Record setting rains

Stage = 53cm, Ta = 19.9C, Tw = 15.5C

This July is already the wettest month on record for the Miomote Basin region. Today was another rainy day of fieldwork, but at least the river level was not so high and we could take a discharge measurement.

July is not yet over, but already an incredible 837mm of rain has fallen at Takane, and 628mm has fallen at Miomote. Since 1978, the wettest month was previously 629mm (Takane) and 520mm (Miomote), so we can see that the precipitation this month has been way above these past amounts which were recorded in November 1985.

Major flood

Stage = 82cm, Ta = 19.7C, Tw = 14.4C

Yesterday we had a major flood at Takiya River, with stage reaching 1.8m and discharge estimated at 60m3/s (basin area is 19.45km2). Over July 17-18, 127mm of rain fell on already saturated ground, with a peak intensity of 35mm/h. Under these conditions flash floods often occur at Takiya River with stage rising by as much as a metre in a matter of minutes. The hydrograph below shows two other large floods during the past week, both of which exceeded 1.4m in stage.

Unfortunately the depth and velocity of the flow was too high to allow wading of the river and so we could not take a discharge measurement. I have used a sounding weight and cable from the road bridge, but this method is hardly effective and prone to large errors. I need to investigate other methods and instruments to estimate peak flows at Takiya River.

Rainy season arrives

Stage = 59cm, Ta = 20.3C, Tw = 15.8C

This year the rainy season is late in arriving in the Niigata region. The hydrograph below shows a series of rainfall events and peaks during early July. After the first peak, river stage quickly returns to low flow levels, but subsequent rains are more prolonged and we can see the baseflow levels between floods are rising as the soils become more and more saturated and groundwater levels rise. The river flow is swelled by a mix of warm surface runoff and colder deeper groundwater circulation which reduces the temperature of the river, and produces a mist above the water as the warm humid air condenses.