Winter stage data download

31 Mar: Runoff is 7.02 mm/day

Today I downloaded both the stage loggers (Kadec, Hobo) to evaluate the winter season runoff. The hydrograph below shows that there are multiple peaks due to the high frequency of rainfall and the absence of any significant snowfall in the basin this winter. Winter rain-on-snow is not unusual for this basin, however, the hydrograph below shows particularly high rainfall activity for winter due to the record warm temperatures. Even over the basin elevation range of 40-950 m, the dominant precipitation phase was rainfall.

Notable runoff events include:

Date                    2-day precip.   Max. intensity
8-9 January            74 mm              9.5 mm/h
16-17 February      50 mm              5 mm/h
10-11 March           39 mm              7 mm/h
27-28 March           41 mm              7 mm/h

The 52 mm of precipitation on 8 January tied with the record for the highest daily precipitation measured in January. The 9.5 mm/h maximum precipitation intensity was the second highest for January (since 1982).

No seasonal snowpack this year

Niigata City and indeed much of Japan just had the warmest January since records began in 1882. The average January temperature during 1981-2010 was 2.4 degrees Celsius, while this year it was 5.2 degrees Celsius. The second warmest January on record was in 2007 with 4.9 degrees Celsius. Globally, January 2020 was also the warmest on record.

Location of snow lysimeter in larch stand near gauging station

Some snowfall occurred in early February, but most of that has already melted away at the low elevations. In 20 years of snow survey at Takiya River basin, this is the first time that there has not been a seasonal snowpack at low or even medium elevations (0-600m).

Stage about 0.8m at the gauging station

Strong warm winds and rainfall (8 m/s, 11.7 degrees Celsius, 51 mm) combined to produce rain-on-snow conditions and high runoff with some suspended sediment load. Even high elevations above 500m only retain patchy snow cover.

Forest harvesting activity near the gauging station (Japanese cedar, "Sugi")

Small mountain shrine about 2 km upstream of the gauging station

Warm December

17 Dec: Runoff is 6.34 mm/day

One of the warmest and driest Decembers ever recorded at Murakami, close to the field site. No sign of seasonal snow cover yet, and unusually for December, we even managed to measure the discharge.

New water year brings autumn rains

27 Nov: Runoff is 6.45 mm/day

In the hydrograph below you can clearly see the low flow at the end of September is followed by a major runoff event in early October which raises the baseflow for the rest of the month and into November. This is typical for increasing precipitation and falling ET to lead to higher baseflows into autumn. October monthly runoff (151 mm) is more than three times larger than that for September (46 mm).

September low flows

Very low flow conditions, equivalent to 1.17 mm/day (30 Sep)

Sand and woody debris deposited around the staff gauge

The month of September experienced exceptionally dry conditions this year, as shown by the stage hydrograph below. Only two minor precipitation events can be seen, and long periods of baseflow recession. The monthly runoff was one of the lowest on record for Takiya River, at just 46 mm. The lowest recorded monthly runoff during the period of record (2000-2019) was August 2012 with 35 mm.

Comparing the Kadec and Hobo stage data, it seems the newer Hobo logger is giving more stable data readings. Instability in the Kadec data during low flows could be due to effects of water temperature fluctuations not being compensated for adequately.

July 28 flash flood

Debris around the staff gauge and extreme pool scour to the right are evidence of the 28 July flood

Rainy season was over by the end of July. However, a localized downpour on 28 July gave the largest flood so far this summer, with rainfall intensities of up to 65 mm/h (Takane Amedas), and a daily rainfall total of 149 mm (Miomote Amedas). The hydrograph response was rapid, reaching over 1.6 m at 10.30am one hour after rainfall intensities peaked at 17.5 mm in 10 minutes. In contrast, almost no rain fell in nearby Murakami - only 14 mm for the day.

This flood was followed by a 17 day period without any rain, giving a long flow recession.

The photos below show the large amount of sediment that was deposited at the mouth of the tributary, pushing the flow to the opposite bank and leading to fresh deep scour beneath the bedrock outcrop. Fortunately the stage-rating curve seems to be unaffected.

Rainy season?

So far not so much precipitation in July. End of June saw some moderate rainfall and peak stage of about 1.0m. The hydrograph below shows the data from the Kadec logger which was reset in a new sensor pipe on June 5. During lower flows there is some instability in the stage readings which is not showing in the Hobo stage data. Suspected problems in the Kadec sensor (temperature/atmospheric compensation not functioning?) mean we should consider installing a second Hobo logger as back-up and retire the 19 year old Kadec soon.