level just a little above the summer low flow stage. The rains also brought some surface runoff and added grey-coloured fine sediment to the water.

Summer low flow

Today I visited Takiya River for the first time in about a month. Over the past month the river has basically shown the summer low flow condition with stage at around 40-45cm. There are some rainfall events, and one flood reached nearly 1m stage, but these are all short-lived events and the river stage quickly fell back to the summer low flow condition. Groundwater levels are decreasing steadily as indicated by the decrease in low flows between rain events. Surface soil conditions are extremely dry.

Stage = 42.5cm, Ta = 23.5C, Tw = 17.9C