June 23 flood stage = 2.126m!!

Today I visited Takiya River to get the data from last week's flood, and to check for any damage. Luckily there was no damage, but there was a large pile of debris hooked around the staff gauge. I cleaned it all away and better secured some wiring with nylon ties.

Staff gauge covered in debris

I could just about wade in the river to take a discharge measurement. I suspect the stage-discharge relationship (H-Q curve) has changed as there seemed to be a fresh accumulation of gravelly sediment in the channel. As often occurs after heavy rain, the water temperature had dropped down so that it was quite cold (14.4C), and the warm humid air above produced a strange fog over the river (see also Miomote River photos below).

Stage = 75cm, air temp. = 18.3C, water temp. = 14.4C

Below I have plotted the hydrograph for the few days around the June 23 big flood event, when peak stage reached 2.126m, about equal 3rd highest flood stage since monitoring began in September 2000. Note how the precipitation intensities of >8mm/10 minutes caused the two largest peaks during the flood.


Stage hydrograph with Miomote (Amedas) precipitation data



Miomote River at Nunobe, below confluence with Takiya River (left)

Miomote River with Takiya River basin in centre-ground between mountains

Arakawa River (and Takiya) in flood

Arakawa River stage hydrograph (updated 6/29)

Yesterday's heavy rain did indeed cause the Arakawa River to flood dramatically. Water levels rose from about 1m to over 5m, and nearly hit the high mark of 5.95m reached during the big flood of July 2004, which brought much destruction and damage to Niigata Prefecture.

Today more heavy rain is causing water levels to rise again! Looking at the precipitation data for the Arakawa River basin above the Odo gauging station (see Tochikura and Gomisawa in links panel) we see that about 300mm has fallen since yesterday morning, with maximum intensities of 10mm/10 minutes (equivalent to 60mm/h). This is an extraordinary amount of rainfall, approaching the daily amounts recorded in Kyushu last week. When the seasonal rain front runs into steep mountain relief we can get these record amounts of rainfall.

If only I had real-time water level data for Takiya! Like the Arakawa River, Takiya River must also be in a major flood. Looking at the Miomote and Takane precipitation data (see links panel) I calculate that 212mm and 283mm respectively has fallen in the last 36 hours, with intensities up to 42 mm/h. Here is yesterday's rainfall data for Takane compared to large flood events which occurred in 2004 and 2005:

Precipitation and Takiya peak stage:
2011/06/23 daily 230mm, max. 42mm/h, peak stage 2.126m (updated 6/29)
2005/08/11 daily 289mm, max. 63mm/h, peak stage 2.590m
2005/06/27 daily 183mm, max. 37mm/h, peak stage 2.145m
2004/07/17 daily 180mm, max. 48mm/h, peak stage 2.302m

Takiya River photos:

Taken 4 days after 2004/07/17 flood

Taken 4 days after 2005/08/11 flood

Honma san shows peak stage for 2005/08/11 flood

Rainy season kicks off

Radar image showing heavy rain over Murakami City area (orange)

Rainy season kicks off today in a big way for the Niigata area, especially northern Niigata around Murakami City and the Miomote River basin. Since early this morning heavy rain has been falling across Niigata Prefecture, but looking at the radar image above for 0930, we see the heaviest rain is falling in a band across northern Niigata. The orange colour is indicating more than 30mm/h! Checking the Amedas data for Miomote it shows that indeed more than 30mm/h has fallen the past two hours. Takiya River is headed for a big flood with these rainfall intensities. Look at the real-time stage data for the Arakawa River (link on right panel) and you can see it is rising steeply already.

Takiya River in rainy season (2007/06/29 10:38), stage = 1.38m



Takiya River's Honma San

Honma san centre, with OBs Hashimoto san (left) and Sekine san (right) taken 2006/06/30

Today I enjoyed field work with my good friend Honma san. Honma san's home town is the small village called Nunobe, located at the confluence of Takiya River and Miomote River, but for many years he has lived and worked in Furumachi of Niigata City. I came to know Honma san when he attended a hydrology seminar at the university, given by a visiting professor from the United States, Dr. Roy Sidle, back in the summer of 2000. Honma san is an experienced fisherman and hunter. He knows many of the rivers in the Miomote basin like the back of his hand, and especially he's known every inch of Takiya River since childhood. He is an endless source of fascinating information on how the river has changed and how life used to be in the village at the mouth of Takiya River. He is also keen to join me with field work when he has time, and find out what I am up to.

Stage = 33cm with clear water

The water level was about 11cm lower than at the end of May. Now we enter a season of relatively little water, as the snowmelt season comes to an end, and we wait for the arrival of the rainy season later this month. Looking at the hydrograph below, we can see the diurnal snowmelt pattern has gone by early June. The small peak on May 31, when there was no rainfall, perhaps marks the end of the snowmelt season for Takiya River. Of course, other basins with higher mountains (e.g. Iide Mts. >2000m) still have lots of snow and snowmelt continues in those basins until late summer. But for Takiya River (max. elevation <1000m), the snow has mostly gone and the water in the river is decreasing day by day.

Water levels are falling at the end of the snowmelt season

After measuring the discharge in Takiya River and one of its tributaries, we download the data for water stage, precipitation and shortwave solar radiation. Then it's time for lunch by the river, and Honma san is in his element as he cooks up some sansai (mountain vegetable) miso soup using fresh sparkling water from Takiya River - absolutely delicious! Thank you every time Honma san.

Sansai (fuki) miso soup