Rainy November

The hydrograph above shows the river water level (at 10 minute intervals) from 19 October to 22 November. Compared to the last hydrograph I uploaded on 19 October, we can see that rain storms are becoming more and more frequent as we move into November. On 23 October there is a medium size flood peak of about 1.1m, but the peak is short-lived and by 28 October the water level has fallen rapidly to only 43cm, close to the summer low flow level of 40cm. In November the rain storms are much more frequent so that water levels are almost always above 60cm. The soils in the basin are becoming wetter and wetter and the ground water levels are on the rise as we head towards winter.



Takiya River stage = 57cm

Autumn storms

Takiya River, stage = 60cm, Ta = 11C, Tw = 12C

The season has really changed now that we are into November. The autumn rains are really picking up, and today we got hit by several thunderstorms. The rain was torrential at times, but when we arrived at Takiya River the water level was still only moderate. This was good. It allowed us to get into the river to make a couple of discharge measurements. We always need more data for discharge measurements when the water level is up - these are vital for making the stage-discharge curve (H-Q curve). But when the river is really high, it's too dangerous or even impossible to make a measurement.

Today we had five members in our team, including one first time member. To everyone, thanks for getting out and working in the rain!

New water year

Flows are up! Stage = 48.2 cm

October marks the start of the new water year in many temperate climates of the northern hemisphere. September brings the late summer minimum flows and generally the river basin is in a very dry condition. The new water year begins in this season when water storage within the basin is at a minimum. The groundwater levels are at their lowest, and soil water content is also at a minimum.

During the autumn season, rainfall becomes more frequent, evapotranspiration levels decrease with falling temperatures and shortening day length, and so the soil moisture and groundwater levels begin to rise. Look at the hydrograph above and see how the low flows between the rainfall events are starting to increase above the summer minimum of around 40 cm stage.

Come early winter and snowpack will begin to accumulate, adding further to the storage of water resources in the basin. In winter, we will switch from measuring the streamflow to measuring the snowpack to keep track of the water resources of Takiya River.

New team members

Stage = 43.5 cm, summer low flow continues

Today we were joined by two new team members. The typical induction to Team Hydrology is to take a discharge measurement, our all-important work at Takiya River. Fourth year student team members pass on their skills to the new third year members.

The hydrograph below shows that there have been three rainfall events during the second half of September, including one small size flood on September 24th. However, streamflows quickly return to a summer low flow condition. The minimum stage of 40 cm around September 18-19th is likely to be the minimum flow for the year.

Summer low flows

This summer continues to be relatively dry, as shown in the hydrograph above for the first half of September. The months of June and August have been especially dry as we can see for the precipitation data at Miomote (Amedas):

2012 Monthly Precipitation (with 1981-2010 mean)
June  59 mm (180)
July  201 mm (263)
August  81 mm (209)

No rain fell at all during the 18 days from July 26 to August 12, and the 13 days from 17-29 August. In fact the month of August recorded only 5 days with rainfall.

Stage = 41.5 cm, close to the minimum flow for the summer

Hot dry summer

Over a month has passed since our last fieldwork at Takiya River. This summer has turned out to be very hot and dry, and river levels are very low throughout Niigata. The hydrograph above shows there has only been two or three rainfall events in the past 5 weeks! There are two very long periods of flow recession without any rainfall. The influence of the forest vegetation evapotranspiration on the low flows can be seen by the daily fluctuations over the past two weeks.

Although this is high season for leeches and horseflies, we were only hassled by a few of the latter. The very dry conditions this year have kept the number of insects to a minimum.

Of particular note is that the authorities have removed all the fallen trees from the river below the gauging point. About 10 fallen cedar trees in total were removed. Apart from the caterpillar tracks on the river bank, the negative impacts on the river environment seem to be minimal.



Taking a discharge measurement (stage = 42cm, water temperature = 21 C)

All the fallen trees have been removed from the river below the gauging point

Uonogawa field trip

Gauging station on the Uonogawa at Horinouchi (A = 1400 km2)

Currently Team Hydrology are working with data from the Uonogawa River in the upper reaches of the Shinano River. This river basin has especially heavy snowpack in winter and very rich water resources which are used downstream throughout the Niigata Plain for rice paddy agriculture.

Today we visited several hydrometric monitoring stations that measure streamflow, precipitation, and snowpack in the basin, as well as the major dam site within the basin at Kuromatagawa Dam. When using data for hydrological simulation, it is important to see first-hand where and how the data has been collected!

Amedas weather station at Irihirose where snowpack exceeds 3m in winter

 

Snow cat machine at Irihirose

Kuromatagawa Dam

Shinano River gauging station at Ojiya (largest river discharge in Japan!)